Ep 38: Propellers. Propellers? Air Screws!

[00:00:07] Welcome to RC Plane Lab, a podcast for anyone interested in RC airplane. We’ll share tips and tricks on how to build models and talk about successful flights, epic crashes and everything in between. Visit us at rcplanelab.com to sign up for our email list and to ask us questions. You can also text us or leave us a voicemail at 818-351-9846. Please help us out by rating and reviewing us in your favorite podcast app. Thanks for spending time with us today. Now here are your.

[00:00:35] Hosts: Ron and Tom. Hello everyone, welcome to the RC Plane Lab podcast. I’m Ron and I’m Tom. Today we are going to tackle propellers. Yes, exciting, it is exciting- little spinny things on the front of the airplane. Yes, that make our airplanes move, and stuff and stuff like what other stuff? Well, I guess just pretty much makes make our airplanes move. Before we get into it, though, I have a couple things I want to talk about. So, first off, reminders: we are now on patreon. If you want more from us,

[00:01:07] Consider becoming a patron. Any money we get from our patrons will go back directly into helping us grow RC Plane Lab. Yep, none of the funds will be used to buy us new toys or new airplanes or anything like that, so don’t worry about that. It all is an investment into the RC Plane Lab, the future of the.

[00:01:24] Rc podcast. Yeah, yeah, so, so yeah. Also wanted to remind everybody that Ron has launched the forums.

[00:01:30] We have launched the forum. Well, I mean, let’s be honest, you more in spirit, you, you still haven’t.

[00:01:36] Been there, not true? I can’t. I can’t say that I have actually, but I plan on it and I encourage all of our listeners to get on there and start putting some, some stuff on there so we can have stuff to look at. I’m sorry I haven’t been on the forums. I a lot of stuff on my plate- yeah, bike rides or anything like that. Well, yeah, bike rides, runs, yeah and work. I do a lot of that.

[00:02:11] As well it does happen and that’s it’s too bad that gets in the way of us having fun with

[00:02:16] Stuff, right, man, if it wasn’t for work, if it wasn’t for work, we wouldn’t probably be able to do this either. So I mean, I guess I have to thank work for that, right? Well, I mean, I don’t know if you have to thank them, but sure. So, folks, get on the get on the forums. Yeah, Tom will be there someday, I will. I promise I’ll post something, maybe this next week. Oh, maybe. I said maybe, maybe. Yeah, that’s all right, we don’t want to, don’t want to hold you to it, just yeah, I. I put a vague enough answer.

[00:02:49] Out there to be, to give you some hope, but also to give you some reality.

[00:02:59] So that you can get some hope, and then it will be crushed, right. So there you go, right, but yeah.

[00:03:04] So if you want to go to the, I mean I don’t really think anybody’s going to be crushed if I don’t go on.

[00:03:08] The forums. I’m just saying you’re looking at the one who will be. No, it’s cool if you don’t support what we do here.

[00:03:19] No, it’s fine. So other thing, the website. I do plan on adding a page for propellers. We’re going to be talking about a lot of stuff here. This is a big deal. This is a lot of information. Yeah, so there’s going to be a website or a web page on the website that kind of goes over all of this. That way, if you can’t pick it up, like talking, if it’s easier for you to read things or something, go on over there and just look at the propellers page. Hey, I hear we have a new supplier for shirts and such. We do. That’s the other thing on the website. So I did switch over who we’re

[00:03:53] Using and I’m kind of excited about it because they have a lot, of, a lot of different items that were not available before so we can get hats and shirts and sweatshirts and hoodies and onesies. If you have a baby, maybe have a little RC Plane Lab onesie for your little baby.

[00:04:07] How cool would that be in training. Oh, you’re welcome, so do I have to do that now too? Well, yeah,

[00:04:14] That’s a good. I kind of like that. Thank you that I like it. That might be up by the time this is out. I

[00:04:19] Can’t, can’t promise I’ll make a deal with you. If you design an rc pilot in training onesie or shirt for a toddler or whatever, I will go to the rc forums and post something. The RC Plane Lab forums or just rc forums, I’m sorry, the rc, yes, our forums. I will go post something if you.

[00:04:40] Design a, a onesie with the that’s. That’s a great idea. So I’ll spend four or five hours designing something, and then you I’ll spend about two minutes in the forums and post something. Hello.

[00:04:52] Exactly, I am Tom. Maybe I’ll post a picture of something that would be awesome boy, yeah, so this is cool new stuff. Yeah, like I said, there’s some cool stuff on there. Holidays are coming up. They make great presents for yourself because nobody else is gonna buy it for you, so treat yourself to one. 15 Off everything store-wide until 10- 14. So october 14th, whatever day that is, I don’t remember, but go over there now and get 15 off your entire. I think that’s a.

[00:05:24] Wednesday, is it? I think so could be. Well, let me check. I’m pretty sure that’s a wednesday. October 14th is a wednesday. Yes, good job, I win. So you have until wednesday, october 14th, at 11: 59 pm, eastern standard.

[00:05:40] Time, 15 off. 15 Off your entire order. That will probably nearly pay for the shipping actually.

[00:05:46] Shipping’s not bad, oh really, yeah, that’s the other thing I like about this place better than

[00:05:50] The other one. The shipping is a lot cheaper, so I like it. Yeah, head on over yep. So last thing, if you don’t mind, we like to hear from you guys and girls. We get emails, texts and submissions on the on the contact us form on the website fairly often, but we haven’t had anybody call and actually leave us a voicemail at our phone, right, what’s up with that? I don’t know why anyone would not want to do that, but I’d like to change that. So please give us a call, leave us a voicemail with your question.

[00:06:22] Or comment and if we like it, we can use the audio right here on the show. How cool would that be. You can hear your own voice. I mean RC Plane Lab. Yeah to hear your own voice ask your question on the show. I think that’d be pretty cool. Yeah, I mean, a lot of people reach out after we.

[00:06:40] Answer their question and say thanks I. I appreciated hearing my question answered on air.

[00:06:45] I appreciate you guys reading it. Well, we don’t have to read it. Yeah, you can, we don’t read.

[00:06:51] Very well. So if you don’t like the way we’re reading your stuff, if the inflection is wrong, if whatever, or if we mispronounce your name, that’s, that could very well be it too. We’re bad at.

[00:07:01] Pronunciation: yeah, so give us a call, leave us a voicemail, the. The number, in case you were wondering, is area code 818-351-9846, and if you don’t remember that, that’s okay, go over and listen to.

[00:07:15] The very beginning or the end of the show? No beginning, I don’t remember saying the end of the show. It’s definitely at the beginning. It’s at the beginning in our intro, so listen to it there.

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[00:07:47] Yeah. So Ron, what is a prop? It’s a spinny thing that goes along the front of the airplane and makes you go forward, sometimes the back or the back, sometimes or the middle, I mean well.

[00:08:01] That’s true, it could be. There are some airplanes that have the propeller in the middle of the airplane. But I’ll give you the google definition quote: a mechanical device for propelling a boat or aircraft consisting of a revolving shaft with two or more broad angled blades attached to it. End quote. But what does that actually mean? Well, it’s a device that has a hub to which angled blades are attached and set to a pitch to form a helical spiral that, when rotated, screws its way through the air or water.

[00:08:36] As in a boat. But what does that mean? So it’s often, it’s often compared to a like a wood screw. Yeah, how, like, when you drive a wood screw into the wood, it sort of pulls itself into the wood because of the angled flutes or blades, if you will, but kind of like that. That’s what a prop does.

[00:08:56] Sort of: well, no, and then that’s a good basic explanation of it. So, and that’s actually why they’re called air screws, which I really likes calling them. I am team air screw. I mean air screws are so much better, I think, than saying propeller, but I get made fun of a lot for.

[00:09:16] But on a boat would you call it a water screw. Am I talking about a? I mean, I guess you could, but am I?

[00:09:21] Talking about boats now? No, but if you were, this is the rc boat lab podcast, so I don’t really care about.

[00:09:27] Boats. Okay, I mean you just offended every boat owner airplane listener that we have. I did not. No, I did not. I just said we are not. You pretty much just said: boats are stupid. That’s pretty.

[00:09:40] Much what I just heard. Boats are awesome they’re. It’s awesome to know somebody that has a boat. I don’t want one myself because there are too much that goes into it. You used to have a boat, yeah.

[00:09:51] You got rid of the boat so apparently the kids got older and we didn’t. We didn’t use it as much, but you could have asked us to go. I called it a propeller on the boat and just like on a boat, I

[00:10:02] Call them propellers on an airplane. Fine, I am still gonna say in my mind, team air screw, team air screw. But I will not say that again because you will make fun of me every time. So it converts rotational.

[00:10:14] Power. What converts rotational power? The propeller, the air, screw that, yeah that thing. It converts rotation into linear thrust. What does that mean? Think of a propeller as a wing right, it develops lift and it lifts the airplane forward. I know it’s a crazy idea, but if you look at the cross-section of a propeller, it actually was an airfoil shape. Yeah, I’m wrapping my mind around it and that I can understand that. So if you spin that thing through the air, that’s kind of the same thing as a wing.

[00:10:45] Moving through the air, developing lift, like spinning your wings. So, yeah, take your wing from horizontal, flip them vertical and now you’re developing lift in the horizontal plane, or thrust, or thrust, exactly nice. Yeah, so bernoulli’s principle. I’m not going to get like heavily into that, but basically you move air through a venturi, it speeds up, and what does it do as a byproduct of speeding up?

[00:11:13] Pushes- I don’t, I’m not, I don’t know- it decreases pressure. So areas of low pressure always want to go into areas of high pressure. Okay, so that’s why our wings are shaped the way they are, so they have a longer surface on the top half of the wing than usually on the bottom half, unless we’re talking symmetrical airfoils, which that’s something else- so that air has to start and finish at the same place. So to get to the same place, it has to move faster over the top of the wing because there’s more area for it to move over than at the bottom. So because the air is moving faster on the top, it develops an

[00:11:47] Area of low pressure on the top of the wing compared to an area of high pressure under the wing, and that high pressure is said to then push the wing up, and that’s lift. So a propeller is essentially a wooden airfoil that is, instead of being set horizontal to the horizon or parallel to the horizon, it’s kind of vertical to the perpendicular to, and as you spin it develops that lift, or thrust in this case, and moves the airplane in that forward motion. And so then, that is the

[00:12:20] Bernoulli’s principle. That’s Bernoulli’s principle, because I’m not familiar with that. Yeah, so that’s a. That’s a real thing. I’m not saying it’s, I didn’t make that up. I’m not that smart, are you Bernoulli?

[00:12:31] I am not. I’m Tommy, and I’m- I am not that smart. I can’t make that up myself, so it’s got to be a thing right. Yeah, I read it on the internet, but there’s lots of other physics involved. Newton’s third law is another one. For every action, there is an equal and opposite reaction, so I think you could probably talk about that one, because you talked about it before. Yeah, so for

[00:12:58] Every action there is an equal and opposite reaction. So I mean that about covers it, I mean

[00:13:04] That’s how thrust works, that’s how propellers work. So by pushing the air like a wing, so by pushing the air down as a result of its angle of attack relative to the to the wind coming at it, by pushing the air down, it then pushes the wind back up and that’s where your lift is also developed. Yep, so there you go, two physics lessons right here on the RC Plane Lab podcast. You’re welcome, folks. And I mean, those were

[00:13:29] In depth and you can pretty much write a dissertation on that, because that was, that was perfect, yeah, and

[00:13:35] You can go ahead and add us to the references. I mean, we, I’d say we’re pretty credited. I mean, but to make it sound better, put doctor in front of it. Doctor, dr Ron and dr Tom. Yeah, so anyway, that’s how I like to think of a propeller, as it sort of lifts an airplane forward instead of up.

[00:13:55] Well, that, I mean that makes sense, works, but it kind of sounds dumb. But it also pulls it forward through the air. It does, I mean it does. I see I think of lift as being in the

[00:14:07] Vertical plane to, I get it gravity. And when I say lift, in that I’m using my air quotes- it lifts. Basically, you’re just saying you’re lift, you’re creating lift, but in a forward direction instead.

[00:14:21] Of an up direction. So if I were to like ask you to slide me that water, I would not say: hey, could.

[00:14:27] You lift that to me please, and well, but that’s what I would do. I would lift it off the table and then move it over to you and then set it back down. See an argument. I cannot win exactly anywho.

[00:14:38] Yeah, so propellers are dangerous? They can be. Yep, why don’t you talk a little bit about?

