Do ultralight engines need a thrust bearing? 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?

If so...

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?
Any aircraft engine that spins a prop to generate thrust will necessarily contain a thrust bearing to prevent the propeller thrust force from pulling the crankshaft out of the block.  But since a bearing designed for mostly radial loads will also be capable of resisting a certain amount of thrust load, some automobile engines converted for aircraft use can get by without having a thrust bearing added to their crankshaft supports.