Best glide with windmilling prop or stopped prop

John Renquist

John Renquist

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John Renquist
Best glide with windmilling prop or stopped prop?

I recently was flying an S-35 Bonanza with an IO 550-B engine. At 4, 500 feet the engine came apart and the prop came to a very sudden stop. I immediately made a 180 turn headed to a dirt runway I was aware of. The best glide in this bird is flaps and gear up, prop to full pitch, and 110 knots. The rate of descent is alarming, to say the least. I initially felt I had the runway made but it became clear the drag the stopped prop was creating was like having three, 3-foot long speed brakes deployed. I ended up landing 1.5 miles short from the target airport on a little dirt road next to a fence. My airspeed bled off to 80 MPH almost immediately after my initial nose over and lowering the nose to 110 mph would have put me into a lake next to the road I landed on. Long story short, no one was injured and I didn't bend any metal! A stopped prop creates much more drag than a windmilling one.
 
John Renquist said:
stopped prop creates much more drag than a windmilling one.
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That an argument as old as the airplane itself. There's tons of anecdotal evidence for both sides, and plenty of "math" for both sides as well.
 
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Great job landing a dirt road!!!

Thankfully the motor didn't break off the motor mounts or anything structurally dangerous.

I think both my instructors said if you can see it over the nose you won't make it when the fan stops. Not sure if you experienced that but given all that went on in that short time I don't think I'd recall.

With such a sudden engine stop do you think the blades even pitched?
 
Regardless of the answer to the question, you had the best possible outcome that one could hope for! Great job!
 
It is an interesting question and not the one usually answered. Usually the answers involve the windmilling prop either being fixed or in high pitch (rpm) setting. The little bit of 182 testing I am aware of it was found that even stopping a constant speed prop can be challenging (More Challenging that a fixed pitch prop) if it will not feather and there is nothing mechanically stopping it. But I am sure this varies from model to model.

Brian
 
kyleb said:
Best glide is 110 so you slowed to 80 and are worried about the prop causing reduced gliding performance?
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If you think your judgment at that moment of crisis is better than the judgment of those that calculated the best glide number for the aircraft, you’re wrong.

You may have stayed in the air longer (minimum sink), but you didn't go as far as you could have (best glide)
 
IMO, “If I do what I’m supposed to, the view out the windshield is too scary” is cause for a significant number of accidents, particularly low altitude stalls. Glad you survived this.
 
So glad that everything ended up as well as it could, nice job!

I'm a fairly new owner of a V35 and one of the first things I did was to fly some glide profiles, but these were with the engine running and the prop windmilling. I bet there will be a good bit of difference if the prop is stopped. From my testing it looks like there was a 200FPM difference just with the prop feathered or in cruise configuration.

Power Idle, Flap and Gear Up, Prop Feathered: 700FPM
Power Idle, Flap and Gear Up, Prop Cruise: 900FPM

I also happened to calculate a best glide table last week, as I'm in the process of making an electronic checklist for the plane. With just me in the plane, there's a 12 knot difference in best glide speed:
V35 Best Glide - By Weight
3400 lbs - 105 Knots
3300 lbs - 103 Knots
3200 lbs - 102 Knots
3100 lbs - 100 Knots
3000 lbs - 98 Knots
2900 lbs - 97 Knots
2800 lbs - 95 Knots
2700 lbs - 93 Knots
2600 lbs - 92 Knots
2500 lbs - 90 Knots

There's a paper on windmilling or stationary propeller drag here: http://www.peter2000.co.uk/aviation/misc/prop.pdf The conclusion in that paper, of course, is that it depends: "It is clear that it depends on the pitch and length of the propeller, and it is probably independent of the wind velocity. A crossover point was discovered where the drag forces for the windmilling and stationary states were the same. This crossover point is also dependent on the pitch, the length, and probably independent of the wind velocity."
 
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Easy! Just go up with you Garmin Aera 660 with "Glide Ratio" field.

SJJQZf.jpg


Test both!
 
kyleb said:
Best glide is 110 so you slowed to 80 and are worried about the prop causing reduced gliding performance?
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And are we talking Knots or MPH? OP uses both. But the lesson is that best glide (for weight) is best glide. Slower does not get you farther. And more people should read Stick & Rudder.
 
