Yamaha Apex internal gear reduction.

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rv7charlie

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Depends on your application, but on most 'conventional' a/c (tractor or pusher), having the prop against the side of the engine would carry a significant aero penalty. And that ignores the radial and gyro loading issues already mentioned. You'd almost certainly need some kind of extended case outside the block anyway, so...
 

Jay Kempf

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Totally agree. The question is where to put the reduction unit. At the end of an extension shaft in the reduction unit or at the engine end. I think the best arrangement is to build a full PSRU separate from the engine and run a driveshaft to the PSRU. Have the driveshaft engineered to be soft enough to absorb the TV. This allows a reasonable sized prop and cooling circuits without 90 degree corners. For a pusher this is ideal because the engine can be placed nearer the CG but the prop can be placed far enough behind the trailing edge to help get it in cleaner air. For a tractor it makes for a more conical nose so easier to design cooling channels and spinner transition to cowl.
 

Ally Wilke

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Totally agree. The question is where to put the reduction unit. At the end of an extension shaft in the reduction unit or at the engine end. I think the best arrangement is to build a full PSRU separate from the engine and run a driveshaft to the PSRU. Have the driveshaft engineered to be soft enough to absorb the TV. This allows a reasonable sized prop and cooling circuits without 90 degree corners. For a pusher this is ideal because the engine can be placed nearer the CG but the prop can be placed far enough behind the trailing edge to help get it in cleaner air. For a tractor it makes for a more conical nose so easier to design cooling channels and spinner transition to cowl.
I have some non greaseable u joints on a semi truck that went 1.5 milliin miles before I had to replace them.A drive shaft system would for sure work.
 

wsimpso1

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In a word, NO! There is also a rubber damper built into the output gear to reduce torsional vibration. These engines turn 10,000 to 11,000 RPM. The internal gear reduction is there so the clutch and primary drive belt survive.
Being as the Yahama application is specifically snowmobiles, I suspect that the elastic element in the primary drive is designed around isolating torsional vibration of the engine from the anticipated downstream powertrain components of a snowmobile. It may or may not be suitable to second gear ratio and propeller, and would require some investigation, even it only to run it with a variety of Eiffel Clubs and over the entire speed range just to demonstrate that it will not quickly tear itself apart in flight.
 
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Marc W

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Yes, the built in rubber damper is not adequate to eliminate destructive torsional vibration. Three solutions available are the RK-400 centrifigal clutch, Skytrax uses a sprag clutch in the gearbox and some have been successful using a rubber guibo with the 4 cylinder RX-1 and props that have a low moment of inertia(light wood props).

I should add that these engines will not even idle well or accelerate without a clutch due to vibration.
 
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wsimpso1

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I think the best arrangement is to build a full PSRU separate from the engine and run a driveshaft to the PSRU. Have the driveshaft engineered to be soft enough to absorb the TV. This allows a reasonable sized prop and cooling circuits without 90 degree corners.
This arrangement worked on the stillborn Teton Aircraft project, but it was direct drive and completely without lash. I suggest that while a design with a shaft between engine and gearbox may reduce resonant mode frequency of engine - prop to near or below idle firing frequencies, it will expose the shaft to engine speeds and require two sets of mounts on the airframe.
  • As to speed and isolation of powertrain from engine, developers should read up on shaft critical speed and calculations, shaft spring rate calculations, Mass Moment of Inertia calculation/measurement of rotating parts, and two-body resonance calculation. Critical speed issues must be precluded while simultaneously giving low enough resonant frequencies. The design space may or may not allow the combination with a suitable length shaft.
  • As to mounts, the engine must safely and reliably carry engine torque and any axial thrust that comes from the powertrain connections. A second mount will be needed for the gearbox that safely and reliably reacts (1+GR) times engine torque plus reacts all propellor reactions.
While this might work as well as a properly sized compact isolator on an engine mounted PSRU, I suspect that the long shaft scheme may produce a significantly heavier airplane than one with a more conventional engine mounted PSRU. Its benefits to CG placement and prop efficiency might or might not be worth the weight

The effects of all of these issues can be known while the project is still on paper, allowing decent decision making to occur.

