RC PLANE LAB LEARNING CENTER

RC Airplane Glossary

Search more than 100 RC airplane terms covering flight, aerodynamics, radios, stabilization, electric power, engines, batteries, building, safety, and field operations. Every definition includes related concepts so you can learn how the pieces fit together instead of memorizing isolated words.

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How airplanes fly
Lift, drag, stalls, stability and control Radio setup
Channels, rates, expo, mixing and failsafe Stabilization
AS3X, SAFE, gain, priority and oscillation Electric power
LiPo batteries, motors, ESCs, BECs and watts Gas and glow engines
Carburetors, tuning, ignition and break-in Building and setup
CG, incidence, linkages, throws and balance

Safety note: Definitions are educational, not a replacement for the instructions supplied with your aircraft, radio, battery, charger, motor, ESC, or engine. Remove an electric model’s propeller when practical before bench-testing its power system, and follow current FAA and club requirements when flying.

Adverse yaw

Flight & aerodynamics

The tendency for an airplane’s nose to yaw opposite the commanded roll. When one aileron moves down it usually creates more lift and drag than the raised aileron, pulling that wing backward. Coordinated rudder, differential ailerons, or proper airframe design can reduce it.

Aerobatic

Flight & aerodynamics

Flight involving intentional maneuvers beyond ordinary straight-and-level flying, such as loops, rolls, spins, snaps, and inverted flight. Aerobatic models generally combine strong structures, generous control authority, and power appropriate to their intended style.

AGL (Above Ground Level)

Safety & airspace

Altitude measured from the surface directly below the aircraft, rather than from sea level. U.S. recreational-flyer altitude requirements are commonly expressed in feet AGL; always check the rules and authorizations that apply to your location.

Aileron

Flight & aerodynamics

A movable control surface normally located near each wingtip. The ailerons move in opposite directions to change lift on the two wings and roll the airplane about its longitudinal axis.

Aileron differential

Flight & aerodynamics

A setup in which the upward-moving aileron travels farther than the downward-moving one. It is used primarily to reduce adverse yaw and can be created mechanically or through transmitter programming.

Angle of attack (AOA)

Flight & aerodynamics

The angle between a wing’s chord line and the relative airflow. A wing normally produces more lift as AOA increases—up to its critical angle. Beyond that point airflow separates and the wing stalls. AOA is not the same thing as the airplane’s nose angle relative to the horizon.

ARF (Almost Ready to Fly)

Building & setup

A largely assembled model that still requires selected components and final work. Depending on the kit, that can include installing the motor or engine, radio equipment, landing gear, control linkages, and performing the complete setup.

AS3X

Radio & stabilization

Spektrum’s stabilization technology that uses gyro sensors and programmed corrections to help reduce the effects of wind and turbulence. AS3X does not make an incorrectly built or balanced airplane mechanically correct; control direction, receiver orientation, gains, CG, and linkage setup must all be verified.

BEC (Battery Eliminator Circuit)

Electric power

A regulated power supply that powers the receiver and servos from the main flight battery. Many ESCs contain a BEC. Its voltage and current capacity must suit the receiver, servo count, servo type, and expected loads.

Balsa kit

Building & setup

A model constructed from cut wood parts—often ribs, formers, spars, sheet, and sticks—rather than delivered as a nearly assembled airframe. Building requires alignment, adhesives, sanding, covering, and installation of the power and radio systems.

Balance charging

Electric power

Charging a multi-cell lithium battery while monitoring and correcting the voltage of each cell through the balance connector. It helps prevent individual cells from drifting too far apart and is the normal charging method for most RC LiPo packs.

Bind

Radio & stabilization

The process that pairs a receiver with a compatible transmitter so it recognizes that transmitter’s signal. Binding procedure, receiver power, transmitter distance, protocol compatibility, model memory, and failsafe behavior all matter.

Bind-N-Fly (BNF)

Building & setup

A Horizon Hobby designation for a model supplied with compatible onboard electronics and receiver. The pilot generally supplies a suitable compatible transmitter, binds it, completes programming, and performs all setup and safety checks.

