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Topic: Virgin ATR-72 Engines Stopping
Username: HarryStanhope
Posted 2012-10-01 19:19:28 and read 7465 times.

Heya everyone

I work as a ground handler for Jet Star in Townsville, I'm also a junior instructor at the local school. I'm only young but oh so curious about aviation.

I have been watching Virgin's new ATR's coming into Townsville and I'm struck by the way the engines stop. The left hand engine stops as I would have expected, slowly and smoothly. I've seen a few times now that when they cut the other engine, the blades stop in an instant when they slow down a tad.

Is this to do with the type of turbine it is? (excuse the dull question, I only know of two types)

Why would one stop so quickly and the other not so?

A lot of times they come in under power from just 1 engine, which is what some JQ flights do as well but the Dash 8's come in all the time and stop as per usual.

Thanks in advance for your responses  

[Edited 2012-10-01 19:52:36]

Topic: RE: Virgin ATR-72 Engines Stopping
Username: intsim
Posted 2012-10-01 21:08:11 and read 7418 times.

Hello,

I am guessing it may be related to the prop brake when using the engine as an apu...?

Jeff

Topic: RE: Virgin ATR-72 Engines Stopping
Username: LimaFoxTango
Posted 2012-10-01 21:17:55 and read 7409 times.

The starboard engine on the ATR is equipped with a prop brake. It stops the propeller from spinning while the engine still runs. Doing this provides bleed air and electrics to the aircraft while on the ground. It's ATR's response to not having a dedicated APU. It's referred to as "Hotel Mode".

Topic: RE: Virgin ATR-72 Engines Stopping
Username: armitageshanks
Posted 2012-10-01 22:33:26 and read 7367 times.

Quoting LimaFoxTango (Reply 2):
It's referred to as "Hotel Mode".

Is it totally automatic or does the pilot have to wait until a certain point to engage it?

Topic: RE: Virgin ATR-72 Engines Stopping
Username: HarryStanhope
Posted 2012-10-02 14:20:21 and read 7118 times.

oh that's really cool, I thought only helicopters had the brakes..do any other aircraft practice this?

and is this just specific to the ATR-72 500 or do the older 42's use the same method?

Topic: RE: Virgin ATR-72 Engines Stopping
Username: VIflyer
Posted 2012-10-02 16:18:52 and read 7069 times.

Quoting armitageshanks (Reply 3):
Is it totally automatic or does the pilot have to wait until a certain point to engage it?
http://www.smartcockpit.com/aircraft-ressources/ATR72-POWER_PLANT.html

See page 8 of the PDF it pulls up.

Vi

Topic: RE: Virgin ATR-72 Engines Stopping
Username: Fabo
Posted 2012-10-02 17:24:50 and read 7042 times.

Quoting HarryStanhope (Reply 4):
oh that's really cool, I thought only helicopters had the brakes..do any other aircraft practice this?

and is this just specific to the ATR-72 500 or do the older 42's use the same method?

Only ATRs AFAIK, but all 42s and 72 use this.

Quoting armitageshanks (Reply 3):
Is it totally automatic or does the pilot have to wait until a certain point to engage it?

There is a button. The brake is operated by hydraulic pressure, which is created by a pump depending on prop turning (AC-W elec), so there is another button to energize the brake, if you need to release it with engine 1 still off.

(this is from memory, some ATR jock correct me if I am wrong).


The idea is kind of neat, but it has many drawbacks... the "other one", being DHC-8 family, went for APU, and many think it was for the better, myself included.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: flymia
Posted 2012-10-02 17:57:14 and read 7031 times.

Quoting LimaFoxTango (Reply 2):
The starboard engine on the ATR is equipped with a prop brake. It stops the propeller from spinning while the engine still runs. Doing this provides bleed air and electrics to the aircraft while on the ground. It's ATR's response to not having a dedicated APU. It's referred to as "Hotel Mode".

Exactly. The second I started reading the OP I thought of this.

Quoting HarryStanhope (Thread starter):
Why would one stop so quickly and the other not so?

I always wondered this also for a while. Then when I got a detailed ATR-72 for Flight Simulator I figured out what it was.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: HarryStanhope
Posted 2012-10-02 18:54:08 and read 6999 times.

Very interesting!

Thanks so much for the information everyone! I'll be sure to pass the knowledge onto my students  

Topic: RE: Virgin ATR-72 Engines Stopping
Username: francoflier
Posted 2012-10-04 13:03:44 and read 6668 times.

Quoting Fabo (Reply 6):
Only ATRs AFAIK, but all 42s and 72 use this.

Actually, a few other turboprops had prop brakes. The F-27 had it, and I guess other Dart driven aircrafts...
It had nothing to do with using the engine as an APU of course. Because of the single shaft design of the turbine, you couldn't feather the prop upon shutdown and it would take half of forever for the blades to stop spinning. They installed the prop brake (pneumatically actioned on the F27 IIRC) to stop the prop quicker and allow ground personnel to approach the aircraft faster.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: CanadianNorth
Posted 2012-10-04 17:07:22 and read 6606 times.

Quoting francoflier (Reply 9):
. Because of the single shaft design of the turbine, you couldn't feather the prop upon shutdown and it would take half of forever for the blades to stop spinning. They installed the prop brake (pneumatically actioned on the F27 IIRC) to stop the prop quicker and allow ground personnel to approach the aircraft faster.

HS-748s have this feature on the port engine as well, but I believe it is operated by hydraulics and controlled with a small lever beside the throttles. However most of them have been removed now for cost savings. I've never seen one but all the old guys tell me they used to see them all the time back in the day, but they weighed a ton and tended to require a lot of maintenance, thus the airlines figured they would be money ahead to just pull them out and wait for the prop to slow down on its own.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: Goldenshield
Posted 2012-10-05 20:51:40 and read 6374 times.

Quoting francoflier (Reply 9):
Actually, a few other turboprops had prop brakes. The F-27 had it, and I guess other Dart driven aircrafts...

I wonder how much more feasible a prop clutch would be instead of a brake, which has a default of disengaged when not pressured.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: skyhawkmatthew
Posted 2012-10-06 03:59:52 and read 6291 times.

Quoting Goldenshield (Reply 11):
I wonder how much more feasible a prop clutch would be instead of a brake, which has a default of disengaged when not pressured.

The brake on the F27 was used to stop the prop as due to not feathering it, it would continue to spin after the engine (gas flow past the drive turbines) was shut down. A clutch would not achieve anything more than shutting down the engine: the brake is to physically stop the prop turning after drive is already interrupted. For the ATR, on which you can and do feather the prop on shutdown (like on the port engine), presumably a clutch could be used instead of the brake.

However, if the brake fails (in either mode), you've got either a normally-operating or frozen prop. If the clutch fails, you either have a normally-operating or runaway prop: not desirable.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: tdscanuck
Posted 2012-10-06 19:30:28 and read 6121 times.

Quoting Goldenshield (Reply 11):
I wonder how much more feasible a prop clutch would be instead of a brake, which has a default of disengaged when not pressured.

In addition to what skyhawkmatthew said, the load paths for a clutch are much more of a pain than a brake. For a brake, you need a way to grab the shaft (usually a disk of some kind), which is additive material that usually doesn't take anything away from the nice clean transmission of torque through the shaft.

A clutch, on the other hand, requires a break in the shaft somewhere. You've got to change torque to friction and back across that gap, which significantly complicates the situation and introduces some unpleasant failure modes.

Tom.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: T prop
Posted 2012-10-06 21:39:38 and read 6105 times.

Quoting skyhawkmatthew (Reply 12):
However, if the brake fails (in either mode), you've got either a normally-operating or frozen prop. If the clutch fails, you either have a normally-operating or runaway prop: not desirable.

On the ATR the danger is of a partially engaged prop brake. The prop will spin and a partially engaged brake will drag, rapidly heat up and catch fire! When engaging or disengaging the brake there is a time limit for the brake to do its thing. If it exceeds these limits, an immediate engine shut down is called for.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: mandala499
Posted 2012-10-06 23:47:34 and read 6079 times.

Quoting Fabo (Reply 6):
Only ATRs AFAIK, but all 42s and 72 use this.

CN235s on the CT-7 uses this, but rarely used... the prop brake maintenance on it is a dog at some operators...   

Topic: RE: Virgin ATR-72 Engines Stopping
Username: T prop
Posted 2012-10-08 02:53:20 and read 5897 times.

Quoting mandala499 (Reply 15):
Quoting Fabo (Reply 6):
Only ATRs AFAIK, but all 42s and 72 use this.

CN235s on the CT-7 uses this, but rarely used... the prop brake maintenance on it is a dog at some operators...

Saab 340 had prop brakes also but I don't know if any operator still uses them.

Topic: RE: Virgin ATR-72 Engines Stopping
Username: NZCH
Posted 2012-11-04 15:47:31 and read 4306 times.

I work for Air NZ, The right engine on the ATR is used as the APU as such, Once landed mostly the left engine is cut completly, and the aircraft taxi's in on the right engine, then once parked right prop is cut, but the engine is still going, generally that is called Hotel mode. Then when starting up, tight engine fires up first into Hotel mode, then the prop goes, then just start engine 1.


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