[00:14:43] The dangers of a propeller. Well, they spin at high rpm and you definitely don’t want to get your fingers in there when they’re spinning, or I have the scars to prove it. Anything in there, by the way. Well, that’s not just fingers, yeah. Yeah, you don’t want to get, like, say, a rag or a tool, which we did, a tie. I did recently broke one of our expensive wood propellers and, by the way, I cannot find that propeller.

[00:15:08] Anywhere the broken one? Yeah, off the Telemaster. No, I mean, like I can’t find that brand to replace it. It, oh, it is not made. It was a bambula, bambula, yeah, whatever it was, I love that propeller. Yeah, yeah, can’t get it anymore. To try ebay, I tried everywhere really. Yeah, I found some in a different size, but that doesn’t do us any good. Huh, I mean it’s weird because, yeah, I mean that’s just like gone.

[00:15:34] And that’s a fairly well. I would assume that’s a fairly common size, because

[00:15:39] Lots of 30 cc airplanes out there, yeah, and probably a few 20 cc ones also, like what that is.

[00:15:45] Oh yeah, that’s a 20 cc I had to tell you about. It’s been such a long time since we’ve messed with that. Yeah, I forgot what size it was. That’s on me, yeah. So yeah, propellers can be dangerous. Probably ought to talk about, as a bystander or as an observer, where you should and should not stand, just kind of as a general warning if you will. Yeah, so if you’re starting your plane on the

[00:16:13] Ground, or if you’re running it up on the ground before you take off and there is a failure on that.

[00:16:18] Propeller. What is going to happen like? Where is it going to go? Well, the shards or pieces of flying debris from that propeller are going to fly out in many different directions along the plane of.

[00:16:32] Rotation of that propeller, not airplane, but like an actual right plane, yeah of, how do you explain that? Let’s just assume everybody knows what we’re talking about. Well, so like as a propeller is spinning,

[00:16:45] It, it, it. It’s like a disc, right like as it’s spinning, it appears to be a disc. So if you were to look at that disc edge on that is the plane of rotation correct, and you don’t want to be standing anywhere in that plane of rotation, and even a little bit forward. Yeah, you don’t want to go forward too, because that’s usually where the pieces are going to go, in addition to sideways. They’re going to go forward because that’s the direction they were trying to go, that’s the direction they were pulling.

[00:17:10] Towards lifting towards. Yes, yeah. So the best place to stand when you’re able to is behind the airplane or behind the that plane of rotation spinning propeller of death while we’re talking about.

[00:17:30] Warnings probably ought to talk about: don’t. If your propeller is damaged, like if it has a nick or a section missing or a split or a deep gouge in the case of like a plastic propeller- just don’t. Don’t risk it, just take it off. Put a fresh one on. Propellers are relatively cheap.

[00:17:54] Compared to an er bill, they’re cheap enough when you compare it to what can happen. Yeah, I agree. Yeah.

[00:18:00] So make sure your propeller is in good condition. Don’t stand in the plane of rotation.

[00:18:07] Anything else on the warnings. I think that’s. We’ll cover some more stuff later, like starting it, and yeah, let’s get into the good stuff and all that. But yeah, so that’s a, a good, a good.

[00:18:17] Overview. Yeah, so propellers can be dangerous. They are probably the most dangerous part of an airplane, so be careful around them. I would agree they are the most dangerous part of an airplane, all right, so how are they Ron? How are propellers classified or labeled by size as in diameter?

[00:18:37] And also pitch. So let’s say you have a 10 by 6 propeller. That means you’re, if you measure it, you’re going to have a 10 inch diameter and then you’re going to have the. As the air screw turns in the air, it’s going to try and pull itself six inches forward for every one revolution. Yep, that’s.

[00:18:58] That’s exactly right. That’s why it’s called an air screw, because it yeah, screws itself forward through the air, which is actually a fluid. Believe it or not, our airs can be considered a fluid. So, just like a boat prop or propeller or screw or water screw, water screw. Yeah, for every, every rotation of a 10 by 6 prop, it would try to move itself forward six inches. Yeah, because we all

[00:19:22] Know the whole fluid dynamic thing and air is a fluid. Yes, well, we don’t all know that, but let’s just assume it for the sake of this episode. For those that don’t, air is a fluid. Doctor remember that has.

[00:19:34] Spoken, but it’s theoretical right, because, because air is a fluid, propellers are subject to things like slip or flex or other factors that make a propeller not 100 efficient at screwing itself through the fluid of air. So slip is obviously. You move a propeller through the air, it’s it’s not going to get a 100 bite on the air, it’s not a solid. So well, and then yeah, unlike actual, like

[00:20:09] Liquids. They- liquids- don’t compress air compresses. So that’s another thing, that as you’re actually trying to pull yourself through the air with that propeller, you’re compressing the air behind it, so you’re not actually getting that full one for one movement exactly. So that’s another thing, yep, and.

[00:20:29] Besides that, it doesn’t matter whether that’s theoretical or actual, it gives us a handy reference to compare other propellers to it. Yeah, so a 10 by 5, say, moves itself one inch further- I’m sorry, one inch less than a 10 by 6 in one rotation. So it gives you a good frame of reference to compare.

[00:20:49] One propeller to another. Yeah, just kind of letting what that angle is, how the blade is set as opposed to how flat it is right, yeah, and we’ll caveat this, like not all propellers are.

[00:21:00] Measured in sae or inch measurements, true, sometimes, yeah, they’re metric, yep, and which is millimeter? Right, and like you were saying, you looked at one of your props and it had sae on.

[00:21:13] One side and the other side had it in metric- yeah, I think it was an apc and it had it both: however many millimeters it was, by however many millimeters it was, and then 14 by 6 or something like that. On the other end, right, and I don’t do millimeters, so I don’t know.

[00:21:28] Well, one inch is 2.54 Centimeters or 254 millimeters. So there you go. Yeah, I’m not doing.

[00:21:36] Math? I’m not, I yeah. Well, let’s say it was a 10 inch propeller then. So it’ll be a 2500, 24 to 8, 2 point. Yeah, it’s big. The number is higher in millimeter than it is in inches. That’s sad. I couldn’t even do base 10 on that and move that’s one point over once in my mind. Yeah, but it’s okay. It’s okay, so yeah.

[00:21:58] That’s. That’s how propellers are measured, by diameter and pitch, and sometimes you’ll actually get a propeller hole or diameter, a whole diameter measurement for the prop shaft- not always, but sometimes. Oh, I’ve not seen that on anyone. It used to be a standard of, I think quarter inch used to be the standard and they used to have that on there, but hasn’t been that way for a long time. So

[00:22:21] So if you have anything from the 40s, when Tom started flying, you might have some. And there’s another age joke, different nomenclature, but most modern things today are just going to have that, the, the two, possibly four numbers on it if it goes in metrical, because I’m pre-modern.

[00:22:36] All right, so prop designations, what are those? What are those? Some of those letters mean.

[00:22:41] Ron. So there’s a bunch of letters that you will find on props every now and then also, and that kind of goes after the 10 by 6, if that’s what it is. So it’ll be like a 10 by 6 e. What does e mean? E is going to be electric only so it’s a thinner propeller that is made not as heavy duty as a regular propeller is. Because you don’t have to worry nearly as much about vibrations from the engine, like from a nitro engine, because electric is so much cleaner and simpler and

[00:23:14] Smoother and boring. But no, what about an f like f, as in foxtrot folding blade? Oh okay, so like a.

[00:23:24] Glider that has a glider or something. Yeah, that’s one that’ll fold back on you sometimes you’ll see sf. What does that mean? That stands for slow fire, propeller, nice, and so a slow pro, or jeez. Okay, that’s why you asked me, that’s why you want to say: because I have not been able to say that all night, tell me what a slow fly he has to say it’s slow. I do because I want to say so. Well, for, oh gosh, I keep wanting to say slow fryer for some reason. I think is what comes out, and I probably because it’s easy.

[00:23:56] For you to say could be, and maybe I’m wanting some fried chicken or something, because that really sounds good. That does sound good, doesn’t it does? So tell us about the slow flyer. Yeah, sf prop.

[00:24:06] Tom tell us: yeah, so they’re designed obviously to fly slow. Ah, so the shape of the propeller is designed to be efficient at a much lower rpm. So the actual shape of the blade is maybe not straight. It actually has kind of a curve to it and it has a really usually really, really, really fat tip or a wider wide tip than at the brute. Yeah, designed to really get a good purchase on the air out there at the tip and they’re just flying because it’s turning slow rpms, yeah, and

[00:24:38] They’re usually not. Well, I mean they’re, they’re not, they’re not going to have a, what’s the word? I’m looking for the angle of attack, the twist that, yeah, the angle of attack of the blade, the twist of the blade is not going to be as great, right, as you would have on regular propellers too, right, normally, like the only ones I’ve ever seen have been electric for electric airplanes, obviously, because you have a more wider range, like higher speeds, that you can get with some of these other electric motors than you can with gas or, yeah, getting a little out of.

[00:25:11] The scope of our episode. Also, rubber powered airplanes usually have that sort of same slow flyer shape to the, to the props. For the same reason, let’s move on. So that’s a slow flyer, yeah, what kind of prop was that? So how, what did you call it? A slow fryer? So that’s a yes, so, but anyway, go on. Sure, let’s talk about pusher props. Oh yeah, so those are designed for either reverse rotation or to be mounted sort of backwards on a rear-facing motor or engine to be used as a pusher. Think of it, if we’re comparing.

[00:25:46] Them to screws. Think of it as the reverse thread or left-handed- left-handed thread. Yeah, that’s the exact same kind of thing, same principle. Yep, what about a w? W is for a wide blade. Oh, when would you use a wide blade when you want to get a little bit more bite out of the air? Yeah, it’s going to be a normally. It’s going to be a slower type airplane where you want more power. I normally go with

[00:26:12] The wides. On my four strokes they turn less rpm, more torque, so I can get a- they can usually a bigger bite out of the air. Yeah, handle swinging that heavier pitch. It’s not really more pitch, it’s just more blade getting a bite on the air, just like you said. Yeah, so you’re taking a bigger.

[00:26:29] Bite out of the air so you’re able to move more air because, like we said, it’s not a solid. So the more you can actually wave over that, the more you can pull it towards you. Yes, the better.

[00:26:42] You’re gonna. Ron is motioning with his hand. Yeah, I know nobody can see it, but it just it looks weird. Anyway, nin in as in november, as in narrow, perhaps, as in narrow, yeah, yeah. So why would you use a narrow one? For the opposite reason, you would use a wide one. Yeah, so if you got a, an engine that maybe you’re flying a p-51- and you want to get a, a really long propeller on there to make it look a little more scale, but a regular size- let’s say 11.6, Is too much propeller for it. So if you could,

[00:27:17] Find an 11.6 Narrow. You’ve taken a little bit of that blade out of the airstream, taking a little bit of load off the engine so that the engine will turn that scale sized propeller at the correct rpm to give you the thrust you need. Maybe that’s one reason, or maybe you’ve got a screamer of a 40 that a 10.6 Is good and a 10.7 Is maybe too much. So maybe a 10.6 Narrow kind of, or, I’m sorry, a 10, 10.7 Narrow, yeah, maybe fits the bill right in between there and gets that, gets that thing.

[00:27:51] Right in its optimum rpm range. So is that kind of a way to think of it too, then? So like a 10.6, Like if, if we’re labeling these in lowest to highest, so you’d have like a 10.6, 10.6 W- okay, and then an 11, no hold on 10.6, 10.6 W, 10.7 N and then 10.7, Yeah. So if you’re trying to dial in,

[00:28:17] That propeller just perfect. Yep, that’s what you would do, so I’m going to say that again: just make.

[00:28:21] Sure, I got it. Yeah, nope, you got it right. So start with like a 10.6 Narrow, start with 10.6, Yeah, start.

[00:28:27] With like a 10.6, Like in the in the same family of propellers, a 10.6 Narrow and then a 10.6 And a 10.6 Wide and then, if it tends- okay, I got you follow. I’m saying I’m starting back one step, I sure, and that makes more sense. So we’re in the same family of size. Yep, okay, gotcha, make sense, sure? So there you go. You can use those the width of the blade to sort of fine tune where that engine is running in the sweet spot. If, like me, you’re into tinkering, which I am, yeah, you don’t have to do as.

[00:28:56] Much with electric motors, which is why I know Ron, I know just saying all right, so what? What did?

[00:29:04] You find about rpm limitations. I know you said you were going to do a little research on that.

[00:29:07] Yeah, so according to apc’s website, because there’s not a lot of people that actually tell you rpm and stuff for these, it’s good. There’s surprisingly little information out there actually on model propellers, which you would think there’d be a lot. Yeah, because this is kind of a thing that spins really fast in the front of your airplane and you don’t want it to get messed up.

