RC Glossary of Terms

Resonance

The vibration frequency of rotating or moving parts. Excessive resonance can cause vibration damage.

Retracts

Short for retractable landing gear. Wheels and struts that fold up into the airplane to get them out of the air stream and present less resistance to the airflow.

RFI

Radio Frequency Interference.

Rib

The internal, vertical portion of the wing that gives it an airfoil-shaped contour.

Roll Axis

The airplane axis controlled by the ailerons. Roll is illustrated by holding the airplane by the nose and tail. Dropping either wingtip is the roll movement. This is used to bank or turn the airplane. Many aircraft are not equipped with ailerons and the Roll and Yaw motions are controlled by the rudder. This is one reason why most trainer aircraft have a larger amount of dihedral.

Roll Coupling

Applying rudder alone can cause the aircraft to bank into a turn without aileron input. The ability of the rudder to perform a banked turn is called roll coupling since the rudder input also induces the roll into the bank. Roll coupling is caused by wing dihedral, (the upward bend in the wing), and rudder placement. The higher the rudder is above the wing and fuselage, the greater its roll coupling effect. Roll coupling in performance aerobatic aircraft is not a good thing as it makes certain maneuvers, like a slow roll or stall turn, very difficult. But it is good in an aerobatic trainer as it teaches the pilot how to coordinate rudder and aileron.

RTF

Ready-to-Fly. Some newer airplanes are now available as RTF models. These planes usually come with everything needed for flight--plane, radio system, engine, and all hardware. The really nice thing about an RTF is that it will almost always be completely pre-built with only a few minor construction steps left for the modeler. If you want to fly and want to fly now, RTF is the way to go.

Rudder

The vertical control surface that controls yaw.

Rx

Abbreviation for receiver.

SAFE

SAFE technology is an advanced flight assistance system that gives pilots the ability to fly without the worry of crashing due to common mistakes such as orientation loss or over-control. Built upon the successful Spektrum AS3X system, models with SAFE technology have multiple flight modes with progressive flight envelope limitations as well as self-leveling and flight stabilization.

Serv Sync

A resequencing of the data the radio transmits based on the type of mixing you select. This feature helps to sync control services that are connected (such as a swash plate on a helicopter) and is used in radios that have many channels.

Servo

An electromagnetic device that moves the control surfaces and is controlled by the electrical impulses from the receiver.

Servo Output Arm

The removable arm or wheel which bolts to the output shaft of a servo and connects to the pushrod.

Servo Reversing

This radio feature allows you to install the servos where they can give the best pushrod routing without concern about the direction of servo rotation. When your installation is complete, turn on your radio and check each channel. If a channel operates opposite of its intended direction, a simple flick of a switch corrects the problem.

Sesquiplane

A biplane having one wing significantly smaller than the other.

Slat

A high-lift device on the leading edge of a wing designed to keep air flowing over the wing at a higher angle of attack than could be achieved otherwise.

Slip

A maneuver where the airplane's controls are used to make the fuselage fly at an angle to the line of flight. This causes a tremendous increase in drag and allows an airplane without landing flaps to increase its angle of descent without picking up a lot of speed.

Slop

Unwanted, excessive free movement in a control system. Often caused by a hole in a servo arm or control horn that is too big for the pushrod wire or clevis pin. This condition allows the control surface to move without transmitter stick movement. (See Flutter.)

Slow Roll

Model rolls at a uniform rate through one (1) revolution in either direction. Center is the inverted portion of maneuver. Inside Loop: Model pulls up and executes the loop. The loop should be completely round.

Smart Technology

Designed and developed by Spektrum, Smart Technology employs the latest advancements in connectivity and integration for a hassle-free and more fun RC experience. This is made possible by an integrated microchip that transmits a vast amount of data to Spektrum chargers, ESCs, and transmitters.

Snap Roll

A type of rolling maneuver that is very quick and violent. It's basically a spin where the flight path is in any direction chosen by the pilot.

Solo

Your first totally unassisted flight that results in a controlled landing.

Speed Brakes

Large panels that fold out of the aircraft structure to provide a lot of extra drag to the air. They are not part of the wing structure, but are usually mounted on the fuselage. Military jets most often have speed brakes, which fold out of the fuselage. Some airliners use spoilers as speed brakes when at altitude.

Spinner

Cone on the front of the propeller made from plastic or metal to improve aerodynamics, looks, and use of an electric starter.

Split S

Model performs one-half (1/2) roll in level flight then immediately executes one-half inside loop to level flight in opposite direction as entry. (This is basically an Immelmann done backwards.)

Split-S

Basically a reverse Immelmann. The airplane rolls onto its back, and then the nose comes down to finish a 1/2-loop. The direction of flight is changed 180°.

Sport Airplane

A model which possesses some attributes of many of the specialty airplanes and is best for general flying as they are the most versatile and durable.

Sputter Bug

(Slang courtesy of RC Universe) A new Nitro owner running his engine too rich, causing all the excess fuel to either run down the fuselage or spill on the track.

SRXL

SRXL is a single wire serial data protocol developed by Spektrum that allows channel data from SRXL equipped receivers to be transmitted to flight controllers and other accessories.

SRXL2

SRXL2 is a powerful bi-directional communications protocol that improves the speed, security, and richness of data transfer between your radio system and compatible on-board devices such as flight controllers and Smart ESCs. SRXL2 lowers the latency compared to legacy protocols and allows flight controllers to be configured directly from your Spektrum transmitter, without requiring a computer or smart device. You’ll also enjoy more responsive telemetry that can be customized precisely to your needs. And it’s all done over one signal wire! Please note that SRXL2 is not backward compatible with the legacy SRXL and remote receiver protocols. SRXL2 support updates may be required for your device to use SRXL2 receivers.