ABC

An ABC engine is one with an Aluminium piston running in a Brass cylinder liner which is Chrome plated. ABC engines have a tighter fitting piston and are therefore more efficient and of higher power output than conventional engines which use piston rings.

Adverse Yaw

This is the tendency for an aircraft to yaw in the opposite direction to a roll, ie when left aileron is applied the aircraft yaws to the left, opposing the roll. Solution is to set up differential aileron throws.

Aerofoil

A lift generating surface designed to produce an aerodynamic force at approximately right-angles to its direction of motion, usually a wing, tailplane or fin.

Aerial

A tuned length of conducting material used to transmit or detect radio frequency signals. The length of an aerial is determined by the operating frequency of the equipment in use. It is important that aerials are not trimmed or twisted back on themselves as this alters the effective length.

Aileron

Ailerons normally form the outer trailing edge of the profile of a wing. Ailerons operate differentially such that when one aileron is lowered creating more lift - that wing tends to rise and conversely, the other aileron being raised destroys lift - and the wing on that side tends to fall. Ailerons are used to rotate an aircraft about it's longitudinal axis producing a rolling effect.

Air Brakes

A predominantly flat surface which when introduced into the airflow disturbs an otherwise smooth airflow and creates a large amount of drag thereby slowing the airframe.

Airspeed Indicator [ASI]

An instrument which compares pitot pressure with the ambient static pressure at that height and resolves the two by a series of capsules and levers into a direct reading of calibrated airspeed indicated in knots. It follows then, that an aircraft flying at an indicated airspeed of 100kts into a headwind of 20kts would have a ground speed of only 80kts.

AM

An Amplitude Modulation radio control system depends upon interpretation of height [or excursion] of a signal at the receiver as a measure of intended control deflection and is very susceptible to interference.

Angle of Attack

The angle between the chord line of an aerofoil and the relative airstream irrespective of the attitude of the airframe.

Angle of Incidence

The angle between the chord line of an aerofoil and the centre line of the airframe.

Anhedral

A wing with tips lower than the point at which a centre line drawn through each wing would intersect the vertical centre line of the fuselage as viewed from the front of the aircraft.

Aspect Ratio

The result of dividing the wingspan by the chord of a wing. For instance, a glider with long narrow wings would have a very high aspect ratio wing.

Attitude Indicator

A device external to the airframe which resolves the angle at which the airframe is being presented to the airflow.

Autogyro

A propeller driven aircraft which depends upon a free rotating rotor head assembly in order to ascend and descend.

Barometric Pressure

The basic unit of pressure is the millibar [Mb]. Air at standard pressure [14.7psi] is capable of supporting a column of mercury to a height of 29.99" or 1013.2Mb. Once airborne, altimeters are set to indicate 1013.2Mb which ensures that all aircraft operate under an agreed international set of standard conditions relative to each other wherever they are in the world. Barometric pressure reduces with height.

BEC

Battery Eliminator Circuit - a type of electric flight speed control unit which allows the motor and the receiver to be powered from the same battery pack.

Boom

A thin rod like rear fuselage which supports the tailplane.

Camber

The curvature [relative to the chord] of the surface of an aerofoil which creates lift.

Canard

An all moving control surface situated forward of the mainplane [normally computer controlled] providing rapid attitude changes in pitch and roll normally only fitted to fighter aircraft where rapid and extreme maneuverability is an essential requirement.

Centre-line Camber

The ratio between the chord of an aerofoil and the maximum height of the centre line above the chord line. In other words, a measure of the amount of curvature between the LE & TE of a wing.

Centre of Gravity

The centre of mass of an object. When applied to aircraft this is the central point about which control inputs are deemed to act.

Centre of Pressure

An imaginary line along the span of an aerofoil on which all the aerodynamic forces on the aerofoil affecting lift may be assumed to act. The centre of pressure of an aerofoil is normally about one-third back from the leading edge but in certain flying attitudes and with flaps extended, it may vary greatly and may even move right off the aerofoil altogether.

