Glossary — R/C Sailplanes

Aileron: Ailerons are movable control surfaces found on the trailing edge of both the right and left wings of a plane. Each surface moves in the opposite direction to enable the plane to roll right or left. For a plane to roll left, the left aileron moves upward (destroying some lift on that wing) while the right aileron moves downward (increasing lift). This unequal lift causes the plane to bank and turn. In German, ailerons are called Querruder — useful when reading those German kit instructions!
Diagram showing the main control surfaces of a typical R/C sailplane.
Ailevator: A relatively modern term that has started to be used in models with computer radio systems. An ailevator is where each elevator half on a conventional or V-tail moves independently, like ailerons on a wing. In addition to both elevator halves moving up and down together for pitch control, each side can move in opposite directions to provide roll control. On a V-tail, this is also known as a ruddervator. Typically, both ailevators and ailerons are coupled together via the transmitter to maximize roll performance, especially on larger wingspan planes.
Each elevator half moves independently for combined pitch and roll control.
AM (Amplitude Modulation): Early radio transmission method. Cheaper but more prone to interference than FM. Largely obsolete. See Radios.
AMA (Academy of Model Aeronautics): The premier US model aviation organization. Provides up to $1,000,000 liability insurance, lobbies for hobbyist interests, and administers contests. Many flying fields require AMA membership. modelaircraft.org
ARF (Almost Ready to Fly): Kit requiring minimal assembly — major components pre-built, needing final assembly and radio installation. (Most ARF's are really not ready and require some head-scratching to get the plane finished.)
Aspect Ratio: Wing span divided by chord. Higher ratios (long, skinny wings) have less drag — why gliders have such long wings.
BEC (Battery Eliminator Circuit): A component (often built into the ESC) that drops the high voltage of the main flight battery down to 5V or 6V to power the receiver and servos, "eliminating" the need for a separate receiver battery.
BNF (Bind and Fly): Plane with receiver installed, ready to bind to a 2.4 GHz transmitter and fly.
Brushless Motor: Motor without physical electrical contacts/brushes. More efficient and longer-lasting. Requires an electronic speed controller.
Carbon Fiber: Ultra-strong fibers woven into mats or cast into rods, used for high-strength wings and structures. Stronger than fiberglass or Kevlar when used correctly.
CA (Cyanoacrylate): Fast-setting glue popular in R/C. Different formulas: thin, thick, foam-safe. Some can cause allergic reactions — see CA Sensitivity. More: Adhesives Guide.
CG (Center of Gravity): The balance point of a plane. HLGs are very CG-sensitive — 1/16" changes matter. Typically balanced at the main spar. See Decalage.Balancing a glider on your finger tips.
Cardiac Hill: What you climb after being 'killed' in combat — gasping for oxygen all the way up, for the 50th time.
Chord: Distance from wing leading edge to trailing edge in the direction of airflow. Related to aspect ratio and MAC.
Clevis: Clevises are small clips used to connect push rods to servos or to movable control surfaces such as ailerons, rudder, or elevator. They come in different materials — plastic, nylon, and metal. For combat and heavier-duty use, the black metal ones (Kwik-Links) are recommended, with a small piece of plastic straw slid over the link as a "keeper" to prevent it from opening during a combat collision.
Common clevis styles used in R/C sailplanes.
Composite: Hybrid construction combining materials like carbon fiber, Kevlar, fiberglass, epoxy, and foam for optimal strength/weight.
Control Horn: Attached to a control surface, connects via pushrod/clevis to a servo. Holes nearer the surface give more movement.
Coroplast: Corrugated plastic material — tough, flexible, lightweight. Great for stabilizers on combat planes. Comes in various colors.Colorful Coroplast corrugated plastic sheets.
Decalage: Angle between wing and horizontal tail surface. Affects pitch trim. See About Decalage.
