C90 prop combination

O-200 Reno race motors (Formula 1) turn outrageous RPM. A Cassutt turning really high can easily get 220 mph. Nemesis could get 240+ in a straight line pretty easily with an O-200.

Gordie, I really don't understand these numbers you mentioned. I don't think anyone is turning 4K on these engines. Please review your comments, and update if possible. Thanks......

Look up "Type Certificate Data Sheet P-842 Revision 16, Oct 26,2006". It is not specific to any aircraft but It does list McCauley props / Continental engine combinations and the associated HP, RPM, and prop diameter limits. See note 9 for those of us with 75HP engines. Per the document, this list meets "minimum standards for Certified aircraft" meaning McCauley, Continental, and the FAA has no problem with the combinations. Unfortunately, using a combination on this list that is not on an Ercoupe TCDS (such as a bigger prop) may get the FAA excited.

As an aside. I had my tach go out and I stuck in a used replacement. I was not getting the rpm I was used to seeing so I checked it with an optical tach and it was 125 rpm slow. I now have an electronic digital tach (Yes, I had to get an effin' field approval) that is extremely accurate. Don't count on the mechanical one being correct, but they will certainly tell you if something changes.

I have a C90-16F in the M10 with a McCauley 71/53. I can climb at 75-78 IAS at 2410 rpm and 7.9 gal/hr. Once level I can get over 2500 rpm. Red line for the gauge is 2475 but the redline for the motor is 2625 and the F-1 guys are turning the O-200s at over 4K so I don't worry too much about over-reving. I cruise at 2350, burning 6.3 gal/hr and indicating (in trim) 96-103 mph, nowhere near the 114 mph that Ed's table says I should get. I can slow to 64 in climb and get 2390 rpm and while I climb higher in a shorter distance, it slows my climb rate by 150-200 fpm. Best rate of climb seems to be 74mph but I normally climb at 80 as the airplane actually covers more ground per unit time.
From what I have been told, Continental shortened the prop on the C-90 and O-200 to increase the rpm as more HP is produced at higher rpm. I would love to try a Sensenich 71/53 as the one on the C-152 seems more efficient and I get 115 cruise at 2400. I would have to get a field approval as the McCauley is the only prop certified on the M-10 aircraft. I did check with Sensenich at Sun-n-fun. The MT folks don't even want to talk to you about an Ercoupe/M-10 prop.

Thanks Keith, just what I was looking for. Very helpful.....Gale

What about MP? Wouldn’t 15”-17” indicate not enough prop load? With a CS prop, I usually
Cruised square, or 22”-23”. What MP should be a good range for fixed props?