Anything new on Yamaha conversions?

[raven-rotor]

Gyro Jockey Gerg

Sorry that you apparently weren't able to grasp my cautionary notes on attempting to adapt a CVT to a prop. Please keep others well away from the sides of your craft as you engage full throttle cause if the CVT does upshift on you, as I expect it will, it will sling a prop blade or two in just a moment without any noticeable shift in engine RPM! That the whole problem in a nutshell with a CVT and has nothing to do with why it works just fine on a snowmobile.

Your other ideas of dampening and running a torsionally flexible shaft up over the top of the engine are things that have been explored extensively by others with mixed results- most of them not at all positive. As I said in my first post, take the time to consult with someone who already has the expertise to steer you in the right direction or you are just wasting your time or worse yet endangering yourself or others. There is also a great article on torsional resonance by Daniel Hessanaur (sp) a torsional engineer who consulted with Bede on the BD-5 which was another drive shaft to prop idea that could never be made to work and put Bede out of business. I consulted with him when we first developed the Geo/Suzuki conversions over 15 years ago.

I was excited too when I first thought of a CVT running a prop years ago- until I did the research. We recycle and convert auto engines for aircraft on a daily basis here at my company, so I'm very into reusing what is available, but I'm not into compromising safety. I have also explored the possibility of running the drive over the top of the engine, but even with 15 years of proven experience in actually dampening torsional resonance. which rubber and springs do not do BTW- they just make it worse, I would not encourage a drive shaft in between a prop and an engine even though we use one to propel cars and trucks all the time.

The info is out there. Take a little more time to do the research.

Fly Safe!

Jeron Smith
Raven ReDrives Inc.

 

[NoWingsAttached]

Jerod, really?

1. The prop. You say the prop will run past its rev limit. Please address the ability to rev limit any drive design with blade pitch, and then explain how this is different with a CVT. I don't grasp the notion that just because you put a CVT between the motor and prop that this magically allows an otherwise pitch-limited system to suddenly spin out of control at ratios that are changing to REDUCE power at the prop at the very same instant the prop exceeds it drag limits-to-power input parameters to exceed its set maximum RPM. Any prop can spin crazy fast if its flat, with very little power from the engine.

2. Torsional resonance. Thanks for your background history. My turn. I've ignored gloom and doom in the past and went on to beat a factory Porsche Le Mans team at Road Atlanta with my home-built 930. I have a BS with 4 science majors from Univ of Mich. The average GPA of an accepted student is 3.85. I had a 4.0 GPA at U of M in Physics lecture and labs. I do not feel the need to immerse myself in torsional resonance articles ad nauseum to relearn what I already know about physics, and if i should forget an equation I always have my college physics book on my shelf to refresh my failing grey matter.

This took 5 seconds to search Wikipedia. "A harmonic balancer (also called crank pulley damper, crankshaft damper, torsional damper, or vibration damper) is a device connected to the crankshaft of an engine to reduce torsional vibration and serves as a pulley for drive belts.[1][2]

Every time the cylinders fire, torque is imparted to the crankshaft. The crankshaft deflects under this torque, which sets up vibrations when the torque is released. At certain engine speeds the torques imparted by the cylinders are in synch with the vibrations in the crankshaft, which results in a phenomenon called resonance. This resonance causes stress beyond what the crankshaft can withstand, resulting in crankshaft failure.

To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft. The damper is composed of two elements: a mass and an energy dissipating element. The mass resists the acceleration of the vibration and the energy dissipating (rubber/clutch/fluid) element absorbs the vibrations."

Read the passage above once again. "The mass resists the acceleration of the vibration and the energy dissipating (rubber/clutch/fluid) element absorbs the vibrations."

Rubber. That's right, r-u-b-b-e-r. What did you say? "...but even with 15 years of proven experience in actually dampening torsional resonance. which rubber and springs do not do BTW- they just make it worse..."

OK, so you have 15 years of experience but you don't seem to understand how a torsional resonance damper works, or what makes torsional resonance worse.