[00:29:27] As far as airplanes are concerned, propellers are kind of a big deal. It’s kind of the thing that makes.

[00:29:32] It a prop driven aircraft, right? I mean, can’t say any better than that, not really so glow engine rpm limits on them. So the way they, they don’t actually tell you each size. They tell you an equation to do it, which is very simple, okay, so it’s 190 000 rpms divided by the diameter of the prop. Is it rpms or rs, pm, rs, rpm, rpm, just rpm, because the r stands for rotations.

[00:30:07] Did I say rpms? Well, I, I’m guilty of it too, but like I’ve often, so I did, though I did. I’m sorry, but I’ve often wondered: like rpms, well, I guess, like wow, okay, I didn’t mean to, I mean I’m guilty of too, but technically wouldn’t it be rs pm, because it’s revolutions per minute? Well, no, then it would.

[00:30:27] Just be r, because r is revolutions. If it was- yeah, you see what I’m saying- yes, so right. So it’s just

[00:30:36] It should just be rpm, not rpms, which I’m guilty of saying. 17 Yeah revolutions per minutes, that’s not.

[00:30:43] Accurate. No, that’s not right at all, right. Well, if I said that, I’m sorry, I’m well, I’m really taking us down. So, 190 000 rpm doctor. By the way, now I’m just like a- yeah, I don’t know what’s under a doctor.

[00:30:56] But that’s what I am. A has revoked your doctor’s license. I gotta try and get that back. See what I did there. The ama- yeah, not the american medical association, but the academy of model aeronautics.

[00:31:08] Has revoked. Oh, I didn’t even think the first one you said I went straight to the airplane thing. Oh, I was so proud of myself. I’m not an actual doctor, so I don’t really do anything with ama. Oh boy, so glow engines. By the way, propellers for glow engines: 190 000 rpm divided by the diameter of the propeller in inches, in inches. Right, so we’ll do this very simply with a 10 inch propeller, I like, because I don’t want to do the math: 190 000 divided by 10 is 19 000, 19 000 rpm, so 19 000 rpm is.

[00:31:47] What a 10 inch propeller would be rated for if it’s a glow engine propeller. So glow engine propellers are going to be the, the, the heftiest of all of them. They’re going to be the thickest plastic, the thickest whatever it’s made out of, right, designed to be durable. And that is because you have a lot of vibrations that come with the gas or glow engines that you don’t have with electric. So because of that, they’re built to handle it and they’re gonna be a lot thicker. Yep, that’s why they can handle the, the higher rpm. So if we go with, like the thin electric prop, the e designation instead of 190 000.

[00:32:23] Rpm divided by the prop diameter it’s 50 000 rpm, so that really lowers the ability, I guess, to spin.

[00:32:34] The propeller at a high rpm because of that, yeah, not designed for terribly crazy rpm numbers, and that is, once again, because it’s thin yep, and they’re designed to be light and efficient. And because electric motors are weak- designed to be, they’re not weak though. That’s, that’s that’s.

[00:32:53] Absolutely not teasing. Well, but tease with facts. Okay, they’re not weak, no, they’re smooth, they are.

[00:33:02] Very smooth, yeah, so anyway, listen, I don’t, I mean I own electrics, it’s like you’re right, I own.

[00:33:08] Nitro, I own gas, I know. I just never fly them because they’re a pain in the butt. What about those, those other props that you like to pronounce the slow flyer propellers, the slow fryers? Did I do it right? Yeah, you did. Yay, the slow, I mean, I see I’m trying to make it worse and do it again- 65 000 really, yeah, 65 000 rpm.

[00:33:28] Divided by prop diameter. My goodness, I cannot imagine spinning a slow flyer prop that sort of that’s. That’s according to the website. So, although I mean really 65 000, that’d be 6500 on a 10 by 6 prop. I guess because of the wide pitch of the blade that’s really not so unreasonable. Yeah, no, it really.

[00:33:51] Isn’t? When you, when you figure out what that actually means, the actual numbers you’re dealing with- like 190 000- sounds ridiculous until you do the math and it is ridiculous, but once you figure out what you’re actually talking about, then it gets to be more in line with reality. Yeah, so interesting. So that’s that’s right off apc’s website. Yes, so if you guys don’t believe me, go check.

[00:34:14] It out? Did you by any chance look at master airscrews website? Do they do they have? I didn’t see.

[00:34:19] Anything on that one? Yeah, well, thank you, apc. Yeah, thanks for letting us know what’s going on giving us.

[00:34:25] Something to talk about. So, did you want to talk about pitch? I would like to talk about pitch. Yeah, I have at it. So unique, unique to airplanes- the pitch changes along the blade and that’s for a very specific reason. So as we turn these propellers, we spin them in a room in a round word direction. Round word direction. Yeah, they go a round word direction right, so we spin.

[00:34:55] Them around, and angular momentum is. A is a. It’s a calculation and so it’s the same reason. Cars have differentials. So when you’re making a turn in a car, for example, the inside tire on that turn has to go much less distance than the outside tire because it has. The outside tire has to cover the same amount of ground, given the speed at which it’s going. Same thing on a propeller: the propeller.

[00:35:27] The portion of the propeller that’s closest to the hub, relative to the tip, is moving slower through the air. Right, so it doesn’t. Yes, it is so it. So it requires more angle of attack at the root to develop the same amount of lift than the blade that is moving much faster through the air at the tip. So along the blade length you’ll see blade twist, so it’ll be thicker, or the angle of attack will be more at the root than at the tip. Like at the tip, a lot of propellers appear almost nearly very thin and very flat. Yeah, yeah, so that’s.

[00:36:02] Unique to airplanes. Boats have a have a very different arrangement of the way their blades are designed, but airplanes are unique in the fact that they actually twist the blade for that.

[00:36:15] Very reason. And what is the reason behind that? Compared to a boat? Just because of the? With a boat you don’t have nearly as much diameter. Is that why? Well so boats- I’m not an expert on.

[00:36:28] Boats, I why are we talking about boats? I like to compare them because, boat, when you, when you turn a propeller on a boat, you’re turning it in water, which is a much more dense. I don’t want to say solid, because it’s not a solid, but it’s a much more solid fluid, dense than air dense, much more dense. Yeah, sure, then we’ll go. It doesn’t, because yeah, so it requires more screwing action, like a wood screw. A wood screw it’s going into a, a solid and water. If you want to think of it this.

[00:36:59] Way. Water is kind of a halfway between a solid and an air kind of. So the shape of a boat propeller is shaped that way, more like a screw, like going into a wood, like a wood screw airplanes. Obviously we’re not dealing with water, we’re dealing with air, which is, like you said, something that can compress. So we need a different shape to handle that and we need a shape that develops, lift to move the airplane forward right. So bottom line, on a on an airplane propeller, we’re looking for a.

[00:37:30] A balanced amount of lift along the length of the blade as we’re spinning it through the air.

[00:37:37] And that’s why it’s twisted like that. So if you spin this in the air, and this is all without variables, this is just perfect. Let’s say we’re going through a solid, as you’re doing, that, you’re not putting more stress on any part of that blade, because none of that blade is actually taking a bigger bite out of the material it’s moving through, so it’s not trying to bend it. I mean, am I correct in?

[00:38:00] Looking at it that way, yeah, kind of yep, yep, so we’re not, we’re not introducing any undue stress along the length of the blade because the load is the same from root to tip. Okay, yep, I got it. That makes sense. So, yeah, and the reason we do that is obviously for we don’t want to propeller coming apart in flight. That would be bad. It’s happened before and you’re right, it’s not fun.

[00:38:25] So we know we talked before about 10 by 6, 10 by 5, 10 by 4, 10 by 7, the 4, 5, 6 and 7, where you’re actually talking about different, different bites going through the air, what like? If you’re, what’s the reason for using, like, a more flatter type pitch as opposed to a greater pitch? Okay, so there’s.

[00:38:52] There’s a couple of rules- not rules but points- to keep in mind when you’re selecting your propeller. It depends on what you want the propeller to do for you, but basically for low speed flying, a flat or a flatter pitch is best, kind of like a low gear in your car, and for high speed flying, a steeper pitch is needed, kind of like the high gear in your car.

[00:39:19] The reason for that is a. A flatter prop will develop a little bit more thrust at a lower rpm. So, just like the, the lower gear in your car- like if you’re trying to take off from a, a grass strip that has a lot of drag and you’ve got to overcome that drag to get airborne, you want to choose a lower gear. So you’ll choose a prop within the same size- now we’re comparing- you’ll choose one with a little bit flatter pitch. Conversely, if you’re flying off of, like a

[00:39:50] An asphalt runway or some smooth runway where getting off the ground isn’t the issue and you want to develop the maximum airspeed that your airframe will allow you, then you’ll, you’ll go the other direction. You’ll choose something with a little more pitch, okay, kind of like a high gear in.

[00:40:06] Your car, and that makes sense. So there’s also a couple different types of propellers. There’s and we don’t. The reason I wanted to bring this up is we don’t see it often in airplanes, but you will deal with it. More helicopters use them and there have been a few people that I’ve seen that have used the what’s called a constant speed propeller. So what those are is they actually have variable pitch.

[00:40:36] On where they can change the angle of the blade while it’s running. While it’s running, yeah so the engine or motor runs at a constant speed, hence the constant speed propeller. So the way they change the amount of thrust, instead of throttling it up and throttling it down, is by varying the pitch of the actual blades themselves. Like I said, I’ve only seen this a couple times in 3d airplane or in rc airplanes, like with certain smaller ones that have been flying. They’re not very common, but it is something that’s.

[00:41:09] Probably going to becoming, I would think, more or becoming more and more common, probably yeah.

[00:41:15] Because- and we’ll talk about this here, but a little bit later- engines and motors are designed, maybe not designed, but they operate within a optimally within a certain rpm range. Yeah, so a constant speed prop is designed to keep that engine in that range by varying the pitch of the propeller and changing the load on the engine so that it can stay in that power band. That’s more.

[00:41:38] For like gasoline or nitro engines where you really have that curve with the throttle, the power curve. Electrics don’t have that as much you get. I mean it’s still there a little bit, but not nearly as much. The biggest reason I think you’re going to see these coming or becoming more and more.

[00:41:58] Mainstream, I guess, is because of the things you can actually do with it. I’ve seen people fly their airplanes backwards, yeah, or vertically, yes, vertically, I’ve seen it too, so, and that’s why I think that’s going to kind of be something possible in the future that you’re going to see more of. Yeah,

[00:42:13] But, but we’re all pretty much familiar with fixed pitch. Yeah, that’s the normal propeller that you buy a.

[00:42:20] Couple dollars, three dollars a piece, that we all use. They’re the ones that I mean. They’re simple, there’s nothing to them. The thrust is varied by varying the speed of your motor. Yeah, so with the.

[00:42:34] With the propeller comes certain unique characteristics or trade-offs, or aerodynamic uniqueness. Are you talking about p factor? Yeah, that’s what I’m trying to talk about.

[00:42:53] Sure, just said it because that took a while to get there. I’m sorry. So p factor is kind of cool yeah, and it really explains some stuff when you get to learn about it. So p factor is caused by a spinning propeller when the center of thrust is not in the correct place. So what that means is so the angle of the attack of the blades aren’t perpendicular to the airplane’s angle of attack. So if the fuselage is tilted outside of horizontal to the actual tail down, tail down position, okay.

[00:43:26] Your right hand blade. So if you’re sitting in the pilot seat- let’s imagine you’re actually flying this thing- the propeller is spinning clockwise in front of you and because of the angle of the blade, when that is on its downward spin. So when the blade is on the right hand side of the airplane, moving in a downward, downward, downward trajectory, it’s actually taking a bigger bite out of the air than the left hand side of the blade is when it’s going up. Yes, because that pitch is changing. Yeah, as to your

[00:43:57] Angle of attack is right. The angle of attack or attack is changing based on the unhorizontalness.

[00:44:04] Of the fuselage. Yes, so the propeller is developing more lift on the right hand side than the left hand side, more thrust on the right hand side, causing the airplane to want to turn to the left, and that’s.

[00:44:16] What increased thrust on the right hand side, correct, and that is what causes the yaw that you have to deal with. That’s why you have to add right rudder and you add right rudder and actually it’s exaggerated in twin engine aircraft and especially twin engine tail draggers, and because of that, that’s why I’m going to be building my duelist with counter-rotating propellers, so I’m going to actually counter-rotate the, the electric engines that I have for that, because when you do a counter-rotation, it cancels each other out, cancels them out, yep, so yep, there’s, there’s.

