TakeOff RPM on 912uls

[kitfox812]

I have 485 hours on a Kitfox s-7 and I have always thought I had low RPM on takeoff.
I have a Powerfin-F prop which is designed for the 912uls.
I have readjusted the pitch numerous times and still end up with a pitch setting that gives about 4700 RPM on lift-off,WOT. Any less pitch will red line at half throttle in cruise. The pitch setting I have set now goes to 5000 about 10 seconds after lift-off depending on my climb rate then up to 5200 in about 15 sec and is good at cruise. Climbing at 5200 or 5400rpm and 600-900fpm is no problem. My WOT is above 5700 RPM in flight so I can't decrease the pitch any more.
Does anybody know if this is normal or could it the Prop or even the Engine.
Any ideas will be greatly appreciated.

Rich

[Slyfox]

I originally had a powerfin on my 912ul and that sounds just about right, I wouldn't change it.

[Av8r3400]

At only 4700 rpm, you are leaving a lot of takeoff power on the ramp. And it will still over-speed in level flight?? Wow, that's weird... Sounds like this prop may not be the optimum item for your plane.

[Dorsal]

I am interested in the responses to this as I had assumed that if you pitch the prop for best take-off you would have to back off the throttle in level flight and that this is a viable option.

[RobS]

These are not my words, but they confirm your assumption:

Fine pitch allows the engine to reach maximum speed and hence maximum power at low airspeeds. Vital for take-off, climb, and for a go-around on landing.

Coarse pitch allows the desired aircraft speed to be maintained with a lower throttle setting and slower propeller speed, so maintaining efficiency and improving range. Coarse pitch will ensure your engine does not overspeed while the propeller absorbs high power, producing a higher top speed.

In a fixed pitch prop, fine pitch is better for take off performance but results in higher RPM for cruise.

[jrthomas]

It seems to me that static rpm should be around 5200 to 5300. If you're only getting 4700 on take off, what's you static rpm? I've seen props do some strange things. A friend of mine had a fresh 447 Rotax that would turn up 6000 static on the 1st run up after warm up but wouldn't go past 4000 or so a few seconds later. After every conceivable remedy failed he gave up and installed another 447. Guess what! It did the same thing. He finally tried a different prop with success. I think I'd call Powerfin. Let us know how things work out. Good luck, James Thomas

[kitfox812]

The SS-7 was DAR'ed in Aug of 07 and I called Powerfin shortly after with the problem. They took it back and shortened it a hair and rebalanced it for me for free. It has operated flawlessly otherwise and I really like the prop. For the price of changing props, I have to. I will give them a call again though.
With Rotax just coming out with the SB about not less than 5200 on take-off,
I was getting a little concerned again. The plane will take-off in a 100 feet or so and stand on the prop. I cruise at 5200 and 115mph so it is great if I don't look at the RPM. Thanks for all the input.

[horsepower]

Not for sure but I think Powerfin may be out of business. I live in North Idaho about an hour from their facility in Spokane,Wa.I have a Powerfin prop on my 582 and I called them to ask a question and got a message that the phone is no longer connected.Bummer if they are just another business to go under with our sinking economy.Hopefully it is only rumor. Randy

[kitfox812]

We have been flying to St Maries for lunches and fly-ins for about 9 years now....great place.

I went to Powerfin.com and there is a msg that they moved to Texas and the 800 no. will be up the end of Dec.. The old number on their site goes to Time Life?? I hope they are still going. I sent them email regarding this problem.

[JimS]

WOW!

If your getting airborn in 100' and cruising at 115 mph at 5200 rpm, I'd say you have the prop dialed in as good as possible.

JimS