Downwash (was Re: [Flightgear-devel] Taildragger takeoff and landing)

[David Megginson]

Getting back on topic, I think everyone agrees that the horizontal 
stabilizer on a typical plane (excluding t-tails) should be seeing downwash 
-- in other words, its relative wind will not be the same as the relative 
wind seen by the wings.  For JSBSim, we don't have to worry about this, 
because the coefficients already take it into account.  For YASim, we *do* 
have to worry about downwash, since it will change the effective angle of 
attack for the tail.

I'd be interested in which approach Andy and others prefer:
1. set the tail incidence down a few degrees to compensate for the lack of 
downwash (as I have done on the DC-3 and J3 Cub); or

2. add a "downwash" parameter giving an offset for the relative wind over 
each lifting surface.  This will normally be 0 for the wings, of course (I 
doubt the downwash from canards is enough the change the effective alpha of 
the main wings, but who knows?).

This problem has little effect on normal flight, but it matters a lot for 
the landing and takeoff rolls of taildraggers -- without it, they have an 
unrealistic tendency to nose over.

All the best,
David
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