The Prop windmilling on RX1/Apex engines

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way_up_noth

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The only issue ... I’ve come up with so far with the Yamaha conversion is that the prop windmills if you have an engine shutdown

I didn't write this as a critique ..everyone involved in the Yamaha conversion is doing out of love of aviation...volunteering time and expertise...

I'm not an expert on windmilling props...so I post this here for others to chime in and educate me on this issue....I'm not that familiar with rotax engines either... do they windmill on some of thier gearboxes also?

To this point it’s not been an issue as nobody yet has had an inflight engine outage...

But as of right now there is no easy means to stop the prop ... other then installing an electric constant speed prop so you can feather the propeller...

Everyone involved has answered all my questions and the Facebook site even compiles all known failures of parts or issues...it’s a good community

Any question I had were answered on the Facebook Yamaha conversion site in minutes...I texted Teal Jenkins with some questions and he responded within an hour...
 
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TFF

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As long as you don’t overspeed the prop windmilling, it’s going to be a non issue. At any one engine out it will help, hurt or indifferent. It would be the engine out and not having one would be the bigger concern.
 

wsimpso1

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You can not stop the prop by pulling the speed back for a few seconds? I would think that between the gearing and the high compression ratio of the Yamaha it would also.
 

rv7charlie

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Freely windmilling props in an engine-out are actually a *big* concern, especially on an a/c that isn't already a 'box kite' in the drag dept. Consider the auto-gyro, and whether a spinning rotor makes a difference. Glide ratio is significantly affected by windmilling prop.

Perhaps a centrifugal clutch would be ok; it wouldn't release until the prop is near idle rpm. But an overrunning type clutch makes me uncomfortable.

Billski,
Some of the Yamaha prop reductions have 'guibo' style couplers; others appear to have overrunning clutches.

Charlie
 

Marc W

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I am using the Rotax C gearbox and guibo on my RX-1. On that setup the prop will not windmill. Teal Jenkins, who is developing the gearboxes, and others, used the C box and guibo on the RX-1. Teal said it works Ok with a lightweight wood prop. For more hp and heavier props he said you should use a clutch.
 

TFF

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I think the choice from the website is either a sprag or a shoe clutch like a go cart. It is what it is.

Yes it’s drag but as the owner you have to fly that defense. Your decisions are made with that as a part. No. It’s not like regular airplane. You are not flying a regular airplane engine.

You can always do like the DC4-6 pilots had to do. If the prop went overspeed and could not be feathered, you kept it overspeed until it departed. Drag problem and engine lockup problem solved.

The spread sheet of airplane engine vs auto conversion is column upon column of trades. The side that has the most pluses for you personally is the side you pick. Neither side gets it all.
 

way_up_noth

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I forgot to mention my application was a twin engine setup ... like the jabiru twin engine ...

A windmilling prop is something I’m trying to avoid...but the cs prop is a work around

Teal Jenkins is working with master propellers on a cs prop hub for the Skytrax gear box
 
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way_up_noth

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You can not stop the prop by pulling the speed back for a few seconds? I would think that between the gearing and the high compression ratio of the Yamaha it would also.
there is a sprag clutch....between the engine and propeller .... so the prop spins freely when not powered....
 
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Vigilant1

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Would it be worth the trouble to just stop the prop with a set of brakes/disc from a mountain bike, or similar? Have them rigged with a spring to apply the needed pressure, you'd just pull a pin from the cockpit and the rest happens for you.
I doubt it would weigh more than a few pounds.
 

way_up_noth

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Would it be worth the trouble to just stop the prop with a set of brakes/disc from a mountain bike, or similar? Have them rigged with a spring to apply the needed pressure, you'd just pull a pin from the cockpit and the rest happens for you.
I doubt it would weigh more than a few pounds.
Funny you mention this... I was thinking the same thing... an idea would be to put a prop shaft extension .... creating some room between the gear box and prop .... in that area a brake disk could be mounted... then a brake caliper on an arm attached to the gear box...

Might also be helpful at engine shutdown to slow the prop down... as it spins freely after shutdown ...if you’re floating into the dock with your float plane and don’t want to deal with a spinning prop while you tie up your plane
 
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mcrae0104

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I forgot to mention my application was a twin engine setup ...
Wait, you said you wanted a twin Viking Bearhawk 5. Now it's a twin Yamahawk?

If you're concerned with stopping the inop prop, google "twin jag corvair site:homebuiltairplanes.com" for ideas. If you can solve the structural & aero issues and build a successful twin Bearhawk, then surely the windmilling prop challenge can be resolved. I wouldn't concern myself too much with powerplant-specific issues until the whole airframe thing is thought out a little more. Engines are interchangeable. Don't marry one until you can't live without it.
 

way_up_noth

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Wait, you said you wanted a twin Viking Bearhawk 5. Now it's a twin Yamahawk?

