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FP Prop that has stopped in-flight

Bad Sheila

Bad Sheila

Active Member
:D I you are at a high altitude and the engine has quit and the prop has stopped. Is there a speed you can acheive that would start the prop windmilling for an engine re-start if the starter motor won't do the job? Just curious? (I have an RV6)
 
yes and it all depends on everything. Your prop, your engine, your compression. Go try it and report back your results. Other results are in the archives under the search function.
 
Bad Sheila said:
:D I you are at a high altitude and the engine has quit and the prop has stopped. Is there a speed you can acheive that would start the prop windmilling for an engine re-start if the starter motor won't do the job? Just curious? (I have an RV6)
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If the engine quits and the FP prop stops, look for a place to land, the engine has seized and no amount of trickery will get it fixed in flight.

If the engine quits and the prop is deliberately stopped by slowing considerably, it can be restarted at some high speed. A couple guys here have done it may report what they saw.
 
Not an RV, but in my C-172 I've stopped it inflight, and I need to get up to about 110 kts to get it turning again without the starter.
 
It's Not Easy To Get It Stopped

IIRC, in my 160HP RV9A, If I pull the mixture in flight, I need to get below 80 kts to stop the prop. To restart, I push the mixture in and just let the nose drop slightly- never had to use the starter.
Terry, CFI
RV9A N323TP
 
I've shut off the engine in flight to do glide testing. At 70 or 80 knots the prop stops. With my wood prop (low inertia which means it stops easily on the compression stroke), I needed 140 knots to get it to windmill sufficiently for a restart. That's a pretty steep power-off dive. ;-)

A FP metal prop would probably continue to windmill at a lower airspeed, and on restart would probably start windmilling at a lower airspeed too, just because of inertia.
 
Kyle Boatright said:
A FP metal prop would probably continue to windmill at a lower airspeed, and on restart would probably start windmilling at a lower airspeed too, just because of inertia.
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A stopped prop has *no* inertia. Wood or metal, the same diameter and pitch will start moving again at the same speed.
 
Snowflake said:
A stopped prop has *no* inertia. Wood or metal, the same diameter and pitch will start moving again at the same speed.
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A stopped prop still has inertia. Inertia just means it resists change in velocity. A wood prop resists change less than a metal prop. I think what the previous post was pointing out is that the prop with the higher inertia will tend to use it's momentum to overcome the compression of the engine. As you dive and start the prop moving it will slowly overcome the compression of the first cylinder. When it goes "over center" and swings into the next compression stroke it will have more inertia to overcome the next compression stroke if it's a heavier prop. I suspect this would be a small difference but real nontheless.

-Andy
 
I copied this post from another thread regarding my testing. Upon further reflection I don't know if it was cooler oil or just a cooler engine that caused different windmilling start speeds. My propeller is a Sensenich 72FM8-83

"I did rudimentary glide tests in my fixed pitch RV-6 with the engine off and a windmilling propeller and with the engine off and the propeller stopped. It did glide better with the propeller stopped but the difference was not great. I attribute that to the very course pitch of an RV fixed pitch propeller.

As you point out, you do lose glide while slowing down enough to stop the propeller so there is a crossover point that I didn't try to figure out. As for me I wouldn't stop the propeller unless the engine failure happened quite high, like maybe 4,000 AGL or so. With a warm engine I had to get down to about 60 knots to stop the propeller. It was more like 70 knots after the oil was cooler.

Another factor, depending on the nature of the failure, is that it would probably be much simpler to get the engine running again if it is already windmilling."
 
simpkinsona said:
A stopped prop still has inertia. Inertia just means it resists change in velocity. A wood prop resists change less than a metal prop. I think what the previous post was pointing out is that the prop with the higher inertia will tend to use it's momentum to overcome the compression of the engine. As you dive and start the prop moving it will slowly overcome the compression of the first cylinder. When it goes "over center" and swings into the next compression stroke it will have more inertia to overcome the next compression stroke if it's a heavier prop. I suspect this would be a small difference but real nontheless.

-Andy
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What you posted is spot-on, except for the last sentence. The difference between an air restart of wood vs metal props is pretty substantial. It is similar to starting an engine with a wood prop vs a metal prop when you have a weak starter or battery - the metal prop's inertia makes a big difference.
 
Stopped prop

We have tried this deliberately (over the airport) and been successful at restart and also inadvertently when the engine quit and stopped rotating in a flat spin. In a Pitts S-1S with FP metal prop had to dive to about 180 mph ias to start rotation. IIRC the Cessna 150 only took about 135. Our Pitts S-2A with CS Hartzell took almost 190 ias (200 hp Lyc). As they say, YMMV!
 
bkthomps said:
i think instead of inertia you guys mean momentum, no?
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Well, we're throwing the term inertia around kind of loosely... The concept of getting something moving again from a standstill is what I was getting at. Until the flywheel effect of the heavier prop takes over (which I doubt would kick in until it is turning), the forces working to get it started are the same... Just the air forces on the blades, balanced against the compression of the cylinder that it's stopped against. To get it to *start* turning is independent of the construction material.

The problem is that there are so many factors affecting each in-air restart that it is probably not realistic to conclude that wood props are easier to get started... Unless someone has two same diameter, same pitch, same shape propellors, one wood and one metal, and wants to do some tests. :)
 
Prop Windmill

My -6 had a 0-320 w/Senenich metal prop. It would windmill down to 75 easy.
 
Kyle Boatright said:
The difference between an air restart of wood vs metal props is pretty substantial.
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This has been my experience too. The metal Sensenich prop did an air-restart much more effortlessly, and at much lower airspeed than either of the Aymar-Demuth or Sterba wood props I've personally observed. O-320's on all three aircraft.
 
