Jet Aircraft Glossary Terms Flashcards
Buffet Threshold
For a given set of conditions, the point at which buffet (either low or high speed) is first felt.
Buffet Boundary
For a given set of conditions, the line of speed and altitude combinations at which buffet will occur
Compressibility Effect
The effect of shockwaves on the aircraft at the critical mach number
Free Stream
The air conditions close to, but uninfluenced by, the aircraft
Incidence
The angle between the wing’s chordline and the free air stream
Lift
CL1/2RhoV2S
Stagnation Point
That point on the leading edge of an aerofoil surface where the upper and lower air streams last separate and where the airstream is locally brought to rest.
THP
Thrust horsepower; the power equivalent of the thrust exerted on the aircraft by the propulsive device.
Bleed Air
Air which has been compressed in the main engine compressor and utilised for cabin pressurisation and the driving of various services.
Bypass Ratio
The ratio of the total air mass flow through the fan stage of a by-pass engine to the air mass flow which passes through the turbine section. Typical value for a CFM-56 is 6.0
EPR
Engine pressure ratio; a ratio of pressures, usually the maximum cycle pressure (compressor delivery pressure) to air intake pressure or ambient pressure (depending on specific applications) which is an important turbine engine parameter and can be displayed to the pilot.
HP (and LP)
High (and low) pressure rotating systems.
N1 (and N2)
The rotational speed of the low (and high) pressure compressor of a two- spool engine expressed either as rpm or a percentage of the maximum value.
SFC
Specific fuel consumption; the quantity of fuel consumed in pounds per hour divided by the thrust of the engine in pounds.
Surge
A condition of aerodynamic instability in the compressor which can cause cyclic reversal of the airflow. It may be caused by disturbance of the air intake flow or by a fault condition and may lead to overheating and serious mechanical damage.
TGT
Turbine gas temperature; a temperature which may be used for engine control purposes, measured between the turbine stages of a multistage turbine engine: sometimes loosely employed for EGT.
EGT
Exhaust gas temperature; also known as JPT (jet pipe temperature). The temperature used for control purposes in many engines but less satisfactory than TGT in certain applications.
Thrust Line
The line along which the thrust acts. In a turbine engine the thrust line will be the centreline of the total exhaust flow, including the exhaust from the fan stage where applicable. The thrust line may not always coincide with the engine centreline since the exhaust ducts may be angled.
Compressibility Error
The error in flight instrument readings due to Mach number effect.
Position Error
The error in flight instrument readings due to the position and system limitations of the static and dynamic pressure sensing sources.
Gross Performance
The measured performance of a test aeroplane adjusted so as to be representative of the type and reflecting either a fleet mean or minimum guaranteed engine power.
Net Performance
The gross performance adjusted downwards to account for reasonable errors in operational variables and flying techniques.
Net Flight Path
The engine out climb after take-off providing adequate obstacle clearance under adverse circumstances. It covers the segment from screen height at V2 to the beginning of the en-route climb and specified powers, airspeeds and flap retraction details.
WAT (limiting conditions)
Conditions of aeroplane weight which, when combined with the aerodrome altitude and temperature, reduce the performance level to the airworthiness minima.
Gradient of Climb
Climb performance expressed as a gradient = the vertical height gained expressed as a percentage of the horizontal distance travelled.
IAS
Indicated airspeed; corrected only for instrument error.
EAS
Equivalent airspeed; IAS corrected for position error and compressibility error.
TAS
True airspeed; the true speed of the aeroplane relative to undisturbed air: EAS/ σ = TAS.
Mach Number
The ratio of TAS to the speed of sound for the ambient conditions.
IMN
Indicated Mach number; corrected only for instrument error.
M Crit
The Mach number at which the aircraft first experiences supersonic flow.
TMN
True Mach number; IMN corrected for position error.
Vs
Stall speed; speed at which the aeroplane exhibits qualities accepted as defining the stall.
Vss
Stick shake speed - the speed at which the stick shaker will activate.