Brownout

Radio & electric power

A drop in receiver-supply voltage low enough to cause unreliable operation or a restart. Possible causes include an undersized BEC, weak receiver battery, poor switch or connector, damaged wiring, or multiple servos drawing heavy current at once.

Brushless motor

Electric power

An electric motor whose commutation is controlled electronically by an ESC instead of physical brushes. Most RC airplane brushless systems use three motor wires. Swapping any two normally reverses rotation.

C rating

Electric power

A battery rating expressed relative to its capacity. A theoretical 20C continuous rating on a 2 Ah pack corresponds to 40 A. Real-world performance also depends on cell quality, temperature, age, wiring, and how the manufacturer established the rating.

Capacity

Electric power

The quantity of electrical charge a battery is rated to deliver, commonly shown in milliamp-hours (mAh). Greater capacity can increase runtime but usually adds size and weight, which may change CG and flight performance.

Carburetor

Gas & glow

The engine component that meters air and fuel into the intake. RC carburetors commonly provide a throttle barrel or butterfly plus high- and low-speed mixture adjustments. Settings interact, so tune in the sequence recommended by the engine manufacturer.

Cell count (S rating)

Electric power

The number of battery cells connected in series. A “3S” LiPo has three cells in series. Series connection increases pack voltage; it does not add the individual cell capacities together. The motor, ESC, propeller, and battery must be matched for the chosen voltage.

Center of gravity (CG)

Building, setup & flight

The point through which the airplane’s weight can be considered to act. CG location has a major effect on stability, control feel, stall behavior, and trim. Use a reliable recommended range and verify it with the model ready to fly.

Chord line

Flight & aerodynamics

An imaginary straight line from an airfoil’s leading edge to its trailing edge. It is used as a reference for angle of attack and incidence measurements.

Class G airspace

Safety & airspace

Airspace that is not designated Class A, B, C, D, or E. Recreational flyers in the United States generally fly at or below 400 feet AGL in Class G while complying with all other restrictions and safety requirements.

Coordinated turn

Flight & aerodynamics

A turn in which roll, yaw, and pitch inputs work together so the airplane follows the turn cleanly without excessive slipping or skidding. The amount of rudder coordination required varies by model and maneuver.

Control horn

Building & setup

The fitting attached to a control surface where the pushrod connects. Hole selection changes leverage, available travel, and the load seen by the servo. It must be securely installed and aligned with the hinge line as the design requires.

Control throw

Building & radio setup

The distance or angle a control surface moves from neutral. Throws should be measured at the location and in the units specified by the manufacturer. More throw increases available control authority but can make the model overly sensitive or cause binding.

Controlled airspace

Safety & airspace

Airspace of defined dimensions where air traffic control services are provided. In the United States, recreational model-aircraft operations in controlled airspace require prior FAA authorization, commonly obtained through an approved LAANC service where available.

Covering

Building & setup

The film, fabric, paper, fiberglass, or other material applied over an airframe. Heat-shrink films are common on built-up balsa models. Proper temperature, adhesion, shrinking sequence, and ventilation help prevent warps and trapped bubbles.

Dead stick

Flight & engines

A flight condition in which the motor or engine is no longer producing power. A dead-stick landing uses the airplane’s remaining altitude and glide performance; maintaining appropriate airspeed is usually more important than stretching the glide.

Drag

Flight & aerodynamics

The aerodynamic force that opposes motion through the air. Drag includes components associated with shape, surface friction, lift production, and interference between aircraft parts.

Dual rates

Radio & stabilization

A transmitter feature that provides selectable amounts of control travel. Pilots often use lower rates for smoother response and higher rates for greater authority, but the exact values should be based on the model’s recommendations and flight testing.

Elevator

Flight & aerodynamics

The control surface normally mounted on the horizontal stabilizer that controls pitch about the lateral axis. Pulling the transmitter stick should command the elevator direction appropriate for nose-up flight; always verify visually before flying.

ESC (Electronic Speed Control)

Electric power

The electronic device that regulates power from the battery to an electric motor in response to the throttle signal. An ESC must be compatible with motor type, voltage, current, cooling needs, and—if used—BEC requirements.