[00:44:49] A few other things that can cause left jaw, or they go into the left jaw tendencies, also the phenomenon. There you go, that’s the word I think I was looking for earlier. P factor is not the only thing that we sometimes have to consider. Correct engine torque, just like on a car, what? When you see the cars launching at a drag strip, they tend to want to pull up one side or the other. Aircraft engines, their engines and or motors. They generate torque as a byproduct.

[00:45:18] Of their rotation, and so the reason that actually would slow one side down versus the other is there’s going to be more force going down. Correct me if I’m wrong, but you’re going to have more pressure on that tire, and so it’s going to be there’s going to be more drag, more friction on the one side than the.

[00:45:35] Other two. Yep, so exactly, okay, gyroscopic precession- that’s another one that you’re making up. No, I’m not making that up. You’re using big words, doctor. So gyroscopic precession. So everybody is familiar with the. Well, maybe not everybody, but most people are probably familiar with little spinning tops. When we were a kid, you spin a little top and it would spin and balance, or the gyroscope. That’s a gyroscope, right? Yeah, so a gyroscope as it spins, if you.

[00:46:06] Apply a force to it. So let’s say we’ve got a, something like a propeller, let’s say, spinning flat on the table here, on a, on a, on a point, like on a motor. Like on a motor. Let’s say exactly, and we apply a force to the one area of that propeller disc, that force will make its presence known 90 degrees from that point in the plane of rotation. So back to our tail dragger. We’ve got the

[00:46:40] Spinning thing on the front, our gyroscope or our propeller on there, and as we, as we rotate that airplane, we get the tail off the ground. Right, that’s the same thing as pushing on the very tip-top propeller disc. Right that force is felt 90 degrees in the plane of rotation. So that force is actually felt due to gyroscopic precession on the right hand tip. So we’ve gone from vertical in the plane of rotation 90 degrees. It’s now on the right hand tip, causing that airplane to want.

[00:47:14] To yaw to the left. Another reason we have to add right rudder. And there’s actually one more reason.

[00:47:19] Too. Everything is just like it’s against us trying to take off without using right rudder.

[00:47:24] Yeah, and what’s the last one? So I’m not exactly sure the official title. We have spiral slipstream written in our notes here. So if you’ll allow me for just a minute, I’ll tell a little story. So I actually have a private pilot’s license. Got it a long time ago. I don’t fly anymore, it’s too expensive, blah, blah, blah. But anyway, in pilot training they actually taught us p factor. Was this phenomenon called spiral slipstream? Although your description and explanation of p factor is accurate, is accurate.

[00:48:00] Get that word out. They taught us in flight school a much simpler version of that, and that was the spiral slipstream. So you can imagine as a propeller turns and moves through the air, it’s actually moving air itself, yeah, and it and it moves that air and it creates a column of swirling air behind it and as that air moves down the fuselage, it comes up and it hits the vertical stabilizer. Guess which side it hits the stabilizer on? Yeah, the left side. Yeah, it’s causing us to add right rudder. That’s what I mean.

[00:48:32] Everything is against us when it’s working against us. But so, yeah- and that’s the other thing I kind of think of too- when, so, when your propeller is spinning, that thrust that it’s creating is not pushing straight back. No, I mean it’s. It’s a swirling, whirling, dervish of this just air, this tornado going around. Yeah, right, I like it. So it’s. It’s a, a spiral that is pushing towards the back, and that’s because, obviously, because you’re having the propellers spinning and instead of pushing the air straight back,

[00:49:04] It’s, it’s also moving it off to the side, which has to do with how it’s flinging it, almost, yeah, and so that’s kind of dirty, that’s kind of- excuse me, very good, so that’s the dirty air that kind of is created around the dirty air and then, yeah, that kind of wraps around and also hits the left of.

[00:49:26] Your the left side of your rudder, yeah, and then when you combine all of those factors together- the p factor, the spiral slipstream, the torque, the, the other things that we talked about, gyroscopic precession- yeah, everything working against us on that takeoff to make us have to add right rudder. So basically, be prepared at all times to add right rudder, mostly, especially on your tail dragger.

[00:49:51] Yeah, especially in a tail drag, yeah, and so I mean, this happens all the time when you’re flying. You just don’t notice it because you’re moving forward so fast, well, and you have that big, big.

[00:50:00] Vertical surface to help counteract that as the air is moving past it, and that’s what I was going to.

[00:50:03] Say you’re moving forward so fast that you’re not actually able to hit that surface as fast as you are when you’re on the ground. So it all kind of straightens itself out when you’re flying.

[00:50:15] Okay, that’s a lot. That was a lot. Are we done? No, we’re not. We’re not finished yet. But oh yeah, let’s talk about what they’re made of these propellers. Actually, that’s going to be fun, yeah, I, I like to talk about what they’re made of because it’s interesting to me. What’s your favorite type of propeller? It depends on. Okay, I’ll just. I’ll just throw it out there- my favorite type of propeller.

[00:50:36] Are wood propellers right? I love, I love wood propellers with the painted tips. Yes, yes, although

[00:50:42] You can. You can paint the tips on any propeller, but a wood propeller to me with the painted tips just looks cool, classic, cool, whatever you want to call it. I prefer, and there’s some.

[00:50:58] Advantages actually to a wooden propeller. Yeah, but first off, let’s talk about the painted tips. Yes, it’s kind of a safety thing absolutely, and it’s actually a good idea to do it. It’s a very good idea.

[00:51:08] And the reason is, when that thing is spinning, those painted tips will create an arc in the sky that you can physically see and keep body parts out of. Yeah, so not necessarily when it’s flying does it matter?

[00:51:20] But it’s when you’re working on the ground, when you’re tuning it, when you’re doing anything on the ground, you can actually see where those tips are. And I, yeah, I really like the, the painted tips, yep, I.

[00:51:30] Yellow for some reason I like well, it’s because the contrast, it stands out against a lot of other.

[00:51:34] Background colors, but I’ve seen white before. Yeah, I don’t like the white ones. As cool as much I don’t.

[00:51:38] Think: oh, you like the yellow, I like the yellow. Okay, well, I do too. Well, you’re smart, then good job. I’m not going to say all of my propellers have painted tips on them, but I try to mine neither. I try to do it on as many of them as I can remember to do, just because they look cool and I like that little added measure of safety so I can see exactly where that propeller is spinning to keep my fingers out of.

[00:52:01] Electric ones. I don’t do it too, because I’m not standing in front of electric ones usually.

[00:52:06] Because, yeah, you don’t have to tinker with needles and things like that. So the risk is a little bit.

[00:52:10] Smaller, probably a lot smaller. I would say, yeah, you’re not supposed to be around it. To start it to.

[00:52:15] Do things exactly. Yeah, so propellers can be made of wood plastic- not wood plastic, but wood plastic. They can also be made out of frp, which is a fiber glass reinforced plastic, and then carbon fiber is out there and each one has its has its advantages and its disadvantages. By far, in my opinion, the cool factor goes to wood. I like the wood, but I also like the look of carbon fiber. Depends on the airplane, but I agree, yeah, on a modern aerobatic 3d style big airplane like

[00:52:52] Your yak over here. Carbon fiber is pretty tough to beat. Yep, yeah, it looks very, very cool and that’s what I have for it. Yeah, and of course, yeah, and it’s tough to beat. But the downside to what we’ll just talk about carbon fiber. So what are some of the upsides? It’s very strong, very strong.

[00:53:09] It’s carbon fiber. Propellers are usually well, what are we talking, pros? Now is that what you said? Yeah, it’s strong, it looks neat, they’re light, they are. You can. You can usually spin them up faster.

[00:53:24] So your throttle response is a little bit better. Yeah, I’m pretty sure mine’s hollow, but yeah.

[00:53:28] I mean, that’s most of. When you get that size, they’re gonna be hollow exactly, which is another thing. They’re so strong. You can actually hollow the inside out and make them a lot lighter and then and a

[00:53:37] Another side effect of them, of their strength, is the fact that they don’t flex. So they’re a little bit maybe more efficient than a, than a similar size plastic one, because just for the simple fact that the, the blades, don’t flex, they maintain their shape even at heavy loads. So that’s an advantage and down, cool downside. Well, the only downside really that I could find on carbon fiber for me personally is the cost. Yeah, they’re crazy expensive. Yeah, for the, for the yak carbon fiber.

[00:54:09] Was almost three times as expensive. Yeah, but we’re also talking about it. What was it? A 33 inch prop, or

[00:54:15] Something 33 inch, prop, 189, goodness gracious. As opposed to like a vest, would one I wanted to say was about 40 bucks or no, about 60, if I remember right, for the same size and there’s definite places you would.

[00:54:30] You would maybe not want to fly with a carbon fiber prop, like if you’re flying on a rough field and the potential for breaking a prop is maybe higher. Maybe you would choose a little bit cheaper wooden prop or even something plastic, if you can get it in that range. I’m not even sure if apc doesn’t go that size, but anyway, yeah, those, those are some of the pluses and minuses of carbon fiber plastic, frp like so, like apc, master airscrew and other manufacturers like that.

[00:55:02] That are making their props out of plastic. Some of the pros and cons of those: they are cheap, they are. Yeah, they’re relatively inexpensive compared to the other props. Yeah, for sure, absolutely simple.

[00:55:13] To manufacture, very forgiving they are. They are pretty durable, compared to wood, especially. Yeah.

[00:55:22] They’re my prop of choice for flying at, at grass airfields, things like that, because they are, they can, they can kind of take a beating, like you can hit a clump of grass with them, and usually they just turn green and it doesn’t matter, and then you have to clean them and then, yeah, oh, you clean them. Well, I try to keep them tip-top shape. It’s a badge of honor to

[00:55:45] Have a green one. It means you fly your plane. At least that’s how I look at it, because I’m okay, I’m.

[00:55:49] Not going to clean my propeller, I’m not. What if you have white tips? You leave the green on the white tips, then they become greenish white tips. Well, I guess it depends on the airplane. Okay, it, I mean it depends on the airplane I got you. So yeah they’re. They’re fairly durable, they’re inexpensive, relatively speaking. They’re a good choice for grass, grass, airstrips and even concrete. If, if, if, nose overs are a problem for your airplane, a plastic prop like a master airscrew might not be a bad choice. Yeah, it won’t. It won’t shatter. Yeah, it gets it. It’ll still break, but it’s not going.

[00:56:25] To shatter like a carbon fiber, one right or wood. The downside to them is they do because they’re

[00:56:30] Plastic. They are somewhat flexible, apc does and master airscrew both. They do a pretty good job of incorporating actual glass fibers in the material and the resin that they use to make them. But yeah, they do flex, especially at higher rpm, so they are not quite as efficient as a wood or carbon fiber prop. But yeah, there you go, pros and cons of plastic, nice cheap, nice cheap is good, cheap. So wood, wood my favorite. I yeah, I agree, stiff, efficient, good looking, very good looking especially.

[00:57:09] With the painted tips, my, my prop of choice. Unfortunately, price wise they’re a little bit more than the plastic props- not by a lot, I mean, there’s no real appreciable difference- and but probably- and here’s the real downside- is they’re probably the least durable of the props out there.

[00:57:27] Yeah, they do not tolerate well impact of any kind. You- you brought it up before, but when you were tuning that, the Telemaster, the 20 cc Telemaster, 20 cc Telemaster, you just barely like- yeah, I’m trying to think what it was. There was a, it was my carb tuning screwdriver just barely touched the tip of.

[00:57:49] One of those. When it was spinning I let it get just a little bit too close so I got a little careless and it hit the prop as it was spinning and took a fairly sizable chunk. It took half of one of the.

[00:57:59] Edges off of that propeller and you didn’t even see it. I didn’t, I was so focused on getting that gosh darn thing running that I didn’t even see it and you were upset with. I mean, you were in a bad mood that day, which I’m not saying it’s a bad thing, but that this was when that was giving us such problems. Yeah, but I turned it off because I saw it go flying. It probably flew, I’d say probably 30 feet. It did. It was quite a ways away in the plane of rotation, if you will- about. Yeah, it was about 30 feet away and you got a little upset when I turned it off. You’re like we just shut it off or it was.

[00:58:31] Running, did you turn it off? And I was like, didn’t you see the piece go flying? And they’re like, oh, now I see it, I see it, yeah, and yeah, half the blade was gone. Yeah, so, and that, by the way, I said I can’t find that blade anymore. That’s. That’s unfortunate. I really wanted to replace it with the same kind, I don’t know why, because it’s a cool name and it’s a wood prop. Not only is it a wood prop, but, like the, the other wood props that I’ve seen are like a lighter color wood. This one was more of a realistic, darker type of wood. I don’t know what it was made over, if it was stained differently or whatever it was, but it looked like an older type of propeller and it really matched that.

