A friend of mine has a Kolb Firestar II, and he recently had an engine-out with his Rotax 503. He was lucky and skilled enough to land the plane with no damage at all, but the experience turned him off to two-stroke engines.
So, he cast around and found someone fabricating all the stuff needed to put a Generac on a Kolb. A Generac is typically used as the motor part of a motor-driven generator. It’s a large bore 2-cylinder, 4-stroke engine. When used to generate electricity, they will run at maximum speed for 24 hours a day. To say they are reliable would be an understatement.
So, my friend borrowed my airplane trailer, and hauled the Firestar up to Rolla, Missouri for a week, and watched while the retrofit took place. The result is a 2-cylinder, 4-stroke powerplant, that’s very compact, and makes about 90% of the power that a 503 generates. He also gets a much more efficient 2 gallons-per-hour! (The 503 usually consumes 5 gph.)
You can see how compact the Generac engine is
He dropped in on Sunday morning, so I got to see it, hear it, and take pictures. The image above shows how compact it is. The exhaust is unique (in my experience), too, in that it’s just a pipe connecting both exhaust ports, with holes drilled into the middle-top. The whole package sounds kind of like a Harley as he’s taxiing, with a very low rumble. No one will ever mistake it for a Rotax 2-stroke!
His climb is fairly poor — for a Kolb, that is; it’s still very decent, though — and he lost a couple of mph at cruise, but he’s pretty happy with it. The package doesn’t weigh any more than the Rotax 503 and — this is really odd — it bolts directly to the motor mount, with no Lord (rubber) mounts at all. Metal to metal. But I sat in it and fired it up, and it was remarkably smooth… much smoother than the 503 with Lord mounts. Maybe even smoother than my 912S. But, more than anything else, he got reliability!!!
The cool thing about experimental aviation is, you can go off and do things like this. There are few limits. It’s also relatively inexpensive. He was able to buy the powerplant and get it custom installed for less money than a lot of Cessna owners spend on their annual inspection!
He’s a happy camper on many levels: a more reliable powerplant, at least twice as efficient with gas, less money than a replacement 503, he bought an American engine, and it was all done in a week. Ask someone with a Cessna 185 about putting a different, more efficient engine in his plane, and how much it would cost and how long it would take, and you’ll get a radically different, and sadder story.