----- 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