[00:59:06] Airframe and I really liked it. Well, we’ll do, we’ll search and find something. But yeah, there’s my choice for my favorite prop: wood. Unfortunately it’s just not durable, so they’re the most prone to breakage and cracking and but they look the coolest. So that’s like I said at the beginning of the show when we were talking about the warnings and the safety: don’t fly with a prop that has a nick or scratch or gouge, especially wooden props. Yeah, I agree. How about two blade versus three break? So you can’t say slow flyer, apparently I can’t say three blade, well, a three.

[00:59:42] Braid plop nice. A three blade prop is not one I really deal a lot with. I don’t like. I know a lot of guys fly them for scale looks, but I just I don’t guilty. Yeah, I know you’re, you’re one that.

[01:00:00] Does that, so maybe you can talk about that more than I can, well. I mean, I like the looks of a three blade, is that right? Yeah, propeller, but there are some things you need to consider if you’re going to choose one of these over a two blade. It’s not a one for one swap, so a 10 by six three blade is going to put more load, obviously, on an airplane or on your power unit than a two blade. You’ve got an extra blade out there and taking another bite of air.

[01:00:31] Putting additional load on the airplane or on the power unit. I keep wanting to say, yeah, I know so it’s not a one for one swap. Usually, well, generally speaking, you have to either go down either in pitch or diameter. When you, when you go up to a three blade, the reason again is because you got that extra blade out there taking another bite of air, so it’s going to create more load on the

[01:00:54] Airplane. Aren’t they less efficient though? So there’s I, or does it even matter? For?

[01:01:01] Something this size. Honestly, if you have the right propeller selected for the, for the engine, the propeller and engine combination, I don’t think a properly sized three bladed propeller is any less efficient than a properly selected two blade. Okay, we’re going to go over here in a little bit on things to consider when you’re choosing a propeller. But if they’re both in the correct range for your engine and they both operate, get your engine operating in the optimum rpm range or motor.

[01:01:33] I don’t think, really, realistically speaking, I don’t think we’re going to notice any efficiency at our scale now. So I guilty. I did a google search knowing that we were going to do this episode, and I read a lot of stuff saying that, yes, they are way more efficient or yes, they are way less efficient. I’ve flown a long time, I’ve been flying a long time and I choose three bladed propellers for several different reasons, but I like the way they look and if the tips are,

[01:02:06] Painted- that’s another tip- going through the air, creating an arc so you can see it. Even that much better scale airplanes. If you look at them- most of them, even civilian stuff, reciprocating engine powered- now have three or more, sometimes four blades. So I choose them for appearance. I like the way they sound and, like I said, I like to paint the tips and then that’s another blade you’ve got creating an arc in this in the air, so you can see it. They do, they develop more thrust and I

[01:02:39] Don’t think so. Not really, especially if it’s if you’ve got one selected to get your engine in the right rpm range. But do they deliver less thrust? That’s not been my experience. They are. They are, like I said, equal apples to apples. Yeah, things considered, they develop, I think, the same amount.

[01:02:56] Of thrust, so not a noticeable difference for anything, and pretty much three blade versus two blade is just going to be for looks, I think so right. I mean, yep, yeah, go more scale or something.

[01:03:05] Like that. There are certainly things to consider when, when you’re going to a three blade- but yeah, a properly selected one- I don’t think we’re going to notice a less or a significant decrease in thrust. What about a four blade? So I have no experience with four blade. Okay, there’s not a lot of four blade props out there. They’re expensive, they’re crazy expensive. Yeah, I’ve seen like apc used to make some, I think, and there’s a few other like wood prop manufacturers that have made them crazy expensive. Beautiful, they look very, very they’re awesome. But I can imagine that.

[01:03:38] Again one that’s selected correctly for the engine or motor. I really don’t think you’re going to notice a significant. You might notice a difference. You may have to play with pitch or whatever to compensate for maybe a lack of top end or low end or whatever. But I think the

[01:03:57] Differences are very minimal. So you’re a, you’re a hand starter guy, I am. Do you take any more precautions with a three blade versus a, possibly a four, if you would ever get one or a two blade prop?

[01:04:09] Not, not really. So I will hand flip my, my airplanes that have three bladed props on them. I use the same technique as I do with a two blade. I just try to be cognizant that upcoming blade is a lot closer than it is on a two blade. So I just make sure that my, my flip is more, maybe a little bit more vigorous to get my fingers out of the way, but otherwise, no, I don’t, I don’t change.

[01:04:32] My technique at all. Yeah, because you do it probably the most dangerous way that you can. I mean honestly, yeah, it’s the best way to do it for the motor or for the propellers, especially too, because you’re not running like you don’t use electric starters. I try not to, because I mean

[01:04:49] That can cause problems on a motor. We’ve talked about that, yeah right in previous episodes, but yeah.

[01:04:54] But from the propeller side of things, the three blade is going to have one coming quicker and closer than the two blade will, but you want to get your hand out of the way very quickly- yeah, just so you don’t have any issues with that coming back and hitting you. And the other thing you want to do is make sure you get it through that compression cycle so it doesn’t backfire, and try and fling the opposite way through your hand right, which- and then we’ll actually talk about a little bit later too- how to set a propeller. Yeah, set up a propeller correctly. Yeah, when you’re bolting it.

[01:05:25] For hand, starting for even using the chicken stick, but just to make sure you do it in.

[01:05:32] The safest manner possible. Yes, exactly. So things to consider if you’re going to go down the three blade route, like I said, it’s it’s not a one for one swap- you’re not going to take a 10 by 6: 2 blade and bolt on a 10 by 6: 3 blade and expect the same sort of performance. So I’ll tell you what I do. I usually go down in one step, either in pitch or diameter, so we’ll take the dualist for an example.

[01:05:59] Are you doing three blade on it? Well, yeah, all right, I didn’t know that. Yeah, I’m sorry, okay.

[01:06:05] So what I’m going to do on the dualist is the engines that I’ve chosen. Those irvine 40s are designed, obviously, to run the standard 10 by 6 propeller, two blade. So what I’m going to do is I’m going to take two 10 by 6 narrow bladed three blade and you can get those through. The company was: oh gosh, I want to say it was zingali z-I-n-g-a-l-I available from macoa.

[01:06:42] We’ve mentioned. I’ve mentioned them, I think, on the on the show before. Yeah, but they’re the blades. Even though it’s a three-bladed propeller and it’s a 10 by 6, same as a two blade, the blades are essentially a 10 by 6 narrow blade, except times three, yeah. So it should sort of balance out. And since I’m putting pipes on these engines, I’m putting them on tune pipes. They’re going to develop a little bit more power than a standard 40. So I feel like- and I’m doing that for ground clearance reasons- like a 10 by 6 on these engines with the pipes is probably not enough prop and I could go.

[01:07:17] With a 10 by 7. Here we go, though, with that wider pitch like we talked about earlier. That’s not the direction I want to go. I want- like I’m going to be flying off of grass, I want to try to maintain a flatter braid blade. Excuse me, so I need to get off the ground. So, because these engines are going to be on pipes, I don’t. I don’t want to go to a 10 by 7: 2 blade or an 11: 6. I don’t have ground. I’m not going to have ground clearance for an 11 inch prop. So next alternative is I’m going to go with that 10 by 6: 3 blade with the narrow blades, or I could also maybe go to a 10 by 5.

[01:07:55] Standard width blade on the three blade. So it’s always a trade-off, right? Yeah, so that’s, that’s sort of the and, and there’s lots of reasons to go with three blades other than looks. Ground clearance, like I said with the dualist is, is one reason that you might want to go to a three blade, but how?

[01:08:12] Does that make any difference, like between a two blade and three blade? So it’s a 10 by 6: 2 blade.

[01:08:17] Roughly speaking, if you wanted to make the same thrust with a three blade and you needed some ground clearance- like maybe you didn’t have room for a 10 inch prop- you could go to like a 97 three blade.

[01:08:27] Okay, and develop about the same thrust. I mean, yes, you could do the same thing with a, with a two blade, but it’s not as cool, so it goes back to being: it’s cool, right? Yeah, exactly, I gotcha. So that’s that’s why I choose them. That’s that’s kind of the rules I use to choose them. There’s lots and lots and lots of information on the internet. Master airscrew still makes three blade props, so there’s a, there’s a resource right there and, like I said, macoa sells these old. I don’t know if these are reproductions or if these are original, because these props have been around.

[01:09:01] Zingali, I’m pretty sure that’s how it’s pronounced. I’ve been around a long time so I don’t know if they’re molding them still or if these are just old, but they’re cool looking and they’re plastic and they’re, yeah, plastic. Yeah, very similar construction to a master airscrew- black one. So there you go two.

[01:09:18] Blade versus three blade or more. Next thing, let’s get in just a little bit more on nitro versus electric.

[01:09:24] I mean we, we sort of hit on the hit on the differences earlier or you did, but yeah, nitro plop, now I’m doing it. Nitro props or propellers designed for gas or nitro are going to be more ruggedly constructed. They’re going to be thicker, heavier even probably- yeah, designed to withstand the vibrations that are coming from those internal combustion engines. Yeah, generally, you’re going to see the

[01:09:51] The hubs are going to be thicker. Yeah, they’re actually going to be wider. Right, then you’re going to see on the electric ones, and once again, that’s just because, well, and also, like, the base where the propeller hooks up to the hub is going to be wider, so the actual propeller blade where it connects to the hub is going to have a wider connection point than you will see on electric one. Yes, once again, that’s because of all the extra vibrations and stuff that goes along with a, an engine, that’s actually pulsing power as opposed to the smoothness of electric, electric props. Again,

[01:10:25] Are designed to be lightweight. Yeah, because electric motors are weak and they need to take all those advantages they can for the lighter weight. Take you to the cleaners again. I’m just teasing, not.

[01:10:36] Weak, come at. Come at me with facts. That’s all I’m saying. It’s not weak, they’re smooth, they’re designed.

[01:10:42] To be light, to take maximum, to take full advantage of the power that they offer. Yeah, I agree because

[01:10:48] They’re not getting beat around the arc of the plane that they’re spinning in. It’s not like.

[01:10:53] Smack, smack, smack, really smack. That’s smack. That was smack. Three rpm, just like was it three or one and a half.

[01:11:03] Well, no, that was, I don’t know. I give up, and that would have been revolutions anyway, not rpm. Yeah, so we’ll.

[01:11:10] Talk just a little bit about the shape of the tip, just the tip of the propeller. So I’ve seen them pointed, I’ve seen them square, and that all comes down to now: hold on, this is just the, the, just the tip, just the tip of the propeller is. It’s important because the shape of the end of the propeller is designed to reduce, in most cases, wing tip vortices which cause drag, which therefore make an

[01:11:42] Airfoil, which an air, a propeller is. You call it wing tip vortices. Wing tip vortices, oh, not propeller tip vortices. Right, because a propeller is a wing, a wing, okay, set on, like I mentioned at the beginning of the show. That’s been so long ago, has it been? What time did we start? I don’t know. I didn’t write it down because I don’t have my watch on. Oh so, sharp pointed tips, reach.

[01:12:11] Sharp pointed tips reduce tip vortices which cause drag, and they will limit the amount of lift or thrust, in this case, that the propeller can develop also causes noise, which I actually kind of think is cool. Yeah, I do too. They don’t bother me and did that. A lot of the noise that comes off of a propeller, especially at a higher rpm, are actually sonic booms. I did.

[01:12:40] Yeah, isn’t that cool, that is cool, that’s I. That’s one thing I love about listening to the yak fly because, oh boy, it spins those propeller or that propeller fast. That propeller is huge and those tips are going very fast, supersonic, very, very fast. I ought to do the math on that sometime to figure out exactly how fast they’re spinning. Yeah, but yeah, and you can hear the, the, what’s it called? The, the breaking, the, what’s it called ripping of the, yeah, the, the prop rip, and it does sound, cool sounds.

[01:13:12] Awesome, and that noise is actually created by sonic booms from the propeller tips going supersonic, and which to me, is just one of the coolest things right you can talk about, which is odd in my opinion: that master air screw, after all these years, still has fairly square propeller tips, but you.

[01:13:32] Know what they work really well. So well, you don’t get that as much with the smaller ones. No, because obviously, once again, talking about the, the, the arc that you’re traveling in, the smaller your, your diameter is, the faster that has to spin to get the same speed on that tip. So just, the tip is not going as fast on the smaller ones, it is on the bigger ones. So right, yeah, nice. So that’s enough about.

