Atr 72 Apu
 

I just drove past the back of a ATR 72 while pax boarding and noticed there was no APU exhaust outlet at the back, but there was power to the a/c with no external ground power. I tried looking for the source from the adjacent bay and saw exhaust plume coming from the No 2 engine.
I asked a colleague of mine( no one has ATR 72 rating here) who told me that this a/c uses the no 2 engine as an apu while "braking" its propellers. Is it really braking the propellers or does it use some form of clutching mechanism to let the turbine run free of the propellers ? And does the APU provide bleed air for the packs as well ?

A pretty ingenious idea I must say !:)

Yep the no.2 or RH engine is used as an APU with "prop brake" on. And it also does provide bleed air for the packs. :ok:

But wouldn't this "brake" put too much stress on the shaft if it's on for a long time. Read that the brake is usually used for engine shutdown and feathered mode. Have very limited knowledge on turboprops. Would like to know more.

...A propeller brake for a twin spool turbo-prop engine which permits the propeller to be locked in a stationary position with the engine running is disclosed. The propeller brake has a hydraulically actuated friction brake and hydraulically actuated locking mechanism rotatably connected to the engine spool turning the propeller. The friction brake stops the propeller from rotating in response to an external command. A hydraulic signal indicating the propeller has stopped rotating actuates the mechanical lock holding the propeller in a stationary position. A safety latch prevents the mechanical lock from being actuated in event of a hydraulic pressure or engine failure in flight. :ok:

and there is still some people who are saying that French and Italians are building sh.ts ...
ATR : Avions Transport Regional , based and built in Toulouse.
Salut.

Thanks for the reply powerstall ! :ok:

Hotel Mode. Good system but watch out for anything more than a 10kt tail-wind especially on the newer 500s.

YouTube - Flight1 ATR 72 Startup Tutorial (Hotel Mode)

Yep 10kts tail wind, and you get a Nacelle Overheat warning! :D

Quite a clever idea, but it makes it impossible to use the rear service door (the only entrance the aft hold unless you use the pax doors) while using hotel mode.

When the AC comes on stand, engine one gets shut down and engine 2 prop brake applied. We connect gound power and engine 2 gets shut down.

The FCOM 2 clearly recommends to park the Aircraft with the nose 45º right to the upwind

For cooling purposes you can even bring the Power Lever up to Gust lock stop and thus increasing the turbine spool to over 75% Nh to increase the bleed air distributed to the cabin and therefore improving the air conditioning throughout the cabin during Hotel Mode

Unfortunately, in a lot of operations, the parking stand does not allow for such flexibility.

I seem to remember the rear service door being used when prop brake applied, dont suppose thats a local procedure you use is it?

Quite possibly, yes. However as it is a running engine, i'm quite glad we stick by this procedure! :ok:

The use of the the service door, depending on where the exhaust gas is going, is entirely dependent on how much noise and smell the ground crew will accept. lt is very, very noisy.

Also, in the power band available, it can run either the electrics or the air-con, but not both.

On one occasion during push back, and prior to official start, "bing-bong, yes ?, Sir, it is very hot in the back.

It`s a bit warm here too mate "

Two of the three companies l`ve operated the type for blanked off "hotel mode" mainly because of it`s documented history of un-commanded prop brake release, and un-commanded prop brake application ( once, to my knowledge ) in flight.

l have to say that my latest 1900hrs on type ( for the third company ) produced no problems other than the heat generated with no prop wash to disperse it.

l hope that helps.

ps, the type is a good`un. We used to power back off stand in Sumburgh as a matter of course back then, and payed nothing to do it :)

hi
 

ATR-72 does not have APU, We use engine no 2 as APU by propeller locking. & this is called Hotel mode. :ok: