HarryStanhope From Australia, joined May 2012, 15 posts, RR: 0 Posted (7 months 2 weeks 5 days 9 hours ago) and read 5004 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.
LimaFoxTango From Antigua and Barbuda, joined Jun 2004, 692 posts, RR: 0 Reply 2, posted (7 months 2 weeks 5 days 7 hours ago) and read 4947 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".
You are said to be a good pilot when your take-off's equal your landings.
Fabo From Slovakia, joined Aug 2005, 1111 posts, RR: 1 Reply 6, posted (7 months 2 weeks 4 days 11 hours ago) and read 4580 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.
The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
flymia From United States of America, joined Jun 2001, 6282 posts, RR: 6 Reply 7, posted (7 months 2 weeks 4 days 10 hours ago) and read 4569 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.
francoflier From France, joined Oct 2001, 3195 posts, RR: 10 Reply 9, posted (7 months 2 weeks 2 days 15 hours ago) and read 4206 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.
Looks like I picked the wrong week to quit posting...
CanadianNorth From Canada, joined Aug 2002, 3371 posts, RR: 10 Reply 10, posted (7 months 2 weeks 2 days 11 hours ago) and read 4144 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.
Goldenshield From United States of America, joined Jan 2001, 5418 posts, RR: 13 Reply 11, posted (7 months 2 weeks 1 day 7 hours ago) and read 3912 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.
Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
skyhawkmatthew From Australia, joined Oct 2005, 99 posts, RR: 0 Reply 12, posted (7 months 2 weeks 1 day ago) and read 3829 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.
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 13, posted (7 months 2 weeks 9 hours ago) and read 3659 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.
T prop From United States of America, joined Apr 2001, 995 posts, RR: 1 Reply 14, posted (7 months 2 weeks 7 hours ago) and read 3643 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.
NZCH From New Zealand, joined Jan 2006, 119 posts, RR: 0 Reply 17, posted (6 months 2 weeks 1 day 11 hours ago) and read 1844 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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