Simviation Forums

according to a friend explanation is

When it comes to APU, the way it works is quite simple.
It's an engine, so you have to start it, and when it's finally running (needs some seconds), you can use the APU generator to make it produce electricity.
So the behavior is not so complex. Switch ON, wait 5 to 10 seconds, switch APU gen ON, you get power

is it a electrical engine ,or Piston engine ?
I found a photo on internet
http://aviationglossary.com/wp-content/ ... Airbus.jpg

A self-contained generator in an aircraft producing power for ground operation and for starting the engines

this engine looks electrical to me ,so is an electrical engine to generate electricity?

according to a friend explanation is

When it comes to APU, the way it works is quite simple.
It's an engine, so you have to start it, and when it's finally running (needs some seconds), you can use the APU generator to make it produce electricity.
So the behavior is not so complex. Switch ON, wait 5 to 10 seconds, switch APU gen ON, you get power

is it a electrical engine ,or Piston engine ?
I found a photo on internet
http://aviationglossary.com/wp-content/ ... Airbus.jpg

Alex, I believe it's a turbine. Not an electrical motor or piston engine.

Yep, turbine engine that requires fuel flow. 

It's a small Electric start jet motor, with a generator on it that produces electricity and bleed air for the packs, so you can have AC and Heat on the ground, and start the motors with out any external hook ups.

Not sure what aircraft you are doing Alex, but an APU on average takes up to

I believe on larger commercial aircraft it produces hydraulic power as well. Not sure if it does that with an electrically powered hydraulic powerpack. That is how the pilots of the US air flight were able to control the A320 that landed on the Hudson river.

I believe on larger commercial aircraft it produces hydraulic power as well. Not sure if it does that with an electrically powered hydraulic powerpack. That is how the pilots of the US air flight were able to control the A320 that landed on the Hudson river.

I am curious where you found that information, because that is not what I have heard.  From what I have read, the engines on the US Airways flight actually never shut down, they just remained at an idle setting because the computers detected the damage and reduced thrust to prevent further damage.  I also heard the crew deployed the RAT (ram air turbine) for emergency power.  But I did not believe they had sufficient time to start the APU before getting wet.

So Its a electricity generator instead the one we knows that uses gasoline the one we use when we go camping this one has a turbine engine

What does make the main engines start ,I mean a normal starter like the one we use in our cars? "Electrical"

Typically the bleed air from the APU is used to get the engine spinning.  The APU is started electrically, then bleed air is used for the main engines.  The reason is the APU is small enough that an electrical starter will work.  It would be impractical to use an electric starter on a large turbine due to the required power and speed to get the turbine spinning fast enough for ignition.

I believe on larger commercial aircraft it produces hydraulic power as well. Not sure if it does that with an electrically powered hydraulic powerpack. That is how the pilots of the US air flight were able to control the A320 that landed on the Hudson river.

-On C-17A the APU's Generator power the Electric Hydraulic  pumps, and burns 500lbs an hour.
-On C-5A/B/C The APU's (2x) power the Air Turbine motors that provide Hydraulic power, with there own Eletric Generators. Burn about 500lbs an hour.(not sure about the M they have new APU's)
-747-2/3 Does the same as the C-5
-747-400 do the same but burn about 800lbs an hour
-C-130A-through-H, has GTC that powers the Air turbine Motors for Hydraulic power and Eletrical
-C-130J has Normal APU. 

http://en.wikipedia.org/wiki/Auxiliary_power_unit
[color=#000000]When my Dad was at Pine Belt with Southern and later Republic, the Hobart APU was piston. He used to put his lunch on the engine to warm it.

When my Dad was at Pine Belt with Southern and later Republic, the Hobart APU was piston. He used to put his lunch on the engine to warm it.

Add an AB to the APU nowadays and you can have BBQ for lunch instead of a tepid sandwich! 

Modern APUs are jet engines...
Usually they are custom built and only run the generator, but some can be used as a real jet engine (RU-19's from the An-24 are used in the super rare Yak-30 trainer)

Basically... its a jet engine that can be started with electricity without draining the battery amps. After you get the APU started, you have more amps (and pressurized air) to start the main engines

When my Dad was at Pine Belt with Southern and later Republic, the Hobart APU was piston. He used to put his lunch on the engine to warm it.

Add an AB to the APU nowadays and you can have BBQ for lunch instead of a tepid sandwich!