avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

Turboprop Pilot Question

Mon Apr 09, 2001 3:38 am

In keeping with an earlier post on autofeather, which would you rather deal with; An engine failure on t/o without autofeather available, or, an uncommanded autofeather? I have only heard of one engine failure on t/o on Dash 8s, but know of several uncommanded autofeathers. Which is worse, and do you cover these scenarios in the sim?
 
cv640
Posts: 843
Joined: Wed Aug 30, 2000 8:10 pm

RE: Turboprop Pilot Question

Mon Apr 09, 2001 7:48 am

I have never practiced an uncommanded autofeather, but would prefer that to an engine failure with negative autofeather at V1. A Saab will barely fly if everything is perfect with an engine failure at V1 with a negative autocoarsen. AN uncommanded auto coarsen would be just like an engine faliure with a positive auto feather.
 
LaTechpilot
Posts: 125
Joined: Sun Jun 19, 2005 3:11 am

RE: Turboprop Pilot Question

Mon Apr 09, 2001 8:21 am

An uncommanded autofeather would have the same effects on aircraft handling characterisics as an engine failure. If given a choice, I'd rather have the uncommanded autofeather because the engine would still be running normally, thus still having the generator on line. After all, you could always just turn off the autofeather and hope the prop will resume normal RPM.
 
tito
Posts: 122
Joined: Sat Feb 17, 2001 1:39 pm

RE: Turboprop Pilot Question

Mon Apr 09, 2001 6:04 pm

I would rather deal with the uncommanded autofeather... because the prop would be feathered, thus better control and performance. I don't remember ever training for an uncommanded autofeather, but I imagine it wouldn't be any different from a V1 cut.

On the 580 the autofeather was triggered by a thrust sensor (as opposed to negative engine torque which activated a separate system that increased prop pitch) and could be triggered accidentally if the power levers were retarded too quickly from takeoff position (for instance during a rejected takeoff). Also, the Allison 501 (T56) is a direct drive turboprop... if the prop stops, everything is stopped, so no generator, alternator etc.
 
T prop
Posts: 910
Joined: Tue Apr 03, 2001 4:33 pm

RE: Turboprop Pilot Question

Mon Apr 09, 2001 7:20 pm

Avt007, I am not a pilot but I do work on dash 8's, here is a link to an uncommanded autofeather incident that resulted in the overtorque of both engines.
http://www.open.gov.uk/aaib/feb98htm/gbryp.htm
The aircraft involved, G-BRYP seems to lead a hard life.
On 28 Feb 1999 this aircraft was involved in a landing accident where the crew put it on a runway with thier rate of decent at 1800fpm, the left gear fuse pin sheared and the gear folded.
On 12 Aug 1999 miscommunication between the flight crew and a push back crew resulted in the tug (one normally used for DC 10 sized aircraft) pulling the nose gear off this aircraft.
As far as a crew having to deal with an engine failure and not having autofeather available, I would hope that one of them would reach forward and pull the condition lever back to feather rather than sit there and fly into the trees.
T prop
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Turboprop Pilot Question

Mon Apr 09, 2001 11:40 pm

I have experienced uncommanded autofeathers on the Dash 8 many times in the simulator. I would never want to experience one for real.

A normal engine failure with autofeather, or even failure to feather is much preferable and easier to control than an uncommanded autofeather.

This is not an opinion!

Best Regards,

Buff
 
avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Turboprop Pilot Question

Tue Apr 10, 2001 2:13 am

Thanks for the responses, guys, especially T prop! That report is very interesting, and I've printed it for the guys at work. The dash 8 a/f system can be a nightmare sometimes, but in this case, was only doing what it was told!
 
TomH
Posts: 950
Joined: Thu May 27, 1999 4:13 am

RE: Turboprop Pilot Question

Tue Apr 10, 2001 3:18 am

Buff,
I would have learned more if you told me why this is so.
TomH
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Turboprop Pilot Question

Tue Apr 10, 2001 5:52 am

Well, OK, since you ask:

The drag created by a windmilling prop is one thing to consider. There is no torque being exerted on the prop if the engine has failed. So it acts as one of those kid's windmills they get at the carnival - they hold it in the wind and it goes around.

A prop that has autofeathered is being turned with an enormous amount of power. The resultant torque has an incredible effect on the rest of the airplane, trying to turn the airplane about the prop (i.e. roll moment) - much the same as a helicopter with a failed tail rotor.

Additionally, if the uncommanded autofeather is not correctly identified, there is a real tendency, demonstrated time and again in simulators, for shutting down the wrong engine. Hence the importance of verifying engine malfunctions from as many indications as possible prior to taking any action towards shutting down.

And that is the control difficulty with an uncommanded autofeather as I remember it.

Best Regards,

Buff
 
TomH
Posts: 950
Joined: Thu May 27, 1999 4:13 am

RE: Turboprop Pilot Question

Tue Apr 10, 2001 7:38 pm

Buff,
Thanks for your time. I'm an occassional pax only, so my ignorance of piloting is great. Upon reading your reply and rereading the topic, I see that an uncommanded autofeather is one in which the blades go to feathered position but torque is still being applied by the engine. Doesn't sound very pleasant-up in the front seats or in the back. Thanks again.
TomH
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Turboprop Pilot Question

Wed Apr 11, 2001 8:57 am

Makes for a great aerobatic manoeuvre in the sim if you don't catch it early enough!

Best Regards,

Buff
 
TomH
Posts: 950
Joined: Thu May 27, 1999 4:13 am

RE: Turboprop Pilot Question

Wed Apr 11, 2001 7:32 pm

Buff,
I'll bet! I recall from my days in tracked vehicles in the Army Guard that the sharpest turn was one where you applied max torque to the outside track and reverse torque to the inside track. Turned on a dime! Well, a big dime.

Just last night I saw where the newest of the solar-powered aircraft (11 props I think) out at Mojave will be using assymetrical prop thrust to turn the aircraft, saving weight by having fewer conventional control surfaces. Guess there's a future in this yet!

Had an ex-P-51 Mustang driver tell me he was able to use prop pitch as a combat maneuvering technique. He stated he could keep the engine RPM fairly high and modulate the pitch for instantaneous thrust variation. He might have been kidding me. I know that on those piston engines spool-up time was much quicker than on a turboprop, so it would have been less necessary, and in the heat of battle he would have been risking engine overspeed. But still, I like the idea!

TomH

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