REFLECTOR:Vortex Generators on XL

[Jim Sower]

<...  I can reduce aft cg by installing vgs on the main wing only ...>
Yes.  But I don't know how to quantify that change in CG relative to AC so don't bet
the farm.

<... 1/2" elevator trim to take off ...>
With what kind of load in front seat?  Just you?  Or you and someone else?  What is
your elevator position flat out at 8k ft?  Is it negative?  If so, how much?

My best understanding of "stall proof" canard airplanes and "deep stall" is that (at
the risk of over simplifying) canard airfoils have more chamber than main wing
airfoils and therefore will stall at a lower AoA.  Negative (nose up, TE down)
elevator increases effective camber and makes canard stall sooner still.  If the
elevator deflection is negative (TE up) the effective camber decreases to the point
that the main wing could stall first.  Soooo, assuming that all the incidences are
correct, the danger of deep stall occurs when a) you are at high AoA, and b) you have
TE up elevator.

To the best of my knowledge, the neutral pitch stability that Scott alluded to does
not really happen with positive (TE down) elevator in the steady state condition.

Alex, please correct me if I'm wrong here .... Jim S.

John Dibble wrote:

> So It sounds like I can reduce aft cg by installing vgs on the main wing
> only, instead of putting weight in the nose.  I'm not concerned about
> defeating the purpose of vgs, because I think in my case I already have
> the benefit by being aft cg.  For example I only need 1/2" of elevator
> trim for takeoff.  I know I don't have any technical data to support
> this, but hey, I gotta start somewhere.
>
> John