Expo (Exponential)

Radio & stabilization

A transmitter setting that changes how rapidly servo output responds around stick center while preserving the commanded endpoint. It can soften center-stick response without reducing maximum throw. Positive versus negative sign conventions vary by radio brand, so verify the monitor and surface response.

Failsafe

Radio & safety

The receiver behavior programmed for loss of valid transmitter signal. Depending on the system, channels may move to preset positions or hold selected positions. Failsafe must be intentionally configured and tested according to the radio manufacturer’s procedure—with the model safely restrained and the propeller removed when practical.

Flaperon

Radio & flight

An aileron that also moves collectively with the opposite aileron to provide a flap-like function. It requires separate control of the two aileron servos and careful verification of roll direction, flap direction, travel, and stall behavior.

Flap

Flight & aerodynamics

A movable wing surface used to change lift and drag, commonly for slower approaches and steeper descents. Deployment can also change pitch, so flap travel and any elevator compensation should be established cautiously at safe altitude.

Flight mode

Radio & stabilization

A selectable group of transmitter settings used for a particular phase or style of flight. A mode may change rates, expo, trims, mixes, flap positions, gyro gains, or other functions together.

Flameout

Gas & glow

An uncommanded shutdown of an internal-combustion engine in flight. Causes can include fuel-delivery problems, mixture settings, overheating, ignition problems, vibration-related faults, or fuel exhaustion.

Former

Building & setup

A transverse structural member that establishes the fuselage cross-section and supports longerons, stringers, sheeting, or equipment. The firewall is a heavily loaded former designed to carry the power system.

Firewall

Building & setup

The strong forward bulkhead to which the motor or engine mount is attached. It carries thrust, vibration, and landing loads and often establishes the designed thrust angle. Cracks, looseness, fuel soaking, or poor repairs require attention before flight.

FRIA

Safety & airspace

A Federally Recognized Identification Area in the United States. A qualifying unmanned aircraft without Remote ID equipment may be operated within the FRIA while remaining within visual line of sight and complying with the applicable rules.

Fuel-tank vent

Gas & glow

The line or fitting that allows pressure to equalize—or supplies muffler pressure in many glow systems—as fuel leaves the tank. A blocked, pinched, or incorrectly routed vent can cause inconsistent running or an engine stoppage.

Gain

Radio & stabilization

The amount of corrective response produced by a stabilization system for sensed motion. Too little may provide little visible benefit; too much can cause rapid oscillation. Gain requirements change with airspeed, control geometry, servo performance, and the airframe.

Glide ratio

Flight & aerodynamics

The horizontal distance an aircraft travels compared with the altitude it loses in still air at a particular condition. Best glide requires an appropriate airspeed; pulling up to “stretch” a glide increases angle of attack and can cause a stall.

Glow engine

Gas & glow

A model engine that usually burns methanol-based fuel and uses a glow plug to support ignition. The plug is heated electrically for starting; once running, combustion heat keeps its element glowing.

Glow plug

Gas & glow

The ignition element used in a glow engine. Plug heat range and type must suit the engine, fuel, and operating conditions. A plug can glow on a battery yet still perform poorly under compression.

Ground loop

Flight & aerodynamics

A rapid yawing rotation while an airplane is moving on the ground, particularly common with taildraggers. Crosswind, excessive speed, poor gear alignment, abrupt braking, or delayed rudder correction can contribute.

High-speed needle

Gas & glow

The carburetor adjustment that primarily controls fuel mixture at higher throttle settings. Final tuning should account for the difference between running on the ground and unloading in flight, following the engine maker’s procedure.

Horizontal stabilizer

Flight & building

The fixed or stabilizing horizontal tail surface associated with pitch stability and the elevator. Its alignment and incidence relative to the wing are important to trim and handling.

Incidence

Building & flight

The installed angle of a wing or stabilizer relative to a chosen airframe reference line. Incidence is a geometric property of the airframe; angle of attack is the surface’s angle relative to the airflow during flight.