Compound wave action makes torsional resonance worse, not springs and rubber. You can send an infinite series of waves down a shaft, and they will NEVER get worse, so long as you kill them - dampen them - at one end of their journey so they dont' turn around and run into the oncoming waves and create compound waves. Of course, conversely those colliding waves can cancel as well, and die right there, but..never mind.

The 10 pound flywheel hanging off the end of the prop driveshaft will suffice to dampen prop resonance. The 10 pound flywheel hanging off the motor will dampen engine resonance. The torsion tube absorbs fluctuations between the prop and the pulleys. The two are isolated before they ever meet via the belt and CLUTCH, another component specifically referred to in this article as a torsional resonance dampener.

I would never redline my motor with a crowd of people standing next to my prop. I am nothing but primarily concerned for the safety of those standing around my spinning prop and rotor.

The driveshaft design killed the BD5 company? Here is aquote from a BD5 article. I can't seem to find anything connecting the driveshaft use to the failure of the company.

"The BD-5 airplanes as originally designed have a well documented, undesirable sharp stall characteristic that has caused numerous accidents, many of them fatal."

What exactly were the problems with the BD5 design?

Please post some photos of your gyros or FWs, I'd love to see your work on the flightline, you're a very interesting guy. How many hours PIC do you have, your profile is empty. Are you the guy with the 5,000 hp snowmobile that has a ten foot long track that folds in the middle to allow mile long "wheelies"?

 

[raven-rotor]

Gyro Jockey Gerg

Looks like I hit a nerve. Sorry about that. My intention is only to encourage you to do the homework BEFORE you spend a lot of time on your project. The track record of piston engine conversions attached to a prop is littered with those who thought that torsional resonance could be solved by 'common sense' solutions. Take the time to look into what Continental went through to certify their gear drive engine back in the day and what's really involved- its not directly related at all to the "torsional dampener" found on the end of many automotive crankshafts that you refer to.

Thanks for the update on your safety concerns. Keep us appraised on your progress. I'm also very stubborn or I would have given up long before solving the resonance issue on the Geo 3 cylinder years ago with eight different groups of people all frantically trying to make it work. We shared info continuously throughout the process and most things that were tried simply didn't work. I always refer people to my 20K pile of metal of the things that didn't work. The value of these forums is an opportunity to keep from having to 'reinvent the wheel' as they say.

One of the statistics that I would like to see change for us 'gyro junkies' is the poor treatment that the gyro community seems to receive at times from the FAA. My own take is that they would like to see more emphasis on safety, time honored testing methods, and a bit more conservative approach to powerplant and rotorcraft design. Unfortunately, the ongoing consideration of converting 10,000 RPM sled engines without a peep about the significant derating required for their use in a reliable aircraft engine conversion, probably doesn't move the gyro community any closer to a more general acceptance and support by the flying community as a whole, let alone the FAA. Ah, but thats a whole nuther topic.

Fly Safe!

Jeron Smith
Raven ReDrives Inc.

 

[NoWingsAttached]

As for famous SUCCESSFUL driveshaft designs, one can start by Googling P39 Aircobra. They showcased these on the Military CHannel, and they are pretty cool. The US sold them to the Russians to augment their air force in WWII. The Russians absolutely loved them, they were great ground attack fighters with a big old 37 cal cannon in the nose cone. The driveshaft allowed room for the big gun and ammo. THey lacked a supercharger or turbo, and were therefore not powerful enough for what the US flyers needed.

To quote wiki, "Although Bell's limited fighter design work had previously resulted in the unusual Bell YFM-1 Airacuda, the Model 12[9] proposal adopted an equally original configuration with an Allison V-12 engine mounted in the middle of the fuselage, just behind the cockpit, and a propeller driven by a shaft passing beneath the pilot's feet under the cockpit floor.[9]

The main purpose of this configuration was to free up space for the heavy main armament, a 37 mm (1.46 in) Oldsmobile T9 cannon firing through the center of the propeller hub for optimum accuracy and stability when firing.[N 3] This happened because H.M. Poyer, designer for project leader Robert Woods, was impressed by the power of this weapon and he pressed for its incorporation though the original concept had been a 20–25 mm (.79–98 in) cannon mounted conventionally in the nose. This was unusual, because fighters had previously been designed around an engine, not a weapon system. Although devastating when it worked, the T9 had very limited ammunition, a low rate of fire, and was prone to jamming.[10]"

The Russians did not seem to experience the same issues with the gun jamming, perhaps they corrected the problem by different maintenance or something else.

