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----- Original Message -----
From: "john" <frmrjohn@netonecom.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, December 30, 2002 10:58 PM
Subject: [FlyRotary] Cruise info
I'm still working out the info to get the prop carved, and am wondering
what
is the optimum engine rpm at cruise and the fuel consumption you fellows
are
getting? All input would be greatly appreciated. Thanks JohnD
If you are using a fixed pitch prop, about the only thing you can do is aim
for target max engine RPM at top speed. A lot also depends on max tip
speed and keeping it in the efficient range below mach .85. If your prop
length is around 68 - 70 inches (typical RV prop) then the highest you want
to go is about 6350 rpm with a reduction ratio of 2.176: 1.
You really don't have much choice but to let cruise rpm fall where it may.
I my case, cruise is between 5000 to 5600 rpm. This is not a bad place to
be as the rotary has its best BSFC in this range. I burn around 6.5 GPH at
econo cruise (175 mph) and 8.25 GPH at 202 (both measured at 14,000 ft).
A little efficiency could be gained by increasing pitch & slowing the engine
down at cruise but you would loose takeoff & climb performance so it's a bad
deal.
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
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