Induced drag

Flight & aerodynamics

Drag associated with producing lift. It is especially significant at high lift coefficients and lower airspeeds, and is influenced by wing loading, aspect ratio, and lift distribution.

Motor kV

Electric power

A motor velocity constant expressed approximately as no-load revolutions per minute per volt. It does not mean kilovolts and is not a direct power rating. Propeller load, battery voltage, winding resistance, efficiency, and current limits determine the usable system.

LAANC

Safety & airspace

The FAA’s Low Altitude Authorization and Notification Capability, which supports near-real-time processing of many unmanned-aircraft airspace-authorization requests through approved service providers. Authorization limits and availability depend on location.

Lateral balance

Building & setup

The side-to-side balance of an airplane. A heavy wing can affect trim and handling. Check it using the manufacturer’s method after the fore-and-aft CG is correct and with the model in ready-to-fly condition.

Leading edge

Flight & building

The forward edge of a wing, stabilizer, or control surface—the part that normally meets the airflow first. Damage or distortion can change aerodynamic behavior.

Lean mixture

Gas & glow

An air-fuel mixture containing less fuel relative to air than a richer setting. Excessively lean operation can cause overheating, sagging, detonation or engine damage. Tune conservatively according to the engine manufacturer.

Lift

Flight & aerodynamics

The aerodynamic force component perpendicular to the relative airflow. Its magnitude depends on air density, airspeed, wing area, and lift coefficient, which is strongly influenced by angle of attack and airfoil shape.

LiPo battery

Electric power

A lithium-polymer rechargeable battery widely used in electric RC models because of its energy and power density. LiPo packs require a compatible charger, correct cell-count setting, physical inspection, appropriate storage voltage, and protection from short circuits, overcharge, over-discharge, puncture, and excessive heat.

Low-speed needle

Gas & glow

The carburetor adjustment that primarily affects idle and transition into midrange. Changes may influence other throttle ranges, so adjustments should be small, documented, and made in the manufacturer’s recommended order.

Maiden flight

Flight & safety

The first flight of a newly built, repaired, or newly acquired aircraft. A maiden deserves a complete inspection, conservative conditions, a suitable field, verified control directions, a range check, correct CG, and a clear plan for trim and landing.

Mix

Radio & stabilization

A transmitter function that makes one control or channel influence another. Mixes can coordinate controls, compensate for known behavior, or create functions such as flaperons. They should refine a mechanically correct setup, not hide binding, wrong incidence, bad CG, or improper control direction.

Model memory

Radio & stabilization

A stored transmitter configuration for a specific aircraft. It can contain channel assignments, rates, expo, mixes, timers, telemetry, and other settings. Confirm the correct model before powering the aircraft.

Heat-shrink film

Building & setup

A thermally activated plastic covering used on many built-up models. Brand-specific adhesive and shrink temperatures vary. “Monokote” and “UltraCote” are product names that are sometimes used conversationally for this larger category.

Nominal voltage

Electric power

A representative voltage used to identify a battery chemistry or pack, not the exact voltage at every state of charge. For example, LiPo cells are commonly described by a nominal voltage even though their actual voltage varies during charging and discharge.

Nitro fuel

Gas & glow

A common name for model glow fuel, normally based on methanol with lubricating oil and often some percentage of nitromethane. The correct blend depends on engine design, manufacturer recommendations, climate, and intended use.

Oscillation

Radio & stabilization

Rapid repeated movement around an axis—often seen as wing rocking, tail wagging, or pitch bobbing. With stabilization, oscillation commonly indicates excessive gain for the airspeed and control setup, though mechanical slop, vibration, or an incorrect installation can also contribute.

Outrunner

Electric power

A brushless motor design in which the outer rotating shell carries the magnets. Outrunners commonly provide useful torque at relatively modest RPM and are widely used to drive airplane propellers directly.

Pitch

Flight & aerodynamics

Rotation about the airplane’s lateral axis, moving the nose up or down. Pitch is normally commanded with the elevator, but power, flap deployment, CG, thrust angle, and trim can all affect pitch behavior.

Preflight check

Safety & setup

A systematic inspection before flight. It should include structure, fasteners, battery or fuel, CG where appropriate, propeller, radio connection, correct control direction, full and free movement, stabilization direction, failsafe, and field conditions.

