What is the “highest” HP someone has put into a Kitfox?

[DesertFox4]

Every Kitfox produced from 1984 until now is a STOL aircraft with only one exception. Come to think of it, it was pretty darn capable too although, not sand bar capable maybe.

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[aviator79]

Every Kitfox produced from 1984 until now is a STOL aircraft with only one exception. Come to think of it, it was pretty darn capable too although, not sand bar capable maybe.

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I see where you are going with this. Why choose between standard and STi, when you can have both?

[Rik]

How many of you have wheel pants?

[kitfoxjim]

Rik, with that engine are you perhaps plotting a Draco killer? With the right prop that can provide some braking, it might be possible!!

[Rik]

That’s very optimistic as they have literally thousands of hours ahead of me so that’s fantasy for me. It would be honorable just to qualify.

I have an Allison C250. Essentially look at any bell jet ranger and you’ve seen one in action. They make about 420 and I’m making like 450ish.

I can change the compressor down to a c18’s and loose 100 hp and the corresponding fuel burn.

[Flyboy66]

Yea, hence the need for some speed as the fuel mileage gets better the faster one goes.

The standard wing on the K5 is kinda scary as it’s what Nick had and we can see he did a stall and... So some of these comments about low, slow and steep turns scare me. Everyone is cooking with the same recipe expecting different results..

I am not familiar with the C-250, so I don’t understand your comment about fuel mileage improving with speed. My aviation experience is based a model that states drag increases exponentially with increase in speed. So, the only way to make an aircraft go faster without increasing fuel consumption is to reduce drag by changing the airframe.

I did look to see what a C-250 is and saw that there are many variations, and I have no idea how much power you have available.

I think that you would experience many problems with any engine that has significantly more than 200 horsepower. First is fuel burn as others have stated. Draco is a flying fuel tank after being modified. The Kitfox only has 27 gallons, which with any turbine engine, goes very fast (example: BD5-J, tiny engine, huge fuel flow).
Even if it had 50 gallons, it is unlikely you could get very far and still have fuel to play with.

The Kitfox was designed for about 100 hp. If you strap on 300 hp and cob the power, I am not sure if it has enough control authority at low speeds to keep you from doing an aileron roll during a go around.

Next: weight. Turbine engines are more efficient (power to weight ratio) than piston engines, but your engine is probably pretty heavy. And with that much power, it will also need a fairly heavy propeller system to absorb the power, so it probably going to need ballast in the tail to keep it in limits. It also looks longer than a Rotax, so the weight would likely be much further forward further aggravating the CG issue. Will you even have available payload to have someone in the other seat?

Edit: just thought if another potential problem with the C-250. Does that engine have a gas generator and power turbine like the PT-6, or is it a single shaft engine with direct drive off of the gear reduction (like a Garett TPE-331)? If it is a single shaft setup like a Garett engine, you will most likely need a prop that stays in flat pitch during start up, and I don’t know where you can source one in the diameter that would be appropriate for a Kitfox.

If you can get around the 1550 lb gross weight, I think the other issues can be solved by limiting the power and adding fuel capacity. The airframe can only be dragged through the air up to Vne. But, with a turbine, you get much better economy with altitude, and the TAS increases relative to the IAS, which would be you limiting factor (Vne.)

[Rik]

With any turbine your going to be sucking fuel regardless of output rpm the variance between the extremes is far less than what one would expect. Example, if your fuel burn is 18 gal/hr at 80 mph but only 20 gal/hr at 120 then its a no brainer to run at 120 instead of 80. Your running it to the lean extremes so to speak as the faster you go the law of % makes you more efficient. Fuel capacity is a concern for any distance however. Max fuel burn is about 24 gph worst case but that on a 5 minute take off rating.

Your backwards on your power to weight ratio. reciprocating engines grow in weight faster than a turbine. My TF50 is only 628 lbs, my T58’s are 328 lbs and so on. I’m far from a novice when it comes to turbines. The Allison is about 158 lbs.

I’m more concerned about a steep full power climb out and having aileron authority to keep it from doing a spiral climb. In a turn there’s no reason to be at full power to have that as a concern.

[Flyboy66]

If you are correct about your fuel burn assumptions, then your statement would be correct. However, your speed increase is 50% in your example, so your drag would increase 225% which would require more than twice the power. Although engines have a sweet spot that they were designed to operate in, I don’t know of any that would give a 225% increase in power on a 11% increase in fuel burn. The fuel flow vs power curve would tell you the optimum power output of the engine.

By the way, the speed of these kits is dependent on configuration (not insulting your intelligence). The guys getting 95 mph are running Cabane gear (more draggy than Grove spring gear) and are also sporting 26” or 29” tires.

Who has wheel pants on their planes? Only those with the 600 x 6 tires.

[Rik]

If 100 hp rotax will get the plane to 120 mph then your assumptions of power needs are off dramatically as the 100 up rotax only produces about 75-80 hp in cruise which is no where near 225% increases you speculate about that would be need to reach the top speed from 100 to 120. Your assumptions would equate to 180hp to reach 120.

However, the fuel burn in turbine is not necessarily a power rating as it is the crappy efficiency at non full power. The turbine will idle at about 13 gph and I don’t think my assumptions are that far off.

[Flyboy66]

Ask the guys with the 912uls what they are getting. I think I just saw a guy post that he got 120mph with Grove gear and a 912 uls. Good luck with your project. It sounds like you have thought it out.