I've been curious for a while to see what the efficiency of the Champ was. How much does engine power buy you speed? What's the most efficient use of fuel vs. travel time?
I don't have a complete answer by any means, but I've collected one form of data:
|Fuel flow (GPH)||Airspeed (MPH)||Miles per gallon|
This data was generated in the X-Plane simulator flying a mostly-accurate Aeronca 7AC model someone made available on the x-plane.org download site. To gather it, I flew at different throttle settings, stabilized the plane so it was flying level, and recorded fuel flow and indicated airspeed. Much easier to do this in the simulator than in real life -- I don't have a fuel-flow meter in real life!
Obviously, this is not Hard Science™. It's still interesting. I only gathered 5 data point over the course of about 15 minutes of flying, but it's representative of the range of speeds you might reasonably fly a Champ. The fuel flow numbers are at least similar to what I would expect in reality, though the RPM indicated for a given fuel flow is substantially high compared to what I see in my own plane.
The conclusion that I see here is obvious: if you're flying a digital Champ in X-Plane, and you have the same model of 7AC I downloaded, aiming for a cruise of about 83 MPH will get you the best fuel efficiency. Pretty much squares with what I see in the real world.
It'd be neat to some day instrument the plane to duplicate this test in real-world conditions, though I doubt I will. Fuel flow meters are expensive, and somewhat counter to the feel of the Champ. If I could do it temporarily, though, that would be very interesting...