Magni M24 Orion May 30, 2023 - Dauphin Island Alabama

[loftus]

I actually had a Boeing engineer arguing with me that a stopped prop makes more drag than a windmilling prop.
I said to him:
This is simple, it takes energy to spin a prop, that energy comes from somewhere, in this case it comes from the moving aircraft, so it has to create drag because the airplane is giving up energy by trading airspeed for prop speed since the prop is now doing work.
He still didn't believe me so I put a 10" airplane prop on a screw driver so it could freewheel against the handle and had him hold it out the window while we drove.
The first test was with the prop stopped, it was easy to hold out the window at 60mph.
He could barely hold it against the wind when he let it spin up, it generated about 10lbs of force and he had to use both hands.
On electric UAVs and RC planes, the speed controller is usually programmed to stop the prop when you throttle off, the difference is huge.
An efficient airplane with a 20+ to 1 glide ratio with power off will lose more than half of the glide ratio if the prop is allowed to windmill.
A feathered prop that is slowly spinning will not produce much drag because it isn't doing much work, it doesn't take much energy to turn a feathered prop a few RPMs. I would guess this could be less drag than a stopped fixed pitch prop.

I understand all this. My question is specifically in a Rotax which does not windmill when the engine stops like a Lycoming. In the case of the engine at idle, the prop is NOT windmilling only due to the airstream it is under power so in fact providing some power and some forward thrust. When one then cuts the Rotax engine, there is no contribution to forward thrust only some drag due to the stationary props. I understand that there is more drag with a windmilling prop if the airstream is powering the windmilling, but if the engine is powering the prop turning, it is the engine providing at least some of the energy, particularly if one increases the power a little as Vance mentions. I would guess that the most efficient glide ratio in a Rotax would also be feathered props, but in the absence of adjustable props, stopped props (not windmilling as in a Lycoming) may still create more drag than props under some power from the engine. this is probably related to the airspeed of the aircraft as well and the idling speed, and which force is contributing more to the prop turning, engine or airstream.
I think the answer to this question may be different depending on different variables for any given aircraft. If you were to repeat your above experiment with the Boeing engineer but add power say with a rubber band to the prop, the effect would be different. I have no doubt in Vance's gyro that what he is saying is correct, I suspect in a Rotax powered aircraft the glide distance increase would not be as pronounced as he notices in his aircraft. It would be an interesting test in a Rotax powered gyro to see if the glide distance is influenced the same in a Rotax vs a Lycoming engine.

 

[Vance]

I understand all this. My question is specifically in a Rotax which does not windmill when the engine stops like a Lycoming. In the case of the engine at idle, the prop is NOT windmilling only due to the airstram it is under power so in fact providing some power and some forward thrust. When one then cuts the Rotax engine, there is no contribution to forward thrust only some drag due to the stationary props. I understand that there is more drag with a windmilling prop if the airstream is powering the windmilling, but if the engine is powering the prop turning, it is the engine providing at least some of the energy, particularly if one increases the power a little as Vance mentions. I would guess that the most efficient glide ratio in a Rotax would also be feathered props, but in the absence of adjustable props, stopped props (not windmilling as in a Lycoming) may still create more drag than props under some power from the engine. this is probably related to the airspeed of the aircraft as well and the idling speed, and which force is contributing more to the prop turning, engine or airstream.
I think the answer to this question may be different depending on different variables for any given aircraft. If you were to repeat your above experiment with the Boeing engineer but add power say with a rubber band to the prop, the effect would be different. I have no doubt in Vance's gyro that what he is saying is correct, I suspect in a Rotax powered aircraft the glide distance increase would not be as pronounced as he notices in his aircraft. It would be an interesting test in a Rotax powered gyro to see if the glide distance is influenced the same in a Rotax vs a Lycoming engine.

The Lycoming IO-320 in The Predator does not windmill when the engine stops producing power at seventy knots indicated air speed. She has a three blade fixed pitch propeller and I have yet to have the engine go quiet faster than seventy knots.

In my opinion based on research a full feathered propeller would likely produce less drag than a propeller at idle or a stopped propeller.

Most in flight adjustable pitch propellers I have used in gyroplanes will not full feather.

My experience with Rotax powered gyroplanes is I glide significantly farther with the propeller stopped than with the engine at idle.

My Garmin 496 in The Predator has a glide ratio read out in relation to the ground and so do many of the gyroplanes I have flown and I have seen anywhere from two to one to six to one in all of the gyroplanes I have flown.

A little tail wind will significantly extend the glide in relation to the ground.

