Maximum engine size

[Danzer1]

Dorsal - I see where our confusion is coming from. I'm reading the 912ULS info from these charts: http://www.rotaxservice.com/documents/912Sperf.pdf

Which is vastly different info than shown from your reference (both from Rotax). So if the info in the Operators Manual is correct - it has much less power and "reserve" than I had been calculating!

Hmm

[Gravity_Knight]

Even at your altitudes, I think you will find the performance of the 100 hp 912 to be just fine in what should be a very light weight plane, Sir Gravity_Knight.

You are correct.. I fly a CTSW now with a 912. Empty it weighs 710 pounds and does pretty well. Although, on a hot day with the DA at 10,700 (highest I've flown in) here with two people and fuel it gets pretty anemic. I like taking friends around Pikes Peak and at 14,500ish it can be a challenge (obviously only going in the morning when DA's / wind are lower) I've flown to Leadville as well with a passenger and climb performance isn't anything real exciting.

To me, lots of power makes a plane safer. My homebuilt runway is about 2200ft, but obstacles on both ends so around 1800 usable. This is plenty for a 912 powered kitfox even up here but I think 115hp or something that is turbocharged up at this altitude would make me feel better. I also come from the drag racing world so a little more go puts a smile on my face

But at the end of the day.. when I can afford my own plane (Kitfox) w/ a 912 it will still perform well enough to have a blast I'm sure!

[Dorsal]

Danzer,
I think your numbers are more correct, the table I was referring to is recommended setting for a variable pitch prop.

[n85ae]

The dry weight of an O-320 is within about 5 pounds of an IO-240B, and even
if you add ballast in the tail you aren't adding a gazillion pounds back there
to get the balance worked out. So yes there are reasons to use an O-320

Regards,
Jeff Hays
N85AE, Series 5, IO-240B

I can think of no reason what so ever that a person would want to put a 300# 320 Lycoming on a Kitfox.

Any power gain would be more than negated by the weight of the motor, not to mention the ballast needed in the tail to balance that giant anchor hanging on the nose. Plus you need to factor in a 10 GPH fuel burn (yes, that is realistic) so you will need to haul around a ton of fuel all the time, too.

An O200, IO240 or 233 Lycoming are probably near the weight limit for a Kitfox to still have a reasonable useful load.

Even at your altitudes, I think you will find the performance of the 100 hp 912 to be just fine in what should be a very light weight plane, Sir Gravity_Knight.

[jtpitkin06]

The development of the Kitfox is not unlike the Piper Cub evolving into the Super Cub.

The Super Cub started with an empty weight of about 800 pounds, 95 hp and a gross weight close to 1500. Sound familiar? Various engines have hung on it from 105 hp up to the “standard” 150 hp. Piper built one with 180 hp and several have been re-engined to 180 hp with an STC.

I suppose one could ask, “why would you want to put a bigger and heavier engine on the Kitfox?”

Let’s say you have a light Kitfox loaded to 1100 pounds and the power is 100 hp Rotax. That’s 11# per hp.

So let’s hang a heavy but more powerful engine on the front and balance the aircraft with a few pounds in the tail (if necessary). We’ll add 160 pounds and we are now at 1260. (Another familiar number) with 150 hp on tap. That’s just 8.4 pounds per horse power with spritelyclimb performance.

“But what about the wing loading?” you say. OK, in the light weight Kitfox you have 1100 pounds / 132 sq ft = 8.33 pounds per sq. ft. The heavier engined Kitfox example is 1260 pounds/ 132 sq ft = 9.54 pounds per sq ft. That’s about the same as the clipped wing speedster version. The only problem I see is that it would be bumping the redline in cruise.

I don’t see the CG as a show stopper. I have my Corvair engine mounted 4 inches further aft than the O-200. The CG is not a problem. No ballast required.

I see no reason why an experimental aircraft builder might want to push the envelope and install a different engine in the Kitfox airframe even though it does not meet the “norm”. Kitfox LLC has done this when they installed the Rotec Radial and then the Lycoming 233 . That’s what experimental aviation is all about. We try different things, different engines and different panels.

I would go so far as to say if someone puts a 160 hp engine in the Kitfox and shows up at Oshkosh they would have an instant crowd around the airplane. I’ll be standing in line to get a ride in what will likely be a screamer.

John Pitkin

[n85ae]

I know that there are a couple of O-320's out there, the problem is I just can't
remember who the guys were that were doing it. But they built a few of them.
It was at least ten years ago, and I recall talking to one of the guys on the
old Sportflight list.

I personally would consider it myself if I were building my plane all over, I have
been flying the IO-240B for a long time, and I think an extra 30-40 would
be a blast. So yeah, why not? I would do it.

Regards,
Jeff Hays

[jiott]

I agree with John. The only other thing would of course be a careful look at the engine mounts and firewall attachment for all that extra weight and power. I personally think an engineering calculation by a knowledgeable person would be in order. Torque reaction on sudden engine accel, as on a go-around, might also be quite exciting!

Jim

[n85ae]

There would not be a weight issue, the dry weight of an O-320 is about
250 pounds, the IO-240B dry weight is 246 pounds. It would balance fine.
You would need to build a new engine mount and probably upgrade the
forward fueslage tubing. There might be "some" torque reaction but I
bet not that much. The more I think about it the more I want to build one

Jeff Hays

[airlina]

Jeff, you better finish the one in the garage first!

[Esser]

I'm sure lot of you know that I am planning on putting a UL520i in my plane. My question is do you think that I should enlarge the rudder create a control horn at the top for it? Having never owned a Kitfox before I'm not sure if the larger rudder is needed or not.