I am building a tractor, side by side, engine behind pilot gyroplane.

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wsimpso1

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=or DIFFERENTIAL gear (circa 3: -/+ 1) , natural aerodempfer, +30 % thrust force.
Please explain how this avoids torsional resonance where a natural frequency is near or coincides with an engine frequency.
 

EzyBuildWing

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Might be of interest....two Tractor Gyros.....anyone got any info on either?
Lower gyro "CutiePie" looks real simple/inexpensive to build out of marine-ply, and a VW 1600.

Tractor gyroMay 2020.jpg

Cutie Pie gyro May 2020.jpg
 

henryk

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how this avoids torsional resonance
=probleme with english...

=engine shaft (engine momentum) drive both propellers via sattelite beavers,whitch axe is mounted in gear case...
first propeller is mounted to the case, second to the output beaver.

the propellers are louded togather via air "transmission"=no resonances...
 

wsimpso1

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=probleme with english...

=engine shaft (engine momentum) drive both propellers via sattelite beavers,whitch axe is mounted in gear case...
first propeller is mounted to the case, second to the output beaver.

the propellers are louded togather via air "transmission"=no resonances...
Your English is WAY better than my Polish, so let's work with what we have here.

As a 23 year automatic tranny guy, and the lead tranny torsional vibe guy in two different car maker's, I think that I understand the first part. Planetary gearsets have three legs - a ring gear, a sun gear, and a carrier with planet gears that engage both the sun and ring gears. It can be used as a differential by driving one leg from the engine and connecting each of the other two legs to props. The speeds of the two props will float a bit to where loads equilibrate. If you added a bunch of load to one, slowing it down, you will speed up the other one, as was shown on the video. So the two props tend to equilibrate on load while running in opposite directions.

So far, so good. I asked how how this handles torsional resonance? We still have the crankshaft accelerating and decelerating with each firing pulse and with each piston being thrust back and forth in their bores. This crankshaft torsional vibration is still fed along the torque paths to the props. The engine and the props all have some inertia, and the shafts and gears between the props and the engine still have spring rates, so there will still be some natural frequency of each prop to crankshaft system. If the firing frequency or the 2x firing frequency made by the engine coincides with the system for either prop, it will be in resonance and will amplify... How does this system prevent this resonance?

Billski
 

henryk

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it will be in resonance and will amplify...
=resonans effect is depressed by dampfing phactor (the "air dampfer") and amplification of amplitude can be small...

-in practice system works good withaut vibration dampfers.

BTW=we have GENIAL centrifugal clutch/rubber dampfers constructed by Bogdan (100 HP, 1 kg !!!)
 

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wsimpso1

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=resonans effect is depressed by dampfing phactor (the "air dampfer") and amplification of amplitude can be small...

-in practice system works good withaut vibration dampfers.

BTW=we have GENIAL centrifugal clutch/rubber dampfers constructed by Bogdan (100 HP, 1 kg !!!)
You are trying to tell us that air friction absorbs enough energy to fight resonance? Normally aspirated gasoline engines make about 2500 rad/s/s, at 2700 rpm and 2 firing pulses per rev, the firing pulse swing is about 0.45 degrees one way, or about 0.9 degrees full swing. Air friction on this oscillation is really tiny, and will not remove much vibration.

If the system shown behaves well, it does so for other reasons, like tuning the mass on the flywheel and putting in a soft element, which might be partially shown in that picture:
  • Bottom of the picture is a flywheel with a bunch of extra weight bolted to it - looks like a tunable flywheel inertia is part of the equipment;
  • The thing upper right contains a piece of a spring damper center for a manual trans clutch - looks like a tunable torsion spring, perhaps a rising rate elastomeric spring - is also part of the equipment;
  • The really massive thing upper left, well, it would have to be explained a lot further for me to believe anything about it. That thing is really massive, are you telling us that it is flying in that little gyro? Are you telling us that it is an air damper device? Sorry, the tiny swing of firing order won't do much with something like this either...
Seems to me that resonance is likely tuned to below idle level firing frequency with inertia and spring rate combination - a classic "soft" system - which is a really good thing. Making me believe anything else will take a lot more explaining.