Dihedral: Dihedral is where the right and left wing tips are higher than the fuselage. More dihedral generally means the plane will be more stable in the air, but harder to turn aerobatically. For planes with only rudder and elevator controls (no ailerons), dihedral is a necessity — it's what makes the rudder produce banking turns. When a wing has more than one panel at different angles, it's called polyhedral.
Dihedral angle — wing tips higher than fuselage for stability.
DLG (Discus Launch Glider): A specialized category of unpowered gliders launched by spinning 360 degrees and throwing the model by a "peg" on the wingtip, reaching high altitudes without a motor.
Drag: Air friction resisting movement. Hard to calculate mathematically — often approximated or measured in wind tunnels.
Elevator: The elevator is the horizontal control surface on the tail of a plane that controls pitch — the nose moving up or down. When the elevator surface moves upward, the tail is pushed down and the nose pitches up, and vice-versa. You want to connect your radio so that pulling back on the stick makes this surface move upward (nose up). Without an elevator, controlling the altitude of a plane is nearly impossible. The German word for elevator is Höhenruder (high-rudder).
The elevator controls pitch — nose up and down.
Elevons: Elevon means both aileron and elevator combined as the same control surface. Elevons are typically used on tailless aircraft such as flying wings. Like ailerons, elevons provide roll control by moving in opposite directions; like an elevator, they provide pitch control by moving up and down together. In order for a plane to have elevons, either a computer R/C system or a mixer (electronic or mechanical) is needed. This movement is very similar to what happens in a V-Tail setup.
Elevons combine roll and pitch control on a flying wing.
Epoxy: Resin+hardener adhesive. Sets in 5 or 30 minutes. See Adhesives Guide.
EPO (Expanded PolyOlefin): Stiff, durable foam. Standard CA works on it without melting, unlike EPS.
EPP (Expanded Polypropylene): Flexible, rubbery foam — bends and bounces from impacts. Used in combat and trainer planes. Attach with hot-melt, shoe-goo, or epoxy.
EPS (Expanded Polystyrene): White foam (coffee cups, packing). Sensitive to solvents — standard CA melts it. Use foam-safe CA or white glue.
ESC (Electronic Speed Controller): An electronic circuit that regulates the speed of an electric motor based on throttle input. In gliders, the ESC often features a Brake setting to stop the propeller from spinning so it can fold flat against the fuselage to reduce drag.
Flapperon: Aileron + flap combined. Both droop like flaps while retaining aileron roll control. Needs separate servo per surface.
Flaps: Trailing edge surfaces that move down to increase lift. The flaps are located inboard of ailerons, closer to the fuselage. Some sailplanes will combine the action of flaps with ailerons in the same motion. These are known as flapperons.
Flaps (inboard) and ailerons (outboard) on a sailplane wing.
FM (Frequency Modulation): Better than AM for interference rejection. Was the standard before spread-spectrum. See Radios.
Full-House: Sailplane with ailerons, flaps, rudder, and elevator. Requires a computer radio. Not for beginners! See Full-House Wiring.
Gold-N-Rod: Tradename flexible pushrod system by Sullivan — plastic outer sleeve with sliding nylon inner rod.
Hi-Start: A hi-start is a length of rubber elastic material (such as surgical tubing) connected to a length of nylon or other cord. Hi-starts are usually constructed of several hundred feet of surgical rubber tubing connected to an even longer piece of line (typically twice as long) — either braided nylon cord or monofilament (fishing line). One end of the rubber is staked into the ground and the other end (the cord end) has a ring fastened to it. The ring slips over a tow-hook on the bottom of the sailplane (just in front of the CG). You stretch the hi-start a considerable distance downwind, then release the plane into the wind. The elastic tension launches the sailplane to impressive heights with minimal effort.
A hi-start stretches rubber tubing and line to catapult the sailplane skyward.
Kevlar (Aramid): Very strong fiber by DuPont. Used for fuselages and wing reinforcement similar to carbon fiber.
Kwik-Link: Kwik-Link is the trade name for a metal clevis that is very popular in R/C modeling. The metal clevises are strong and have very little flex when installed properly. These are the preferred type of clevis for combat and other high-stress applications versus using nylon clevises. A small piece of plastic tubing, metal clip, or section of drinking straw acts as a "keeper" to prevent the link from opening under impact.
