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Part of the RC Airplane Building & Repair Center

How to Resize and Print RC Airplane Plans

Sometimes I find a plan I really like, but it is not quite the size I want to build. Maybe I want a little more wingspan for a calmer airplane, or I need to shrink it enough to fit in the car. Resizing the drawing is the easy part. The part that deserves some thought is deciding what else must change so the finished airplane is still strong, balanced, and properly powered.

This guide supports projects such as the free SandPiper profile-foamy plans. Before changing a design, also review the Building & Repair Center; resizing can affect structure, control surfaces, power requirements, and finished weight.

First, Decide How Much You Are Changing

A small change is usually straightforward. If I enlarge or reduce a plan by only a few percent, I can often keep the same basic construction and use standard wood sizes that are close to the original. A large change is different. Bigger airplanes carry more weight and higher loads, while very small airplanes can become heavy if every former, spar, and sheet is simply scaled down from the original.

Every line on the page changes size, including spar notches, landing-gear blocks, holes, sheet thickness, control horns, and hardware locations. The lumber at the hobby shop does not change with the printer setting. If a resized notch comes out at an odd dimension, cut it to fit the wood you are actually using. Do not force a standard piece of wood into a scaled opening and distort the structure.

The Simple Scaling Formula

For printing, the most useful number is the final print scale:

Desired size ÷ original size × 100 = print scale

If the original wingspan is 24 inches and I want 30 inches, the calculation is 30 ÷ 24 × 100, which equals 125 percent. I print the plan at 125 percent.

If the original plan is 50 inches and I want a 45-inch wingspan, the calculation is 45 ÷ 50 × 100, which equals 90 percent. I print that plan at 90 percent.

Use the same unit on both sides of the calculation. Inches divided by inches or millimeters divided by millimeters will give the same percentage. I also write the percentage directly on the working copy so I do not have to remember later which version I printed.

What Does Not Scale Automatically

A larger drawing does not automatically produce a sound larger airplane. Wing loading, structural loads, control authority, and power requirements do not all change at the same rate. A major enlargement may need thicker spars, additional shear webs, stronger landing-gear mounts, different hinges, and a completely different power system. A major reduction may need lighter wood, smaller hardware, and fewer parts so the airplane does not end up overweight.

Control surfaces deserve special attention. Scaling them exactly can produce more control authority than expected, especially when the airplane is made larger and flown faster. Start with conservative control throws and use the control throws, dual rates, and expo guide before the maiden flight. Recheck the center of gravity from the completed airplane rather than assuming the printed balance mark will be perfect after a substantial redesign.

Printing at a Copy Shop

A local copy shop is usually the easiest way to get a one-piece plan. Tell them the exact scale percentage and ask them to turn off any setting that says Fit, Shrink Oversized Pages, or Scale to Printable Area. Those options can quietly change the size again.

Before leaving, measure one known dimension on the printed plan. A wingspan dimension, rib chord, scale box, or ruler printed on the drawing will tell you whether the output is correct. I would rather catch a printer setting at the counter than after cutting a stack of ribs.

Printing Tiled Plans at Home

Adobe Acrobat Reader can divide a large PDF across ordinary sheets of paper. Other PDF programs may use different names, but the process is similar:

  1. Open the PDF and choose Print.
  2. Under Page Sizing and Handling, select Poster.
  3. Enter the scale you calculated. Use 100 percent for the original size, 125 percent for the 24-to-30-inch example, or 90 percent for the 50-to-45-inch example.
  4. Add a small overlap so neighboring sheets have enough paper to align and tape together.
  5. Turn on cut marks and labels if they help identify the sheets.
  6. Print one test section that contains a known dimension and measure it before printing the entire plan.

Lay the sheets on a large, flat surface. Trim the same edges on each sheet, overlap the printed lines carefully, and tape the front in a few places before turning the plan over and taping the seams from the back. Check long reference lines as you work. A small alignment error repeated across several pages can leave a wing panel noticeably crooked.

Check the Plan Before Cutting Wood

Once the sheets are assembled, I measure the wingspan, root chord, fuselage length, and a few matching parts. I also compare the printed notches with the actual spars and stringers on the bench. This takes a few minutes and catches scaling or assembly errors before they become airplane parts.

Resizing a proven plan can be a great way to build the airplane you actually want, but the farther you move from the original size, the more you are designing rather than simply copying. Make the print accurately, choose real material sizes deliberately, and treat major structural or power changes as engineering decisions. Then you can get to the enjoyable part: cutting wood and watching a flat sheet of paper turn into an airplane.