Chord

The width of an aerofoil section measured in a straight line from leading edge to trailing edge.

Clevis

A connecting link between the end of a push rod and a servo or control horn.

Clunk

A weight used to keep the fuel tank pick up tube immersed in fuel during manouevers

Cockpit

The pilot's office!

Control Horn

A lever fixed to the control surface which connects with the pushrod or control cable.

Creep Marks

A white rectangle painted where the tyres meet the wheel rims in order to spot tyre creep.

Crystal

A crystal consists of a thin slice of quartz placed between two electrodes. When the electrodes are subjected to an alternating voltage the quartz tends to vibrate at a frequency dependant upon the mechanical characteristics of the quartz slice. When the frequency matches the mechanical resonance of the quartz the amplitude of the vibrations become very large and the strain of these vibrations causes the quartz to produce an output which in turn is used to fine tune the frequency of the RF circuit.

Decalage

The difference in angle of incidence between the upper and lower wings of a biplane.

Differential Throw

Ailerons may be set for differential throws in order to counteract adverse yaw tendencies.

Dihedral

A wing with tips higher than the point at which a centre line drawn through each wing would intersect the vertical centre line of the fuselage as viewed from the front of the aircraft.

Down Thrust

Inclining the thrust line of an engine downwards to counteract excessive climbing tendencies.

Drag

The opposite to thrust. When an aircraft is cruising drag exactly equals thrust.

Ducted Fan

A totally enclosed short bladed fan operating within a close fitting tube or shroud to generate thrust.

DSC

Direct Servo Control - provision found on more expensive receivers for a lead directly linking the receiver to the transmitter enabling all receiver functions to be exercised without the transmitter being switched on.

DV Window

Direct Vision window - a small heated window providing at least one clear view forward for the pilot.

ESC

Electronic Speed Control - electric motor speed controller connected directly to the throttle channel of a receiver.

Ejection Seat

When all else fails ... "Let down courtesy of Martin Baker Limited". Today's ejection seats are fitted with rocket motors, the latest having gyros which if ejection occurs other than in straight and level flight "fly" the seat towards the vertical plane maximizing a pilots survival prospects when ejecting within the bounds of the survival envelope.

Elevator

Hinged horizontal surface at the rearmost part of the tailplane which provides longitudinal control in the pitch axis.

Elevon

Control surfaces at the rear of a flying wing or delta model that serve as both elevators and ailerons.

F1

Another named convention for the engine mounting firewall.

Fail Safe

A safety system to set the throttle to idle [or closed] in addition to moving the primary flying surfaces to pre-determined positions in the event of loss of radio signal.

Fatigue Meter

A device fitted as near to the centre of gravity of a full size aircraft as possible whilst still allowing easy access on the ground. It consists of a mass suspended by springs and incrementally measures the number of positive and negative 'G' transitions an aircraft makes during each flight. The readings are collected after each flight and are used to assess the life of an airframe.

Fin

Fixed vertical surface usually at the tail of an aircraft designed to contribute to both directional and lateral stability.

Firewall

The former to which engines are conventionally mounted.

Flaps

Integral areas of the inboard trailing edges of a wing which are extended by preset amounts in order to create more lift at low speed to assist takeoff and landing. Extending flaps by greater increments during the landing phase increases lift, steepens the glide and acts as an airbrake enabling slower approaches. Typical values would be 5 for take-off and 30 to 45 for the landing phase. Flaps are set flush to the wing profile during normal flight.

Flaperons

Ailerons which, by signal mixing in the transmitter, can act simultaneously as flaps.

Flare

The action of "rounding out" at the last stages of an approach by use of up elevator which results in a smoother landing attitude.

Flutter

Rapid oscillations of flying control surfaces in flight due to either excessive gaps between hinged surfaces or excess play in the linkages between control horns and the servo. Likely to end in a crash.

FM

A Frequency Modulation transmission system relies upon interpretation of frequency as the measure of control deflection when decoded by the receiver. FM signals are much less susceptible to interference than earlier AM systems.

