Hello and thank you for your answers.
the Canards stall before the wing?
http://en.wikipedia.org/wiki/Stall_(flight)Check at the end just before Spoilers. My reasoning is that because canard stal before the wing you never want your wing to stall unless you have a tail control as well. Hence the SU-47 design with canards and tails. :
[//quote]
Well the problem with that is that is assumes the canards are at the same AOA than the wing wich is not the true especially on unstable plane that pitch by themselves.
The same applies for aft tails, except the aft tail can stall by being in the wake of wings. Yes i know tails are below the wings but Air masses flow goes downward especially at high AOA's.
I think then all is a matter of wing/Tail/canard interaction, and canards do not make bad controlls for low speed manoeuvrability at all.
Now do not forget we're talking about devices that make the plane move not (mainly) lift it.
That is the max AOA capabilities of Rafale and eurofighter Vs F-18 and F-22 for example come from their wings.
In the case of F-18 the straight wing+Lerx cleary helps, for the F-22 it is unclear if the TVC is necessary for the 60° AOA sustained or not since it is blended in the FBW at those AOAs.
My Mistake :-[. Its the Center of Lift that moves forward in supersonic flight. Basically the CG and the CL for a canard design should be swapped. My CG estimation was based on the main landing wheel position and book says CL it approximately 1/3 down the wing chord.
[/quote]
I think this not correct, the CL moves AFT, wich has for consequence to make the plane more stable and in this case canards are very good for trim drag.
This is not a surprise that a non coupling canards plane like the typhoon has outstanding possibility in supersonic like sustaining more than 6G's at mach 1.5 or pull 9G's all over the transonic regime.
The position of canards make that the plane needs less canards AOA to trim and pitch the plane compared to a conventionnal aft tail.
Now what lockheed said about the position of the tail of F-22 was precisely becaue of that, as the CL moves aft they needed to pull the tail far aft of the plane to conserve a good leverage.
To finish; things not to confuse with:
Instability is a matter of WING (as she's the main contributor) CL position relative to CG.
If two plane had the same wing, one with the aft tail, the other with the canards, the canards one would be the unstable, but in real life, no plane has same wing, so no plane has same CL-CG repartition, so a plane can be unstable or stable be it an aft or canards plane.
(as said, the viggen is stable, the F-16C is stable too)
Canards/tails main action is leverage. they rotate the plane so when discussing capability it is important not to mix controls VS states (leverage vs lift).
While we can see some definite "specs" of some configuration in planes, some of them are quite surprising..the Drakken ability to pitch at high rate is clearly something we don't expect from a delta plane...however it can!
It is because all is matter of interaction between parts of the plane. Nowadays when you see a plane, it almost impossible even for a professionnal to say what is the use of this or that thing on the plane without seeing actual CFD or directly hearing this from the creators.
What do you think is the use of the Rafale's nose bump just below the cockpit? What is the use of the Raptor Boat like nose and forward fuselage section's shaping?
