Why not more motorcycle engines?

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Georden

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A 1000cc sport bike engine weighs 150lbs dry and produces 170hp. Why not reduce rpms to bring it down to ~125hp and have a package that weighs under 200lbs?

A suzuki 1300cc weighs 20lbs more an gets another 20hp running at a lower rpm for an extra 20lbs. And people modify those to over 500hp, seem like 150hp and ~220 lbs would be doable.

Is it the rpm or packaging issues? Stock motors are used for racing, so they should be fairly durable. Maybe not 2000 hours durable, but they are also cheap to replace. the built in transmission could even be used as a psru.

What issue am I missing?

I know some smaller engines (eg BMW) have been used in lower power applications, but haven't seen the newer high power ones used.
 

Tony

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Springfield IL
A 1000cc sport bike engine weighs 150lbs dry and produces 170hp. Why not reduce rpms to bring it down to ~125hp and have a package that weighs under 200lbs?

A suzuki 1300cc weighs 20lbs more an gets another 20hp running at a lower rpm for an extra 20lbs. And people modify those to over 500hp, seem like 150hp and ~220 lbs would be doable.

Is it the rpm or packaging issues? Stock motors are used for racing, so they should be fairly durable. Maybe not 2000 hours durable, but they are also cheap to replace. the built in transmission could even be used as a psru.

What issue am I missing?

I know some smaller engines (eg BMW) have been used in lower power applications, but haven't seen the newer high power ones used.


This is a very good question. I am sure you are aware that years ago they used motorcycle engines like HD on small ultralight style airplanes. I am not sure why they stopped. If you do some research on the net you will find many motorcycle engines where used.
This is why I only look for info that is up-to-date. If I am reading something and it was posted in 2004 I take that info with a grain of salt, so to speak. I have had others tell me to look up info that was from this time period or older and I myself look for newer info.
There is a reason you do not see these engines and certain airplanes flying anymore. When I say airplanes I mean homebuilt ultralight style planes. I myself believe people got tired of hearing and reading about all the deaths from using this type of equipment.

I could be wrong but I have wondered why no one uses motorcycle engines or other engines that where used in years past. They stopped using them for a reason. I believe they just did not work correctly in an airplane.

I hope other's chime in here with more info on this subject. I have wondered the same thing, just never asked.


Tony
 

Head in the clouds

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The internal gearboxes aren't well suited to PSRUs and many of the engines don't have a halved crankcase (the engine oil lubes the gears usually) so you can't cut the gearcase away even if you empty the gears out. A couple of Yamahas in the offroad range do have separated oils/halved crankcases, and aircooled rather than liquid.

Then you have the problem of mounting the engine, the mounting points are not convenient generally and if you've cut the gearcase away you've probably cut them off.

And the crankshaft output end is not well suited bearing/shaft size-wise to taking power off there because it has been optimised for PTO at the gearbox output instead. It's do-able but not easy.

The overhead cam Harley engine is very good for it, as are a couple of models of BMWs, in the 100hp range, because the engines are fully separate from the gearboxes. There was an outfit (Harleyair??) converting the engines but the Harley factory closed him down by refusing to supply parts, I think it was worry about liability issues or similar.

Personally I think it would be good to cast crankcases and build crankshafts for 250cc and/or 500cc Yamaha barrels and pistons (the aircooled trials bike ones), could make great boxer twins or fours...
 

Georden

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Calgary, AB Canada
What is the issue using the built in gearbox?

An online magazine put a motorcycle engine into a miata (search miatabusa) and I believe they cut off the internal gearbox and welded up the hole. They kept the 2:1 or so reduction built into the crank output to bring the rpm down to one that would work with a car transmission. I don't know if they ever finished it though, so might not be a good source to reference.

Can see how the mounts would cause difficulty.

Thanks for the reply.
 

Head in the clouds

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What is the issue using the built in gearbox?

It's a while since I had a go at devising an engine conversion using the gearbox, but from memory there were a few problems -

I think the main one was that if you used the internal gears that might well get you down to the rpm you were after, using 2nd gear out of a 5 or 6 speed box but then you have an output coming from a shaft, of which the bearings or bearing mount output area (the case metal) just weren't solid enough to carry the airscrew with its thrust and gyroscopic loads. So you had the rpm right but stll had to have a remote bearing structure to sustain the airscrew loads, in which case it was easier to build the whole reduction externally.

Another issue was that the low speed gears aren't designed to be used constantly, their bearings to the lay shaft weren't good enough and the bearing surface area (width of the gear wheels) was small so the case hardening of the gears would heat up and suffer from physical overload causing surface fracturing quite soon if in constant use at the high hp loading that you would use in aero use.

There were other things I can't remember right now but those were enough to end the prospect.
 

litespeed

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The internal gearboxes aren't well suited to PSRUs and many of the engines don't have a halved crankcase (the engine oil lubes the gears usually) so you can't cut the gearcase away even if you empty the gears out. AThen you have the problem of mounting the engine, the mounting points are not convenient generally and if you've cut the gearcase away you've probably cu couple of Yamahas in the offroad range do have separated oils/halved crankcases, and aircooled rather than liquid.

