APU (Oral)

What is the typical relationship between an aircrafts APU generator and the engine driven generator?

They are identical.

Where does the APU fuel supply come from?

Main fuel supply.

How is the APU rotated during start up?

With an electric starter.

What is the function of an APU air inlet plenum?

Stabilize the pressure of the air before it enters the compressor.

When operating at high loads, what is the speed of an APU?

The APU remains at or near rated speed regardless of load.

What is the effect of the pneumatic power when being used in conjunction with maximum APU shaft power output?

The pneumatic loading is automatically modulated to maintain safe EGT.

Before shutdown, how would APU cooling be accomplished?

Closing the bleed air valve, thus removing the load.

When is most of the load placed on an APU?

When the bleed air is open.

What regulates fuel scheduling during APU start and under varying pneumatic bleed and electrical loads?

Fuel control system automatically regulates.

What is the primary function of the load compressor on APU's equipped with a free turbine and load compressor?

To provide bleed air for the aircrafts pneumatic system.

To prevent rotor seizure, "shock cooling" how long should an APU idle before being shutdown?

3-5 minutes.

How long is a typical APU cool-down period?

3 minutes

How is an APU's operating speed maintained despite variations in the loads imposed?

By the APU's fuel control automatically adjusting the fuel flow

How is the cool-down for many APU's accomplished prior to shutdown?

By running the APU for a specified minimum period of time after closing the bleed air valve (unloaded)

What is the operating effect of following a required cool-down period prior to APU shutdown?

The APU's EGT is lowered and stabilized

Name at least 2 uses for APU produced pneumatic power

Engine starting,Ground air conditioning,Anti-icing

What is the usual source of a gas turbine APU's fuel supply?

Aircrafts main fuel tanks

What usually places the greatest demand on a gas turbine APU?

Bleed air loads

What is the function of an APU on modern transport category aircraft?

To supply ground electrical and pneumatic power to aircraft systems when the engines are not operating, and in some aircraft as a backup source of inflight electrical power.

Of what does a typical APU consist?

A small turbine powerplant with provisions for supplying bleed air, and an electrical generator that is usually identical to those mounted on the aircrafts engine

What is typically used to start an APU?

Its own electric starter and battery power

At what speed does a gas turbine APU operate?

Rated speed

What is the function of the interconnect tubes between the cans of a turbine engine

They allow the flame from the igniters to travel to all cans