Fixed Pitch Info

I had a Sensenich 85 inch pitch on an RV7 with an O-360 and a Pmag. At 8500 ft I would show an indicated 171 mph with an OAT of 60 degrees F at 2700 rpm and 19 inches MAP. Is this consistant with your experience? Climb out was very good with this prop but I wanted to use more of the potential in cruise.
I repitched it to 88 inches, IAS when up to 177 mph at 8500ft 59 degrees. Now I get a MAP of 20 inches at red line of 2700 rpm. I'd like to hear how others with Fixed pitch are performing.
My Climb performance is still good but probably slightly off what the 85 inch did. With me alone I can not really tell the difference.
John Adams

My RV8 with an o360, dual mag., fixed sensie ( 72x85) will produce 186ktas @ 7500 msl, @ 2700 rpm, about 19" m.p.
you really need to work in tas to compare aircraft performance.

When I convert my numbers to Ktas I was at 175ktas with the 85 inch pitch prop (at 2700 rpm, 8500ft, 19 map and 60 Degrees F OAT) and am now at 180 ktas with the 88 inch prop. So, I'm not sure I trust my TAS numbers, but the difference I believe is real.
John Adams
P.S. What performance are you seeing with your combination for airplane, engine and Fixed prop? It may be useful to builders to have a set a data from other builders. Is the RV8 faster than the RV7? Probably, but is this backed up with real builders experiences. How does the RV9 compare? Probably pretty well.

Recently I had a chance to fly with two big guys (400 lbs total) in my rv7 with 88 inch pitch prop and the take off roll was probably 100 ft longer. Once at airborn and at speed the climb performance was surprisingly good still but the take off was noticably longer than with the original 85 inch prop.
John Adams

smoke said:

My RV8 with an o360, dual mag., fixed sensie ( 72x85) will produce 186ktas @ 7500 msl, @ 2700 rpm, about 19" m.p.
you really need to work in tas to compare aircraft performance.

Click to expand...

Neat. I get about 200mph (172ktas) with O-360/RV8/one mag and one Lightspeed on an 83" Sensie. The climb is excellent. I'm based at 4800'MSL here in New Mexico so the climb performance on hot days is appreciated. But man it sure would be cool to be consistently over 200mph at full throttle in cruise. Alas, tis all a tradeoff.

Tach error

On another thread some one suggested the tach can be wrong, this week-end a friend loaned me a PropTach (a really good optical tach which we validated with a Mercury vapor light at 3600 rpm). My Vans' tach in the dash was reading 200 rpm high at 2700 rpm according to the optical tach. The Vans tach is an electronic analog needle reading from the P lead. I never guessed the tach could be so far off and this now puts my previous posted data all in question. I am going to double check with two more tachs, but I may have 200 rpm more to play with which should be about 13 more knots! That is more like it.
John Adams

I had exactly the same problem... I found it hard to believe that I was turning 2700 with the throttle lever only 1/2 open. I got a optical tach from a friend... free speed ! well, not exactly, the last 10 knots will cost you 2-3 GPH ! you pays your monies...