Formation Lights

Not normally observed, formation lights are fitted to military aircraft on the upper fuselage and wing areas for use by the higher aircraft as points of reference when formation flying at night. Similarly larger military aircraft are fitted with small signalling lamps used for the transmission of totally secure morse messages within a formation day or night.

Fuel Dot

An aluminium "peg" which has the dual function of sealing the end of fuel tubing and securely seating itself within a mating housing set flush to the fuselage yet remaining easily accessible without tools when required for filling the fuel tank.

G Force

Positive G is an increase in effective weight [bottom of a loop] and Negative G is a decrease in effective weight, as when a body tends towards weightlessness at the top of a loop.

Glitch

A degradation of signal due to either temporary loss or interference when the model is observed to respond to un-demanded inputs.

Glow Fuel

Glow fuel is a volatile mixture which burns with a clear flame. A typical mix referred to as 10% would consist of 10% nitromethane, 25% of synthetic or castor oil [for engine lubrication] and 65% methanol.

Glow Plug

A device with a platinum element which initially requires a low voltage source to heat up but continues to glow and ignite the fuel air mixture on the compression cycle when exposed to the heat and pressure of combustion unlike a spark plug which requires a permanent high voltage electrical supply.

Glow Starter

Low voltage adapter used to make a glow plug element heat up at normal atmospheric pressure during engine starting.

Gudgeon Pin

A small pin fitted within the piston assembly of an internal combustion engine which is linked by the connecting [con] rod to the drive shaft of the engine.

Gull Wing

A "cranked" wing. On some glider variants the wings rise initially from the fuselage then descend towards the wing tips. Examples of aircraft designed with an inverted Gull Wing are the Stuka JU87 and the F4U Corsair, both of which had wings which were inclined down from the fuselage then up towards the wing tips.

Gyro

A flywheel supported within a cage [gimbals] which when spinning at high rotational speed has the property of always pointing in the same direction. When mounted in a moving body it is possible to detect changes in direction of the body via electrical detectors fixed to the gimbals. Mechanical gyros are being replaced in many applications by solid state electronic gyros.

Hangar Rash

The growth of dings, dents and scrapes through poor handling, transportation and storage of a model.

Head Up Display [HUD]

The means by which a pilot can monitor essential systems and aim weapons without looking down into the cockpit. These functions are projected either onto a fixed screen directly in his forward field of view or, as is becoming more prevalent, into his visor which means that an attack can be progressed without waiting for the aircraft to turn to face the target in turn subjecting the pilot to lower gravitational forces during combat.

IMC

Instrument Meteorological Conditions. Flying solely on instruments without reference to any external datum or horizon.

Knot

A knot is a speed of one nautical mile per hour. 100kts = 115mph [To convert kts to mph multiply by 1.15]

Lift

The normally vertical force produced at right angles to an aerofoil when it is moved through a medium such as air.

Longeron

A main longitudinal strength member of a fuselage attached to the fuselage formers.

Longitudinal Axis

The line running fore and aft through the centre of gravity of an aeroplane parallel to the line of flight.

Mach

Mach number is a relative figure concerning the speed of a body relative to the speed of sound. A Machmeter functions much like an ASI, with altitude and temperature being taken into account because the speed of sound varies as air density and temperature change. Under standard barometric conditions Mach 1.0 at sea level is 761mph yet at 50,000ft where the air is considerably thinner and extremely cold, Mach 1.0 is reached at an indicated 286mph.

Mainplane

The major lifting surface of an aircraft.

Main Spar

The major longitudinal load bearing beam of a wing.

Millibar

One thousandth part of a bar, a bar being equivalent to 29.99 inches of mercury under standard barometric conditions.

Modulation

The 3 types of modulation relevant to the operation of model aircraft are AM - Amplitude Modulation, FM - Frequency Modulation, and PCM - Pulse Coded Modulation.

NACA 4-Digit Aerofoils

The first digit represents the maximum camber [as a % of the chord] while the second digit [x10] refers to its location behind the leading edge [as a % of the chord]. The third and fourth digits combined relate to the maximum section thickness [also as a % of the chord]. A NACA 2412 section therefore has 2% maximum camber located 40% from the leading edge and is 12% thick.