But no where are there any reports of problems with the drive train.

The Military Channel documentary on this plane, which I've seen a couple of times a while back is actually one of the big inspirations for what I am attempting to do now.

Your point about research and safety is spot-on. That is definitely the two-pronged, primary approach being taken here as I seek help with design, principles and research. Hope I didn't come across too roughly, I really do welcome your input! My boss spent years on me, finally getting me to tone down my lambasting emails in 2010. Perhaps i allow myself too much emotional latitude when i am on this forum still, and don't self edit as much as I should. I am continuing to work on that. I'm really not a bad guy in person. A couple of people from RF here actually changed their minds about me and wound up liking me after meeting face-to-face. Of course it doesn't help that I'm antagonistic, sarcastic, and often have disagreeable opinions in most conservative circles. I think there is a ban on all my RF postings that include any political reference whatsoever. LOL! That's OK, I need censoring now and then, I admit it.

 

[NoWingsAttached]

A Little Wing builder and I are discussing belt drives. Jon C. has said an idler pulley is best way to help absorb prop pulse while tensioning the belt. The LW builder has room for this on his Yamaha 3 cyl design.

Comments please. A suitable belt, pulleys, and prop hub have been identified, now we need to come up with the best tensioning system.

 

[scottessex]

Greg, For a belt tensioner I would try to stick with something "off the shelf"
That way you are not having to re invent the wheel so to speak..Are you going to use a spring loaded tensioner, or a manually adjusted one?

 

[Vance]

Hello Gerg,

Many toothed belts are not designed to be bent backward.

I worked with a Gates engineer trying to better manage the belt on an Indian motorcycle and he was very specific about a tensioner needing to be on the inside of the belt.

He also wanted the belt very tight.

Thank you, Vance

 

[NoWingsAttached]

Wow, that makes perfect sense, and yet it never entered my mind! Thanks you, Vance

 

[NoWingsAttached]

Greg, For a belt tensioner I would try to stick with something "off the shelf"
That way you are not having to re invent the wheel so to speak..Are you going to use a spring loaded tensioner, or a manually adjusted one?

The only thing we could use off the shelf are the belt and pulleys. A same-size wheel as the powered sheave would work, mounted on a sprung idler arm.

Pretty sure i saw an idler used on a gyro that showed up at Mentone in '07. Anyone know who that might belong to?

 

[Lee Scatt]

A Little Wing builder and I are discussing belt drives. Jon C. has said an idler pulley is best way to help absorb prop pulse while tensioning the belt. The LW builder has room for this on his Yamaha 3 cyl design.

Comments please. A suitable belt, pulleys, and prop hub have been identified, now we need to come up with the best tensioning system.

I still don't think you understand. There are no "prop pulses". There are engine pulses that the prop is attempting to damp through the redrive.
I think what you might have seen is a pre-rotator drive, not a tensioner.
My gut feeling is a tensioner would self-destruct within hours.

 

[groundhog]

why not a belt tensioner off a chevy pickup ?

 

[NoWingsAttached]

Well, I have been misinformed before, and it is sure to happen again Lee. Someone told me there are pulsations that originate with the prop. Is this not true? I always thought about it the way you describe until I was told this other thing is happening.

 

[WHY]

Greg

The "pulses " in the prop are more like a "echo" or a recoil, that originates with the power pulse in the engine.

Tony

 

[Vance]

Hello Gerg,

I do not have you engineering background so I only speak from my personal observations.

In my opinion with a pusher there are pulses from the propeller as it moves from clean air to turbulent air.

In my opinion with a tractor the air can back up against things and cause a similar pulsing.