Personally I think it would be good to cast crankcases and build crankshafts for 250cc and/or 500cc Yamaha barrels and pistons (the aircooled trials bike ones), could make great boxer twins or fours...


The only purpose built engine from bike parts I know of, is the JCV 360.


This is a flat twin made to use the water cooled cylinders and heads from a 180cc Aprilia scooter.
Light, small and efficient. But 32hp max is small for most applications.

If only they did a little 4 version or much bigger cc as a twin.

The Harley stuff just vibrates way to much in general from its narrow V and crank throws.
 

Head in the clouds

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The only purpose built engine from bike parts I know of, is the JCV 360.


This is a flat twin made to use the water cooled cylinders and heads from a 180cc Aprilia scooter.
Light, small and efficient. But 32hp max is small for most applications.

If only they did a little 4 version or much bigger cc as a twin.

The Harley stuff just vibrates way to much in general from its narrow V and crank throws.

I hadn't heard of it before but googled it and that JCV sounds interesting for the AirToy perhaps, any idea of price? 4 cyl would be nice! Verner do have that big twin but that vibrates heaps and breaks cranks (or used to anyway, they say they've fixed that with extra main journals now).

The newer overhead cam Harleys run very smooth but are heavy, both due to the countershaft. Many of the Harley riders around here remove the countershaft, then they run rough! I spoke to a bloke the other day about his - I said "geez that's a bit rough isn't it", he said "I guess you haven't seen my missus".
 

litespeed

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I have never seen a confirmed price and have not asked.

But I think they are around $5000.

I know some are fitted to paragliders in Oz and SD1's have them as well in Europe.

It is a lovely engine and would be a pefect thing for some light designs, smooth, small exhaust system, no smoke, no premix...........

Nice PRSU as well- and that is a big plus.

Turns a nice big prop, could be three blade if ground strike is a issue.

Girlfriend has the same Aprilia in her bike- a good little motor.
 

4trade

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Motorcycle engines (high power ones) have high piston speed at high hp area. You can build aircraft engine for those ones, but engine wear much faster than conventional aircraft engines. Piston speed add piston travel (miles/ hour),friction and G forces and that will reduce your TBO.

Average piston speed that exceed 15/m/sec (50/feet/sec) start to be unreliable for long time use. Here is piston sped calculator, run some rpm level/ stroke and you know that speed:

Piston Speed Calculator - Universal Entry


...and engines like Speedway bikes have close to 30/m /sec piston speed...those will last approx one hour running time at that speed because fatigue of piston and overall stress....
 

Head in the clouds

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Motorcycle engines (high power ones) have high piston speed at high hp area. You can build aircraft engine for those ones, but engine wear much faster than conventional aircraft engines. Piston speed add piston travel (miles/ hour),friction and G forces and that will reduce your TBO.

Average piston speed that exceed 15/m/sec (50/feet/sec) start to be unreliable for long time use. Here is piston sped calculator, run some rpm level/ stroke and you know that speed:

Piston Speed Calculator - Universal Entry


...and engines like Speedway bikes have close to 30/m /sec piston speed...those will last approx one hour running time at that speed because fatigue of piston and overall stress....

Very good point 4T. That's why I like the 4 stroke Yamaha dirt bike piston/cylinder option, I think they're long strokers and they seem to last well in the bikes even if driven hard.
 

Topaz

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What about jet ski or snowmobile engines? Anyone tried one of the newer 4 stroke models?

Basically the same problems. The problems of reliable reduction, then the need for thrust and gyroscopic-force bearings, have sunk most, if not all, of the modern attempts to do these kind of conversions. Older motorcycle engines didn't turn nearly as fast as their modern counterparts, so the older conversions (20's-40's) you see only had to deal with the bearings problem, and those older engines usually had a separate gearbox. It was a lot easier conversion than a modern, high-RPM, integral-gearbox motorcycle engine.

If you want to use jet-ski or snowmobile type engines, it's best just to get a Rotax. The aircraft models of these engines already have the necessary modifications made, professionally.
 

deskpilot

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Morphett Vale, South Australia. Just south of Adel
This Vija engine looks great! 100hp at half the price of the Rotax. Things are looking up.

Yes and no. It looks a bit out of balance to me but then, would suit the single pilot in a 2 seat plane.

there's an interesting configuration in the presentation as well.

IMG_2737.jpg

OOPs, sorry for double post.
 

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litespeed

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Interesting use of the UJM engine.

I wonder how well the clutches will take the strain of the prop pulse. Box seems nice and chunky.

I guess we should keep our eyes out for machines using it.

The old school bike motors are a tuff unit and much better than a higher revving water cooled unit.

This one looks like a Suzuki and the old ones of these are often abused in drags and survive- so has merit.
 
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