Metal Kwik-Links with keepers — strong and reliable for combat use.
Li-Ion (Lithium Ion): Cell-based rechargeable battery. 2-cells = 7.4V — can damage non-6V-rated receivers without a voltage regulator! See also LiFe batteries.
LiFe (Lithium Iron Phosphate - LiFePO4): Safer lithium chemistry than LiPo. 2-cell = 6.6V — better for receiver packs. Won't catch fire from air exposure due to damage.
LiPo (Lithium Polymer): Lightweight rechargeable battery with similar chemistry to Li-Ion batteries. 2-cells = 7.4V — can damage non-6V-rated receivers without a voltage regulator! See also LiFe.
MAC (Mean Aerodynamic Chord): Chord through the centroid of the wing plan area. Most wings' aerodynamic centers are at 25% MAC. Related to aspect ratio.
Mixer: Device or radio function that combines control inputs for elevons, flapperons, or ruddervators. Now usually done inside the transmitter. See V-Tails.
Mode I & II: Radio control transmitters are available in two main configurations. Mode II (standard in North America): the left stick controls throttle (if any) and rudder, while the right stick controls elevator and aileron. Mode I (common in Europe): the left stick controls elevator and aileron, while the right stick controls throttle and rudder. Most sailplane pilots in the USA use Mode II. If you're just starting out, go with whatever is standard in your region — switching modes later is very difficult!
Mode I stick assignments.Mode II stick assignments.
Model Memory: Transmitter feature storing separate settings for multiple planes. Switch between models without reprogramming.
NiCad (Nickel-Cadmium): Rechargeable battery. 1.2V per cell. Hundreds/thousands of recharge cycles. Being replaced by LiPo/LiFe.
NiMH (Nickel Metal Hydride): Higher capacity than NiCad at similar weight, but higher internal resistance can cause voltage drops under load. Safer to charge than lithium.
Open Class: Large wingspan, high-performance sailplanes (100"+). See Open Class listings.
Oxygen: What you gasp for after climbing Cardiac Hill retrieving your downed combat plane.
PCM (Pulse Code Modulation): Digital form of FM. Data sent as digital pulses rather than analog. Heavier receivers. See Radios.
Pitcheron: Plane with no moving elevator — wings pivot together for pitch. Usually combined with wingeron for roll.
PNP (Plug 'n Play): A Plug and Play model is a nearly completed R/C aircraft that includes the airframe, motor, ESC, and servos pre-installed. To fly, the user must provide their own compatible transmitter, receiver, & flight battery (and charger).
Polyhedral: Polyhedral describes a wing that has two or more separate wing panels on each side, each at a different dihedral angle. Planes with polyhedral wings are typically more stable and more forgiving in most flying conditions, at the expense of being less maneuverable. This design is common in handlaunch sailplanes and beginner planes where stability is valued over aerobatic ability.
Polyhedral wing with multiple dihedral breaks for enhanced stability.
Push Rod: Rod connecting a servo to a control surface via clevises. Can be wire, carbon rod, or Gold-N-Rod flexible type.
RCSE: Radio Controlled Soaring Exchange — a mailing list connecting R/C soaring enthusiasts worldwide.
Receiver (Rx): Component in the plane that receives signals from the transmitter and drives servos.
RTF (Ready To Fly): Mostly or fully assembled — just add radio (or sometimes nothing at all). See also ARF.
Rudder: The rudder is the vertical control surface on the tail that moves left and right to yaw the plane. Moving the rudder to the left causes the tail to swing right, turning the nose left. On simpler 2-channel planes (rudder and elevator only), the rudder works together with dihedral in the wing to produce banking turns. Many sailplanes — especially handlaunch and beginner planes — fly beautifully with just rudder and elevator control. The German word for rudder is Seitenruder.
The rudder provides yaw control — turning the plane left and right.
