David,

Congratulation on the Cheetah. a great plane. Good questions.

Figure to save about 0.9 gph improvement on the high-compression STC. The Sensenich is a better airfoil and you will need the extra pitch with the HC STC.

Powerflow produces more power, 4-7% by what Powerflow says and what we have seen in real installations. You also burn about 0.8 GPH MORE with the Powerflow as you are making more HP. You can get the short stack and yes, you have to modify the lower cowling (we have videos of that) https://youtu.be/YNZjcfSY-T4
but you have to make sure the baffles and seals are in good shape for cooling.

The other option is the ElectroAir EIS 41000 Electronic Ignition system, it adds 11-17% power increase while dropping fuel flow another 1-1.5 GPH and giving great high altitude performance due spark advance up to 40 degrees BTDC. Good bang for the buck.

Now for real life example, we had a Cheetah come in the shop, get 4 new Lycoming cylinders for the HC mod, port and polished by Lycon in California, added a Sensenich prop and electronic ignition. Result? A cheetah that would turn 2950 at 11,500, burning 6.9 GPH true airspeed 150 knots. Was the owner happy? Yes! We are now working with the FAA to pitch his new prop to 64 inches.

Happy flying.

Roscoe

Roscoe,

How did the aircraft perform after the pitch change on the prop?

I would love to hear the results too!!

After prop change the engine was closer to the higher end of the static runup (still would beat it) and still able to turn 2800 at altitude if full throttle, but at 2700 and leaned to 7.0 gph speed was Tiger or better. That means plus 135 knots.

I have the Precision STC for HC pistons, the flight manual supplement only authorizes 2 McCauley propellers. How do I get the approval for a Senesnich 61? 74 AA5

Call Fletchair and get the Sensenich prop and the STC so that you can use it.

I called them and they said the approved propellers were listed on the STC…

I will call again.

I have heard better climb and cruise with the sensenich propeller. True?

You would think that they would help you buy the 74DM7S10-1.5-61B SENSENICH prop you want.  After all it’s only 4300 or so.

Yes, you would think so. I will call again Monday…

Thank you Roscoe!

• This reply was modified 3 years, 9 months ago by Wes Sears.

Roscoe, what were the required mods to support a 64 inch pitch approval? i.e. was the porting and polishing a factor? Or just the HC and Electronic Ignition?

Eric,

It is a combo of all. What got it over the hurdle with the FAA was that we exceeded max manufactures static RPM by quite a bit. We repitched to 64 (Rocky Mountain Propeller) recommended 68. We are still over max static but as the engine ages it will come down. Would not want it just above the min static RPM.