I use three to one to figure out where I can land because I can shorten the glide but I have not found a way to extend the glide beyond pitching for best glide speed.

I have found when the engine stops making thrust; developing a plan and sticking to it as soon as practical is an important part of being able to reuse the aircraft.

More than once my impression of my landing zone has changed as I get nearer to it and I had to modify my plan.

In my opinion an engine out in a gyroplane is not a nonevent as many people claim and luck is involved with being able to reuse the aircraft.

 

[loftus]

The Lycoming IO-320 in The Predator does not windmill when the engine stops producing power at seventy knots indicated air speed. She has a three blade fixed pitch propeller and I have yet to have the engine go quiet faster than seventy knots.

In my opinion based on research a full feathered propeller would likely produce less drag than a propeller at idle or a stopped propeller.

Most in flight adjustable pitch propellers I have used in gyroplanes will not full feather.

My experience with Rotax powered gyroplanes is I glide significantly farther with the propeller stopped than with the engine at idle.

My Garmin 496 in The Predator has a glide ratio read out in relation to the ground and so do many of the gyroplanes I have flown and I have seen anywhere from two to one to six to one in all of the gyroplanes I have flown.

A little tail wind will significantly extend the glide in relation to the ground.

I use three to one to figure out where I can land because I can shorten the glide but I have not found a way to extend the glide beyond pitching for best glide speed.

I have found when the engine stops making thrust; developing a plan and sticking to it as soon as practical is an important part of being able to reuse the aircraft.

More than once my impression of my landing zone has changed as I get nearer to it and I had to modify my plan.

In my opinion an engine out in a gyroplane is not a nonevent as many people claim and luck is involved with being able to reuse the aircraft.

So never having actually turned off the engine in engine out emergency practice, and never having experienced a real engine out; a real engine out may in some respects be easier to manage than a simulated one due to having further gliding latitude?

 

[Vance]

So never having actually turned off the engine in engine out emergency practice, and never having experienced a real engine out; a real engine out may in some respects be easier to manage than a simulated one due to having further gliding latitude?

In my opinion based on my experience; yes.

It is something I like to show learners on Santa Maria's hundred fifty foot wide, eight thousand foot long runway.

I feel being able to land in a chosen landing zone has value in an emergency landing where the landing zone may not be so generous.

We typically practice engine out landings with a 180 degree turn.

For the practical test we practice engine at idle accurate landings to practical test standards.

 

[Aerofoam]

I understand all this. My question is specifically in a Rotax which does not windmill when the engine stops like a Lycoming. In the case of the engine at idle, the prop is NOT windmilling only due to the airstream it is under power so in fact providing some power and some forward thrust. When one then cuts the Rotax engine, there is no contribution to forward thrust only some drag due to the stationary props. I understand that there is more drag with a windmilling prop if the airstream is powering the windmilling, but if the engine is powering the prop turning, it is the engine providing at least some of the energy, particularly if one increases the power a little as Vance mentions. I would guess that the most efficient glide ratio in a Rotax would also be feathered props, but in the absence of adjustable props, stopped props (not windmilling as in a Lycoming) may still create more drag than props under some power from the engine. this is probably related to the airspeed of the aircraft as well and the idling speed, and which force is contributing more to the prop turning, engine or airstream.
I think the answer to this question may be different depending on different variables for any given aircraft. If you were to repeat your above experiment with the Boeing engineer but add power say with a rubber band to the prop, the effect would be different. I have no doubt in Vance's gyro that what he is saying is correct, I suspect in a Rotax powered aircraft the glide distance increase would not be as pronounced as he notices in his aircraft. It would be an interesting test in a Rotax powered gyro to see if the glide distance is influenced the same in a Rotax vs a Lycoming engine.

I am fairly certain the answer will always be: It Depends......
There are a lot of aircraft variables. One of the early posts indicated a high idle, which combined with a fat prop on a draggy slow aircraft may still be net positive thrust at idle.
My 12ft. span 65lb. high efficiency UAV has a 10hp engine with a large prop cut down to have a fat chord.
At 1200 RPM idle, it can almost maintain altitude and cruise speed below 5000ft. ASL.. It doesn't act like an air brake unless I dive on it and exceed 75mph.
I always kill the engine at about 200ft. and glide in because the only graceful way to land with power is to fly it into the ground at an angle and it will hit at over 35mph. without a flare. It survives this but gliding in is much better. (Skid landing)

I wonder about a windmilling prop when diving. It would seem that the span wise flow across the prop and the disk solidity would cause a large spill over and disturb a lot more surface area than the diameter of the prop, so the breaking effect would be much more pronounced at higher speeds.

