Van's Air Force
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85 vs 87 pitch
- Thread starter JDeereGn
- Start date
Randy Hooper
Well Known Member
I flew behind an 87 inch prop for more than 800 hours. Static was 2150 rpm’s and 90 knots was 2500 on take off. At higher altitudes you still were not able to use full throttle. If I had the choice, I would choose 87 inches.
Thanks for your reply. If the 87 takes more bite it still overspeeds at full throttle?
There is a specific density altitude for each pitch value where the RPM will be limited to 2700 at wot. It all depends on what you want that altitude to be.
My RV-4 has a 180hp and the standard (at the time) Sensenich prop, I believe it’s the 87 pitch. Yes I can overspeed it in level flight, but just pull back the throttle an inch and it’s good. I delivered a -4 with a 85 pitch Sensenich, and it climbed great, but I had to throttle back a lot in cruise.. it was like riding a bike around stuck in fist gear..
Some data I have on my 180hp IO-360 with 85” pitch Sensenich prop from 10+ years ago. I concluded that 85” was about right For my flying.
vansairforce.net
Fixed Pitch Prop; Do I need more?
I decided a few months ago that, after flying for 4 years, I wanted to go back and get some really accurate performance points for my RV-6A. Therefore I have been busy the last few months (weather permitting) converting avgas into data points. My RV has an Aerosport Power IO-360-B2B (180 hp)...
vansairforce.net
I’m basically at sea level and all my flying is 8K or less and no short strips. Is there a chart some where? Tks. R
Jerry Fischer
Well Known Member
I had Sensenich Gainesville, Ga repitch to an 87 on my RV-7 and picked up about 8mph. no issues
Laird
Well Known Member
I had an 85" for several hundred hrs on my 180hp RV-6. I couldn't afford a CS at the time. A friend let me use his 87 to do some back to back testing. Totally agree with Randy, go with the 87.
A short time later, I swapped my 85 for a constant speed, and boy, 1800hrs later it was still a great decision to CS.
I have an 85 inch pitch on my 180 hp RV 6A. I wouldn’t want the 87, but that doesn’t mean that it’s not a good match for some people.
A key detail is what your typical cruise altitude is. If you live in a part of the country that is predominantly flat with low ground elevations, then the 87 would be a good match as long as you rarely fly high on long cross countries (as in above 9000 feet or so).
Out here in the west, if we are traveling very far towards the east, 9000 feet often won’t be a comfortable altitude. From a ground clearance, and turbulence standpoint.
For that type of operation, the 85 inch pitch gives better cruise speed up at high altitudes and gives better takeoff and climb performance when you need to make a takeoff from higher elevation airports.
I can true out at about 172 kts at about 2650 rpm and WOT at 12.5K around 7.8 gph just slightly lean of peak. I can go a little bit faster if I keep it rich but it will be over 2700 rpm. Not enough benefit in speed gain for the amount of fuel flow increase.
A key detail is what your typical cruise altitude is. If you live in a part of the country that is predominantly flat with low ground elevations, then the 87 would be a good match as long as you rarely fly high on long cross countries (as in above 9000 feet or so).
Out here in the west, if we are traveling very far towards the east, 9000 feet often won’t be a comfortable altitude. From a ground clearance, and turbulence standpoint.
For that type of operation, the 85 inch pitch gives better cruise speed up at high altitudes and gives better takeoff and climb performance when you need to make a takeoff from higher elevation airports.
I can true out at about 172 kts at about 2650 rpm and WOT at 12.5K around 7.8 gph just slightly lean of peak. I can go a little bit faster if I keep it rich but it will be over 2700 rpm. Not enough benefit in speed gain for the amount of fuel flow increase.
The RV-4 is lower in drag than the side-by-side RVs so the optimal prop for what a particular person wants in performance will not necessarily be the same between the two.
Roger. I was responding to the OP, who has an RV-8. I thought they (the 4 and the 8) were very similar in drag profiles, and have even heard the RV-8 has less frontal drag than the 4 (and I'm curious to know if that's true).