NACA 5-Digit Aerofoils

The first digit [x0.15] gives the design lift coefficient while the second and third digits [x0.5] give the location of maximum camber [as a % of the chord]. As with the 4-Digit series, the third and fourth digits combined relate to the maximum section thickness [also as a % of the chord]. A NACA 23012 aerofoil therefore has a design CL of 0.3 with its maximum camber at 15% chord from the leading edge and is 12% thick.

Nautical Mile

A nautical mile is the universal geographical distance applicable to charts and maps. 1 nm [nautical mile] = 6080ft, whereas 1 mile = 5280ft.

Navigation Lights

Aircraft, like shipping, display a green light to starboard [right wing tip], a red light to port [left wing tip] and a white tail light to the rear in order to display presence and direction of motion at night.

Overshoot

Flying an aircraft as if on a landing approach and going round again at the last moment - also the name of the area just past the end of the runway.

PCM

With a Pulse Coded Modulation system the signal is transmitted using FM as a base, but is digitally encoded with a signal consisting of 1024 encoded positions ensuring totally accurate interpretation of the transmitted signal at the receiver. This in turn ensures that the servo moves to a precise position. PCM systems also include as standard fail-safe options.

Pitch

Movement in the vertical plane about the Centre of Gravity.

Pitot Head

Forward facing probe which connects directly to the aircraft pressure instrumentation line measuring the compressible component of the airflow. Some pitot probes are dual function and have slits which enable the static air pressure to be routed directly to the aircraft pressure instrumentation. All aircraft have pitot heads and static vents of some description and many have their static vents on both sides of the fuselage rather than being incorporated within the pitot head.

Propeller

Airscrew fitted to the front of an engine. The pitch is the theoretical distance that the propeller would move forward in one revolution.

QFE

The current barometric pressure measured at that airfield. In other words, an altimeter set to the QFE figure for that airfield would indicate zero feet when the aircraft was on the runway. Q codes historically began with wireless transmissions around 1912 and were introduced to speed communications whilst reducing scope for misunderstanding messages. [Q Field Elevation]

QNH

The current barometric pressure setting adjusted for the height of that airfield above sea level. In other words, an altimeter set to the QNH figure for that airfield would indicate the actual height of the airfield above sea level when the aircraft was on the runway. It would appear that the meaning of the N in QNH has been lost throughout the ages. [Q N Height]

Rate Of Climb Meter [ROC/VSI]

Instrument which detects minute changes in the detected ambient pressure as the aircraft climbs and descends and produces an indication in feet per minute for say, gliders, or hundreds of feet per minute when installed in powered aircraft.

Receiver [Rx]

The receiver decodes the incoming transmitted RF signals and sequentially routes the outputs to drive servos in the appropriate direction.

Remote Glow

A separate power supply installed in a model to provide a power supply to a glow plug at times when it might fail to function - eg during prolonged low throttle manouevers.

Reynolds Number

A computed number which is of interest to designers of aerofoils suitable for operation at certain design speeds.

Rib

The component in a wing which determines the aerofoil shape and size at a particular station along the wing.

Roll

The act of turning about the longitudinal axis of the aircraft.

Rudder

The hinged vertical surface at the rear of the fin providing horizontal directional control about the vertical axis of the centre of gravity ie in the yaw axis which, in combination with other controls, is used to steer an aircraft.

Servo

A device which translates electrical signals from the receiver into useful mechanical output to move controls. The power of a typical servo might be expressed as 3.2Kg/cm at 0.23secs/60. In the case of such a servo this means that it would take 0.23 seconds to move the servo arm through 60 with a load of 3.2Kg linked to the hole in the servo arm which is 1cm from the centre of the servo output shaft. As the distance from the centre of the servo output shaft increases then the maximum rated load decreases proportionally. The servo supply voltage [4.8v or 6.0v] affects the speed and power capabilities.