John Renquist said:
Best glide with windmilling prop or stopped prop?

I recently was flying an S-35 Bonanza with an IO 550-B engine. At 4, 500 feet the engine came apart and the prop came to a very sudden stop. I immediately made a 180 turn headed to a dirt runway I was aware of. The best glide in this bird is flaps and gear up, prop to full pitch, and 110 knots. The rate of descent is alarming, to say the least. I initially felt I had the runway made but it became clear the drag the stopped prop was creating was like having three, 3-foot long speed brakes deployed. I ended up landing 1.5 miles short from the target airport on a little dirt road next to a fence. My airspeed bled off to 80 MPH almost immediately after my initial nose over and lowering the nose to 110 mph would have put me into a lake next to the road I landed on. Long story short, no one was injured and I didn't bend any metal! A stopped prop creates much more drag than a windmilling one.
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A stopped and feathered prop wins in every test I've seen. Where do you think the energy to spin the engine comes from?
 
John Renquist said:
Best glide with windmilling prop or stopped prop?

I recently was flying an S-35 Bonanza with an IO 550-B engine. At 4, 500 feet the engine came apart and the prop came to a very sudden stop. I immediately made a 180 turn headed to a dirt runway I was aware of. The best glide in this bird is flaps and gear up, prop to full pitch, and 110 knots. The rate of descent is alarming, to say the least. I initially felt I had the runway made but it became clear the drag the stopped prop was creating was like having three, 3-foot long speed brakes deployed. I ended up landing 1.5 miles short from the target airport on a little dirt road next to a fence. My airspeed bled off to 80 MPH almost immediately after my initial nose over and lowering the nose to 110 mph would have put me into a lake next to the road I landed on. Long story short, no one was injured and I didn't bend any metal! A stopped prop creates much more drag than a windmilling one.
Click to expand...

Figure 12-3 in the Airplane Flying Handbook indicates that a windmilling prop offers maximum drag.

Bob Gardner
 
There was a thread about this a while back. While a stopped prop will give you a longer glide than a windmilling prop the question is, does stopping it negate the advantage. How slow do you have to get to stop the windmilling? In some airplanes you’ll have to slow down to almost stall speed to stop the prop. There goes a lot glide distance right there. If I recall right, in a C172, you would need be starting out at about 7000 feet to get back the distance gain you lost by slowing that much to stop the prop to begin with.
 
luvflyin said:
There was a thread about this a while back. While a stopped prop will give you a longer glide than a windmilling prop the question is, does stopping it negate the advantage. How slow do you have to get to stop the windmilling? In some airplanes you’ll have to slow down to almost stall speed to stop the prop. There goes a lot glide distance right there. If I recall right, in a C172, you would need be starting out at about 7000 feet to get back the distance gain you lost by slowing that much to stop the prop to begin with.
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This is why I don't worry about it personally. There is no way to know if you are high enough AGL to see any benefit from stopping the prop because I have never seen that data in any manuals. Having dealt with two engine failures and one partial loss of power I would be willing to bet even if the data was published very few people would actually use it in an emergency.
 
Tarheelpilot said:
This is why I don't worry about it personally. There is no way to know if you are high enough AGL to see any benefit from stopping the prop because I have never seen that data in any manuals. Having dealt with two engine failures and one partial loss of power I would be willing to bet even if the data was published very few people would actually use it in an emergency.
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Need an 'engine seize' button.
 
I am a Bonanza BPPP instructor. Every type checkout I demo the glide with a wind milling prop at 105 Kts (best glide for the S35). With the prop windmilling and the control set to anywhere other than near the rear stop, one sees about 1400 FPM and an RPM near 1800 RPM, pitch down roughly -3 degrees to maintain glide, 7 to 1 ratio. With the prop set to the rear stop, RPM is reduced to around 1200 RPM and decent rate near 900 FPM, pitch close to 0 degrees, about 10 to 1 glide. It is a dramatic demo. Turning the engine over without power absorbs a tremendous amount of energy which translates to drag. If you stop the prop or it stops by itself, I would expect greatly improved glide performance, above 10 to 1. A friend had a catastrophic engine failure and was able to glide from the point of the engine failure to a runway at an estimated glide ration of 13 to 1 in his V35B, which is essentially the same airframe. Slowing to 80 Kts will end up way short. Don't deploy gear until the runway is about to pass out of view below the nose. With the gear down, keep the speed at 80 Knots, nose down so you will have reserve energy for the flare. If you lower the flaps, keep the 80 Knots to the flare. The airplane will use up about 500 feet to 700 feet in the flare before wheels touchdown, but ground roll will be well under 1000 feet, more like 800 feet. If you get too slow on short final, you will not have sufficient energy to arrest the sink rate with gear and flaps down.
 