Priority

Radio & stabilization

In stabilization programming, priority describes how gyro correction is reduced or modified as the pilot gives larger stick commands. The purpose is to preserve a natural commanded response while retaining stabilization nearer neutral. Exact behavior depends on the system.

Propeller

Power systems

A rotating airfoil system that converts shaft power into thrust. Diameter, pitch, blade count, shape, material, RPM, and air density all affect load and performance. Use only combinations approved for the power system and balance and install them correctly.

Propeller pitch

Power systems

The theoretical forward distance a propeller would advance in one revolution through a solid medium, usually stated in inches. Actual advance is lower because air is not solid and the propeller slips. More pitch generally increases load and potential pitch speed.

Pushrod

Building & setup

The linkage that transmits servo motion to a control surface or engine control. It should be stiff enough for the load, supported against flexing, free from binding, and connected with secure hardware.

Range check

Radio & safety

A ground test performed according to the radio manufacturer’s procedure to help verify dependable transmitter-to-receiver operation at a specified distance or reduced-power mode. Perform it before a maiden, after significant radio work, and whenever reliability is in doubt.

Receiver (RX)

Radio & stabilization

The onboard radio component that receives commands from the transmitter and sends output signals to servos, ESCs, and other equipment. Installation must account for antenna placement, power integrity, vibration, orientation, and manufacturer requirements.

Receiver battery

Radio & electric power

A dedicated battery supplying the receiver and servos, common in gas, glow, sailplane, and larger-model installations. Chemistry, voltage, capacity, switch rating, connectors, and load capability must suit the radio system.

Receiver-ready / Plug-N-Play

Building & setup

A model supplied with many onboard components installed but generally requiring the pilot’s own compatible receiver and transmitter. Exact included equipment varies, so check the product description rather than relying only on the label.

Relative wind

Flight & aerodynamics

The airflow experienced by the aircraft opposite its flight path through the air. Angle of attack is measured between an airfoil’s chord line and this relative airflow—not simply against the horizon.

Remote ID

Safety & airspace

The capability of an unmanned aircraft in flight to broadcast identification and location information. In the United States, aircraft that must be registered generally must comply with Remote ID unless operated under an applicable exception, such as within a FRIA.

Rib

Building & setup

A spanwise series of shaped structural pieces that establishes a wing’s airfoil contour and transfers loads into spars and sheeting. Damaged ribs should be repaired without distorting the intended airfoil.

Rich mixture

Gas & glow

An air-fuel mixture containing more fuel relative to air than a leaner setting. Slightly rich operation is often used for cooling and reliability, but excessively rich settings can reduce power, foul plugs, and cause rough running.

Roll

Flight & aerodynamics

Rotation about the airplane’s longitudinal axis, normally commanded by ailerons. Roll rate and feel depend on airspeed, wing design, control throw, differential, expo, and mass distribution.

RTF (Ready to Fly)

Building & setup

A package intended to include most or all equipment needed to fly, often including a transmitter. “Ready” does not eliminate assembly, charging, programming, CG verification, control checks, or the need to learn safe operation.

Rudder

Flight & aerodynamics

The movable surface on the vertical tail that controls yaw. It is used for ground steering on many airplanes, turn coordination, crosswind correction, slips, aerobatics, and recovery from certain unusual attitudes.

SAFE

Radio & stabilization

Spektrum flight-envelope assistance that can provide features such as bank- and pitch-angle limits and self-leveling, depending on the product and mode. SAFE is different from basic AS3X stabilization and does not replace correct setup, adequate altitude, training, or pilot judgment.

Servo

Radio & setup

An electromechanical actuator that moves a control surface, throttle, landing gear, or other mechanism in response to a receiver signal. Selection must consider torque, speed, voltage, size, gear material, accuracy, and the loads imposed by linkage geometry.

Servo arm

Building & radio setup

The lever attached to a servo’s output spline. Moving the pushrod outward on the arm generally increases surface travel and reduces mechanical leverage; moving it inward generally does the opposite.

