航空发动机术语

Acceleration lag --

in the turbine engine, delay between the time instant power is requested and when

power is available. The time it takes the engine to accelerate and give the required

power increase.

Aerodynamic drag --

force which thrust must overcome to move an aircraft forward. Design can lesson

aerodynamic drag through streamlining. Drag increases with increased speed.

Airbleed actuator --

device

that

operates

the

interstage

bleed

system,

to

improve

compressor

acceleration characteristics by unloading small amounts of compressed air

.

Air density--

total mass of air per given volume, the weight of a given volume of air

. Air is denser

at lower altitude, at lower temperature, and lower humidity.

Airfoil profile --

outline of an airfoil section.

Airfoil section --

cross section of an airfoil parallel to a specific reference plane.

Air-fuel ratio --

Ideal mixture of 15 parts of air to 1 part of fuel by weight; the mixture to be burned

in the combustion chamber

.

Air inlet --

large, smooth aluminum or magnesium duct at mouth of engine which conducts air

into the compressor with minimum turbulence and restriction.

Aluminum alloy --

any of a variety of alloys formed by combining commercially pure aluminum with

other metals or materials such as copper

, silicon, manganese, magnesium, and zinc.

These alloying agents maybe added singly or in combination to produce a metal with

desired characteristics or strength, heat resistance, corrosion resistance, and the

like. Both wrought-and cast- aluminum alloys are widely used in the manufacture of

rotor blades and aircraft propellers.

Ambient --

condition of atmosphere existing around the engine, such as ambient pressure or

temperature.

Annular combustion chamber --

two-part combustion chamber made up of an annular liner and a housing assembly.

The

compressed

air

goes

into

a

ring-shaped

space

formed

by

the

annular

liner

around

the

turbine

shaft

rather

than

into

individual

combustion

chambers.

The

space between the

outer liner wall and the housing assembly allows

the flow

of

cooling air

. Used with axial-flow and dual compressors.

Annular reverse-flow engine --

type of gas turbine engine most commonly used in Army aircraft. Airflow direction is

reversed in the combustion area.

Anti-icing system --

device

that

supplies

hot

air

under

pressure

to

prevent

icing

of

the

inlet

housing

areas and inlet guide vanes. Hot scavenged oil is also circulated through internal

passages in the walls and struts.

Army Spectrometric Oil Analysis Program (ASOAP) --

periodic

oil

analysis

for

microscopic

metal

particles.

This

takes

place

at

an

oil

analysis laboratory.

Atmospheric pressure --

barometric

pressure

exerted

by

the

atmosphere

as

a

result

of

gravitational

attraction above the point in question.

Atomizer --

nozzle that creates minute particles and accurately shaped spray of fuel suitable for

rapid mixing and combustion.

Axial-flow compressor --

one in which the air is compressed parallel to the axis of the engine. It is made up of

a series of alternating rotor and stator vane stages.

Bending --

combination of tension and compression. The inside curve is under compression;

the outside is under tension.

Bleed system --

device that unloads small amounts of air to relieve pressure.

Boss --

raised rim around a hole; e.g., axle hole in a wheel. Circular projection on a casting,

usually serving as the seat for a bolt head or nut.

Brayton cycle --

constant

pressure

cycle,

with

four

basic

operations

which

it

accomplishes

simultaneously and continuously for an uninterrupted flow of power

. The turbine

engine operates on this cycle.

Camber --

the curvature of an airfoil's surfaces from the chord line. It maybe positive, negative,

or zero.

Can- annular combustion chamber --

one

with

characteristics

of

both

the

annular

types.

It

has

an

outer

shell

and

a

number of individual cylindrical liners.

Can combustion chamber --

one

made

up

of

individual

combustion

chambers

in

which

the

air

from

the

compressor enters each individual chamber through the adapter

.

Center of pressure --

aerodynamic center of an airfoil; the point where all forces act.

