To throw some more math in:
Your "actual speed" (120) vs. "theoretical speed" (132) would be
120/132=0.9090909 or 91% efficiency (over simplification): not too bad.
Mark W
N952MW (res)
On 8/27/2023 10:28 PM, Phillip Matheson via KRnet wrote:
I had the tach overhauled, ASI checks out
I’m looking at props and prices. The same male prop, 60 x 68 is around $2700
Aust
Your saying 156 mph (135 kts) not a hope
My 70 “ pitch gets 120 kts 2300
My prop 60 x 70 p
70 x 2300 x 60 / 12 /5280 = 152 mph. (132 kts)
Phil.
Sent from my iPhone
On 28 Aug 2023, at 00:45, Larry Flesner via KRnet<krnet@list.krnet.org> wrote:
On 8/27/2023 4:18 AM, Phillip Matheson via KRnet wrote:
FYI I removed my 60 x 70 today and put a 68 x 59 ( too low of a pitch) but
gave it a single flight
Static, brakes wouldn’t hold but around 2400
Climb 2500 70kts over 1000 rpm
WOT over 2750 only 100kts
Phil.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Phil,
Have you verified your tachometer and ASI? Generally speaking a longer prop is
more efficient. Your numbers for ground run and climb with the new prop seem
to be in the ball park but your cruise number looks to be in serious error. In
theory that prop should result in 150+ mph at 100% efficiency. (pitch in
inches X 2800 rpm X 60 minutes / 12 in. per foot / 5280 feet per mile = 156 mph
) . We can't expect 100% efficiency but often the numbers compute that way.
Any chance you can get the original prop re-pitched? With a good set of wheel
covers and a properly sized prop you should get a cruise at 2500 rpm in the
150 to 160 mph range. Keep working at it. You'll get there.
Larry Flesner
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