Do ultralight engines need a thrust bearing?
Most gas engine applications only have a radial load ( perpendicular to the shaft).
Aircraft, not only have a radial load but also an axial prop thrust load pushing/pulling the shaft out/into the engine depending on whether the prop is a tractor or pusher prop, which usually requires a different kind of bearing able to take a thrust load.
So...do ultralights need a thrust bearing?
I assume the bearing of the output shaft of a reduction drive would have to be a thrust bearing.
However, we see 1/2 VW engines being used in direct drive applications, and I don't think they change the final bearing into a thrust bearing.
The reason I'm asking is, that I'm thinking of using a $400 15hp 4 stroke industrial engine for an ultralight application, just as we see in Rutan's quickie(?), ultralights using the vanguard brigs and stratton engines, and M Columbine's new design ( designer of the Cri Cri). Yes they are heavy, but they are cheap, 4 stroke, a TBO of 2,000 hrs, and are rated for continuous duty.
I plan to run at 75% power, which is about 2,500 rpm so I really don't need a reduction drive.
If I need a thrust bearing, I could have a reduction drive with something with a 1.1 reduction. I could also have just a support thrust bearing bolted directly to the engine.
If I don't need a thrust bearing, then I would be off to the races.
I don't think the Lazair had a thrust bearing or a reduction drive when they used the non rotax engines.
So... do GA airplane engines need a thrust bearing, in the 15 to 30 hp range?