Centrifugal axial-flow compressor --

combination

of

the

centrifugal-flow

and

the

axial- flow

compressor

.

It

usually

consists

of

a

five-or

seven-stage

axial-flow

compressor

and

one

centrifugal-flow

compressor

. Also called the dual compressor

.

Centrifugal-flow compressor --

one with an impeller (rotor), stator

, and compressor manifold. The rotor revolves at

high speed drawing air into the blades. Centrifugal force accelerates the air

, and it

moves through the stator and through the manifold.

Centrifugal twisting movement --

force that tends to streamline rotating blades with the plane of rotation.

Choked nozzle --

a nozzle whose flow rate has reached the speed of sound.

Chord line --

imaginary line drawn between the leading and trailing edges of an airfoil.

Combustion --

process of burning the fuel-air mixture in a gas turbine engine.

Combustion chamber --

part of a turbine engine in which the propulsive power is developed by combustion

of the injected fuel and the expansive force of the resulting gases.

Combustion chamber liner --

engine part usually constructed of welded high-nickel steel, subjected to flame of

extremely

high

temperature.

It

is

behind

the

compressor

and

receives

the

compressed air which is mixed with fuel and ignited. The combustor is where the

combustion takes place.

Compressibility effects --

the phenomenon encountered at extremely high speeds (near the speed of sound)

when air ceases to flow smoothly over the wings (or blade) and piles up against the

leading edge, causing extreme buffeting and other effects.

Compressor --

that section of an engine that produces an increase in air pressure. It is made up of

rotating and stationary vane assemblies. It is the gas producer

, or it may be thought

of as an air pump.

Compressor rotor --

impeller

, may be thought of as an air pump. It accelerates the air rearward into the

first stage vane assemblies.

Compressor stall --

separation of the airflow from the suction surface of the freed or rotating blades of

a compressor

. Any degree of stall reduces airflow.

Concave --

pressure side of an airfoil.

Conduction --

transfer of heat through material by communication of kinetic energy from particle

to particle rather than by a flow of heated material.

Convergent area --

place where the cross-sectional area of a duct becomes smaller

.

Convergent exhaust duct --

duct used on fixed-wing aircraft; formed by tapering toward the rear of the duct.

Convex --

suction side of an airfoil.

Crossover tube --

duct carrying flame to the individual cylindrical liners of the can-annular combustion

chamber

.

Diffuser --

aft structural member of an engine. It receives high velocity air from the centrifugal

impeller

and

decreases

velocity

and

increases

air

pressure.

In

the

combustor

,

a

diffuser forms a divergent flow path for the exhaust gases.

Diffusion --

process by which gases intermingle as the result of their spontaneous movement

caused by thermal agitation.

Directional references --

specific definitions of terms referring to gas turbine engines to identify front and rear

,

right and left, bottom and top.

Divergent area --

place where air flows from a smaller into a larger area.

Divergent exhaust duct --

used on helicopter

. Device to diffuse the exhaust gases rearward and to eliminate

thrust.

Drag parasite --

drag caused by any member or structure which does not contribute to lift, such as

engine cowlings.

Drag profile --

friction resistance produced by a member moving through the air; in simple terms,

the

Dry-cleaning solvent --

cleaning compound that maybe used for all metal parts.

Dry-sump engine --

one in which the oil is stored separate from the engine.

Dual compressor --

see centrifugal-flow, axial-flow compressor

.

Duplex nozzle --

dual-orifice channel through which highly atomized and accurately shaped sprays of

fuel go into the combustion chamber

.

Dynamic load --

load on an aircraft due to a dynamic force.

Effective angle of attack --

that part of a given angle of attack that lies between the chord of an airfoil and a line

representing the resultant velocity of the disturber airflow.

End play --

longitudinal back-and-forth play of a shaft.

Engine airflow path --

route of the airflow through the engine.

Engine oil pressure indicating system --

device that gives continuous readings of engine oil pump pressure in psi.