Billski
 
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henryk

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=6 rubber "inertia" element mounted on standart SUZUKI SWIFT flywheel +alu disc...=NO problems with small,light gearbox !


+500 HP 1.6 l rotational engine ,40 kg... (left)
 
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GeeZee

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I thought this guys experiences with torsional vib were interesting. He worked for Bede for a while and came up with the “broomstick” drive shaft that seemed to work.
 

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Sabine

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thank-you everyone for your input- I promise i will be listening very carefully to all of your advise and will let you know how I get on. Regards Sabine
 

Sabine

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I thought this guys experiences with torsional vib were interesting. He worked for Bede for a while and came up with the “broomstick” drive shaft that seemed to work.
Thanks I have read this- brilliant.
 

Deuelly

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There is no comparison of the TV induced by a camshaft compared to a propellor. As I said all of the successful PSRUs, either toothed belt or gear use an uneven ratio, Rotax is the best example.
"All" is a pretty bold statement considering one of the most successful aircraft reduction drives in history has a 2:1 ratio. Thousands have flown and are still flying.

Brandon
 

wsimpso1

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True that, although many engine designs starting with even reduction ratios ended up with gearing using different prime numbers of teeth on the mating gears of their reduction units. Gear, bearing. and vibration issues are less when you avoid even number ratios. This was known way before the big piston engines came along, but ended up being proven again and again during development of the big engines.

Billski
 

rotax618

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There was a Honda aero conversion that used a toothed re-drive belt to also drive the camshaft, it was a total failure , the teeth stripped off the belt in a very short time because at 2:1 ratio the same teeth were subjected to the power pulses on every revolution. You might get an even ratio to work by beefing it up and extra dampening, but it is bad engineering.
 

jeff naul

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Hello, I'm an outboard mechanic and would like to share some thoughts. First Im not partial to any brand engine but have been racing mercury V6's since high school (1994). In an early post you mention using the mercury 125 h.p. I understand why because its a 4 cylinder inline which would lay down nicely in the fuselage. The exhaust is on the side and wouldnt interfere with the gearbox. But there are much much better engines than that one. They have a problem with turning the sleeves when ran hot, and a very weak crankshaft/ bearing arrangement. Also they idle like crap so mercury had to shut off the top two cylinders with fuel to make it manageable. Works OK when everything is set up properly. It is also the weakest of engines in that class. I wouldnt ever feel safe flying behind it.
The yamaha V4 115 h.p. is a stud. Bulletproof ignition componets with huge upper crankshaft bearings. Ive seen these motors come in with 2 blown headgaskets, rusty cylinders and still running decent. Put new gaskets and scotchbrite the cylinders and they run like nothing ever happened. Years ago I watched a stock one dyno 138 h.p. at the propshaft tuning 6200 rpm. Yamaha had to add rev limiters to keep the h.p. down... you could raise the compression and easily have a engine making 140-150 h.p at 5500 rpm before any kind of gear reduction.
So if the mercury is still your best option i would atleast pull the sleeves and have the block fitted with new oversize sleeves and pinned to to stop them from turning. Use a SDS ignition and fuel system so you can limit the fuel to the top cylinders to have a ok idle...have the crankshaft crack inspected and cyro frozen after. But without some kind of VST tank I dont know how you could keep the stock oil injection with the fuel injection, because you will be returning now premixed fuel back to the main tank. The yamaha injects the oil into the intake which then mixes with atomized fuel from the carburator. So efi wouldnt change anything on a yamaha.
Now if you only need max 125 h.p. before gearbox losses the yamaha 90 h.p. 3 cylinder inline will make that with mainly compression mods. They make almost 100 h.p. at the propshaft in stock form. Then you will have the same simple oil injection setup and exhaust outlet on the side. Just some more ideas, jeff
 
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