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Old Nov 02, 2012, 05:59 PM
PeterVRC is online now
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Australia, VIC, Melbourne
Joined Nov 2006
13,926 Posts
Su, you read my post the 'opposite' way that it meant....

Flaps add negative moment - nose down. Slats add positive moment.
"The slats (whatever they are) camber re-profile probably exceed what pitch down the flaps/flaperons add."
That statement means... the slats effect of reprofiling the camber of the wing adds MORE positive moment than the flaps add negative. Thus the end result is the nose up attitude.
Not that I know that is what happens for sure, but it seems a likely reason.
The slats don't LOOK big enough to cause that much effect, but there can be other unseen resultants fo airflow redirection etc from them - so looks alone don't make something possible or impossible.

Much like was mentioned about down aileron/flapeon causing downwash over the elevator/s.
After I looked at the plane, about that, it is clearly going to be an issue.... down aileron/flaperon is going to 'blanket' the elevators into a dead zone... even if the aircraft can end up with positive AoA from inputs. The elevators are in the 'perfect' position to be affected by that!!!
F-22's have that issue (models anyway... and probably real ones too). But I would expect FBW can overcome ANY of such issues - to a very good, or total, degree - whereas model RC fliers can't do (monitor) all these factors when controlling a plane (like FBW can do perfectly). So if we move into such areas, we suffer and can't 'correct' it properly.

If the Su was set up with 'elevons' - ailerons move in unison with elevators - that issue would not occur then (it still will, but will be far less effect or issue, possibly negligible). The biggest issue comes if they operate 'against' each other - ailerons down, elevator up, (which what flaperons do) because this state is moving the elevators right into the peak area of aileron downwash.. Until the elevator has a large enough angle and 'clears' the peak downwash area some useful amount - which would be a lot of angle by then! So it possibly would never really be used to such an angle that it return to any area where it could get 100% effectiveness again.
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Last edited by PeterVRC; Nov 02, 2012 at 06:07 PM.
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