Engine oil temperature indicating system --

device electrically connected to the 28 VDC system which transmits temperature

readings to the indicator in degrees centigrade.

Engine speed notation --

the capital letter N, which represents the rotational speed of the engine. When a

number is placed after the N (as in

Engine stations --

specific

locations

on

the

engine

designating

temperature

or

pressure-measuring

locations. For example, T3 means the third temperature pickup on the engine.

Engine surge --

result of compressor stall. The complete engine in stall.

Exhaust --

hot gases discharged from the engine through the exhaust diffuser section.

Exhaust diffuser --

section composed of an inner and outer housing, separated by hollow struts across

the exhaust passage. It forms a divergent flow path for the exhaust gases.

Exhaust gas temperature indicator --

sensitive millivoltmeter calibrated in degree centigrade, activated by an electrical

force generated by its thermocouple.

Feedback --

relay through the controls of aerodynamic forces exerted on the control surfaces

and felt by the pilot.

Fir tree mount --

manner of attaching the blades to the disk in the turbine rotor assembly. The root of

the blade where it is attached to the disk is shaped like a fir tree.

Foreign object --

any object such as a tool, piece of equipment, engine part (nut, bolt, lockwire) that

could in any way damage the engine.

Foreign object damage --

commonly called FOD, harm or destruction to the turbine engine caused by foreign

objects sucked into the inlet area of the engine with the required air

.

Forged --

shaped

by

hammering.

Only

the

malleable

metals

are

worked

successfully.

The

application of heat increases plasticity.

Free-power turbine engine --

the

turbine

engine

used

by

the

Army.

Sixty

percent

of

the

energy

produced

by

combustion is extracted by the gas producer turbine to drive the gas producer rotor

.

The rest of the energy is converted to shaft horsepower to drive the output shaft of

the engine.

Frictional loss --

resistance to the relative motion of air flowing along a duct.

Frontal area --

front

part

of

a

gas

turbine

engine,

smaller

than

that

of

a

reciprocating

engine,

therefore producing less drag.

Front of engine --

end from which power is extracted. An exception is the T73 engine on the CH-54, in

which the power is extracted at the end where the exhaust gas is expelled.

Fuel-air ratio --

see air-fuel ratio.

Fuel atomizer --

see atomizer

.

Fuel controls --

devices to control fuel flow. They are usually hydromechanical and include speed

governors, servo systems, valves, metering systems, and sensing pickups.

Fuel divider --

device that meters fuel to the engine nozzles according to a predetermined schedule

of secondary flow versus primary flow.

Fuel nozzle --

device

to

inject

fuel

into

the

combustion

chamber

in

a

highly

atomized

and

accurately shaped spray.

Fuel pressure indicating system --

device that gives continuous readings in psi of fuel pressure in the main fuel supply

line.

Gas producer--

the compressor in a free-power turbine engine.

Gas turbine engine --

aircraft power plant that is adaptable for both airplanes and helicopters.

Gerotor pump --

modified gear-type pump with two moving parts, an inner toothed element and an

outer toothed element. The inner one has one less tooth than the outer

.

Glow plug --

device that consists of a heating element in a short conventional-looking spark plug.

Ground angle --

angle between the wing chord and the horizontal plane when the airplane is at rest

on the ground.

Heat exchanger --

fuel-oil

cooler

,

to

help

cool

the

oil.

The

exchanger

is

a

cylindrical

oil

chamber

surrounded

by

a

jacket

through

which

the

fuel

passes.

Heat

from

the

oil

is

transferred to the fuel by conduction.

Hot start --

overtemperature during starting.

Hung start --

failure to reach normal idling RPM during starting.

Igniter plugs--

spark plugs which function only during starting and cut out of the circuit as soon as

combustion is self-supporting.

Imbalance --

uneven

distribution

of

weight

resulting

in

rotating

parts

being

out

of

balance.

Measured in inch- grams or inch-ounces.