Maximum engine size

[War Eagle]

Also curious about this. I have a sport license now, but have been considering "upgrading" to a private. Operating at the 1550 instead of 1320 MTOW so I could legally run a larger engine, and still fill up on fuel etc. I live at 6700ft elevation in colorado and fly to 14,500 in the mountains quite often. I don't have a Kitfox yet either, but plan to buy one with a 912, so I'm just looking at options for down the road...

Another option you could go with is the turbo charged Rotax 914. No density altitude problems and less weight and full 100 HP to somewhere about 16k feet. You'll likely save at least 70 to 80 pounds dry weight and climb rate will be pretty nice too.

[GuppyWN]

Another option you could go with is the turbo charged Rotax 914.

MSRP is $32 tttttthousand!

[Av8r3400]

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.

[Danzer1]

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,

That might depend on the mission and the density altitude at the time. We very often have 8000'+ density altitude which would give that engine max at takeoff 76hp (for 5 minutes). Drop that to max sustained at 5500rpm and it's closer to 70. The 912hp curve drops off even quicker from there. Cruise at 4000 and it's down to 67hp (s.l.) and closer to 51hp at 8000 d.a.

That might work for some.

[Dorsal]

Cruise @ 4000?? My typical cruise is 5200 RPM.

[Danzer1]

Dorsal, That's kind of my point - you can't. The idea when flying from altitude airports, with high d.a.'s and potentially in or above mountainous terrain, is to have as much "get out of trouble" power available as you can on the right side of the curve. To illustrate:

I picked 4000rpm, as in a direct drive you often would cruise at 70 to 75% and in a 912 you really can't.

Using your number of 5200, about 95% or about 2100 prop rpm and approx. 90hp (s.l. ratings). You only have about 5% of the curve left for "get out of trouble" hp.

Compare that to say the UL 350is at 2100, about 63% and about 94hp (again s.l. ratings for comparison). You would still have 1/3 of the power band left - 36hp and 1200rpm of "get out of trouble" power available on the right side of the curve.

More safety margin before running out of engine. And, installed weights compare almost equally for lbs/hp fwf.

[Dorsal]

I think you will find that 5000 rpm is 75% power.

[Danzer1]

Not sure how you figure that - 5800 is max for 5 min and 5500 max continuous. Even if using hp ratings or prop speed at those figures, nothing comes out to 75%. Can you expound on your thinking as to how 5000 rpm can equal 75% power? I'm not following.

[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