I went to a Rotax seminar and they are very specific about a maximum moment of inertia for the propeller with one of their re-drives. They also didn’t want low RPMs because the pounding was worse.

I feel that an engine accelerates each time it fires and is slowing down the rest of the time. The propeller does not want to follow if there is a re-drive between the engine and propeller. I feel the trick is to keep it from resonating.

When Harley Davidson went to a belt primary drive and a belt final drive they had a rubber insert in the front primary pulley to cushion the pulses. They eventually went back to a chain primary with a cam and spring arrangement to cushion the pulsing. It is also to keep the starter from blowing the starter off the primary when the engine kicks back. A tire on the road makes the entire mass of the motorcycle a flywheel so there is often a quarrel between the engine and the rear wheel. Different makes find different ways to lower the frequency of the pulses but it is a challenge that they all address with some sort of soft coupling.

I mention this as an example showing that a toothed belt may not have enough give in it to soften the pulses.

A re-drive appears simple and some poorly designed ones give reasonable service.

There are belts that can have a tensioner on the outside but Gates isn’t one of them. My limited experience with the fuel dragsters that use a Gates belt with an external tensioner on their blower drive suggests that they have a lot of trouble and replace them often.

My personal preference is a multiple V belts that can slip to manage the disharmony. Some Helicopters have done well with this and use it as a clutch.

Micro V belts are interesting too and I have seen one re-drive for a Volkswagen that uses two of them.

I used two spring loaded tensioners on a very long rear chain on one of my Bonneville bikes and it markedly reduced problems with the entire drive train. On the Dynamometer we could watch the tensioners with a strobe light and see them mover with each firing. The bike only runs about 50 miles per year so it may not be comparable to something that needs to operate for a longer time. We replace everything each season because of corrosion. It has been setting records for more than 25 years without drive train problems other than the clutch.

I look forward to seeing what you come up with.

Thank you, Vance

 

[NoWingsAttached]

Vance - do you agree or disagree with the idea of a tensioner on the cog belt, mounted inside? It sounds like you are leaning toward agree, but I can't tell if you're willing to commit, lol.

 

[Vance]

Sorry to be unclear Gerg,

I feel that doing it without an idler is best.

I feel if you do use an idler it is best to have teeth.

At the risk of seeming pedantic I will try to cover what I feel are the basics.

This is how I consider anything so please don’t imagine I am talking down to you.

An inside tensioner reduces the toot contact on one or both of the pulleys.

With large pulleys it is not very important.

The strain on the belt goes up as the drive pulley gets smaller.

To get the ratio you want in the space you want I feel that the drive pulley may get small.

It is like a short handle on a wrench and increases the strain on the belt to transmit the same torque.

At some diameter of sprocket the belt speed may get to high.

If a belt is not kept tight the teeth climb under load and you have less tooth engaged in the pulley.

With aluminum pulleys they grow as they get hot significantly.

If they are held together with an aluminum plate the heat of the motor will spread the shafts increasing the tension.

If the sprockets get too hot it tends to delaminate the belt.

The belt should grow very little over time so you can set a tension and it probably wouldn’t change tension much over its lifetime.

Systems that are not well designed are still giving acceptable performance.

Good luck on your project, I look forward to pictures and the testing.

Thank you, Vance

 

[Arnie Madsen]

Rotorway Helicopter Forum has 12 pages and about 174 posts on Cog belt setup and tension . They use a cog belt to drive the main rotor shaft. One broke in flight thus the discussion. Lots of good information .

Along with what Vance said ... "Many toothed belts are not designed to be bent backward" ... the Gates factory rep said the same. Even if a new belt was folded over by hand , it would have to be scrapped. It stresses the Kevlar cords. Post #27 is the belt mfg's reply.

I am pretty sure this thread is open to the public. Lots of good discussion on belts and how best to tension them
http://www.rotorwayownersgroup.com/forums_c/showthread.php?t=5710
Hope the link works.

 

[NoWingsAttached]

Yeah, I signed up, you need to have a member ID. Guess what? i am NoWingsAttached there, too, lol. I'll read into it a little later. Thanks!

