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In a previous email Bill asked me for some performance numbers. I suppose he wants them to compare 4 blade MT to a 3 blade Hartzell? As with most numbers you have to take into account several variables when comparing from plane to plane and the only real way to fly both in a back to back test on the same airplane on the same day. Without this I offer some numbers form my last flight.
After leveling off at FL 230 my Sierra said it was 5*F OAT, DA of 24,410, or you could say a warm day up there.
Going LOP, which I always do, and I will give you 2 sets of numbers. One is from the Sierra Flight System and the other from the Round Lancair Airspeed indicator.
SFS, IAS 172, TAS 249, LOP at 18.5 GPH and 32.7/2500, TIT 1640.
Round Ind. IAS 179, TAS 263.
All instruments tied into the Same Pitot static system. These number difference remain thoughout the flight envelop.
If I go Rich of peak my fuel burn goes from 18.5 to 25 GPH and lowers my range by 200/300 kt m. and 1 hour flight duration. My SFS TAS goes up about 10 Kts.
The main reason there is a difference in the two system is that the SFS corrects for Compressibility and Mach heating. I'm told that this is about the difference. Some folks claim faster airplanes and one other reason is I have Wingtits that cost about 10 Kts. in cruise speed but sure make it stable at high altitudes and look sexy.
From what I have investigated the 4 blade MT prop is about the same speed as the last generation Hartzell 3 blade scimitar prop but the New generation Hartzell Scimitar with the high twist, three blended airfoils, and a lot of development on the Lancair Race planes is much more efficient across the flight range, i.e., climb, cruise, and top speed. It would be a much tougher decision now on which prop to use. Trade some sexy for speed?
For the number guys, this flight was 500nm and took 2:13 hrs from SFS 1500 rpm to 1500 rpm, and I had 10 to 20 kt. headwinds and used 44 gals total.
Hope this helps? But I'm happy,
Jim Hergert
N6XE, "An Sex Y" L4P
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