Billski
 

wsimpso1

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Yes, the built in rubber damper is not adequate to eliminate destructive torsional vibration. Three solutions available are the RK-400 centrifigal clutch, Skytrax uses a sprag clutch in the gearbox and some have been successful using a rubber guibo with the 4 cylinder RX-1 and props that have a low moment of inertia(light wood props).

I should add that these engines will not even idle well or accelerate without a clutch due to vibration.
I should point out again, that all of the Yamaha designs are intended for other types of downstream systems - small diameter/low inertia waterscrews and snowmobile powertrains/drives. Looking into the various inertia and isolators for driving airscrews would be prudent. Guibo are much used to make these systems work, but must be selected to suit the system needs. Slipper clutches and one-way clutches are great for getting through resonance rpm if it occurs in below idle. If they are "working" up the powered flight rpm range, they will still give problems...

Next point is I agree with Marc W above that if you isolate the large inertia items downstream from engine torsional vibration, the downstream elements do not contribute to flywheel effect needed for low speed operations. You still need a substantial flywheel on the engine for that purpose, and it will also be needed to substantially isolate the engine vibrationally from the downstream components. The system will never be as simple as one might initially imagine.

Billski
 
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slociviccoupe

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1.47:1 on the mr1 marine engine. Rev limiter at 10,500 rpm. Makes about 160hp. 1052cc almost identical to apex and r1 engine. Shares same stroke just 2mm bigger bore than the r1.
 

Jay Kempf

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Yes, driveshaft at engine speed. It is a tricky balance between strong enough to survive and soft enough to provide any damping. What it does do is that it allows all the tuning to go into one component. The Torque tube on my 928 is a perfect example of this. If it is too soft the driveline "snatch" becomes unbearable as it unloads between shifts. Gotten right it allows a perfect balance (5-600hp have been put through this setup). The driveshaft of the 928 is about 7/8" diameter some of the later ones hollow. It's about 5' long and splined on both ends. Clutch is on the front end. So a similar setup would have a rigid cage going from the engine to the PSRU and a supporting input bearing. The PSRU would be a contained unit without a Guibo. The Guibo would be at the engine end. Perhaps a pinned coupler with a rubber isolator plate would be a simple to make and easy to tune isolator an would take the thrust loads off of the engine as well.

Most PSRU extenders are on the order of 10-12" so it might be hard to make it a soft enough shaft in torsion.
 

cblink.007

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I don't think there is room for that sort of gear reduction in that case. I looked up the MR-1. Nice engine but replaced by the 3 cyl TR-1. Both no gear box at all.

You cannot just use the direct drive gear box as is. The Skytrax deals with the prop loads and has isolation from the primary. It is a system.

Like what is going on in the Yamaha experimental world. But still would like a largely extended prop/psru system for pushers.
No, there is no room internally for additional gearing. Attach a SkyTrax or Rotax-C. We used a SkyTrax on ours.
 

GTX_Engines

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Is there enough room in the gear reduction case of the Apex motor for me to machine some gears to get the out put shaft speed down for prop use?Or would I have to machine a case and gear set?It does not make sense to me to use 2 gear boxes on a motor.Lots of mechanical loss and more moveing parts to fail.All advise is welcomed.Thx.
No.
 

Ally Wilke

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No, there is no room internally for additional gearing. Attach a SkyTrax or Rotax-C. We used a SkyTrax on ours.
There are companies already making gears for these engines.There is room to change them.Maybe not enough to get the output shaft rpms we need.
 