If you're concerned with stopping the inop prop, google "twin jag corvair site:homebuiltairplanes.com" for ideas. If you can solve the structural & aero issues and build a successful twin Bearhawk, then surely the windmilling prop challenge can be resolved. I wouldn't concern myself too much with powerplant-specific issues until the whole airframe thing is thought out a little more. Engines are interchangeable. Don't marry one until you can't live without it.
Yamahawk...that’s funny...lol

1568176F-BEF6-4EC1-B9E9-B1BC81D3A338.jpeg

There is no airframe modifications to be done... take a look at the jabiru twin .... it’s all firewall forward... it’s a complex engine mount... bolted onto a standard airframe

Thanks for the link... I read the thread and other articles about the jag-2....what a great plane ... too bad the builder caught so much grief from VAF....I watched his YouTube channel also... very cool stuff...
 
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lear999wa

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Something akin to this I assume. My understanding is the teal has made a clutch-less apex psru in the past. And although he said on the Facebook that going forward he was only making the gearbox with a clutch. I'm sure that he might have an older one laying without a clutch for your application.
 

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way_up_noth

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Something akin to this I assume. My understanding is the teal has made a clutch-less apex psru in the past. And although he said on the Facebook that going forward he was only making the gearbox with a clutch. I'm sure that he might have an older one laying without a clutch for your application.
Thanks for the tip.... I was unaware...
 

wsimpso1

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there is a sprag clutch....between the engine and propeller .... so the prop spins freely when not powered....
Oh. Energy used is torque to turn times rotation speed. Conventional airplane engines - you are turning the engine at medium speed and that amounts to a bunch of energy when left windmilling. With a OWC, the torque to turn the prop is quite small. The only way that will be much energy is if the windmilling speed is really high. Is it?

Billski
 

cblink.007

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As long as you don’t overspeed the prop windmilling, it’s going to be a non issue. At any one engine out it will help, hurt or indifferent. It would be the engine out and not having one would be the bigger concern.
I am of the mindset that if I lose an engine in flight, prop speed on the non-functioning engine is not exactly going to be my primary concern. I would be more concerned with getting the aircraft to its best glide speed, and getting to a good spot to land. If the prop overspeeds at that velocity, well.....
 

rv7charlie

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cblink.007

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It's not prop overspeed that's the issue. It's the greatly increased drag from the windmilling prop, which may keep you from reaching a safe landing spot.
From 'the google' :
https://www.google.com/search?q=windmilling+propeller+vs+stopped+propeller&oq=windmilling+prop+vs+stopped+prop&aqs=chrome.1.69i57j33.27218j0j7&client=ms-android-google&sourceid=chrome-mobile&ie=UTF-8
I get what you are saying. But, unless the prop is feathered at a stop, you will have the drag, windmilling or not. I did some experimentation years ago when prepping for the "Power Off 180" for the commercial check ride. Being an FTE at the time, I set up an experiment. Would advancing the pitch at engine idle cut drag and offer just a little more time/distance? It did. All that said, a bird like a Cessna 152 seemed to glide great with the fixed pitch prop at a full stop than if you had it turning at the lowest drag RPM.

I do know from alot of helicopter flying experience that if you are in an autorotation and flare to build RPM before the final pitch pull, you'll slow down alot...but the blades are barely....barely at a negative pitch if any (airframe depending), so you have a ton of drag in that situation.

My aircraft design will have a pusher configuration, I will run some prop stopped v prop windmilling drag comparisons just for grins!

I do not think there are any folding props (the ones that fold downstream when not under power) out there that can take the HP/Torque output of the Apex.

05-L.jpg
 
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ScaleBirdsScott

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Could one use electrical braking? I know on my mill when you hit spindle stop it takes a 6-10k rpm spindle to zero in the blink of an eye by switching the rotational energy in the motor over to a massive resistive braking unit. And that unit is basically some oven heating coils in a box. Just wondering if there's something that could be taken from that concept and applied to this scenario. I'm just talking mostly out my butt here cuz I know it means basically strapping a serious alternator around your propshaft; and in any case I'm not much of an electrical rocket surgeon.

Taking it further, in theory on a twin if it was wired correctly couldn't you have each propshaft hooked up to their own motor/alternator, and then those connected to either just have no load at all, or as available siphon some of that extra energy to charge some batteries which maybe could be tapped to provide some emergency electrical boost to the props, say on takeoff (or in an engine-out) which would help claim some of that extra potential of having a twin in the first place by covering some of the engine-out margin.

But also if there was an engine out when it wasn't a super critical moment, such as at cruise vs at climbout, one could either dump the energy from the failed engine's windmilling prop into a resistive braking unit, or somehow siphon the power off the good engine's driven electrical motor to drive the second prop directly (with battery assist) ideally at a speed more useful than nothing at all.

Now, obviously, compared to a simple set of dirtbike discbrakes with an emergency release actuator, a pair of stripped down 30hp motors built into each propshaft is probably not even in the same universe. But if it was something that could benefit normal flight ops and still come in... clutch (hah) during an engine-out contingency maybe there is something to it.

Barring of course the immense electrical engineering work and testing that would go into such a bespoke system. Besides that.
 
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