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The Prop windmilling on RX1/Apex engines

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GTX_Engines

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Gyrocopters are in autorotation at all times. Helicopters are not. When a helo engine quits, the helicopter must have at least 45 MPH foward true AS in order to autorotate and glide to a safe landing. This requires a minimum 200' AGL from a hover, zero AS.

Since a gyrocopter is ALWAYS in autorotation, then it does not need to transition, BUT - just like the helo - it MUST maintain minimum 45 MPH fwd AS in order to keep the rotors spinning and creating lift.

In every case with no power, helo & gyro, you must point the nose down to gain and maintain AS.

What is auto-rotation and how does it work? Lift is perpendicular to the surface of an airfoil. Look at any airfoil and you will quickly see that there are surfaces that have a forward componet vector of lift. It may be small, but it's there. As air flows over ANY wing, there is a small fwd component of lift - and this is true on EVERY wing, whether it is rotating or fixed in position.
 

Vigilant1

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Mohawk Aero has a variety of gearbox options, as well as clutch and no clutch. They always have, and they always will, since 2012. These are now available to work with RX1, Apex, Phazer, Nytro, Attak, Vector, Rage, Mountain...in other words ALL Yamaha Genesis (YG) engines.
A chart with the various engine/gearbox combinations and the key attributes of each would help make this more clear. Anything like that in your web site?
 

cblink.007

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What is auto-rotation and how does it work? Lift is perpendicular to the surface of an airfoil. Look at any airfoil and you will quickly see that there are surfaces that have a forward componet vector of lift. It may be small, but it's there. As air flows over ANY wing, there is a small fwd component of lift - and this is true on EVERY wing, whether it is rotating or fixed in position.
This article explains it well...and you can apply the exact same principles to a windmilling propeller, with the stalled, driving and driven region et al:

 

lear999wa

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Vlad Serge also does psru conversions for the 4 cylinder (maybe others). I believe he has the most competitive price at $~2000 for the gearbox (spg4 derivative) and adapter. Tangogyro also has adapters and gearboxes for the 3 and 4 cylinder. Furthermore Teal is currently working on what appears to be the final throes of a gearbox for the 2 cylinder. He has also stated publicly that he intends to make one for the 3 cylinder in the future.
I have no affiliation with any of them, however this is what I have gathered on the Facebook forum.
 
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way_up_noth

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Mohawk Aero has a variety of gearbox options, as well as clutch and no clutch. They always have, and they always will, since 2012. These are now available to work with RX1, Apex, Phazer, Nytro, Attak, Vector, Rage, Mountain...in other words ALL Yamaha Genesis (YG) engines.

In some cases, such as the Arrow PSRU, the clutch is inside the gearbox, and is a sprag like that used in automatic transmissions for autos. In most other cases, a clutch is an option, and becomes the shaft coupling between the engine and the gearbox. If a clutch is not used, then a rubber flex shaft coupling is used as the coupling. This allows imperfections in axial alignment up to easily .030", as well as radial alignments of incredible angles. In fact, the Rotax rubber donut is the coupling for the rear half shaft on early 1960's Lotus and other small, ~100HP range Euro sports cars from the 1960's. Porsche only ever used CV joints.

The much beefier AK7 (an Airgear Type "B" PSRU) gearbox Mohawk Aero uses on nearly all of the YG3 and YG4 installations sold has a BMW drive shaft harmonic damper for the flex shaft coupling between the PTO and gearbox, and is sturdy enough that spinning up the prop from start and then flying will not tear it up like the smaller Rotax donut. Rotax and AK7 rubber donuts are a completely different size and are not interchangeable. Mohawk does offer a special adapter that will allow the use of the larger BMW coupling on the smaller Rotax C.

With a Skytrax (which can be confusing, since when you do a google search you come up with a company based in London that rates international airline companies, while the guy who builds the Yamaha stuff using this name has no website) RX1 PSRU adapter you are limited to the Rotax C gearbox only - which was designed for use with their 582 65 HP 2-cycle motor. You MUST use the RK400 centrifugal clutch with this set up because if you try to use the Rotax rubber donut (what is technically called a flex shaft coupling) supplied and intended by Rotax, the shear power of the 140 HP RX1 Yamaha will shred the donut in less than 10 hours.

There are other problems associated with this equipment, some of which were only discovered this year. One of those is that it is impossible to align the clutch drum with the hub due to the imperfections of the Rotax PSRU drive flanges which are usually at least +/- .015" out of tolerance, whereas is must be +/-.0005 for proper clutch wear. That pinion flange must be re-machined to the finer spec.

Now where was I....

With the old Arrow gearbox the pinion gear bolts directly onto the YG4 taper shaft PTO. I make the adapter such that the gearbox then bolts onto the engine crankcase. The sprag clutch is inside, slap on a prop and away ya go.

