Amiga500,
I am saying that there are a lot of photos which show what would only be a downforce on the nose (and a pretty large one) if the relative angle of the canards were acting as a control effectors. They are not.
Do not confuse a negative setting angle with respect to the airframe as a negative setting angle with respect to the freestream (AoA).
When an aerofoil section (or wing) experiences a positive AoA, the c.p. moves forward as the effective camberline (cambersurface) changes with leading edge and trailing edge stagnation point (line) movement;
The canards equivalent function is to ease pitchup requirements on what would otherwise be an entirely out of balance airframe with the wing so far back.
If they were worried about the balance of the airframe due to the wing being so far back, they’d have went for a conventional tail, moved the wing forward and made both the LE and TE have positive sweep angles. (or stuck with a smaller canard and done the same with the main wing)
That said, at high speed, canards have no function because they are attached to structure which would fold under the torsional loads if they were used as pitch effectors at speed.
The canard doesn’t carry the weight of the entire aircraft, nor is it expected to. I don’t know where you are going with that. The use of canards as high speed pitch controls is well demonstrated over a long time period.
The canards have another problem and that is that they are typically either slightly dihedraled or massively anhedraled to stabilize directional control and prevent excess rake.
But by the time you are playing superman with the nose honked way back, you may well -want- added yaw effect (from the twin rudders) so you can coordinate turns. Having canards neutralize sideslip is contrary to the point here.
The dihedral/anhedral on a canard is more due to vortex control at higher AoA than traditional stability. Especially in an aircraft with FBW on all control surfaces.
Keeping the canards neutral to the angle of flow in high AOA conditions thus looks like significant downforce, but it’s exactly the opposite: neutral, taking them out of the game altogether.
The photos do not have the canards neutral to the flow, they are still at a positive AoA (albeit negative setting angle). Also see the earlier point about shifting aero-centre of the wing with AoA.
Canards are generally worthless above what we would consider landing speeds and while this can (because of pilot G tolerance restrictions in using true accelerative departure rather than lift induced pitch pointing) include a lot of post stall nose control, it doesn’t make the canard penalty worth their restricted use overall.
I cannot begin to emphasis just how off the beaten track that is.
What canards do in highspeed flight is act as a big LEX which keeps trim forces on the tail small so that you don’t lose supersonic maneuver authority keeping the nose from Mach tucking. They become a necessary evil when you have such a long fuselage that you have to push the wing back to get the proper static margin relief between CG and ACL.
Agh. No. No no no no.
Mach tuck occurs in transonic flight only.
Shifting aero centre from subsonic -> supersonic will persist above ~M1.2. The c.p. at M0.6 will not be the same for 99.9% of aircraft at M1.5. [Interestingly, the YF-23 was supposedly close to being an exception to this – hence its alleged superior high speed maneuvering relative to YF22, which itself is top of the pops right now for supersonic turns.]
The canards in high speed flight are a more authoritative trim and control mechanism than anything on the trailing edge (or an elevator without TVC trim).
And actually, if you look at fluid dynamics, it is possible for a center of pressure to be so large as to act -outside- the body of the airframe and thus outside it’s total mass footprint. As I recall, it doesn’t typically happen outside of high end supersonics (around Mach 3.6 or 3.8 IIRC) but it is possible and it is what waveriders use to surf the shock with.
I believe you are confusing aero centre with mass centre. An aircraft will always pivot about its mass centre.
If the aero centre is outside of the mass footprint, then the aircraft will not fly very long. End of. There may be regions of higher Cp away from the aircraft near-stream, but the aero centre will always reside on the airframe.
The mass centre is the pivot about which the aero-centre acts when it is turning an aircraft. If an aircraft is in steady level flight, then by definition the aero-centre (of the entire aircraft, not just wing/body) and the mass-centre are co-located. There can be absolutely no exceptions on that point [well, assuming the thrust of the engine is also acting through the centre of mass].
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