REFLECTOR: Pitch trim and pitch stability.

[Al Gietzen]

There are two basic areas that builders are struggling with.  First is
having more than enough up trim and not enough down trim.  A change in the
spring torque tube attach to give more down trim and less up trim is likely
the simplest solution.  A more difficult problem is lack of trim range.
This is the situation if you have enough up trim, there isn't enough down
trim and visa versa. The increased flight envelope from minimum to maximum
speed is likely the culprit here.  A longer linear actuator or a stiffer
spring could help.  I don't like the idea of reducing the incidence angle of
the canard unless it was set wrong in the first place.  The unintended
consequences are reduced pitch stability, increased stall speed and rotate
speed.

 

It may not be important, but this may need some qualification. I expect that
even if set correctly, reduction in the canard incidence (AOA) can decrease
stall speed.  It is deliberately higher than minimum stall to ensure stall
before the wing. The bad consequence would be when the wing stalled before
the canard.  And it's a bit complex because it is not a fixed airfoil -
shape changes with elevator position.

 

Mine was set "correctly" according to the incidence gauge, but the incidence
gauge is only correct for the factory canard; not for the Alan Shaw canard.
Reducing the incidence about a degree reduced the stall and rotate speeds.
My flight experience suggests I still have good margin of canard stall
before wing stall - could possibly reduce incidence a bit further; but doubt
I ever will.

 

Al

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