REFLECTOR: Velocity 20B update

[Al Gietzen]

Elevator is not at max up position, but I do run out of trim, at about 170
KIAS.  Faster than that the trailing edge is up 1 ½” or more, and that is
just a bit much.  Also, at the low end the canard is stalling (gear down) at
75-80 kts, meaning landing speed is 90+, and end up with only about ½”
trailing edge down on landing. 

John wrote:

I'm far from an expert here, but it seems like shortening the canard will
make the stall problem worse.  Seems like the canard incidence is up too
much.  When you do a power off stall (flying solo) is the bucking strong,
mild, or just a mush?  If it is strong-mild, then perhaps there is room to
reduce incidence. 

I’m no expert either, but it’s more complicated when you add a ‘fowler flap’
elevator to the airfoil.  The issue seems to be the canard stalling before
you can get full down elevators. The incidence was initially set exactly to
the gauges (presuming they are correct).  I then reduced the canard
incidence by about 1 degree (roughly 3/16” front to back on a 12” wide
canard).  It helped, but not a lot.  The advice from the factory was not to
decrease incidence further because of risk of reducing the differential
between canard and wing too much.  The suggested options were to add VGs to
the wing, or shorten the canard.  If my logic is correct, VGs on the wing
will help the low end condition, but not the top end.

Canard stall is more of a buffet and mush than pitch buck.  I still have
about half the elevator cuff on, which reduces the pitch buck.  Although at
the current landing condition trim of only ½” trailing edge down, the gap is
small and the cuff likely makes little difference.

 I can trim the elevator full trailing edge down (on the ground), but not
full up – so I am going to put a block between trim spring and the torque
tube bracket for more trim up 

I don't recall the spring arrangement, but I seem to recall that a block
will move it in the other direction (less trim up).  Maybe someone else
knows. 

The trim spring attaches to the backside of the bracket on the torque tube.
The spacer block goes between the spring and the bracket which brings the
trailing edge further up.  

I’d thought about reversing the sparrow strainer, but I’m concerned about
making it more pitch sensitive. 

I did not notice any change in pitch sensitivity when I reversed the
strainer. 

I think that is very interesting.  Unless I misunderstand, the sole function
of the sparrow strainer is to increase the stick force in pitch at higher
speeds to reduce the ‘apparent’ pitch sensitivity.  It makes you push harder
against the spring in one direction, and the airfoil load in the other.

 Steve Murphree is suggesting I should put on a larger sparrow strainer. 

Seems like this would cause you to run out of trim at an even slower IAS
because the strainer is working against the spring, pushing the elevator
down. 

That is true.  More work to be done.  I am going to add some VGs on the
wings, and the spacer on the trim spring as the next step; and see how
things work.  That should have effect (hopefully good) at both high and low
speed ends.

Al 

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