TakeOff RPM on 912uls

[av8rps]

A friend of mine had a similar issue once with a ground adjustable prop; lower than desired rpm for climbout, but yet would very easily redline in straight and level flight.

We flew together half way across the country trying to figure out why his plane performed so poorly compared to an identical one just like it with the same prop and engine. What we ultimately discovered was that one blade was adjusted with more pitch than the other (that specific prop had a very sensitive and difficult to adjust hub). After setting both the same, his airplane performed just like the other one we were comparing it against. It made a huge differnce.

So I would make absolute certain that all prop blades are adjusted EXAXCTLY the same. We used at that time an electronic level to insure the most accurate measurement. Then we played around until we learned the best technique for tightening the hub bolts. Most importantly is checking the prop not only for proper tracking, but to assure both blades are pitched exactly the same.

Might sound trivial, but I would say having one blade off more than the other(s) would be the equivalent of having one wing on your airplane having a different angle of incidence than the other. Imagine how poorly that would work? Well, a prop is in effect just a wing...

Paul S

[Dave S]

All of you guys are an inspiration to me - between this thread and the one on "warp drive Pitch settings" you got me thinking about my prop settings; and, decided to go back and experiment a bit. My biggest problem was trying to figure out which of the two threads to reply to...oh well...

1) Our airplane has the 912ULS with the Warp 70" tapered tip - (FYI - also have the air intake plenum which is suppose to be good for 5 horsepower - everything else being equal. The warp folks told me over the phone that the pitch range for this application in a Kitfox is 10 to 15 degrees. Also - Warp said the tapered tip behaves differently than the square tip once the airspeed picks up at cruise.

2) First setting we tried was 12 degrees - great acceleration and climb - but in cruise - ran out of green RPM before I ran out of throttle.

3) Set the prop to 14 degrees - Climb out rpm was barely 5200 - going to a little less than best rate was necessary to keep above the 5200 RPM but cruise at 5400 resulted in 118 - MPH true. Have been running with 14 degrees for a while.

4) This weekend - went and reset the prop to 13 degrees - Conditions = altimeter 29.96, OAT 19 degrees F, Altitude 3000 MSL Results = Full throttle @ best rate held a smidge over 5200 RPM - noticable improvement in acceleration (not that it was bad before) - a bit better climb and a cruise of 115 TAS under the above listed conditions and 5400 RPM.

I know I need to do some additional testing with more presicion with the new setting - but this appears to keep the Rotax SB happy and not interfere with the cruise too much - It is real obvious that a person will run the RPM into the yellow if not throttled back some now at cruise with the 13 degree setting.

However - all of this and the discussion on the list sure makes one lust for a constant speed or flight adjustable pitch prop. I never used to think about stuff like that when I was flying a rental 152......

Also think I am going to take Steve's advice about cutting the idle back a bit and just get better at using the throttle during landing.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp

[Slyfox]

I have the same engine. You mentioned the inflight adjustable. I tell ya, if you did go with an inflight, it will totally spoil ya. But you will need to anti up the denaro. Cutting back the idle is a total blast. I did a drop in on an air field. It was one that has 150' trees on one end with most being to one side, I came in from the side that had the worse trees, I did a 60mph over the trees than made a sharp turn to the right and pull back all power, with flat prop also, and literally dropped onto the runway. This was a base to final right over the runway, I didn't slip any, but with a slow speed already and by the way the turn was mainly rudder, I only turned maybe 15degree bank, swung the tail around and pulled the power, down like an elevator, pushed in a little power down at the runway and did a beautiful touch down, wheel landing on the runway, way fun. Truelly amazing what these kitfox's can do.