 

[WaspAir]

I have done a dive to airstart an Aeronca with a stopped prop (no electric starter), and found the speed necessary and altitude used to be truly eye-opening. That particular airplane would glide better with the prop not turning, as windmilling (without ignition) sucked up plenty of energy. Idle thrust (ignition on) was not huge but did contribute.

 

[Abid]

So never having actually turned off the engine in engine out emergency practice, and never having experienced a real engine out; a real engine out may in some respects be easier to manage than a simulated one due to having further gliding latitude?

I can just assure you test flying and gathering data for POH to get glide ratios using sensitive altimeters and stop watches with many Rotax 9 series engines. Most of the time I got better glide with engine at idle.

 

[WaspAir]

This might be a good time to remind the not-yet-experienced that there is not just one best glide speed. The optimum varies with weight on board (faster when heavier), with wind (faster into headwinds), and with airmass motion (faster through sinking air). Your POH typically gives a figure that is valid for still air and max gross weight to use as a starting point, and allow you to adjust for conditions.

 

[Tyger]

No doubt Tyger can adjudicate...

I just simply always use "further". It's basically never wrong in any context. I also almost always use "till" instead of "until". KISS.

 

[Tyger]

Funny: I'm hearing impaired and for years I ve had a problem understanding Pakistanis, Indians, others speaking English. I think my main issue has been with the speed in which some speak . I've had to appologize repeatedly when this happens, "I'm sorry but I just can't understand you"

This started in Saudi Arabia after I was in a bombing, never got any better even with hearing aids. At the time I had a crew of great Paki outside plant guys, they were great and I was always struggling to understand.

Just FYI, "Paki" is considered quite pejorative in the UK.

 

[Tyger]

In what way did he say it was "much different?"

He really had to push the nose down must faster/harder to regain/maintain airspeed

 

[Abid]

Just FYI, "Paki" is considered quite pejorative in the UK.

Yeah I think in the UK they use Paki as a derogatory term. In the US no one gives a crap so do not worry.

 

[Tyger]

Yeah I think in the UK they use Paki as a derogatory term. In the US no one gives a crap so do not worry.

Well... except not everyone reading this is going to be in the US, of course.

There are tons of little one-syllable words that many of our grandfathers once used, often innocently, to refer to members of various ethnic groups. Almost all of these are now considered... in very bad taste, to say the least.

 

[Sv.grainne]

I had the absolute best crew, nothing meant to be demeaning with my use of the term

 

[Tyger]

We all know that, Bobby. I certainly wasn't taking any offence, and Abid has already said not to worry; I just wanted to mention it for future awareness.

 

[Sv.grainne]

I knew that but thought I would post.

 

[Abid]

Well... except not everyone reading this is going to be in the US, of course.

There are tons of little one-syllable words that many of our grandfathers once used, often innocently, to refer to members of various ethnic groups. Almost all of these are now considered... in very bad taste, to say the least.

True. I think the only place it is considered bad is the UK. Pakistanis themselves have no clue about the word in general except few that know.
Pakistanis I remember clearly called Britishers "Ferangi" (yes that is also used in Star Trek). It literally means a foreigner that cannot be trusted. So not like they don't have words for the British that are not quite great. The younger generation does not care about all this stuff much anymore.
The PM of UK has family that technically came out of Punjabi area now in Pakistan. The Scottish First Minister is a Pakistani immigrant. Irish PM is half Indian. Things have improved and moved forward quite a lot and will continue to.

 

[Doctordantodd]

I think this was Mark Sprigg DPE. I cannot think of a person I would rather be with if my engine suddenly quit--he flies those magni's like 8 hours a day. I will be interested to hear what happened to him as I have the exact same plane. I heard that neither pilot needed any medical attention, that is usually considered a win.

 

[Abid]

I think this was Mark Sprigg DPE. I cannot think of a person I would rather be with if my engine suddenly quit--he flies those magni's like 8 hours a day. I will be interested to hear what happened to him as I have the exact same plane. I heard that neither pilot needed any medical attention, that is usually considered a win.

I think Mark was hoping to milk that ground effect float to some dry land but didn’t quite make it. Unfortunately in a real emergency one slight bad call can put you committed to a situation that can convert the outcome and that is why you never really want to have a real engine out out if the airport area if possible. If something isn’t working on the ground properly then time to check it and fix it before leaving. Not that I think Mark had any clue what was going to happen. Just making a general point.

 

[PJB]

Happily just a bent aircraft, I guess the root cause is nothing too dramatic and the actual reason is well known by those who simply phoned the guy and asked the question....