[01:13:59] The tip of the propeller. So some things to consider when selecting the right propeller, if I may. All engines and motors to a lesser degree motors, but all power units. They run in an optimal rpm range. Nitro motors and gas motors: the range is not maybe as wide as an electric motor, but still optimum. Maximum power output efficiency is going to happen within a range of rpm and we select a propeller to try.

[01:14:38] To get our engine to operate in that range. Getting back to what you were saying about constant speed propellers, that’s why they do that: to keep that engine in its maximum operational.

[01:14:51] Efficiency, maximum power output, yep. So like here in my notes I wrote down: too big a prop is going to cause the engine to lug or to work hard to try to spin that propeller up into its maximum operational range, and that’s going to cause a lot of heat. Heat causes damage. It’s not something you want to do to your engine or your motor and electric motors especially susceptible to being over propped. You pull too many watts, is it? Then you run the risk.

[01:15:22] Just talk about your glow stuff. I’ll give you a little bit. Okay, fine. And if you put too big a prop on your nitro or gasser, it’s gonna. It’s gonna consume more fuel, it’s gonna generate more heat, it’s gonna cause a lot of abnormal wear onto those expensive engine parts, but it’s not nearly as.

[01:15:42] Bad on a glow engine to go big as it is to go small, correct? Yeah, yeah, too small, you’re gonna run.

[01:15:51] Outside on the top end of that optimal rpm range and stretch a connecting rod or score a sleeve. Yeah, definitely, definitely, definitely worse to go high on the on the rpm range than then to go low. But you don’t want to do, you don’t want to really go in either end. You really want to get that engine operating in its optimum rpm range. And how do an engine’s optimum rpm range? It’s usually in the instructions that come with the engine and if not, man, google search. Yeah, that’s why 10 by

[01:16:24] 6 Is sort of the standard for 40. Size 11 by 6 is kind of the standard for 60. And if you go to apc’s website or master rescue, they have the like charts to: hey, I have a 124 stroke, what prop should I put on? They’ll tell you yeah, and then once you get that general, that baseline, then you can fine tune plus or minus, but not too far outside those ranges because you can cause damage. So, talking about that, these engines usually can operate within a range of propellers.

[01:16:58] So let’s take the standard 40 again. The 10 by 6 is the standard, but it’ll also swing. A 9 by 7 might also swing an 11 by 5. So plus or minus one on either, not both, but on either.

[01:17:14] Dimension. Usually you’re pretty safe. So plus one minus one for each one, or minus one plus one, right.

[01:17:21] But not for both. Like you can go plus one in pitch if you stay the same diameter and vice versa. You don’t want to, you don’t want to take a two-step right. No, what I’m saying is: if you, if you’re.

[01:17:32] Adding one inch to your diameter, you’re going to subtract one inch from pitch. Yes, exactly right. So a 10-6 is not an 11-6, it’s an 11-5, right, so right, but some engines depending on the engine.

[01:17:45] They may turn a 40, a really strong 40 may turn a 10-6, just fine. But it may also turn an 11-6, just fine. It’s, it’s, and in the instructions for your engine it’ll tell you. They’ll tell you what range is, but sometimes you can fine tune. Going back to what we’re talking about, the gears in a car, if you want to gear your airplane to get off of a rough field, then you can play with those figures to get the performance you want out of your engine.

[01:18:16] But, like I said, always refer to the engines manufacturers instructions.

[01:18:20] They’ll usually give you a range, and if you stay within that range, you’re usually pretty safe.

[01:18:25] Usually, usually. But yeah, a good general rule of thumb is: plus one minus one or minus one plus one. Never plus one plus one or minus one, minus one minus one. So yeah, bolting a 10, a 10 by 5, to the front of your 40 size sport plane to overcome a short field, take off all that drag. It’s going to come with a trade-off of speed, just like we talked about top end speed, yep.

[01:18:50] Yeah, exactly so. It’s going to get you there faster, but that top end is going to be slower. Exactly have. That didn’t sound right, but that was right. That’s exactly right. So it’s gonna. It’s gonna have more.

[01:19:00] Acceleration more, it’ll have more torque. Yeah, if you want to think of it that way, I’ll have more torque to get you through that rough draggy grass off the field, but then, unfortunately, your top speed is going to be a little bit less. Yeah, it’s always going to be a trade-off. Yep, so electric motors you want to?

[01:19:15] Talk about propping those bad boys, so sizing propellers to electric motors. You’re really going to stick with the recommendation from the manufacturer. They’re going to kind of like you’re talking about. They’re going to give you propellers to start with and you can go either way, like you’re talking about, on your gas or glow engines. Biggest difference, though, is electric motors are just the opposite, so you can under prop them and not have any issues whatsoever. Yeah well, that makes sense. The only thing that’s going to be wrong is you’re not going to create as much thrust as you could.

[01:19:48] Get out of it, but you’re not going to hurt anything, you’re not going to overheat anything, you’re not.

[01:19:52] Going to stress anything. I’m going to over, rev it and right up a connecting rod or right, whereas going

[01:19:57] The opposite way is bad. If you put too much of a of a propeller on there, you’re going to overheat things because electric motors are going to try to constantly go to that speed at which you’re telling them to go to and they will pull as much current as they need to get there. So if your motor is pulling too much current through your esc, you’re going to start creating heat. You’re going to burn it up. So you can very possibly mess up your motor, your esc or your battery or all three.

[01:20:32] And that’s an expensive mistake might not happen, but it’s possible that you could catch your plane on fire because of all the heat and stuff. That’s kind of scary. Well, scary, yeah. Fire and LiPos scares me to death. Let’s be honest, how cool would that be? Well, flying along for a short period of time and then

[01:20:52] All of a sudden like whoa, look at that. And then, oh, looks like I gotta buy another airplane. Yeah, yeah.

[01:21:00] Because you’re not getting anything back on that one. So that’s the nice thing about checking with electric motors: you can actually check to see if you’re pulling too many watts through it by using a watt meter and that will tell you, based on what your motor is rated for, if it’s pulling too many watts. If it’s pulling too many watts and that means you have a propeller on that’s pulling too much or that has too much resistance and it’s pulling too much power through it, therefore you’re going.

[01:21:25] To mess it up: watts, amperage, volts. Folks refer back to the motors episode where Ron did a fantastic, really did a fantastic job of going through all that for us. So it kind of explained a lot.

[01:21:38] But wattage is what you’re going to be reading with a watt meter, quite obviously, and that’s going to tell you where you’re at, based on what your motor can withstand, and that what your motor is rated for kind of comes with the motor. So it’s going to be with your documentation and stuff when you buy it, cool. So yeah, use a watt meter, make sure you’re under the rated wattage and you’re not going to mess anything up. Yay for electric. So how can you tell with that, like there’s watt meters for electric motors, what is there for a nitro motor?

[01:22:08] Well, I use a non-contact thermometer, oh so an actual thermometer, so I can measure cylinder head.

[01:22:15] Temperature thing, like things like that. So then what’s a good temperature for a cylinder head? That’s.

[01:22:21] A good question, so I asked. There is a lot of information and misinformation out on the web.

[01:22:28] And well, let’s, let’s not talk about the web, let’s talk about, let’s talk about Tom tommy. Tommy does not.

[01:22:35] Like to get his cylinder head temperatures. He tries not to get them above 200. So I try not to run my engines with a cylinder head temperature above 200. I believe you can go higher than that, but why, if you don’t need to? Yeah, because heat is not a good thing. No, I really like the 185 to 195 ish range. That seems to be the best compromise for they get.

[01:23:10] If you want to measure fuel economy, that they probably get the best economy there and there’s going to be people that are going to argue that point and other points that I’ve made regarding temperatures. But a ringed engine at 190 is usually pretty safe. 185 Is even better and a cooler engine usually will kind of develop more power. It burns more fuel but it develops more power and lasts longer because you don’t have all that extra heat an abc engine relies on.

[01:23:42] Heat to make that good seal. Because remember, back in the did we talk- yeah, did we talk- about temperatures? Though I don’t remember talking about temperatures, we touched on it. Well, forgive me for not remembering, that’s okay, it was nitro. You weren’t interested, I? I don’t even know if I listened.

[01:23:56] To that one? Probably not. I didn’t even like when I edited, I just played it. Whatever nice, but an abc.

[01:24:04] Engine. That doesn’t depend on a ring to seal the combustion chamber. It depends on temperature to swell those parts to make that seal. So the temperatures are a little higher, you run those a little higher. But yeah, I, I generally stay away from 200 and above. So when you’re checking your

[01:24:24] Different propeller sizes. Yep, that’s how you check them. Yep, that’s one way to do it. I do it by ear.

[01:24:29] I’ve been doing a long time, but you can back it up with a thermometer, yep, so there you go. How about?

[01:24:35] Spinners. Do you want to talk about spinners? Yeah, let’s talk about spinners really quick. Why? Why would you use a spinner other than it looks cool? Or is that the only reason? Well, that’s probably the primary.

[01:24:45] Reason to smooth, to kind of make the airplane smoother, looking sleeker, sleeker, thank you. Yeah, but honestly I believe it probably will actually make the airplane sleeker so you develop a little more top-end speed and maybe make the airplane a little more efficient, less drag on the front, so you don’t have to put as big an engine on it to overcome that drag. Do you really?

[01:25:09] Think it’s going to make that much of a difference, though I mean, like, honestly, with something that small.

[01:25:14] For a general purpose, flying, no, yeah. No, it’s cool, it’s a, it’s about looks, yeah, and some of them I.

[01:25:22] Actually think look better, depending on the airplane, without a spinner. Yeah, a big old propeller hub like.

[01:25:28] On a world war ii? Yeah, I agree, and it depends. It depends on what you like. I tell you what, though? Having a spinner on there? Having a spinner on there, it’s a handy place to use an electric starter, which you don’t do. So I do. I mean, I own electric starters and I do use them from time to time. I mean, I have some stubborn engines that don’t like to be started by hand. Yeah, but a spinner makes it pretty handy to use that. The big cone on the like: yeah, I’ve used one, an electric starter on one.

[01:26:00] That doesn’t have the spinner on it. Yeah, you can do it, but it’s not fun. It’s hard to keep it centered. Well, you have to flip the cone around and use the small hole, right, but so well, yeah, because then the small hole lets it make more contact with the extra or actual hub on that propeller. But

[01:26:17] Yeah, it’s just it’s harder to do. Yeah, so, yeah, so that’s in my opinion. That’s kind of the only reason I use them. There might be other reasons, but mostly just for looks, yeah to be.

[01:26:32] Honest. Well, and I- and I can appreciate that because I most planes look better with it but, like I said, not all of them. So one of the other things I want to talk about with propellers: let’s say we just got a propeller, it’s brand new in a package and we’re going to put it on our airplane. Yes, walk me through what needs to be done with that, because there are a few things. I mean you can’t go from package to airplane. You have to do some things to it. You should- I should say you should- do some things to it in order to make it work better. Yeah, so what I do is

[01:27:05] First thing I do when I pull a brand new propeller out of a package or pull it out of the my parts drawer or whatever is, I will dull the trailing edge of the of each blade and try to smooth the leading edge as well, because that’s, that’s not wood, no, no. So make sure we’re talking about the right kind. Thank you, yeah, on a wood propeller. I don’t do that on a carbon propeller. I don’t do that especially to a carbon propeller, but yeah, on a on most like apc plastics. Yeah, apc.

[01:27:36] Master screw. There’s usually a seam, a molding seam, on the leading edge of the propeller that I like to smooth down and make- try to make it nice and smooth and efficient- and then the trailing edge is usually very, very sharp. Yeah, and let me tell you, paper cuts are bad, but a cut from the trailing edge of a propeller- I don’t know what it, probably because you’re messing with nitro fuel at the same time- and it gets in that, and let me tell you that’s no fun.

[01:28:02] At all. Yeah, and those are, those are very. I mean, they’re like razor sharp sometimes they, they do they.

[01:28:07] Are very sharp when they come out of the mold. Yeah, so I’ll basically what I do is I take the sharp edge of my X-Acto. I mean, I keep an X-Acto in my field box, which, yeah, covered in what’s in Tom’s field box, and I’ll just basically scrape the trailing edge of that and just kind of dull it and smooth it as best I can. Not gouge it now, just right, just kind of run it along the trailing edge.

[01:28:29] So you can do the same thing with same paper. You’re not doing it like how do we describe this? To make sure it’s not being done wrong. So you’re not actually doing it to like cut, no, so you’re not running that blade parallel to the, the edge, you’re running it perpendicular right and just kind of using it as a scraper. As a scraper, right. So don’t, you can do the same thing, probably in a little.

