REFLECTOR:Vortex Generators on XL

[Chuck Jensen]

Jim, assuming the angle of incidents of the canard and wing to the plane is
correct rigged, the high AoA is not the cause of the stall; just how you get
can get into a deep stall.  One can certainly have a high AofA and there is
ZERO danger of deep stall if the CG is properly forward.  If the CG is too
far aft, you don't need a particularly high AoA and you still have deep
stall potential.  

If I understand all this, the plane must always be in a configuration that
the canard provides lift to fly.  If you get the CG way too far aft, the
canard would need to provide downforce on the nose to keep the nose from
popping up due to the heavy tail.  And canards are not designed to provide
downforce on the nose, only lift. 

Yee gads, its easy to understand (I think?) but it's even easier to confuse
when writing it down.  Help, before I drown in confusion...is the inability
of the canard to provide down force the reason (one of many, perhaps?) why a
Velocity can't do an outside loop??

Chuck Jensen

-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Jim Sower
Sent: Sunday, December 07, 2003 1:53 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Vortex Generators on XL


<...  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

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