Side Thrust

Setting the thrust line of an engine to counteract torque to achieve a straight flight path - particularly noticeable on take-off if insufficient side thrust has been built in.

Slats

An exotic means of generating extra lift from a low speed wing. Slats are fitted to the forward upper surface of a wing.

SOB

Souls on Board - a figure passenger plane aircrew communicate to the control tower just prior to take-off.

Spar

The main longitudinal beam of a wing or control surface. Secondary structures are built around the spar to transfer the loads to it and, in the case of wing-ribs, to give the correct aerofoil section.

Spats

Streamlined fairing covering virtually all of the main wheel on a fixed undercarriage.

Spoilers

Spoilers are designed to destroy lift and take many forms. They are extensively used on glider wings and generally appear as vertical slabs extended at right angles to the airflow from the wing structure.

Spin

A phenomenon which occurs when all lift is lost and the aircraft descends like a falling leaf. Control is normally restored by centering all control surfaces.

Spinner

Streamlined cover fitted over the propeller boss, required on all model aircraft to minimize impact damage.

Stall

The point at which lift is no longer generated by an aerofoil due to an extreme angle of attack coupled with low speed which in turn causes the airflow over the top of the aerofoil surface to degenerate into turbulence with consequent loss of lift.

Starter

Full size engines employ various starting techniques including high volume air supplies from an on board gas turbine or ground trolley or even the gasses rapidly generated from a large cartridge struck by a firing pin whilst others use electric starter motors.

Static Vent / Static Slot

Polished paint free areas either on both sides of an aircraft or integral with the pitot head which are the points from which the ambient air pressure is detected for use by the aircraft instrumentation.

Stringer

Longitudinal secondary members of an aircraft structure usually running parallel to the main spars or longerons which assist in maintaining the external profile.

T-Nut

A blind fixing nut with spiked lugs which penetrate into the wood so that the screw or bolt may be tightened without the nut rotating.

Tailplane

The fixed horizontal tail surface.

Three Greens

Term used by aircrew on approach to finals to confirm that all three undercarriage legs are displayed as down and locked. A moving [ie retracting or extending undercarriage] shows red and when fully retracted all lights are turned out.

Thrust

Opposite to drag. When an aircraft is cruising thrust exactly equals drag.

Torque

Torque is a measure of the amount of force generated by the rotation of a shaft. At the levels of power developed by an IC engine it is normally measured in BHP [Brake Horse Power] whereas in lower torque devices such as servos it would be specified in Kgs/cm.

Track

The direction in which an aircraft is moving relative to the ground.

Transmitter

Means by which RF signals are transmitted to the model in order to have it follow the commanded input.

Trim Tab

A small area generally to the rear of a control surface which is used to trim out the forces necessary to keep an aircraft flying straight and level with hands off.

Turbine

A turbine is a small jet engine which runs on kerosene or white spirit in a similar fashion to the earliest jet engines. Typically turbines are spun up to approximately 26-30,000 rpm before the introduction of gas when they reach self sustain speed. The gas supply is then switched to kerosene and the turbine may be accelerated to produce maximum thrust at around 120,000rpm or greater. The gas efflux exits at around 650c and may produce anything from 12 - 30lbs of thrust depending upon the construction of the turbine. Fuel consumption is high at around 2 litres for an 8 minute flight.

Undershoot

The area immediately before the runway threshold. Performing a landing short of the runway.

V1

Computed speed below which a full size aircraft is able to come to rest within the length of the runway should the take off need to be aborted.

V2

Computed speed at which a full size aircraft is rotated into controlled flight.

VFR

Visual Flight Rules - pilots operating under rules which restrict them to flying only when the ground is visible.

Wash-In

More incidence at the tip than at the root of a wing or tailplane.

Wash-Out

Less incidence at the tip than at the root of a wing or tailplane.

Wing Loading

The weight of an aircraft divided by the area of the wing produces a wing loading figure such as 1lb/sq foot.

Yaw

Side to side movement about the centre of gravity controlled by rudder input.