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Old Nov 02, 2012, 09:37 PM
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High Orbit.....
Joined Jun 2009
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Wow Pete! Just Wow!

If you look at oodles of posted data (the sample is a slat though the SU has a dropped LE Device), these simple forms even at a higher AoA just increase lift while keeping the airflow efficient like a under cambered wing. Note they don't necessarily place the flaps at high angle avoiding them reaching stall. So your thoughts on what the Lift devices are doing are tangents because its not a flying wing as an isolated system. It has a stab around a 1/3 the area of the wings that holds the wing AoA in a high lift position. Very different from a habu.

Next.....Down wash is an effect that all aircraft experience even just by increasing the AoA without lift devices. Thus you see T tails and ... lots of different thing to keep some clean flow. SU's answer was they put the tailerons slightly lower than the wing so that it pitches up slightly the tailerons remain in sufficient flow. Many of the US designs keep the tailerons in line with the wing. You start seeing interesting base shapes around the bottom of the rudders to deal with some of the adverse wash etc but thats really all a tangent because its not a show stopper. So the tailerons aren't blanked as pitch devices from the ordeal. So no worries there.

The entire purpose of the stab is to set the angle of the wing. So while you are getting so focused on all the possible effects from the wing with lift devices extended, it is entirely irrelevant to so large a surface, the tailerons, that maintains authority of where the pilot directs.

Oh and everyone keeps going on about unstable and flight control systems. The SU-27 didn't have one till long after. The dynamics are basically the same so this is not magical computer stability control. So like I said, you keep over thinking it. ....

All this talk I wish I could have finished my finding. Its so nasty out I can only fly my nCPX in the living room.
Oh and I'm really trying not to argue. I'm just free writing in response to your comments where you might be getting a little mixed up.

Either way cheers Pete.

Originally Posted by PeterVRC View Post
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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