Jim Wilson wrote: > Speaking of which, in the prop config, what exactly do the "cruise" > numbers do? If I'm not getting enough thrust still out of the prop, > what should I mess with first?
This is the black magic part, and could really use a redesign. The "cruise" pitch (the RPM and an airspeed) defines the point of maximum propeller efficiency. Anything faster or slower will be less power-efficient according to a curve I reverse-engineered out of a textbook. The cruise-power then defines the engine power needed at that speed. But that's for a fixed-pitch prop. For a variable one, it's only for the "one" point of the pitch multipler (which is allowed to go from 0.25 - 4.0). Which is basically useless, because the second the governor starts it pulls the multiplier off of the default value. The end result is that it's pretty much impossible to predict which part of the efficiency curve a variable pitch propeller will be operating under in practice. That's not a huge issue, I don't think, as the efficiency curve is pretty flat. But it does make the solution very sensitive to input values. The idea of using an efficiency curve to define the prop (instead of, say, a pitch value and takeoff thrust/power) has some merit, but it ended up being difficult to tune -- David M. has had trouble with getting the windmilling speed to be correct, for example, because that number (which is basically the same thing as pitch) is a derived value, not a core tunable. Andy _______________________________________________ Flightgear-devel mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
