Allison 250 C30P

Question 1

“Free turbine”

Answer 1

The two turbines are not mechanically coupled and can rotate independently.
Gas producer turbine (N1) drives the compressor.
Power turbine (N2) powers the helicopter.

Question 2

Fuel system

Answer 2

FUEL CONTROL: Mechanically connected to throttle to allow for starting.

GOVERNOR: Mechanically coupled to collective pitch control (“droop compensator”) through linear actuator. Linear actuator allows for GOV “beep” “INC/DCR” trim.
GOV is mechanically coupled to N2 and compressor discharge pressure to automatically maintain constant N2 speed.

PC FILTER filters the air.
ACCUMULATOR smooths out air pressure signals……………………………………………………………..

Question 3

N1 components driven through gearcase

Answer 3

N1 tach/generator
Fuel pump
Starter/Generator
Fuel control
Oil pump

Question 4

N2 components driven through gearcase

Answer 4

N2 tach/generator
Power turbine Governor
Torquemeter
Freewheeling unit

Question 5

Fuel burn

Answer 5

225 lbs/hour for Longranger

Question 6

Horsepower

Answer 6

• 650 SHP engine
• Flat rated to 525 SHP by fuel flow.
• Derated to 435/370 SHP for performance at high DA.

Question 7

Sections of the 250 C30P

Answer 7

Intake
Compressor
Combustion
Turbine
Exhaust
Gearcase

Question 8

Intake

Answer 8

Air scoops an side of fuselage

Can have inlet barrier filter or particle separator

Question 9

Compressor

Answer 9

Single stage centrifugal impeller accelerates and compresses air through diffuser, into diffuser scroll, through compressor discharge air tubes, into combustion chamber.

Automatic bleed air system allows air to be vented during start cycle and as compressor speeds up (to prevent compressor stall)

Question 10

Combustion

Answer 10

Outer case and liner “burner can”. 25% of air used for combustion. 75% of air used for cooling.

Fuel is sprayed by fuel injector while air through holes in the combustion liner guides the flame away from surfaces and keeps things from melting.

Question 11

Turbine

Answer 11

Convert gas energy to mechanical energy.

N1 “gas producer” has two stage turbine powering compressor and N1 components.

N2 “power turbine” has two stage turbine powering helicopter and N2 components.

Question 12

Exhaust

Answer 12

Directs exhaust gases out of exhaust air outlet

Question 13

Torquemeter

Answer 13

Uses oil pressure to move a piston to determine torque. Lubricated by engine oil.

Question 14

TOT

Answer 14

measured by 4 thermocouples between N1 and N2 turbines

Question 15

Ignition

Answer 15

Spark ignitor powered by the ignitor excitor during starting

Question 16

Anti icing

Answer 16

Compressor discharge air is routed through and out the 5 hollow compressor vanes. Controlled by a solenoid via switch.
FAIL SAFE ON

Question 17

Compressor bleed air

Answer 17

Permits rapid engine response and ability to operate at low power RPM. Bleed valve opens and closes automatically based on pressure. Automatically fully open during starting. sometimes modulating.

Question 18

Engine Oil System

Answer 18

Dry sump
Oil pump assembly
1.5 gal engine oil tank
2 chip detectors (bottom of gearbox and engine oil outlet)
Scavenge pumps
Oil cooler
Oil filter with LRB installed near oil cooler and tank.

Question 19

Engine Fuel System

Answer 19

Fuel pump
Fuel control
Governor
Accumulator
Fuel nozzle

Question 20

Fuel flow is controlled by…

Answer 20

A function of compressor discharge pressure, engine speed, N1 lever angle, and governor lever angle

Question 21

Fuel Control

Answer 21

N1 RPM and throttle position

Question 22

Governor

Answer 22

collective position, linear actuator, and N2 speed

“droop compensator” system