View attachment 99547 View attachment 99551 View attachment 99548 View attachment 99549 View attachment 99550 View attachment 99552
View attachment 99553

Teal took this design and added a third gear to the mix, combined it with the crankcase cover and that is the gearbox he now sells.

Mohawk Aero (MAC) also uses a number of different clutches which are NOT in the gearbox like this, but replace the shaft coupling. THese include the popular RK400 from Air-Tech, Inc. the MAC GT3, which has a sprag element inside, the MAC GT4 which has a roller ramp element inside, the Air Trikes "BMW" centrifugal clutch, and the Tango Gyro centrifugal clutch. MAC partners with Air-tech, Inc., Air Trikes, and Tango Gyro in each case, and enjoys a cozy relationship with each.

That should answer the first question.

I've already answered the next question. But to say it again, YES:

MOHAWK AERO and Teal Jenkins are the only vendors for YG4 conversions.

MOHAWK AERO and Tango Gyro are the only vendors for YG3 conversions.

MOHAWK AERO is the only vendor for YG2 conversions.
Can you send me contact information for anyone of your customers that is using your direct drive.....I would like to get thier opinion ...I don't want to have a windmilling prop... I'd like to confirm what's going on with torsional vibrations on your direct drives...

I'm asking because someone on the Yamaha Facebook conversion site said they used one of Teals direct drives and it suffered a lot of torsional vibrations ...so he switched to the sprag clutch...are you doing something diffrent in your direct drive...is there dampening...
 

Pilot-34

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I think we are not clear on the terminology and the differences.
There is a stopped propeller there is a free wheeling propeller That doesn’t drive anything and there is a windmilling propeller that drives an engine .
I suspected the stopped propeller and the free wheeling propeller are very close in the amount of drag and that is a lot less than a propeller windmilling and turning over a engine.
I suspect that a free wheeling propeller is actually the lowest drag but I also suspect the difference between it and it stopped propeller is insignificant.
 

cblink.007

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I suspected the stopped propeller and the free wheeling propeller are very close in the amount of drag and that is a lot less than a propeller windmilling and turning over a engine.
I suspect that a free wheeling propeller is actually the lowest drag but I also suspect the difference between it and it stopped propeller is insignificant.
If I can offer food for thought with respect to rotary wing aerodynamics...

Being a helicopter/tiltrotor guy at heart, let me offer a rhetorical question:

You have two helicopters. Both at 1000 feet above ground level, flying at 80 knots, same type/model/series aircraft, weight, power settings, etc.

All of a sudden, at the exact same time, both lose all power, but one difference between them: the rotor on one keeps turning in an autorotative state and the other is stopped completely.

So you have one helicopter in an autorotative state (identical aerodynamically to a windmilling prop), and another in complete freefall due to no rotor turning (a stopped prop).

Which one arrives to the ground first and why?
 

way_up_noth

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If I can offer food for thought with respect to rotary wing aerodynamics...

Being a helicopter/tiltrotor guy at heart, let me offer a rhetorical question:

You have two helicopters. Both at 1000 feet above ground level, flying at 80 knots, same type/model/series aircraft, weight, power settings, etc.

All of a sudden, at the exact same time, both lose all power, but one difference between them: the rotor on one keeps turning in an autorotative state and the other is stopped completely.

So you have one helicopter in an autorotative state (identical aerodynamically to a windmilling prop), and another in complete freefall due to no rotor turning (a stopped prop).

Which one arrives to the ground first and why?
Very few people here understand the problem you just posted......(plane pilots)

The stopped prop heli will drop like a rock...

A freewheeling prop becomes a disk....or a parachute of similar size to the prop..if it's on the nose of your plane
 
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way_up_noth

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I think we are not clear on the terminology and the differences.
There is a stopped propeller there is a free wheeling propeller That doesn’t drive anything and there is a windmilling propeller that drives an engine .
I suspected the stopped propeller and the free wheeling propeller are very close in the amount of drag and that is a lot less than a propeller windmilling and turning over a engine.
I suspect that a free wheeling propeller is actually the lowest drag but I also suspect the difference between it and it stopped propeller is insignificant.
It's counter intuitive ....but the free wheeling prop makes a lot of drag...you would not think it...but it does...and the faster the plane...I suspect the worse it gets....the air piles up in front of a freewheeling prop...not pass thru it...it creates a disk...same size as the prop
 

way_up_noth

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On the Yamaha Facebook conversion site...2 planes are close to completion....I'm not that familiar with the makes...but by the looks they are fast...rans...and a sonerai 2....To this point I believe most conversions have been stol aircraft...or high wing cub type planes...

They are both fitted with sprag clutch gear boxes...so the props will windmill at idle or in an engine out....

I tried to share my concerns there...

A few pilots spoke up also with concerns...but the sexiness of the this new engine and gearbox....has everyone smitten..