Kenny Phillips said:
Need an 'engine seize' button.
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They have that! I've flown a motorglider (SF-25) which had a propeller brake, for the sole purpose of bringing the prop to a standstill when you wanted to fly without the engine running. Glide performance was noticeably better with the prop stopped than with the prop windmilling.

In most single engine airplanes, the question "stopped or windmilling" is more academic in nature, isn't it? I mean, it's not like we have a choice. Depending on the reason for the engine outage, something is either mechanically blocked and thus preventing the prop from turning, or not, in which case the prop can and will continue to turn. Slowing down to stop a windmilling prop is possible in theory, but will cause a significant altitude loss just for that maneuver, so I doubt this makes much sense in real life.

What we DO have to play with in case of a windmilling prop is the prop lever (assuming constant speed prop). Pull it back and see the glide performance improve.

- Martin
 
Lindberg said:
And are we talking Knots or MPH? OP uses both.
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Which is why I didn't reference the units. I think the OP is/was a troll. On top of the first post/controversial subject, the mix of units was another curious thing. The name raised a flag too.
 
luvflyin said:
Ok. I'll bite. Is there a story here?
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When the Staggerwing came out, as basically the first GA retractable airplane, the public was nervous about it, so among other things, the factory outfitted a couple of them with skids and a brake on the prop.

take off, shut down, stop the prop horizontal, land gear up. Safe, see!

jack the airplane up, crank the gear down, and on to the next demo.
 
John Renquist said:
Best glide with windmilling prop or stopped prop?

I recently was flying an S-35 Bonanza with an IO 550-B engine. At 4, 500 feet the engine came apart and the prop came to a very sudden stop. I immediately made a 180 turn headed to a dirt runway I was aware of. The best glide in this bird is flaps and gear up, prop to full pitch, and 110 knots. The rate of descent is alarming, to say the least. I initially felt I had the runway made but it became clear the drag the stopped prop was creating was like having three, 3-foot long speed brakes deployed. I ended up landing 1.5 miles short from the target airport on a little dirt road next to a fence. My airspeed bled off to 80 MPH almost immediately after my initial nose over and lowering the nose to 110 mph would have put me into a lake next to the road I landed on. Long story short, no one was injured and I didn't bend any metal! A stopped prop creates much more drag than a windmilling one.
Click to expand...
 
Great job, I hope I never get a chance to test this out...:rolleyes:
 
Great discussion and appreciate the comments. My unqualified understanding is that flying fixed-wing aircraft the ultimate "best glide" rate would be to have no prop at all. Next would be a full feathering ability followed by setting prop control to full high pitch (constant speed propeller) then windmilling under power followed by rotating propeller producing no power.
I guess the jury is out if a stopped prop creates more drag versus one that is windmilling and not under power.
 
John Renquist said:
Great discussion and appreciate the comments. My unqualified understanding is that flying fixed-wing aircraft the ultimate "best glide" rate would be to have no prop at all. Next would be a full feathering ability followed by setting prop control to full high pitch (constant speed propeller) then windmilling under power followed by rotating propeller producing no power.
I guess the jury is out if a stopped prop creates more drag versus one that is windmilling and not under power.
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I don't think the jury is out. This post makes it pretty clear to me

kyleb said:
Alternately, which comes down faster? A helicopter auto rotating or one with the blades stopped?
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John Renquist said:
Great discussion and appreciate the comments. My unqualified understanding is that flying fixed-wing aircraft the ultimate "best glide" rate would be to have no prop at all. Next would be a full feathering ability followed by setting prop control to full high pitch (constant speed propeller) then windmilling under power followed by rotating propeller producing no power.
I guess the jury is out if a stopped prop creates more drag versus one that is windmilling and not under power.
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Whether or not the jury is still out doesn’t change the fact that in order to get the most distance you have to fly the appropriate speed, which is not based on the propeller.
 
