Not sure about that. Here are the actual accounts of one Radial powered Kitfox owner. I’d be surprised if any Rotax (even at 6,000rpm) could match these numbers. No cowl fitted NACA or otherwise!
Due to landing gear length, I know some Rotec/Kitfox owners have compromised performance by running smaller props on there Rotec which is designed to run larger props via its superior torque. 76" diameter is the optimum.
Kitfox Classic IV: Brian Henneman
Engine R2800 MkI
Prop: 76"D x 50"P then to 76”D x 55”P.
Burn: 6 gal/hr
Max RPM: 3600 (via 3:2 gear box)
Cruise RPM: 3000 = 2000 at prop.
Comment (26th June 2002): I did a static thrust test this past weekend and it will pull 480 lbs. Very impressive. More later.
Comment (11th June 2002): Just wanted to let you know I received my new prop a 76"dia. X 55" pitch and the performance really increased. The climb is still about 1500'/min. and the top speed is 130 mph. I can still exceed the red line up to about 3700 rpm. I have been cruising it at 3400 rpm and I am indication 110 -115 mph. I could use about another 5" of pitch to have a really good cruise prop but I will keep this one for demos.
Comment (28th April 2002 “I got in a couple of hour flying this weekend so far and I took Steve up in it with me. With the prop I have on it, it is really a climbing machine. I can peg the VSI at 2000' / min. and that is really going up for a little airplane”