REFLECTOR: Pitch trim and pitch stability.

[Laurence Coen]

Al,

I did qualify it when I said, "unless it was set wrong in the first place", which I think applies in your case.  Set correctly the elevator should stall before the canard thus limiting pitch-up.  On the early Velocities that experienced deep stall prior to the re-design of the wing and canard, cuffs were added to the leading edge of the elevator causing it to stall sooner.

Larry Coen
N136LC


From: Al Gietzen 
Sent: Monday, November 23, 2009 12:39 PM
To: 'Velocity Aircraft Owners and Builders list' 
Subject: Re: REFLECTOR: Pitch trim and pitch stability.


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



--------------------------------------------------------------------------------


_______________________________________________
To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20091123/641cefb1/attachment.htm>