Ruddervator: Combined rudder+elevator surfaces on a V-tail. See V-Tails & Elevons.
Servo: A servo is a small electromechanical device containing a motor, gears, and a feedback circuit that moves control surfaces in response to signals from the transmitter via the receiver. Servos come in many sizes — standard, mini, micro, sub-micro, and nano — with varying torque, speed, and weight characteristics. Choosing the right servo for your application is critical: lightweight servos for handlaunch, strong/fast servos for combat, and high-precision digital servos for competition flying. See Servo Wiring for connector details and The Gigantic Servo Chart for comparisons of 900+ servos.
A digital R/C servo with output arm and connector cable.
Spoileron: Aileron that moves upward to spoil lift. With computer radios, easily combined with flapperon function.
Spoiler: Surfaces that 'spoil' lift for landing precision or altitude reduction. Can be dedicated plates or spoilerons. German: Landeklappen.
Raised Spoilers on a sailplane.
Spread-Spectrum: Modern radio technology using frequency-hopping across 2.4 GHz. Each Tx/Rx pair has a unique pattern — no frequency conflicts. Types: FHSS, DSSS, DMSS, AFHDS, FASST, ACCESS, and more. See Radios.
T-Tail: A T-Tail is a tail configuration where the horizontal elevator is mounted on top of the vertical rudder fin, forming a "T" shape when viewed from the front. This design is common on sailplanes and commercial jets because it places the elevator up out of the turbulent wake of the wing, giving cleaner airflow and more effective pitch control. It also makes the elevator less likely to break during hard landings since it's elevated above ground level. On sailplanes with a single main wheel, a T-tail provides crucial ground clearance that a low-mounted tail would not. The trade-off is that the rudder must be strong enough to support the elevator's weight and aerodynamic loads.
T-Tail — elevator mounted on top of the rudder.
Thermal: Column of rising warm air used to gain altitude. Can be small puffs or powerful columns. The art of finding and riding thermals is one of the cores of the hobby.
Diagram of air flow in a thermal.
Torque: Force × distance. For servos: measured in oz-in or kg-cm. Convert: divide oz-in by 13.9 = kg-cm. Weight Converter.
Transmitter (Tx): The transmitter is the handheld radio controller that the pilot uses on the ground. It contains two control sticks (see Mode I & II), various switches and knobs, and — in modern computer radios — a programmable processor with an LCD screen and model memory. Transmitters range from basic 2-channel units to sophisticated 24+ channel systems capable of complex mixing, multiple flight modes, and telemetry feedback. Modern transmitters use spread-spectrum 2.4 GHz technology, eliminating the frequency conflicts that plagued older AM and FM systems. See Radios and Radio History for more details.
A modern R/C transmitter — the pilot's primary control interface.
Triple Taper: A triple taper wing has three different leading-edge sweep angles along each wing panel, creating a planform that's a compromise between a crescent wing (best aerodynamic efficiency, but very difficult to build) and a simple single-taper wing (easy to build, but less efficient). The triple taper approximates an elliptical lift distribution — the ideal for minimizing induced drag — while still being practical to construct from straight-edged panels. Many high-performance competition sailplanes use triple or even quadruple taper wings.
Triple taper wing — three sweep angles approximate an elliptical planform.
V-Tail: A V-Tail is a tail configuration where two control surfaces are mounted in a V-shape, combining the functions of both rudder and elevator into a single pair of surfaces called ruddervators. When both surfaces move in the same direction, they act as an elevator (pitch); when they move in opposite directions, they act as a rudder (yaw). A mixer — either in the transmitter or as a separate device — is required to blend the two control inputs. V-tails produce less drag than a conventional tail (fewer surfaces in the airstream) and look distinctive, but can behave oddly in sharp turns if not properly set up. See V-Tails & Elevons for a detailed explanation with diagrams.
V-Tail — two surfaces combine rudder and elevator functions.
Wingeron: Wings that individually pivot for roll control — no separate ailerons needed. Often combined with pitcheron.