Ally Wilke

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1.47:1 on the mr1 marine engine. Rev limiter at 10,500 rpm. Makes about 160hp. 1052cc almost identical to apex and r1 engine. Shares same stroke just 2mm bigger bore than the r1.
Which one does not have the internal gear reduction?
 

Marc W

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The Yamaha 3 cylinders as used in the Nytro snowmobiles and others. The link to the new engine I gave you above is it.
 

cblink.007

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There are companies already making gears for these engines.There is room to change them.Maybe not enough to get the output shaft rpms we need.
I've only built and operated an RX-1 and a YG4i on both snowmobiles, F1000 cars and aircraft, so my experience may severely wanting (sarc). If you already know the answers, why are you asking questions of us already well familiar with the powerplant here?

If there was a way to achieve a solution without an external PSRU on this plant, believe me it would have been done. Many of us here may be incredibly credentialed & experienced mechanics and engineers (like myself and many others), but that doesn't mean we go all out to make things unnecessarily complicated. If there is a simple way that works, we gravitate toward it- no need to reinvent the wheel at expense if the solution already exists.

But if you have the answers, go for it, and show us your achievement... in fact I encourage it.

Mohawk Aero, SkyTrax, Rotax-C for the RX-1/YG4-YG4i. As the Mandalorian says, This is the Way.
 

Ally Wilke

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I am wanting to know if there is room to put the size of gears needed to get to prop speed with the internal gear reduction.I know there are after market ones,but they only drop the output shaft 1500 rpms.That is not enough reduction.I would like to find out of it can be done before spending 4 grand on a donor sled,because frankly I live in WI. I would have a hard time tearing apart a perfecly good sled.The trails are full open here right now.I could just ride it until it is time to canibalize it I suppose.They are nice machines.All the drawings and images I have got my eyes on tell me there is not enough room.If we got close power bands can be manipulated.Running 2 gear reduction boxes is not logical to me.There is always a better way.No one has came up with it yet.
 

Ally Wilke

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I've only built and operated an RX-1 and a YG4i on both snowmobiles, F1000 cars and aircraft, so my experience may severely wanting (sarc). If you already know the answers, why are you asking questions of us already well familiar with the powerplant here?

If there was a way to achieve a solution without an external PSRU on this plant, believe me it would have been done. Many of us here may be incredibly credentialed & experienced mechanics and engineers (like myself and many others), but that doesn't mean we go all out to make things unnecessarily complicated. If there is a simple way that works, we gravitate toward it- no need to reinvent the wheel at expense if the solution already exists.

But if you have the answers, go for it, and show us your achievement... in fact I encourage it.

Mohawk Aero, SkyTmy freightliner swmi teuck was designed by great engineers rax, Rotax-C for the RX-1/YG4-YG4i. As the Mandalorian says, This is the Way.
My freightliner semi truck was designed by great engineers and cost as much as a house.It was a pos that I spent 2 times as much money getting it to be reliable with the knowledge,tools, and brains of others and myself.My neighbor is a mechanical engineer and I had to show him how to change a spark plug in his Briggs and Straton push mower.Sometimes other people see things that others don't.I hope I find that or I want others to get there.Even physics are not set in stone in this universe.We can always be and do better.I take great joy in that.
 

Ally Wilke

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Being as the Yahama application is specifically snowmobiles, I suspect that the elastic element in the primary drive is designed around isolating torsional vibration of the engine from the anticipated downstream powertrain components of a snowmobile. It may or may not be suitable to second gear ratio and propeller, and would require some investigation, even it only to run it with a variety of Eiffel Clubs and over the entire speed range just to demonstrate that it will not quickly tear itself apart in flight.
Almost all snomobiles are belt driven to the cementrifical clutch.That will soak up a lot right there.The reason for the internal gear drive is belts don't hold upwell at 10,500 +rpms.Some race sleds hit 12,000 rpms and use after market internal drive reduction gears.Hell they even use after market blocks.The thing I am trying to do is get this reliable engine to be cost effective for home builders.
 
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