MauleSkinner said:
Whether or not the jury is still out doesn’t change the fact that in order to get the most distance you have to fly the appropriate speed, which is not based on the propeller.
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The jury's not out on that, but hmmm... the airspeed for best glide is where the aircraft's L/D is maximized. If a windmilling prop increases drag (D), then L/D changes, too. The airspeed for best L/D will depend on how the drag of the windmilling prop changes with airspeed.
 
Dana said:
The jury's not out on that, but hmmm... the airspeed for best glide is where the aircraft's L/D is maximized. If a windmilling prop increases drag (D), then L/D changes, too. The airspeed for best L/D will depend on how the drag of the windmilling prop changes with airspeed.
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True. But how much? I think you’d be much better off flying the published speed than experimenting after an actual engine failure, even without adjusting for weight.

If somebody wants to go out and do flight testing to determine the actual best L/D speed, go for it. But making up procedures that contradict the manufacturer’s during an actual emergency, particularly when the need for it is based on not following the manufacturer’s procedure to start with, seems like a really bad plan to me.
 
Think the best answer for the aircraft and pilot in the op was given by the BPPP instructor ( @John Collins )who has demonstrated the closest parallel possible without a prop brake. In type.

fly to the scene of the incident, or be recovered at the scene of the tragedy
 
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MauleSkinner said:
True. But how much? I think you’d be much better off flying the published speed than experimenting after an actual engine failure, even without adjusting for weight.
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Agreed, just pointing out that it would be different.

I suspect (perhaps Ron W will chime in here) that most engine failures other than fuel starvation happen at relatively low altitude, since failures often happen when large power changes are made, and that's where messing with trying to stop the prop would cost more altitude than you'd save in glide ratio anyway.
 
Dana said:
Agreed, just pointing out that it would be different.

I suspect (perhaps Ron W will chime in here) that most engine failures other than fuel starvation happen at relatively low altitude, since failures often happen when large power changes are made, and that's where messing with trying to stop the prop would cost more altitude than you'd save in glide ratio anyway.
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I’m not even talking about “trying “ to stop the prop. The OP’s prop stopped on its own, and through gross misunderstanding of what was happening apparently determined that a slower speed was appropriate.
 
Dana said:
failures often happen when large power changes are made
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I have heard this repeated, but do not know why it should be so.
 
GeorgeC said:
I have heard this repeated, but do not know why it should be so.
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When nothings changing except the clock ticking there's less chance of moving into a failure mode.

Moving a control could dislodge a piece of crud. A linkage that's barely hanging together could come loose. A power increase could stress that almost ready to break component that last tiny bit. A mixture setting that's ok at one power setting might starve or flood the engine at another. A pitch change could unport a tank fitting. A pilot might do something wrong when previously he wasn't doing anything.
 
GeorgeC said:
I have heard this repeated, but do not know why it should be so.
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I was going over some Bonanza training yesterday and in the video they mentioned that topic and just said something like there was no statistical basis for it that they could find. I personally do agree with the idea of not messing with too much while in a critical phase of flight though, regardless of statistics, so the idea behind it makes sense to me.

Edit, went back and found the part of the training video, and here's what it said: "Notice we're suggesting delaying power changes until 1000 above ground level, not because of any increase in likelihood the engine will quit when you change power, because that can't be statistically proven as a threat."
 
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After reading the many comments on this subject, I reached pout to several experts including the an of a local College Dean who heads up the Aeronautics Department and Tom Turner, of the American Bonanza Society. They all had the same answer: A stopped prop creates less drag than a windmilling prop. My assumption all these years was incorrect. That's what I love about flying, you learn something new every day!
 
Pulling the prop to high pitch (low rpm) will help even if still windmilling. Put your plane at idle sometime, set up best guide and move the prop from one end to the other. You'll feel the difference.

The question on non-featherable props is whether the maneuvers it will take to stop the prop are going to waste more glide distance than just letting it windmill. Of course, if it's possible, pick a landing spot well within the glide ratio of the current configuration. In my engine out, I was able to use the alitude to give me some more time to set up on the field of intended landing rather than having to put it down where the glide ran out.
 
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