Convert an outboard (boat) engine to an ultralight aircraft engine?

Question

I'm just kinda curious, is it possible to convert a small-horsepower (25-30) outboard marine engine so that it'll power an ultralight airplane, weighing no more than 250 lbs empty? I know that other types of engines are converted, but I've never heard of someone converting an outboard engine, and I don't know why because it seems like a rather good idea...horizontal shaft, compact size, all-weather operation, and lots are even electric start and come with the throttle control lever, which would work well if used for an airplane. So why don't I see people doing this all the time? Is there some impassable design flaw or other reason not to do this?

Just wondering :)

Answer 1

Outboard boat motors are cooled by the water that they are in. If one is run in air it will burn itself up, so I would not use one in an aircraft. Better that you convert a lawn mower engine.

Regards,

Dan

Answer 2

Cooling was my concern as well.  Outboards draw water directly from the lake to cool the engine.  It's a long way to the lake from an ultralight.  Snowmobile engines are (and have been) a better choice.

Answer 3

Cooling is one problem- an outboard motor for a boat is water cooled, not air cooled. The othe problem is the low horsepower range you cite.  25 to 30 hp isn't really enough for most applications for an ultralight.

Rotax makes a variety of engines that are air cooled and meet the need much better.

Some eltralight builders use a Rotax 447 engine, about 40 hp. Many of those decide to upgrade to a 65 HP for better performance.

See the specs on a Rotax 582. It's 65 hp.   There are also a variety of props already made for those engines.

If you are planning on flying, isn't it worth it to choose a purpose built engine?  LIfe is worth more than trying to save a few bucks...

Answer 4

It's been done with larger marine outboard engines for 'homebuilts'.

Do be aware that a liquid cooling system is a heavy burden to lay on an ultralight.