Slip

Flight & aerodynamics

An intentionally uncoordinated condition using crossed aileron and rudder. A forward slip can increase descent rate without a large airspeed increase; a sideslip is commonly used to correct for crosswind during landing.

Slop

Building & setup

Unwanted free movement or backlash in a linkage, hinge, servo gear train, or mounting. Slop reduces precision, can worsen flutter risk, and can make stabilization systems work unnecessarily hard.

Spar

Building & setup

A primary spanwise wing structure that carries bending loads. Spar caps, webs, joiners, and surrounding structure work together; damage deserves a structurally sound repair rather than a cosmetic patch.

Spinner

Building & setup

The streamlined nose covering fitted ahead of the propeller hub. It must be correctly sized, centered, secure, and compatible with the propeller. A poorly fitted or damaged spinner can create dangerous vibration.

Stall

Flight & aerodynamics

A loss of smooth airflow and lift caused when a wing exceeds its critical angle of attack. An airplane can stall at any attitude and airspeed if the critical AOA is exceeded; steep turns and abrupt control inputs can raise stall speed through increased load factor.

Stall speed

Flight & aerodynamics

The speed at which a particular aircraft reaches critical AOA under a stated condition. Weight, load factor, flap position, CG, turbulence, and maneuvering all affect the speed at which the stall occurs.

Static margin

Flight & setup

A measure relating CG position to the aircraft’s aerodynamic neutral point. In general, greater positive static margin increases pitch stability but can reduce responsiveness; too little can make the model unstable. Practical builders normally use the designer’s CG range rather than calculating it from scratch.

Storage charge

Electric power

A charger program that brings a lithium battery to a moderate per-cell voltage suitable for storage rather than leaving it fully charged or deeply discharged. Use the battery and charger manufacturers’ guidance and store packs in a cool, dry, protected location.

Taildragger

Flight & aerodynamics

An airplane with two main wheels ahead of the CG and a tailwheel or skid. Taildraggers demand active directional control during takeoff and landing because their ground geometry is less directionally self-correcting than tricycle gear.

Telemetry

Radio & stabilization

Data sent from the model back to the transmitter or another display. Depending on the equipment, it can include receiver voltage, flight-battery voltage, current, capacity used, RPM, temperature, altitude, GPS data, or link-quality information.

Thrust angle

Building & flight

The installed direction of the motor or engine thrust line relative to the airframe. Designers may use right or down thrust to manage power-related pitch and yaw. Preserve the specified angle when installing or repairing the firewall and mount.

Tip stall

Flight & aerodynamics

A stall that begins strongly near a wingtip, often producing an abrupt wing drop and possible autorotation. Wing taper, twist, airfoil, surface condition, control input, and flight condition all influence tip-stall behavior.

Trailing edge

Flight & building

The aft edge of an airfoil or control surface where airflow leaving the upper and lower surfaces meets. Ailerons, elevators, rudders, and flaps are commonly hinged along trailing-edge areas.

Transmitter (TX)

Radio & stabilization

The pilot’s radio that converts stick, switch, knob, and programmed inputs into commands sent to the receiver. Proper model selection, battery state, antenna use, programming, and range checking are essential.

Travel adjustment / End point

Radio & stabilization

A transmitter setting that limits or expands servo output at one or both ends of travel. Use it to achieve specified surface movement and prevent binding, while preserving sound mechanical geometry.

Trim

Radio & flight

A small control offset used to establish hands-off or desired flight behavior. Large trim requirements can indicate an incorrect mechanical neutral, CG, incidence, thrust angle, warp, or alignment problem and deserve investigation.

TRUST

Safety & airspace

The Recreational UAS Safety Test required for recreational flyers in the United States. It is free through approved test administrators, and flyers must carry proof of passage while operating.

Vibration

Building & power systems

Repeated mechanical motion that can loosen fasteners, fatigue structures, damage electronics, disturb stabilization sensors, and reveal wiring faults. Common sources include damaged or unbalanced propellers and spinners, bent shafts, engine problems, and loose mounts.