 

[NoWingsAttached]

Vance
Same as what Jon C was saying, and now I understand better about why the belt gets tighter as things heat up.

As to taking belt length out of contact with teeth on the drive pulley, my thoughts exactly. The idea is to keep the belt in contact with as many cog teeth as possible. If a belt is tensioned properly, there is what, 1/2" - 1" of play? How much belt deflection would you need to create, beyond that, to make the idler effective? Imagine loosening the adjustments in any typical belt setup, all the way. Now stick and idler in there, that should be plenty of deflection, without reducing contact and tooth engagement significantly. The setup we are discussing is 80 teeth and 25, 8mm pitch. So 6 inch and 2.4 inch dia cogs. The take up angle is so steep there can't be more than a negligible loss of contact, and the farther apart the cogs are, the better the angle.

I probably need to learn more about what makes a belt climb out of the cog teeth. As for that, I am thinking an idler should help prevent it as it dampens pulses and belt movement, and maintains a consistent, easily-adjusted tension. The tension on the takeup side of a belt drive is negligible under load, anyway. Heck, if you had an endless belt, it would still work with zero tension from a non-existant return side. All you are doing with an idler/ tensioner is taking out the "slap", keeping the belt pulses in check.

More, please. you've given me 2 new ideas.

I have some reservations about slapping a straight-up cog belt on a motor I expect to turn 8700 RPMS at the shaft, at 150 hp, on a ~600lb gyro, the same as someone might do with a Soob turning 5700 rpms - straight up with no damping device. May be a good way to practice forced landings.

 

[Vance]

Sorry for being obtuse.

Sorry for being obtuse.

I am afraid I wasn’t being clear again Gerg.

I feel a better solution would be to make the propeller side adjustable.

It takes very little adjustment so it could be done with shims or some mechanical form of adjustment. I like shims best.

You are only dealing with 90 foot pounds of torque at peak horsepower probably less than 100 at peak torque. This is a lot less than a Subaru. You also have more firing pulses so the pulses are smaller for two reasons.

I feel your concern about pulses may be misplaced.

To get an idler to dampen pulses I feel you need one on each side of the belt.

The small pulley sounds a little small to me. A 2.4 inch pulley has an effective radius of just over an inch so multiply the 90 foot pounds of torque by 11andyou get 990 pounds pulling on the belt. I feel you would only be pulling on about 4 teeth just because of the way a cog belt works.

If I was to copy a Subaru belt drive I would start with the same size pulley on the crank as the Subaru and make the pulley on the prop as big as it needs to be. If you do that yours will probably work as well as a Subaru belt drive.

The finer toothed belt can handle more belt speed but less torque.

An engineering catalog for Gates will tell you how much surface speed you can have. That is an important thing to watch because the belt will climb the teeth by getting air under it. It will also tell you how much torque and horsepower it can handle.

The width is important. Wider handles more torque.

I would have less than a quarter inch of play in the belt on a run like that. You need to load the taught side and measure the slack side. You only need about ten pounds of force to check belt tightness.

Gates has an excellent engineering department, unfortunately they recommend against using one of their belts on a Propeller speed reduction unit so they won’t be much help. I would still contact them and ask for their assistance. The rpms, ratio and horsepower is all they need to know. It could just as well be driving a dune buggy.

I feel an outboard bearing on the crank is important because of how the belt tightens up with heat. Otherwise you are putting bending loads on the crank.

A substantial bearing set on the prop is important. There should be at least two and widely spaced.

I have had no belt experience on aircraft propeller shaft reductions units. I feel it would be good to get in touch with someone who has. Everything I know comes from motorcycle rear drives and blower drives.

I would spend several hours testing it on the ground before I flew it if it were my program.

The best scheme may to get a gear drive. It is a little heavier and more expensive but if it is well designed it may be a less troublesome approach. If I were doing it I would use one of Neal’s. You might have to cut back a little on the rpm to keep from exploding his donut.

This is opinion and conjecture from a person with no engineering education. Please take it as such.

Thank you, Vance