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Turboprop Pilot Question  
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Posted (13 years 8 months 3 weeks 5 days 17 hours ago) and read 3524 times:

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?

11 replies: All unread, jump to last
 
User currently offlineCV640 From United States of America, joined Aug 2000, 952 posts, RR: 5
Reply 1, posted (13 years 8 months 3 weeks 5 days 13 hours ago) and read 3443 times:

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.

User currently offlineLatechpilot From United States of America, joined Jun 2005, 0 posts, RR: 0
Reply 2, posted (13 years 8 months 3 weeks 5 days 12 hours ago) and read 3427 times:

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.

User currently offlineTito From United States of America, joined Feb 2001, 125 posts, RR: 1
Reply 3, posted (13 years 8 months 3 weeks 5 days 3 hours ago) and read 3409 times:

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.


User currently offlineT prop From United States of America, joined Apr 2001, 1029 posts, RR: 1
Reply 4, posted (13 years 8 months 3 weeks 5 days 1 hour ago) and read 3414 times:

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


User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 5, posted (13 years 8 months 3 weeks 4 days 21 hours ago) and read 3387 times:

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


User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 6, posted (13 years 8 months 3 weeks 4 days 18 hours ago) and read 3383 times:

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!

User currently offlineTomh From United States of America, joined May 1999, 960 posts, RR: 2
Reply 7, posted (13 years 8 months 3 weeks 4 days 17 hours ago) and read 3371 times:

Buff,
I would have learned more if you told me why this is so.
TomH


User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 8, posted (13 years 8 months 3 weeks 4 days 15 hours ago) and read 3371 times:

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


User currently offlineTomh From United States of America, joined May 1999, 960 posts, RR: 2
Reply 9, posted (13 years 8 months 3 weeks 4 days 1 hour ago) and read 3350 times:

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


User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 10, posted (13 years 8 months 3 weeks 3 days 12 hours ago) and read 3341 times:

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

Best Regards,

Buff


User currently offlineTomh From United States of America, joined May 1999, 960 posts, RR: 2
Reply 11, posted (13 years 8 months 3 weeks 3 days 1 hour ago) and read 3333 times:

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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