tffy wrote:
This is for a hypothetical ultralight design, so just looking for
suggestions here of where to look at... hopefully a 4-stroke, purchase
price doesn't matter much, certification status doesn't matter either.
Long time before overhaul matters A LOT... so, the longer the better.
Is there anything out there in the 80-hp range? How about a motorcycle
engine conversion - how long can those go before needing to be
overhauled?

Thanks!


If it's going to be a true ultralight (meets part 103), there probably
isn't a 4-stroke on the market that'll allow you make weight, much less
anything that puts out 80hp......

For true part 103 ultralights, the Rotax 447 is still the best motor
available. One of the neat secrets of 2-strokes is they fairly easily
allow you to install excessive power. The result here being a loafing
engine most of the time - the side effect of that being increased
reliability and longevity. This mostly due to the power/weight. A 447
with a good prop on a part 103 aircraft is more than plenty power and
will loaf along most of the flight.

Another neat thing about the 447 is that the crank assembly used is in
spittin' distance of the one in the 503 (the 50hp motor) in terms of
size and strength, yet the motor makes only about 40hp max. So the crank
assemblies in these things last for a long long time (600 hours or
more). Mag-end electric starts and big heavy 3-blade props reduce that
lifetime a lot, but if you stick to a good 2-blade woodie and the pull
start, a 447 will run for years and years.

If the plane is 400lbs or less, the Rotax 503 is probably the next best
bet for similar reasons.....

If you just have to have a 4-stroke, you're going to have to spend a
good deal more money and deal with a bit more weight. But there are some
good options he

- Jabiru 2200. A local has one of these on his Kolb and he's getting
really good results with it. Very reliable running motor.
- HKS 4-stroke. I have no experience with these.
- Rotax 912. Expeeeeeensiiiiive.... cost as much as my entire plane! But
a very good reliable motor.


LS
N646F