Fixed Pitch Props

[cubtractor]

I'm anxious to hear the results. I been wanting a Prince for a while now.

[av8rps]

That sounds really exciting Larry. Congrats. You are gonna have one kickass Model 4 when you are done!

Are you planning to install an airbox on your 912ul 105 Zipper? Just curious as I am absolutely positive we are losing at least 5 hp by not getting cooler air into our carbs.

But I think it's funny...no one ever talks about that? Yet it is probably one of the easiest and least expensive mods we could do to get increased performance, while also providing us with carb heat (which I personally have many times wished I had on mine). But as we both know, making a Rotax airbox fit under the cowl of a model 4 would be nearly impossible. So the airbox I'm thinking about would have to be different than the Rotax airbox.

I've often thought about modifying the old Kitfox manufactured airbox (that mounted to the top front of the engine) so that it had a better way to get more cool air to the carbs (start by getting rid of the filter blocking the air into the box, or at least turn it so it has some ram air effect), so that you gain power rather than lose it. I never tried it, but I think if we could have just flown one of those old airboxes without the air filter, rather thank blocking outside air into the carbs, we'd be ramming air in. That alone would have to make more power in my opinion.

I know the 912 will work ok with just air filters sucking warm air right above the exhaust pipe, tight against the firewall. But most engine people would call that "just plain stupid".

Paul

[Av8r3400]

Actually, Paul, I removed the "cold air" air box system from my Yellow plane and gained about 250 static rpm. Providing evidence to me, that this system is a power loss rather than gain.

Through the build of this plane, I have gone over the FWF coming up with different plans. At one time I was considering a turbo kit which would have required building an intake plenum to fit the existing engine mount and oil tank. Then I considered building a completely new engine mount which would interface with the proper "horse collar" Rotax engine mount. This would have allowed the use of all of the OEM supplied intake parts.

For the sake of simplicity I went away from all of this in favor of the Zipper system. I can now leave the Kitfox IV FWF in place as supplied. At this point I have no further plan for any "hot rod" power modifications to the engine other than the Zipper.

[av8rps]

Yeah, I removed that airbox from mine too for the same reasons that everyone that had one said it just robbed power. But I always wondered if anyone tried it without the air filter on it. That air filter had the blunt closed-end pointing directly into the airstream, so it was far from a ram air function.

Unfortunately when I redid my plane I utilized the area where the airbox went for other things so it isn't a real simple thing for me to just bolt it on to try it. But I sure would like to have known.

That's why I ran it by you, figuring it would get your engineering brain going and you'd solve the problem for all of us