REFLECTOR: Best Configuration for Trailing Edge Fences

[Al Gietzen]

Dennis;

 

I also have aileron fences - inboard of the aileron.  I don't have the
dimension handy, but you can see them on the attached photo.  I don't have
before/after experience with them as I put them on at the get-go - prompted
primarily by tuft-testing done by local EZ flyers showing a layer of
span-wise flow at high AOA.  At high AOA the normal flow begins separation
toward the trailing edge, and flow comes down off the sides of the fuselage,
and flows outward under the separation. The slower the speed, the thicker
and more forward the layer.  I chose to assume the same would be true for
Velocity - and possibly further aggravated by the air exiting my wing-root
oil cooler and radiator.  That's a factor for you as well.

 

Of course the span-wise flow would negate the effectiveness of the 'up'
aileron, and add to the adverse yaw.

 

Those same tests showed nothing but straight flow under the wing, so my
guess is that extending them below the wing would have little effect, except
possible inhibiting some spill off the end of the aileron in the down
position.  I extended mine an inch or so below following the example of
Claus Savier.

 

I also have VGs on the wing, only in the area of forward of the aileron.
That did seem to make some improvement is low speed handling.  Still, lazy
use of rudders as you get slow on landing will result in considerable
adverse yaw when making corrections with the ailerons.

 

I may at some point experiment with some VGs on the canard.

 

On a related issue, some have noted improved aileron response by sealing the
gap at the aileron hinge line.  I taped the gap and could not tell any
difference in handling. Perhaps it has to do with the size of the gap, which
is very small on my plane.

 

About time for your first flight?

 

Al

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Dennis Martin
Sent: Friday, April 03, 2009 10:57 AM
To: reflector at tvbf.org
Subject: REFLECTOR: Best Configuration for Trailing Edge Fences

 

Rodney, thanks for the photos & dimensions on your trailing  edge fences .
I'm ready to install fences - just a few questions for those flying with
fences:

1) If you have trailing edge fences, how many are recommended on each wing?

2) I have a photo of a FG 173 with 3 fences on the leading edge. What's the
difference in performance vs trailing edge?

3) Science requires replication of the experiment. Besides Rodney, is anyone
else flying with trailing edge fences?

4) My primary objective is to reduce landing speed, and  increase control.
Besides VGs, which fence formula is best to achieve this goal?

Thanks in advance,

Dennis

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