Prop pitch in emergency

deyoung

deyoung

Line Up and Wait
Joined
Nov 13, 2014
Messages
508
Location
Tucson, AZ
Display Name
Display name:
Chris
I fly a Cherokee-235 with constant speed prop, but the prop does not truly feather, which I expect is typical for aircraft in this class.

Two questions... if my engine quits, how much extra glide (roughly) is to be gained by pushing the prop full coarse?

And, I have not tried this, but in simulated engine failure practice when pulling the throttle to idle is it okay, bad, indifferent, or something else to go ahead and put the prop full coarse? I haven't thought of the question when I had a CFI handy to ask, though I will, but I figure someone here has likely explored the question already...

Thanks!
 
You can sorta try it for yourself... just set up for a power off glide to a landing, and then *pull* the prop back (cough, you said push...) and you'll feel the airplane accelerate slightly. Don't attempt a go-around without shoving it back up...

As another thing to think about, what holds the prop in a single at the higher pitch position? Will it work during all types of engine failures? (Hint: Still have oil on board, or is there a big hole in the engine and oil all over the windscreen this time?) :)
 
Try it---you'll see it's like taking your foot off the brake. Makes a big difference. I'm surprised this isn't mentioned in the Emergency Procedures section of the POH. It is in my Bonanza's.
 
Yes, I know the prop governor works on oil pressure, but good to mention. If the engine really does quit and the prop is windmilling, I think that will still maintain enough oil pressure for it to do as asked, though I haven't tested it.

I haven't tried it just because I hadn't checked with someone who knows more than me that nothing surprising would happen, like the engine stalling or something---I wouldn't expect it to, but I like to ask before just trying new things out. :) It's not mentioned at all in the POH, which is pretty bare-bones for this airplane, but it makes sense that it would help at least some.
 
deyoung said:
Yes, I know the prop governor works on oil pressure, but good to mention. If the engine really does quit and the prop is windmilling, I think that will still maintain enough oil pressure for it to do as asked, though I haven't tested it.

I haven't tried it just because I hadn't checked with someone who knows more than me that nothing surprising would happen, like the engine stalling or something---I wouldn't expect it to, but I like to ask before just trying new things out. :) It's not mentioned at all in the POH, which is pretty bare-bones for this airplane, but it makes sense that it would help at least some.
Click to expand...

All very dependent on what the failure mode is... if the engine seized from lack of oil... :) :) :)

Yeah, as far as the "surprises"... the engine shouldn't stall or anything, but that's why you would set up a power-off glidepath to the runway that would guarantee you make it there... before trying it. :) :) :)

Also, I don't know of any light GA aircraft that have any limitations on it, but obviously if your prop has a mandatory operation range in the POH, don't go outside of it... you can show yourself what it will do just by coming to the bottom of the green arc, if you have a marking/limitation on RPM... it still makes enough of a difference you'll feel it.

Surprised you haven't noticed it the other direction when putting the prop forward in a long descent to an airport... I know a lot of people wait until they have the MP low enough that they're out of the governing range before that last push forward, but whatever technique one uses... you can feel the deceleration in both your butt (sliding forward feeling) and also the airspeed indicator on most singles when you put the prop full forward at a lower power setting...

You REALLY feel it in a twin... it's like having two big trash can lids out there blocking air... hahaha...
 
deyoung said:
I fly a Cherokee-235 with constant speed prop, but the prop does not truly feather, which I expect is typical for aircraft in this class.

Two questions... if my engine quits, how much extra glide (roughly) is to be gained by pushing the prop full coarse?

And, I have not tried this, but in simulated engine failure practice when pulling the throttle to idle is it okay, bad, indifferent, or something else to go ahead and put the prop full coarse? I haven't thought of the question when I had a CFI handy to ask, though I will, but I figure someone here has likely explored the question already...

Thanks!
Click to expand...

In a simulated engine failure, moving the prop control to full course is the proper procedure. If you maintain best glide, what ever increase in glide can be measured by a decrease in vertical speed.
 
The other school of thought says to stop the prop in it's entirety for least drag, even though it will be at fine pitch.
 
Sac Arrow said:
The other school of thought says to stop the prop in it's entirety for least drag, even though it will be at fine pitch.
Click to expand...

Have you tried to stop a prop? Takes a serious pitch up. Did it once in a Cessna 120 and it was educational.

Bob
 
bobmrg said:
Have you tried to stop a prop? Takes a serious pitch up. Did it once in a Cessna 120 and it was educational.

Bob
Click to expand...


Because you did it the hard way. Next time just take off with no oil in the crankcase.
 
Might want to think about it. You don't always want best glide. Tendency in an emergency is to overshoot. Then there is the risk of the training exercise itself and the fact its not in the POH. I opted not to fool around with "pulling the prop" all the way out in an engine out practice. Its a "cutie" I don't need, although I have tried it. Might be worth trying it. And if your only hope is a long glide in a real situation, might want to use it, yes.
 
bobmrg said:
Have you tried to stop a prop? Takes a serious pitch up. Did it once in a Cessna 120 and it was educational.

Bob
Click to expand...

Not saying I've had or would. I'm just saying other people and publications have suggested so.

In the end, it's dependent on the situation. I'm going to be focused more on getting to a survivable landing scenario than quabbling over minutiae. If my engine takes a poop at 12K, I'll probably stop the prop and go from there. I guess. I don't know because I haven't been there. If it quits at 2K, we're wasting no time.
 
Good read! https://www.amazon.com/Engine-Out-Survival-Tactics-Emergencies/dp/1483594556

51i8wXEQ8GL._SY346_.jpg
 
What do your emergency procedures advise? In my planes a low oil pressure environment will have the prop go to flat. If you want to practice an engine out you should practice what you'll have to work with. That is the point of the exercise. Assuming a partial power engine out is practicing for a statistically unimportant non-emergency.

In a partial power failure, say when a rod breaks and punches a hole in the case, the engine will run for a short time. While running it's making so much metal that the oil galleries and governor are choked. The prop goes flat as a result. At that point your workload is too busy to eff with the prop control.
 
Sac Arrow said:
Not saying I've had or would. I'm just saying other people and publications have suggested so.

In the end, it's dependent on the situation. I'm going to be focused more on getting to a survivable landing scenario than quabbling over minutiae. If my engine takes a poop at 12K, I'll probably stop the prop and go from there. I guess. I don't know because I haven't been there. If it quits at 2K, we're wasting no time.
Click to expand...

Get some altitude. Clear area. Pull mixture to idle cutoff. Wait for engine to stop. Note that prop does not stop. Consider pitching up to near-stall attitude to stop prop. Reconsider. Push mixture in and continue on your way. (If engine does not respond, "go from there.")

Bob
 
You must log in or register to reply here.
Back
Top