V1
The latest speed by which:
a) the decision to reject the take-off should have been made; and
b) the first action of the rejected take-off drill should have been taken.
VR
Rotation Speed
V2
Take-off safety speed; the lowest speed at which the aeroplane complies with those handling criteria associated with the climb after take-off following an engine failure.
V3
The all engines screen speed; the speed at which the aeroplane is assumed to pass through the screen height with all engines operating on take-off.
V4
The all engines steady initial climb speed; the speed assumed for the first segment noise abatement take-off procedure.
Vat
The target threshold speed for a specified flap setting; for landing in relatively favourable conditions.
Vat1
The target threshold speed for an engine out landing.
Vtmax
The maximum threshold speed; the speed above which there is an unacceptable risk of overrunning; normally assumed to be VAT + 20 kts.
VMU
The minimum demonstrated unstick speed; the minimum speed at which it is possible to leave the ground, all engines and climb out without undue hazard.
VMCG
The minimum control speed on the ground; the minimum speed at which it is possible to suffer an engine failure on take-off and maintain control of the aeroplane within defined limits.
VMCA
The minimum control speed in the air in a take-off configuration; the minimum speed at which it is possible to suffer an engine failure and maintain control of the aeroplane within defined limits.
VMCL
The minimum control speed in the air in an approach or landing configuration; the minimum speed at which it is possible, with an engine inoperative to maintain control of the aeroplane within defined limits while applying maximum variations of power.
VNO/MNO
Normal operating speed; the maximum permitted speed for normal
operations.
VNE/MNE
Never exceed speed; a higher maximum permitted speed when operationally desirable.
VMO/MMO
Maximum operating speed; the maximum permitted speed for all operations.
VRA/MRA
The rough-air sped; the recommended speed for flight in turbulence.
VF
Flap limiting speed; maximum speed for flight with the flaps extended.
VIMD
Speed for minimum drag.
VIMP
Speed for minimum power.
Screen Speed (and screen height)
The speeds assumed at 35 ft above the runway after take-off and at 30 ft above the runway on approaching to land used in establishing the field performance of the aeroplane.
Zero Rate of Climb speed
The speed at which, for a given thrust from the operating engines, the drag of the aeroplane reduces the climb gradient to zero.
Static Stability
The tendency of an aircraft following a disturbance from a trimmed condition to return to or diverge from the initial trimmed condition.
Manoeuvre Point
The CG position, usually aft of the neutral point, at which the stick force per g becomes zero.
Manoeuvre Margin
The distance of the CG forward of the manoeuvre point expressed as a percentage of the wing chord.
APS Weight
Aircraft prepared for service weight; a fully equipped operational aeroplane - but empty; ie. without fuel or payload.
MZFW
This is the weight of the aeroplane above which all weight must consist of fuel. This limitation is always determined by the structural loading airworthiness requirements; unlike the other weight limitations, it is not associated with any handling or performance qualities.
ADC
Air data computer; a device for correcting the information from the usual pressure and static sources and supplying it to servo driven flight instruments, the autopilot and flight director.
Clean
The aeroplane configuration with all extensible devices (gear, flaps, etc) retracted; also referred to as “en-route”.
Droop
On a fixed wing leading edge this refers to a drooped nose profile to improve lift at high incidence: some aeroplanes have an extensible droop leading edge to the wing.
Green Band
The range of stabiliser trim settings for take-off against weight and CG marked as a green segment on the longitudinal trim scale.
LCN
Load classification number. A numerical method of matching the footprint pressures of an aeroplane to the strength of rigid and ‘flexible’ pavements.
PCU
Power control unit (refers to powered flying controls).
Slat
A wing leading edge flap which extends to increase lift.
Slot
Either the space between the wing and an extended slat or flap, or a gap, either permanently open or openable, aft of the fixed wing leading edge.
VASI
Visual approach slope indicator; a system of coloured light beams defining a safe approach angle to a runway.
VSI
Vertical speed indicator.
IVSI
Instantaneous vertical speed indicator.
