Author Topic: Hirth F- 23 and F-33  (Read 848 times)

Offline 3D2

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Hirth F- 23 and F-33
« on: June 14, 2021, 09:08:26 AM »
A question was asked pertaining to performance of 2-cycle engines in another thread...

The Hirth (50 HP) 2-cylinder F-23

With 2.5:1 reduction, on a 485 pound gross RW-2 that I fly which has nothing superfluous-- like a tach, fuel gauge,  or flow meter-- just four temp sensors. Based on average fuel flow of 2.25 US gal per hour, I can work backwards from the chart and throttle position that it's probably turning the 72 inch x 39 pitch Culver prop at 1900 or so rpm at 65 percent or so doing 60 - 65 mph or so according to the strut mounted pressure gauge.

I also fly a Part 103 RW-5 powered by the single cylinder (28 HP) Hirth F-33

With the same 2.5:1 reduction unit on a 315 pound gross weight the average fuel flow is 1.67 US gal per hour. Working backwards from the chart-- because it has just one CHT, one EGT, throttle, choke, and kill switch on it's panel-- and throttle position turning a 56 inch x 30 pitch Culver prop at roughly 1900 or so rpm and 65 percent power doing 50-55 mph or so according to the strut mounted pressure gauge.
--Barb (RW-2 Aviatrix)


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