Lynn,

I know you are a very creative and talented guy. So I just want to plant a seed with you that might make the biggest difference ever with your Kitfox.

Think about the possibility of putting some sort of a prop reduction unit on that Jabiru so you can spin a longer, larger prop. I am absolutely convinced that if that were done to the Jabiru that it would truly be a kick-ass motor for a STOL type airplane like a Kitfox. Yeah, I know it would add weight, and it might require a bigger effort than it sounds. But I'm convinced it would produce so much more thrust that you wouldn't even notice the extra 10 or 20 lbs for a PSRU. And you'd be very happy with the extra effort to do it.

I say all that because of knowing how well my 80 hp 912ul with a gearbox reducing the prop speed works on my Kitfox IV amphib. I do cheat a bit by having an IFA IVO prop, but even if I use a fixed pitch prop setting it performs really well. As an example, the other day I was cruising around (on floats) at 105 mph at approximately 5000 rpm, which is only about 70% power with the prop setting I was using. While we probably can attribute most of that to the efficiency and performance of a 912 matched to a really good airframe, the reality is that turning a prop at a very efficient speed produces the most thrust for the available horsepower or torque. That in my opinion is where a 912 Rotax prevails over most other engines in its weight class. Turning a small and lightweight engine at high rpms so it can make the most horsepower and torque out of its size, coupled to a gear reduction that makes the propellor most efficient is why I believe the 912 does so well.

So with that said, now compare your Jabiru to the 912 ul. It is approximately the same weight as the 912ul (actually lighter), and produces about 4 hp more, with similar torque, but at much lower rpm. But then consider engine displacement. The 912ul is only 1,211 cc, or 74 cubic inches. By comparison the Jabiru is nearly 1,000 cc's more than the 912ul, with a displacement of 2,200 cc, or 134 cubic inches. So in a nutshell, the Jabiru actually has the same or more power than the 912ul (and probably way more potential for more due to more available displacement), but just doesn't apply that power to a prop as effectively or efficiently as the 912.

So imagine if you could add a prop speed reduction unit to the Jabiru that would allow it to turn a propellor at similar speeds to what the 912 does? I personally believe you would actually have as much or more power than the 912 ul.

To support my reason for feeling a PSRU would do so much for a Jabiru Kitfox, I will share a story most here probably don't know about our airplanes;

I remember Dean Wilson (designer of our airplanes for those that don't know) telling me about the first flights of the Avid Flyer prototype being a huge disappointment. It was powered with the most popular ultralight aircraft engine at the time, a Cuyuna 43 hp two stroke engine with a standard 50'ish inch ultralight prop bolted right to the crankshaft. Even though Deans calculations said 43 hp should be more than plenty HP for the very lightweight 364 lb Avid Flyer prototype, test flights returned poor at best performance numbers. Climb rate was only 200 fpm, and cruise only 55 mph. Frustrated, Dean almost scrapped the whole idea of the Avid Flyer. But after thinking about it more, even though the entire ultralight industry was using that engine and prop combination on most every ultralight, he came to the conclusion that turning that short prop at the rpm of that Cuyuna (about 6500 WOT) was making for a very inefficient propellor, resulting in very little thrust for the available horsepower.

So Dean went down to a local junkyard and bought the planetary drive out of a Ford C3 transmission. Then he machined a gearbox housing that held the ring gear and sun gears in place, and a adapter that would bolt all that to the crankshaft of the Cuyuna. Now he had himself a 43 hp Cuyuna that would spin a 6 ft diameter propellor with 36 inches of pitch at only 2200 rpm!

The test flight that followed the gearbox addition produced amazing results from the little 64 lb, 43 hp Cuyuna;

Instead of 200 fpm climb, he now had a 1,460 fpm climb rate!

And cruise jumped from 55 mph to 80 mph!

So every Avid Flyer kit was sold with a PSRU installed on the Cuyuna. And shortly after that (about the time Kitfox started), Rotax showed up on the light aircraft scene with their PSRU equipped 2 stroke aircraft engines. Of course we all know where that all went, with Rotax now being the number one aircraft engine manufacturer in the world (I often wonder if they ever gave Dean Wilson any credit for any of that, as they should have IMHO ...)

So, imagine discovering the true capabilities of the Jabiru engines by adding a gearbox that allows for a larger, more efficient prop, just like Dean Wilson did with the Cuyuna? I could be wrong, but I'm willing to bet you would see an amazing difference in your Jabiru Kitfox with the addition of a PSRU. And it would improve in all operational modes, climb and cruise, and land or sea, .

There you go Lynn...there's the seed I wanted to plant