[01:28:48] Safer method with a little piece of fine sandpaper. Just, you just want to dull that trailing edge, especially if, like me, you use your fingers to start your airplane. I don’t want that cut in my fingers every time I’m trying to flip the, the darn thing over. So that’s the first thing I do is I dull the trailing edge and I’ll try to smooth out the leading edge, either with my

[01:29:07] X-Acto or sandpaper. Exactos, I actually think, work better than sandpaper, though yeah, they just they seem to not use, they seem to not take as much off, like with an X-Acto knife, you can actually get just that seam and you don’t scrape any of the other stuff off that you don’t really want to be messing with, right? So, yeah, I prefer the X-Acto knife also. So that’s the first thing I do. The next:

[01:29:30] Thing I mean it’s, it’s six, one half a dozen together. You can either ream the, the, the hub hole, the prop shaft hole, or you can balance it. But you got to do both right well usually.

[01:29:44] You have to do both. Yeah, if you have the right size hole. If the propeller already fits over the shaft that you have for your motor, you don’t have to worry about reaming it. What if it’s too big? If it’s too big, then they actually come with the spacers and you can use the spacers to shrink the hole so it fits the shaft just perfectly. Yeah, yep, yeah, kind of. Yeah, you’re right.

[01:30:05] It shims it down. So yeah, so I’ll balance it. There’s lots of different techniques people use to balance their props. None of them are wrong. I’ll just say that, yeah, it depends. Some are more right than others. I would. Some are more right than others. Don’t remove material, I do not like. I’ve seen people sand the tips to remove material. I’ve seen people sand the back side of the blades to remove material. I’ve even seen people like drill holes in the hub. Yeah, that’s, don’t do that.

[01:30:39] Because, especially, especially on a nitro or a gas propeller, because that hole, that hub is molded thick to resist the stress of you torquing down on it, to keep the darn thing on the front of the engine.

[01:30:51] So don’t don’t drill holes in the hubs, and they’re also engineered that way because of the stresses that come with the motors that run them. Yes, so the material that’s there is there for a reason, right, and the same with you’re talking about sanding the back of it. It’s a blade. Yeah, so it’s not flat, it’s an air, actually is an air foil. Sorry, right, if you’re balancing laterally your airplane, you’re not going to sand off the top of your wing in order to make it work. You’re going to fix it another way, which is the same with your propeller. You don’t want to sand off any material, right? So, yeah, I agree with.

[01:31:24] Them. So the technique I use- and we mentioned it earlier- I like to paint the tips of my propeller blades, if they’re not already painted, so I’ll use that to balance my, my propeller. Yeah, so I’ll paint the tips yellow or white or whatever, and then I’ll just keep adding paint to one tip until I get them to balance. And we’re talking minuscule, I mean like probably one hundredths of grams of material to

[01:31:56] Get a propeller to balance, because they’re actually pretty doggone close out of the package usually.

[01:32:02] Yeah, most of them are pretty. I mean, yeah, obviously the bigger the prop, the more.

[01:32:08] You’re gonna have to add. But so a contrasting color on like a black master air screw prop is one technique I use. If, for whatever reason, I don’t want to paint the tips a contrasting color, I’ll shoot just some clear polyurethane just a little bit at a time until on the back side of it, yeah, the blade, to get until they balance. That’s one technique. Another technique I use. But I never, ever, ever, remove material from the, from the propeller itself, either at the hub or the blade or the tip.

[01:32:38] Especially don’t say like I don’t. Why would I mean? Don’t say in the tips, folks, because now you’re altering the diameter on one side right, developing asymmetric lift or thrust and causing dynamic vibrations and all these other bad things. Just add a little bit of weight. Yeah, I, I.

[01:32:57] Normally like I don’t. I don’t paint the tips on mine most of the time. If I buy them that way, awesome, but I’ve never done that myself. Okay, so I will do the whole shellac or whatever on the back of the propeller and it’s a couple quick spritzes and usually, and then usually that’s too much. So you have to go to the other one a little bit on the other side until you get it. Just right. But

[01:33:21] It is an important step, though you don’t. It’s not a step you want to omit especially.

[01:33:26] Having electronics on board. Electronics do not like vibration. Yeah, so walk me through then. Actually balancing it. What tool do you use to balance the propeller? So I use what’s going to be.

[01:33:36] This week’s tool of the week. It’s time for rc plane labs. Tool of the week: a prop balancer. I use one.

[01:33:47] From dubro. There’s master airscrew makes one great planes makes one dubro. I mean, there’s still a lot of them, unlike a lot of the tools that we like. There’s still a lot of these tools out there being made. But basically you just set your prop up on whatever balancer method you’re using and the heavy blade is always going to fall and you add weight to the blade that’s sticking up in the air until they, until neither one falls consistently every time, and you should be able to keep that blade.

[01:34:18] At any angle. Correct, exactly so you’re not. If it’s balanced, it will. It will sit any angle: five degrees, 10 degrees, 20, all the way around the circle. It’s not just going to be 90 degrees or not, horizontal or vertical. You’re going to want to actually make sure it stays at any. It will stop.

[01:34:38] At that at any position and stay there. Yeah, a heavy blade may not always go to 90 degrees pointing straight down. A heavy blade may sit, say, 45 degrees, but it will always rotate to that point. Yeah, properly balanced propeller will stop at any point. Yeah, wherever you stop, inconsistent, place where it.

[01:34:57] Stops. Yeah, yeah, and so, like with balancers, most of the time you want as little friction as possible between the blade and what it’s actually balancing on right. So if you’ve never balanced a propeller before, there’s a shaft that goes through the. With the balancer, there’s a shaft that goes through the hub on the propeller, and then most of the ones that I’ve seen, and the only ones I’ve used, have been magnets, so they’re magnetized on the end, so there’s no actual physical connection.

[01:35:33] Holding. So there’s not going to be any kind of resistance. Resistance, thanks, it’s gonna. That’s gonna keep it from spinning. So it’s gonna be able to spin very freely, yeah, and no drag, no friction, anything like that. So it’s gonna be the best way to actually check the downside to that method.

[01:35:51] Unfortunately, is there’s a limit to how heavy a prop it will actually suspend in midair. Yeah, so you.

[01:35:59] Can also like if, if, when I balance the big one that I got, which the big ones come pre-balanced most of the time, like your carbon fiber ones and stuff, and you don’t touch them, I mean, yeah, I don’t, that’s all, they’re out of the pack. Well, I don’t own. I think I own one. Yeah, but right, when you buy those, those are done. That’s one of the reasons they’re so expensive. You can check them. I mean, it’s probably

[01:36:22] Not a bad idea to check them, but I personally wouldn’t, yeah, so spend a lot of time trying to.

[01:36:26] Balance them. I’ve checked them, especially after they’ve been drilled, just to make sure that they were okay after that. But yeah, you can still use- like I still use- that same shaft that goes through the middle and that still works, and then I just set it on top of the balancer and then it. When you’re dealing with something that wide, a little bit of friction is not going to hurt nearly as much as on a tiny one, so I wasn’t concerned about that, but that one was balanced perfectly. Anyway, I didn’t have to do anything with it. So, yeah, make sure you balance all of your props, though.

[01:36:58] Yep and the. I use the same technique for two blade or three blade heavy prop or, I’m sorry. The heavy blade is going to always drop and then I’ll add weight. And then three blade is a little bit different. Sometimes it’s hard to figure out where to add the weight if the same blade is always falling. So I’ll I’ll determine, like, if the blade is falling straight down and you’ve got two other blades, I’ll add weight equally to both of those blades and then if it’s a if it’s a if.

[01:37:30] The heavy blade doesn’t fall straight down, but it’s pointing, maybe at an angle. Maybe I’ll put more on the uppermost facing blade than the other, more weight on the upper face. Basically it’s a balancing act. They’re more difficult to do, they are, but it can be done. Yeah, and it should be done, right. I mean yeah, but yeah, it’s. It’s hard to make them worse, like because the physics is not going to lie. The heavy blade is always going to fall. So if you’re adding a little bit weight to the light blade, you’re making the it better instead of worse. So that’s a good way to look at it, right.

[01:38:06] I thought so. That’s why I do it that way. So, yeah, another tool that’s handy is the prop reamer I mentioned. You can do the kind of in any order. Usually reaming the hole is not going to change the balance much, so usually I balance first and then I ream. It’s six, one half dozen, the other, I think. On the order, yeah, but I use a great plains again prop reamer tool, and I have two of them. I have one for standard and one for metric, because for whatever reason, we’ve not adopted the metric standard. So there is some sae stuff out there.

[01:38:40] Even on engines that aren’t manufactured here, like some weird. Some of the stuff coming from china and overseas still has sae. I can’t figure it out either, but it’s out there, so a prop reamer is.

[01:38:52] Another handy tool to have. And why would you use a prop reamer over like a drill bit? So a drill bit.

[01:38:57] Is not designed to ream. Okay, a drill bit is designed to drill, it has it’s. The flutes are designed to cut and be very aggressive and if you go taking a drill bit into a hole, there’s a good chance it’s going to grab, it’s going to dig into the- yeah, it’s going to try to twist the thing out of, and there’s a good chance you’re going to drill the hole off center, and that’s bad. A reamer, on the other hand, is designed to fit in the hole almost like a, a pilot, if you’re familiar with a.

[01:39:28] Manual transmission. The pilot shaft goes into the pilot bearing in the back of the crankshaft.

[01:39:32] And gets everything in perfect alignment. I love how you use something that is very antiquated to describe something that is not. Well, a manual transmission? Well, that’s true, there’s.

[01:39:46] I guess not as many of those out there as there used to be, but at any rate, a prop reamer is designed such that it will center itself in the hole, so that you ream your hole centered. Yeah, so you’re not going to get your hole off center and, to be honest, I use a drill press, so my prop reamer has a little handle on it that’s removable and that leaves you with a nice shaft that you can.

[01:40:10] Chuck into the drill. You use a drill press with your prop reamer. I absolutely do. I never thought of that. Yeah, that’s actually a great idea, because I hate sitting there- it’s a pain and twisting it.

[01:40:22] A quarter turn at a time. Yeah, and I’m always really super concerned, especially on some of these more expensive, like wood, the big wooden props or even a carbon fiber, that I’m going to ream the hole off at an angle. Oh really, even though it’s, it would be really hard to do. Well, I wasn’t concerned about it before, but I guess I am now. But, but, yeah, I’ll, I’ll go ahead and chuck my reamer in my drill press and run it at a low rpm and actually use that to, and I’ll, I’ll hold the prop by hand. I don’t clamp it or anything, because I don’t want to damage the prop. Well, you,

[01:40:53] Want to be able to move a little bit if it needs to. Yeah, yeah, because the spindle on my drawer press isn’t perfectly true. It may maybe a little bit half degree and I’m okay with letting it do its wobble a little bit on the flat on the table, as long as it’s flat. I know I’m not going to be reaming my hole at an angle. That’s it. Yeah, I’ve never thought so. I use a drill press. But you can, you can do it, you can certainly do it by hand, if you, if you.

[01:41:16] If you’re cautious, I will not do it by hand anymore. I mean that, no, that’s, that’s great I don’t know why that one blows my mind so much right now, but that’s a great idea. I mean most. Most.

[01:41:25] Prop rumors. Have a, have a t the t handle. Usually they’re removable. I always thought they were removable for that reason, so you could chuck them in a. I didn’t. I don’t think I’ve ever had one come.

[01:41:35] Off on me, so I never even thought about removing them. Oh, and if they’re not, you can just stand the little flat spot off to make it removable. So but yeah, that’s how I, how I remember, and that’s and.

[01:41:45] Those are the. Those are the things you should probably do to a prop rough. Smooth out the edges, take away the sharp edges and balance them and ream them and then use them, bolt them onto your airplane- I’m sorry, bolt them onto your power unit. Well, that’s still on the airplane.

[01:42:02] But that’s okay, that’s true. So, speaking of bolting them onto your power unit, if that’s the word you

[01:42:09] Want to use. Well, I’m trying to accommodate them all: nitro, gas and electric. Those are all power units, okay when they’re all. When combined with your propeller, they’re like a power system technically.

[01:42:22] They’re all like motors or engines- you could say that too. Okay, so let’s talk about how we connect it to the motor engine- whatever you want to call it. Okay, there’s a few, a few different ways that they connect to your, to your motor. So if you have a big airplane, you’re gonna have to drill it out for the mounting bolts that go on the front of the motor. Yeah, because usually the prop is not simply held on by a washer and nut, not when you get to bigger ones. You’re correct, so you have to buy.