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Prop Stopped!

I suppose the consensus is that you keep the prop windmilling until all efforts of a re-start have failed. (Assuming you have altitude to play with) You then make the decision whether to stop the prop or not with the realization that you will lose some glide distance by slowing down enough to stop the prop? Comments? :confused:
 
Prop Stopped Conclusion?

I suppose the consensus is that you keep the prop windmilling until all efforts of a re-start have failed. (Assuming you have altitude to play with) You then make the decision whether to stop the prop or not with the realization that you will lose some glide distance by slowing down enough to stop the prop? Comments? :D
 
How About Density Altitude

Another consideration that needs to be factored in to this discussion is density altitude.
 
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Neal@F14 said:
This has been my experience too. The metal Sensenich prop did an air-restart much more effortlessly, and at much lower airspeed than either of the Aymar-Demuth or Sterba wood props I've personally observed. O-320's on all three aircraft.
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What diameter and pitch were the wood and metal props? All identical?

Bad Sheila said:
I suppose the consensus is that you keep the prop windmilling until all efforts of a re-start have failed. (Assuming you have altitude to play with) You then make the decision whether to stop the prop or not with the realization that you will lose some glide distance by slowing down enough to stop the prop? Comments?
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At university we ran some simulation calculations to see what made the most sense in the case of an engine failure. I looked but I can't find my course notes right now... There is a loss of glide distance due to the exercise of stopping the prop, but above a certain altitude you can gain that loss back with the longer glide distance with a stopped prop. For a 100HP Cessna 150, I seem to recall that break point was in the low 1000's of feet, like 2000-3000'.
 
Starter inop?

I probably missed something, but what's wrong with just using the starter?

But, just like Brian. I've been drinking...
 
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I was wondering the exact same thing. Your having a really bad day if your engine quits and the starter fails at the same time.

George
 
If your engine quits you're already having a bad day. :)

The question is what do you do when your engine quits and it can't be re-started... No fuel, ingested valve, electrical gremlin, etc. obviously if you can re-start, do that first.
 
The Sound of a Windmilling Prop

Just curious... probably a silly question.

I believe a stopped prop is is mostly quiet. I assume that a windmilling prop is still making noise, since it's spinning the engine and pumping air in and out, and beating the air as it turns.

So...

The difference in the sound of a windmilling prop is the lack of the sound of the burning fuel/air mixture. Is this combustion that noisy? Is the sound of a windmilling prop that different from the sound of a engine at idle with a spinning prop?

Or to put it another way... If my engine stops will it be obvious to me by the sound, without looking at any instruments?
 
TThurston said:
Just curious... probably a silly question.

I believe a stopped prop is is mostly quiet. I assume that a windmilling prop is still making noise, since it's spinning the engine and pumping air in and out, and beating the air as it turns.

So...

The difference in the sound of a windmilling prop is the lack of the sound of the burning fuel/air mixture. Is this combustion that noisy? Is the sound of a windmilling prop that different from the sound of a engine at idle with a spinning prop?

Or to put it another way... If my engine stops will it be obvious to me by the sound, without looking at any instruments?
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You will notice the sound is gone. And the aircraft will slow down right now if you maintain level flight. It will be VERY obvious........:eek:
 
Neal@F14 said:
Aymar Demuth wood prop on an RV-4 (68x74)
Sterba wood prop on an RV-6 (?? x ??)
Sensenich (74 x 58) on a Cherokee.
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So a prop with a coarser pitch on a faster airplane has an easier time getting started than a prop with a finer pitch on a slower airplane. I agree, that's exactly what should happen. Doesn't matter if it's wood or metal. Put a 68x74 metal prop on the RV-4, and it will start turning at the same speed as the wood one.
 
TThurston said:
...
So...

The difference in the sound of a windmilling prop is the lack of the sound of the burning fuel/air mixture. Is this combustion that noisy? Is the sound of a windmilling prop that different from the sound of a engine at idle with a spinning prop?

Or to put it another way... If my engine stops will it be obvious to me by the sound, without looking at any instruments?
Click to expand...

If the engine quits at a high power setting it is very obvious. At idle the difference between engine running and not running is not noticeable at all.
 
Snowflake said:
So a prop with a coarser pitch on a faster airplane has an easier time getting started than a prop with a finer pitch on a slower airplane. I agree, that's exactly what should happen. Doesn't matter if it's wood or metal. Put a 68x74 metal prop on the RV-4, and it will start turning at the same speed as the wood one.
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Actually the metal prop on the Cherokee with the finest pitch was by far the easiest to air start (began to turn and restarted at about 125 MPH). The Aymar-Demuth wood prop on the RV-4 was the hardest (took almost 160MPH before it started to turn again). The Sterba on the RV-6 was somewhere in between. The engines on both the Cherokee and the RV-4 were fairly new and tight with good compression. The O-320 on the RV-6 was approaching TBO and was "loose" enough the owner could hand-prop it without much trouble (until he finally bought a new starter :D )
 
Back to the Original!

Back to my original question? I have an RV6 and
1) The engine has stopped at a decent altitude
2) The prop has stopped because I got too slow
3) My electrics have failed.

I want to attempt an air re-start so what speed could I expect the prop to start windmilling? 120 kts? 130 kts?
Go for it. LOL :)
 
Bad Sheila said:
Back to my original question? I have an RV6 and
1) The engine has stopped at a decent altitude
2) The prop has stopped because I got too slow
3) My electrics have failed.

I want to attempt an air re-start so what speed could I expect the prop to start windmilling? 120 kts? 130 kts?
Go for it. LOL :)
Click to expand...

Go try it under suitably safe conditions.
 
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