Engine Failure: Windmilling Prop or Stopped Prop?

HighFlyingA380

HighFlyingA380

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Jim F.
I've been doing some research on something I hard from my old chief CFI a couple years back, but I'm not finding much on it. He is the only person I've heard this from, and any CFI, DPE, ect. I've talked about this to since have not heard of it. That being that when you have an engine failure more than several thousand ft. with a non-full-feathering prop, that you should pitch up and decrease airspeed, sometimes to an intentional stall, to stop the rotation of the prop/engine. (Of course, only after you have attempted to restart.) The reason being that you will see a greater gain in glide distance by reducing the drag created by forcing thee air to turn over the engine. He claimed that while you would most likely be off of Vl/d for a short amount of time, thus not gliding in the most efficient manner, that is outweighed by the decrease in drag. (As I said, do this only with several thousand feet and plenty of time.) He claimed that in the case of something such as a 172, doing this procedure at, say 10,000ft, you would gain several more miles of glide distance.

Sure, the theory sounds plausible, but unless there is some hard data (which I've been unable to find), it's just that, a theory. So, what are your thoughts on this? Have you heard of this or done it before? Any links to data/research on the topic would be much appreciated. Thanks.
 
Richard L. Collins wrote up in Flying many, many years ago a test he did in a 182 in which he found that 8000 AGL was the break point where the energy you lose in stopping the prop is exceeded by the L/D ratio you gain with it stopped. I believe others have found similar altitudes in other light singles in later experiments, but the break point will vary some with aircraft type. Only way to know for sure is to try it yourself, but an intentional stopped-prop condition in a single is a condition I avoid whenever there is space between the wheels and the ground, and I don't think the value of a precise answer to this question is worth the risk of an inability to restart.
 
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Ron Levy said:
Richard L. Collins wrote up in Flying many, many years ago a test he did in a 182 in which he found that 8000 AGL was the break point where the energy you lose in stopping the prop is exceeded by the L/D ratio you gain with it stopped. I believe others have found similar altitudes in other light singles in later experiments, but the break point will vary some with aircraft type. Only way to know for sure is to try it yourself, but an intentional stopped-prop condition in a single is a condition I avoid whenever there is space between the wheels and the ground, and I don't think the value of a precise answer to this question is worth the risk of an inability to restart.
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I think this is a good exercise over an airport. IMHO a lot less people would die in engine out scenarios if they had the skills to become glider pilots. It is the fear of the engine quitting that is killing people. Yes, I have done it many times.

Years ago the FAA required spin training as part of the PPL, I believe. That seemed to kill more instructors and pilots so they stopped that requirement. I don't see the "Engine out" training as the same situation though.

JMHO. :yes:
 
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HighFlyingA380 said:
I've been doing some research on something I hard from my old chief CFI a couple years back, but I'm not finding much on it. He is the only person I've heard this from, and any CFI, DPE, ect. I've talked about this to since have not heard of it. That being that when you have an engine failure more than several thousand ft. with a non-full-feathering prop, that you should pitch up and decrease airspeed, sometimes to an intentional stall, to stop the rotation of the prop/engine. (Of course, only after you have attempted to restart.) The reason being that you will see a greater gain in glide distance by reducing the drag created by forcing thee air to turn over the engine. He claimed that while you would most likely be off of Vl/d for a short amount of time, thus not gliding in the most efficient manner, that is outweighed by the decrease in drag. (As I said, do this only with several thousand feet and plenty of time.) He claimed that in the case of something such as a 172, doing this procedure at, say 10,000ft, you would gain several more miles of glide distance.

Sure, the theory sounds plausible, but unless there is some hard data (which I've been unable to find), it's just that, a theory. So, what are your thoughts on this? Have you heard of this or done it before? Any links to data/research on the topic would be much appreciated. Thanks.
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If you look at the FAA pub "Aircraft Flying Handbook", page 12-3, it has a chart that suggests a windmilling propeller at a low pitch has significantly more drag than a stopped propeller. So there probably isn't much difference in drag on a fixed pitch prop, but I guess it could be significant on a constant speed prop.
 
King Schools teaches to increase gliding distance in a constant speed prop piston engine airplane by:

wide open throttle to minimize drag from pistons sucking air through the throttle body, then low RPM (max pitch) on the prop control.

