550 engine for ultralight plane-is a 650 head on 550 case reliable and tough?

[trescojones]

My GS 550's frame was hacked by a previous owner. Because its such a beautifully made and over engineered motor, Im thinking of making it the powerplant for a 2 seat ultralight plane(the two strokes often used arent that great and are often very overpriced).
It would have a performance exhaust and be converted to fuel injection, with induction and exhaust pipe lengths the same-always in phase, and a speed reduction gear. No effort would be spared making it a happy engine that can deal with the work,total rebuild from the crankshaft up, new rods,valves, seats reground etc etc.
Aviation runs engines reasonably hard, constantly for long periods and any strength and redundancy in doing this is a good thing.

I have read of people putting 650 heads on 550 cases. While the extra horsepower would be useful, I dont want to ruin a successful, smooth running formula.
I have concerns about its durability and reliability. If it fails/blows a seal or busts valves because of a bad match etc etc in the air its not a good thing,you cant just pull over.

Does anybody have any opinions or experience with this mod, thanks

[tkent02]

The 550 needs to spin at really high rpm to make any power. The 650 slightly less so. Don't think either one would be a good choice for an airplane.

[JEEPRUSTY]

awfully heavy for an airplane at 150-200 pounds.
My engine make good power at 6-to redline how do you adapt this to an aircraft with a reduction gear? Do you just hook up the rive chain to the propeller via the drive line of the engine?

[blowerbike]

plus i think this engine is to heavy..you do not need a gear box.
maybe a polaris..something light without a tranny.
hard to beat the power to weight ratio of a 2 stroke.

[postman_pat]

My GS 550's frame was hacked by a previous owner. Because its such a beautifully made and over engineered motor, Im thinking of making it the powerplant for a 2 seat ultralight plane(the two strokes often used arent that great and are often very overpriced).
It would have a performance exhaust and be converted to fuel injection, with induction and exhaust pipe lengths the same-always in phase, and a speed reduction gear. No effort would be spared making it a happy engine that can deal with the work,total rebuild from the crankshaft up, new rods,valves, seats reground etc etc.
Aviation runs engines reasonably hard, constantly for long periods and any strength and redundancy in doing this is a good thing.

I have read of people putting 650 heads on 550 cases. While the extra horsepower would be useful, I dont want to ruin a successful, smooth running formula.
I have concerns about its durability and reliability. If it fails/blows a seal or busts valves because of a bad match etc etc in the air its not a good thing,you cant just pull over.

Does anybody have any opinions or experience with this mod, thanks

Interesting idea. Will you be making a new crankcase with the reduction gear designed in, or using the existing crankcases?

My only concern with using an inline 4 motorcycle engine in an ultra-light is, will you be able to ensure cooling air flow to all cylinders especially the rear ones. Assuming of course, that you're mounting it longitudinally...i.e the axis of the airframe and crankshaft aligned.

As for durability, I don't see why there should be any problems.

Edit: Have you looked into Hummel engines?

[trescojones]

thanks for replying all. It would have to use a gearbox like the Rotax C which the stock engines already use as they also spin too fast , these weigh 15lb.or thereabouts . 100% aero engines that dont need reduction seem to start at 80hp and just a bit heavy for this. They used to be made but seem not to be now. People have even cut VW engines in half to get the same sort of slow big volume beamer 2 cyl 50hp type thing.
From a vendor "The C gear box is available in ratio's 2.62-1, 3-1, 3.47-1, 4-1 and is generally used with larger diameter propellers or heavier mass weight propellers.
A clutch is available for the C drive which makes the engine easier to start, and is recommended for float equipped aircraft.".
These bolt to the end of the crankshaft, I would probably wanna have another one built up anyway for engine renewal and could ask that it have the fitting, and move the timing or alternator to the side.

I did think about adapting the tranny, but I suspect the case isnt meant to have too much sideward force, more back and forth between the wheel and crankshaft. Perhaps could be done through the clutch housing with a longer custom shaft to clear the tranny housing and chain drive on the end. I hadnt considered having a case made thus far.
I think without the tranny its no heavier than a rotax 503 or Hirth 50hp, (the GS gearbox seems heavier than the engine)Hummel which are the originals engines used for the design which are also 50hp, also weigh 83 pounds without carbs, gearbox exhaust etc,110 with these things. these engines are rougher to operate, can have sudden stopping issues,and sell for 5k new. Once power starts getting up there 4 stroke and 4 cyl can catch up.
Im interested in (a tandem airbike, http://www.jordanlakeaero.com/duo.html a larger one, more like a really stripped piper cub than a powered hang glider,400lb dry and empty) I asked the manufacturer what they thought, they were convinced it would do a good job, just would be more work.
I think the original 550 engine is more than reliable enough and was just thinking a 650 head might be pushing it too far. The airflow would be helped by a cowling/pipes with vanes that forces air around it, it is longitudinal. At least the speeds are consistently high and the airflow is there to be used. I have also thought of a radiative exhaust to help suck some more heat out.

[postman_pat]

I hadnt considered having a case made thus far.

I think you might have to to make the idea work. The crankcases are designed to transmit forces laterally, not longitudinally (along the axis of the crankshaft, that is) as you've noted.

A modern multi-axis CNC milling machine would be able to do a crankcase
in a jiffy. It's the preliminary design work that costs the money!

I think without the tranny its no heavier than a rotax 503 or Hirth 50hp, (the GS gearbox seems heavier than the engine)Hummel which are the originals engines used for the design which are also 50hp, also weigh 83 pounds without carbs, gearbox exhaust etc,110 with these things. these engines are rougher to operate, can have sudden stopping issues,and sell for 5k new. Once power starts getting up there 4 stroke and 4 cyl can catch up.

Using the original block, cylinder heads, crankshaft, etc. mated to a custom made crankcase with reduction gear - I think you'd have a very lightweight motor. I wish you all the best in your endeavours!

[trescojones]

thanks for your encouragement postman pat, gonna be exciting and an excuse to pull out all the stops with the best possible tech. I thought it through and realised as long as its cradled properly it wont see that much longitudinal force if an external gearbox like the rotax does the prop torque handling for it, be just like in the bike frame. I wanna do coil per cylinder and am thinking of using the clutch drive gear as a signal generator as it appears 2:1 reduction from the shaft and would be ideal. A backup magneto could be stuffed in there too.