[01:42:56] A jig. Unfortunately, it’s another tool for each engine really that you have. I don’t know how.

[01:43:03] Like. I don’t think all 50 cc’s are the same, are they? I don’t think so. However, I have one jig at home that I have used for every 50 cc engine I’ve had to drill a prop for so, which has been several. So that’s hopefully. Maybe they’re, maybe they’re standardized, I don’t know that. But if in doubt, buy the jig from the manufacturer of the engine. Yeah, for instance, if you’re drilling a prop for a

[01:43:31] Dle buy your jig from dle. So what, like, how many bolts are on the 50 cc? Do you remember? So on my da, I believe it has four, four, yeah, I think my the big one’s six on six, yeah and yeah. So that tells you where to actually drill in order to get the bolts to line up with the back plate on.

[01:43:59] That motor. It’s a handy dandy and you can use it to drill your spinner back plate as well. Yeah, but it’s a handy dandy tool. It’s got a pilot on it, a shouldered pilot that fits in the center of the prop hole and then sort of keys in there and then it, yeah, you just basically run a drill bit down through those holes. I would also recommend doing that in a drill press. Yeah, definitely, to keep it.

[01:44:20] Straight on that one. But yeah, that lets where to drill them and that’s very important because you want everything to line up just right so that you don’t have any vibrations induced into your engine or into your propeller because of that. So, like I said, some of those could be four bolts, some could be six bolts and that’s how they’re connected to the front. When we go smaller. Now, I

[01:44:42] Do want to say I’ve seen some guys try to use. So let’s, let’s take your, your big guy, over here with six bolts. It’s got a. It’s got the washer on the front with six holes in it that the bolts go through and then they go through the prop and then they go through the, the back plate, back plate, and then they thread into the prop, thrust drive washer. Excuse me, don’t use the washer on the front with the holes in it as your jig. Buy it, buy a proper jig. Well, and the reason you don’t.

[01:45:11] Want to do. That is, you could be off by a sixteenth of an inch or more or more. Well, even at even it’s something that small that you don’t realize you’re off. That’s really going to mess with the balance and throw off the whole system on the airplane, right, and it’s not worth. I mean, the jigs are not expensive. No, comparatively no, compared to buying a new prop because you drilled it incorrectly, right? That’s what I was going to say. It’s not worth taking that chance, right to save a few bucks on a on a jig, when you have to go out and buy a new propeller for, like I said, I think the one for

[01:45:41] My big one was 189, so you don’t want to spend that more than once. Yeah, I think the dredge is about 20 bucks, probably, right, a lot cheaper, yeah. So, moving down in size, let’s go to something a little bit smaller. How do you connect most of, like, your nitro engines or even your 50 cc? Those are the same. You said, right, the four bolts that go on front. So if you go down a couple steps, how are

[01:46:07] Those held on, so on my night, my larger nitro two strokes. It’s basically just a big washer and a big nut that threads on the, just a single one that holds on. Yeah, there used to be back in the day, I think, SuperTigre on some of their bigger, bigger two strokes. I think they may have had either bolts or what they. I think they actually had pins, yeah that.

[01:46:34] You would then drill and they kind of engage the back side of the prop. But yeah, on most,

[01:46:39] Of my nitros, on my two-stroke nitros anyway, it’s just a big thrust washer and nut and I torque that bad boy down. I’m sure there’s probably a torque specification and if you’re into that sort of thing you can certainly look it up by manufacturer. But I just hoss it down, I mean I just make it tight. Yeah, on my four strokes most, maybe even all of my four strokes, come supplied with actually two nuts, double nut. It’s a, yeah, it’s a, it’s a, it’s a big nut that goes up against the.

[01:47:12] Thrust washer usually, and then a tapered jam nut that gets threaded on top or into, I should say, the big base nut, so and that locks it in and it’s sort of yeah locks, because four strokes have a nasty habit of sometimes chucking a propeller by trying to fire backwards. Yeah, so that is, that are the manufacturer’s attempts to keep the propellers on the front of the engine where they belong.

[01:47:34] And that’s where you want to keep them. So if it works, that’s a great thing. So that’s how, that’s how.

[01:47:39] I how I bolt them up to all my, all my nitros- yeah, smaller electric ones, as we’re kind of moving.

[01:47:45] Down in size. Some of them will actually have just a single set screw that kind of holds the collet on. Okay, to the, to the shaft like an adapter. Yeah, okay, I don’t think you like those. I’m not a big fan of those. I definitely don’t like those either. There’s, there’s just too much that can go wrong. If that set screw comes out a little bit and it’s, it’s not going to hold on very well. So they also have the, the collet style that, as you, as you tighten it, it pulls it tighter on the.

[01:48:16] Shaft. The collet actually tightens up on the shaft as you, as you tighten the nut on the front.

[01:48:21] Kind of like the fingers on a drill: chuck, yeah, there you go kind of kind of in reverse sort of.

[01:48:26] Yeah, yeah, that’s a good way to think of it. Not exactly, but close enough for what we’re talking.

[01:48:32] About. It’s something that compresses fingers against the shaft to hold it in place. Yeah, and.

[01:48:35] Then that locks on really well, yes, it does. You’re not pulling that off? No, I mean there’s. There’s no way, if you have that tightened the way you’re supposed to have it, that you’re going to have that coming off. So that’s how most smaller type electric ones work. Bigger electric motors actually will have a, a piece on the front that bolts onto them, and then it works the same way like your small nitro ones. You have just the shaft and then you tighten the nut on the end of it. Yeah, it has a drive.

[01:49:05] Washer, and then your- yeah, your propeller- goes over the shaft and then a, a thrust washer and a nut, yep.

[01:49:11] So same setup as a as a nitro. If you’re going a lot smaller for, like some of the foamy, smaller engine or smaller electric motor ones, especially ones without landing gear, they’ll have what’s called a prop saver that you can get for them and that’s a shaft that goes over the or a collet that goes over the motor shaft, with two set screws that come out on each side and then your propeller goes on that and then there’s a little o-ring that goes from one screw to another over your propeller.

[01:49:46] And then that holds the propeller on kind of sketchy. Well, yeah, I wouldn’t fly anything big with it, yeah, but it does great for the smaller planes that with no landing, no landing gear. So when you hit the ground you might hit it at 90 degree like your propellers, 90 degrees to the horizon right, and therefore your propeller will come off before you break the propeller. So I don’t have any with those right now. I had one airplane like that before, but it really wasn’t anything that I was.

[01:50:20] Interested in. Yeah, if you fly airplanes that have those, check those o-rings frequently because they’re rubber. Yeah, when rubber is exposed to the atmosphere, it deteriorates over time and then they lose their elasticity and you don’t want a propeller coming off at your face. No, no, you don’t. But

[01:50:39] Like I said, mostly those are slow flies, so it’s not anything that’s going to be big propellers bending fast or anything like that, so they’re just small foamies. Yep that you put those on, so not a lot to worry about, because I mean, really you’re not going to be pulling a lot of weight with them anyway because they’re o-rings, they’re slow flyers and you’re not going to have a lot of pressure behind it without breaking them. Not a lot of rpm either. Yeah, so usually low rpm stuff. Oh, and I forgot one other thing I wanted to bring up. Do you mind if I take this one? No, okay, so when you’re, when you’re putting a propeller on the front of a nitro engine or a gas engine too, you want to get it to where that?

[01:51:13] Compression stroke, the beginning part of that. The compression strokes when you’re starting to feel the, the compression start, when it starts to get tight. Is it about two o’clock, right? So when the propeller blade is about two o’clock, that way your hand kind of gets out of the way as you flip it by hand, exactly and you’re going in a nice even arc. Do you agree with that? Yes, okay,

[01:51:37] With electric motors it doesn’t matter at all, because they’re a little bit better than nitro and you don’t have to worry at all about where the propeller is on. Do you have anything?

[01:51:46] Else you want to say. So there you go. That’s our. Oh well, did you want to talk about your biggest and smallest? Do you want to outdo me? And? And no, I don’t. I don’t need to outdo you on that.

[01:52:01] So between the two of us, Ron has both the smallest and the largest propellers of between the two of us. It’s not a game, it’s okay. What’s your smallest? You one upped me and one down to me. That was not on purpose, by the way. So my smallest propeller in my fleet, if you will, is a. I have a five by four in inches. That’s on an electric pusher. That’s my smallest. I just barely beat you then, because

[01:52:33] The one I have, I think, is on that mini vapor and I think that’s 125 millimeters, which is just under five inches. Oh, that’s pretty small, yeah. So, yes, I, I, I won down, yeah, just a little bit, but not by much.

[01:52:47] And then you several upped me: how big is your biggest? Like I don’t know what year, my biggest is the, the one that’s on my the newest acquisition is, which is a 2310. Really, I yeah that car would have been bigger than that carbon fiber one is a 2310. Huh, yeah, that’s pretty small. What’s your all right?

[01:53:07] It’s. So what’s your biggest one? My biggest it’s a 33. Oh goodness, it’s a 33, 10 meslick. That is a german large propeller, beautiful, I wonder if it’s made in the. I don’t know what you’re talking about. Oh yeah, so Tom’s making fun of me because I was talking about the nurburgring a while ago and for some reason I kept saying nurinburgring, talking about the racetrack, and he would not correct me. He just because it was making funny fun of me, and he but.

[01:53:40] You kept telling me: no, you’re saying that. Right, that’s fine. Well, of course, I want to pro prolong.

[01:53:44] The joke, so I can keep laughing at you, but I want to know if I’m sound like a fool nurinburgring okay. What I was going to say, though, is the one for the yak. It’s carbon fiber, and really they’re beautiful, beautiful propellers. It’s a work of art. Yeah, I mean for that.

[01:54:03] Airplane. It’s a great fit. Yeah, it looks the part. It’s actually a little bit over diameter for a da.

[01:54:08] 170 You’re. You’re supposed to run. 32S is the biggest that they say on that, but due to the whole one inch, one inch thing, it went up a size just because of how huge the cowl is on that. Oh yeah, it does have a very large cowl so you needed to be able to get air movement around the airplane, not just hitting the front of it. So that’s why we went up a little bit bigger on it.

[01:54:32] Makes sense to me. Yeah, wow, propellers, can you believe it? We’re done. I, I, yeah, hopefully our listeners, you, you guys found that interesting, enlightening, informative and hopefully you will be able to make better selections with your propellers after listening to this episode. Yeah, is anybody? They’re still here, I don’t know if. If you guys have questions, as always, hit us up on the

[01:55:04] On the email. On the you can also text us at the 818-351-9846 number or call and leave a voicemail. Maybe if we- if we can work it in- to actually play your voice on the show, I think that’d be really cool. If you have a question, yeah, I will have you ask your question in your voice on our show, I think.

[01:55:23] That’d be neat. Or, if you want, you can also sign up on the forums and ask it over there, right?

[01:55:27] Forumsrcplanelab.com and I promise I will attempt to get on the forums very soon. It’s so difficult.

[01:55:36] Isn’t it well? The problem is- I mean it’s well- you have to type, like what, 12, 13 letters into a web search.

[01:55:42] Bar. Here’s the thing, as, as I’ve mentioned before, where I work, we have a lot of restrictions on our computer use. Yeah, so by the time I get home- and that’s what I do- I work on the computer all day, pretty much all day, and then you come home by the time. By the time I get home, I the last thing I want to do is sit in front of a computer or a laptop or whatever cool stuff, though I agree, I don’t disagree. I don’t disagree. I see airplane stuff, but I promise in the near future I will.

[01:56:15] Participate in the forums, that’s. That’s the only promise I can make because, like, I haven’t even been on my the other forums in a while, I just haven’t had time. Yeah, it happens, it’s okay, I understand, but the forums, hopefully you, you guys, will find them useful and we’ll put some stuff on there. So

[01:56:37] We can see what you guys are up to. There you go. Do you have anything else you want to say, or can we?

[01:56:44] Put this to bed. I think we can put this to bed. I will apologize in advance if, if we’ve put anyone to sleep, you can wake up now and resume your normal activities- awesome. Well, until next time.

[01:56:58] Thank you for listening. Yes, I am Ron and I’m Tom. Good night, good night. We hope you enjoyed this.

[01:57:03] Episode of the RC Plane Lab podcast. For topic suggestions, to ask questions or to give anything back, connect with us at rcplanelab.com or email us direct at either Ron at rcplanelab.com or Tom at rcplanelab.com. You can also text us or leave us a voicemail at 818-351-9846. Please subscribe, rate and review us on your favorite podcast app until next time. May your landings be gentle.