VLOS (Visual Line of Sight)

Safety & airspace

A condition in which the operator—or a co-located visual observer where permitted—maintains continuous unaided visual contact with the unmanned aircraft, apart from corrective lenses. This allows the flight to be monitored and other aircraft and hazards avoided.

Voltage sag

Electric power

A temporary drop in battery voltage when current demand increases. Excessive sag may indicate a weak, cold, undersized, aged, damaged, or poorly connected battery and can trigger reduced power or electronic resets.

Warp

Building & setup

An unintended twist or distortion in a wing, tail, or control surface. Warps can create trim changes, unequal stall behavior, or constant rolling and yawing tendencies. Check structure and covering tension before trying to hide the symptom with transmitter trim.

Washout

Flight & building

An intentional wing twist that gives the tip a lower geometric angle of incidence than the root. It can help the root stall first and preserve aileron effectiveness longer. Washout is designed geometry; an accidental twist is a warp.

Wattmeter

Electric power

A test instrument placed in an electric power circuit to measure values such as voltage, current, watts, and accumulated capacity. It helps verify that a propeller and battery combination stays within the motor, ESC, connector, and battery limits.

Watts

Electric power

A unit of power. In a direct-current RC system, electrical input power is approximately voltage multiplied by current. Input watts are not the same as propulsive output because the motor, ESC, propeller, and wiring all have losses.

Wing loading

Flight & aerodynamics

Aircraft weight divided by wing area. Higher wing loading often increases characteristic speeds and landing energy, but comparisons are most meaningful between geometrically similar models because scale and Reynolds-number effects matter.

Wing tube / Wing joiner

Building & setup

A structural member that joins removable wing panels and transfers loads into the airframe. It must be fully seated, undamaged, correctly oriented where applicable, and retained as designed.

Yaw

Flight & aerodynamics

Rotation about the airplane’s vertical axis, moving the nose left or right. Rudder is the primary yaw control, while propeller effects, adverse yaw, crosswind, thrust angle, and alignment can also create yawing moments.

Airfoil

Flight & aerodynamics

The cross-sectional shape of a wing, propeller blade, or other lifting surface. Camber, thickness, leading-edge shape, Reynolds number, surface condition, and angle of attack influence its lift, drag, and stall behavior.

Control direction

Radio & safety

The physical direction a control surface moves for a transmitter command. Before every flight, view the model from behind and verify that right roll, up elevator, and right yaw commands move the appropriate surfaces correctly. Stabilization correction directions must also be checked separately.

Crosswind

Flight & aerodynamics

Wind with a component blowing across the runway or intended flightpath. Crosswinds require directional and drift correction during takeoff and landing, and may make a different runway, delay, or experienced assistance the safer choice.

FAA registration

Safety & airspace

Registration required in the United States for many unmanned aircraft operations. Recreational aircraft weighing 250 grams (0.55 lb) or more generally require registration, and the pilot must follow current marking, proof, inventory, and Remote ID requirements.

Flutter

Flight & building

A potentially destructive aeroelastic oscillation of a control surface or airframe component. Slop, flexible linkages, weak hinges, poor balance, structural flexibility, or excessive speed can contribute. Land immediately if flutter is suspected.

Longeron

Building & setup

A longitudinal fuselage structural member that ties formers together and carries bending loads. Longerons are generally more structurally significant than light stringers used mainly to establish shape.

Spin

Flight & aerodynamics

An autorotating descent in which the airplane is stalled and yawed, with one wing generally more deeply stalled than the other. Recovery depends on the aircraft and must follow the manufacturer’s guidance; sufficient altitude is essential.

Visual observer

Safety & airspace

A person designated to help the pilot see and avoid other aircraft, people, or hazards. Under U.S. recreational rules, a visual observer used to satisfy the VLOS provision must be co-located with and in direct communication with the operator.

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How the concepts connect

Many RC problems cross categories. A model that pitches up under power, for example, may involve center of gravity, trim, thrust angle, incidence, angle of attack, and airspeed—not just a transmitter mix. Likewise, a twitching servo may involve the servo, linkage, BEC, receiver power, wiring, or vibration. Follow the related links inside each definition to trace the complete system.