All assuming the prop still turns...
 
bnt83 said:
King Schools teaches to increase gliding distance in a constant speed prop piston engine airplane by:

wide open throttle to minimize drag from pistons sucking air through the throttle body, then low RPM (max pitch) on the prop control.

All assuming the prop still turns...
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Or the mode of failure. If you have no oil pressure, you have no means of maintaining any more than minimum pitch.
 
An instructor and I did a bunch of test runs on this in his 172. The best result is if you immediately pitch up turning your excess airspeed into altitude in a ballistic arc ending in a pitch for best glide. Anything below 3500' it was not worthwhile. The reality to stopping the prop immediately though is that it would only be viable if you knew you couldn't restart, or were shutting down preemptively due to a known failure that was streaming oil, especially if it was loading your windshield, or was shaking the plane so hard it may cause the engine to depart the aircraft, or as most common, you ran it out of fuel. Most of the time though, that isn't going to be the situation on an engine failure and you're going to keep the engine windmilling for a while in your restart attempts. If you are at 10,000' AGL and haven't managed a restart by 7000', yep, go ahead and pull up to stop the prop if you think you're going to need the extra glide range. If you have a perfectly good landing spot made well within glide range, don't as you are not going to be familiar with the glide characteristics and may very well end up hot and high for the overshoot.

It's like anything else, it's a tool to have in your bag of tricks. No emergency is going to follow a preconceived script, so it's best not to have a preconceived course of action beyond the basic and obvious and just pull things out of your bag as they become appropriate.
 
Sac Arrow said:
Or the mode of failure. If you have no oil pressure, you have no means of maintaining any more than minimum pitch.
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If there was no oil pressure, the engine most likely isnt turning anymore as the failure probably caused complete crank or rod bearing failure which most likely would seized the engine.
 
bnt83 said:
If there was no oil pressure, the engine most likely isnt turning anymore as the failure probably caused complete crank or rod bearing failure which most likely would seized the engine.
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Again, a possibility, another possibility is a failed oil line that pumped all the oil overboard. The engine will spin just fine with no oil in it for a long time, especially if you shut the power down. It's all situational and each situation will have its own best choices.
 
Sac Arrow said:
Very possibly, yes.
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Unless the crew discovered the loss of oil pressure and shut the engine down prior to self disruction. Seems like most often the engine was run till it broke...
 
Sac Arrow said:
Or the mode of failure. If you have no oil pressure, you have no means of maintaining any more than minimum pitch.
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Exactly....that is why I don't like training that way with a single engine constant speed prop. IF you still have oil pressure, you can increase your glide distance, but if you train that way and end up with a failure and no oil pressure....you are going to come up short. For simulated engine failures/power off 180s, I prefer to train for worst case.
 
bnt83 said:
Unless the crew discovered the loss of oil pressure and shut the engine down prior to self disruction. Seems like most often the engine was run till it broke...
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That is the advantage to having 2 engines which I have opted for 3 times, preemptive shut downs prior to secondary damages. I effected repairs for the cost of oil lines rather than replacing engines.
 
Henning said:
That is the advantage to having 2 engines which I have opted for 3 times, preemptive shut downs prior to secondary damages. I effected repairs for the cost of oil lines rather than replacing engines.
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The older GA fleet (especially singles) don't have anunciators so the pilot discovering no oil pressure and shutting down before its too late seems unlikely. They don't run long without oil at 65% - 100% power.

But then again the mass of oil smell and possibly seeing it on the cowls or windshield would be a great clue something was amiss. :hairraise:
 
bnt83 said:
The older GA fleet (especially singles) don't have anunciators so the pilot discovering no oil pressure and shutting down before its too late seems unlikely. They don't run long without oil at 65% - 100% power.

But then again the mass of oil smell and possibly seeing it on the cowls or windshield would be a great clue something was amiss. :hairraise:
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Yep, it makes a big old mess out there on the wing long before it runs out of oil, and when a line ruptures, it's immediately visible on the pressure gauge, at least it was on mine which is what clued me to look at the nacelle, go "oh crap" and secure the effected engine.
 
I know this isn't conclusive, but I've experimented with my DA20 -- stopping the prop vs. mixture cutoff/prop windmilling -- and was surprised to find that there's no observable difference.
 
N5922S said:
I know this isn't conclusive, but I've experimented with my DA20 -- stopping the prop vs. mixture cutoff/prop windmilling -- and was surprised to find that there's no observable difference.
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Considering the wing and prop on the DA-20, I'm not surprised.
 
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