A few have seen the need for side by side testing of similar planes one with windmilling prop the other without...

I hope it all works out
 
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cblink.007

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On the Yamaha Facebook conversion site...2 planes are close to completion....I'm not that familiar with the makes...but by the looks they are fast...rans...and a sonerai 2....To this point I believe most conversions have been stol aircraft...or high wing cub type planes...

They are both fitted with sprag clutch gear boxes...so the props will windmill at idle or in an engine out....

I tried to share my concerns there...

A few pilots spoke up...but the sexiness of the this new engine and gearbox....has everyone smitten..

A few have seen the need for side by side testing of similar planes one with windmilling prop the other without...

I hope it all works out
I have no intention for a free drive type system for my Yamaha, as the drag of an autorotating prop will simply kill some glide range. Non free-drive systems are available, so all good. But I do want some vibration v PSRU lifespan data... if some are dealing with excessive torsional vibration, then some quality issues may exist, be it gear or bearing machining angles, gear cutting and tolerances! Steve Henry has had little problems with his Yamahas, and they're turbo'ed out to 300+ hp!! We have vibration spectrum test equipment, and plan to gather data on our prototype...and will share findings with the community!
 
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TFF

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A freewheeling prop is going to be a lot freer than a windmilling prop. A big reason a windmilling prop is bad is it is driving the engine. The engine is slowing the prop down to a speed slower than actual airspeed. Mismatch. Let’s change the helicopter analogy. Two helicopters one the blades stop the other is immediately rolled inverted so the blades are in the same direction of the fall, not much braking there. The autorotation is windmilling the blades; the inverted helicopter is freewheeling the blades.
Almost all my helicopter flying is in piston helicopters. The starting clutched out I can see being an advantage for a small engine. Add the prop and drive and now that little starter is trying to start the engine and the load like being in gear and hitting the starter. Free turbine helicopters are not in gear so to speak, they are free to start and then the blades catch up.
 

way_up_noth

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A freewheeling prop is going to be a lot freer than a windmilling prop. A big reason a windmilling prop is bad is it is driving the engine. The engine is slowing the prop down to a speed slower than actual airspeed. Mismatch. Let’s change the helicopter analogy. Two helicopters one the blades stop the other is immediately rolled inverted so the blades are in the same direction of the fall, not much braking there. The autorotation is windmilling the blades; the inverted helicopter is freewheeling the blades.
Almost all my helicopter flying is in piston helicopters. The starting clutched out I can see being an advantage for a small engine. Add the prop and drive and now that little starter is trying to start the engine and the load like being in gear and hitting the starter. Free turbine helicopters are not in gear so to speak, they are free to start and then the blades catch up.
I think the idea in a plane...is the faster the prop is free-windmilling ...the more it becomes a solid disk/air piling up in front of it........if the prop is slowed down for any reason...engine connection or friction....ect....then it's allowing some air to pass.....
 

Pilot-34

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Do the math and you will find the free wheeling prop to be using the least least energy .
 

cblink.007

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Do the math and you will find the free wheeling prop to be using the least least energy .
A free-driving rotating wing, be it a propeller, wind turbine or helicopter rotor, uses the energy of the freestream air passing its airfoils to get its drive, but due to the fact that there are three distinct regions across the span of the blade from root to tip (stalled, driving and driven), you will still have net drag (from the stalled and driven regions) as a function of the entire system being driven by said airflow. I assume this is what you were trying to verbalize? See this chart:

Fig6-2.jpeg

I've done plenty of autorotations over the years. If you lose RPM during the maneuver, you are screwed and will drop like a rock (eg "low drag scenario") unless you can get the RPM back up (higher drag, lower rate of decent, relatively speaking). Of course, you can really drive Nr way up above prescribed limits, but then you risk rotor hub failure...but we are not talking about that here.

My time flying the V-22 Osprey was a good example. You can be hauling tail at 220 knots, and when you pull power back and advance Nr to covert back to VTOL mode, the flat pitching as a result of the proprotor acceleration feels like deploying a parachute out of the back of the bird!

Read my previous reply to your traffic with the two helicopter examples. A free drive prop is simply being driven by the passing wind, and still creates drag. More than if the prop was not moving at all. Simulations and actual use prove the theory, its purely aerodynamic.
 
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BJC

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Very few people here understand the problem you just posted......
Perhaps most of the people that you are around do not understand the problem, but I encourage you not to extrapolate that to “very few people here ...”


BJC
 

way_up_noth

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Perhaps most of the people that you are around do not understand the problem, but I encourage you not to extrapolate that to “very few people here ...”


BJC
I’m not trying to be rude... the phenomenon is not well understood by many... we are all trying to make aviation safer... but sometimes on that process somebodies toes will get stepped on... my apologies
 
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