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REFLECTOR: Elevator wells and airflow



Hi all,

I don't remember if it was Alan Shaw, Mark Machado or Duane Swing that I heard
this from. If the surface of the elevator well in the rear most portion of the
canard is left unfilled i.e. with the tri-ax surface as rough as possible, the
elevators will work better as the airflow is enhanced.

Looking at this with the experience that I have in hi-perf engine prep and
racing, I can see how this may be true. In an engine port, one of the toughest
things that airflow has to do is to turn the "short side radius". This is the
part of the port that would be the floor of the port. Many things are done to
keep the airflow from shearing away from the port floor: raise the port, shape
the port and recently, surface treat the port in such a way that the airflow
stays attached.

One way to keep the airflow attached to the short side radius is to slow the
airflow down so that it doesn't have as much inertia, thus able to turn a
tighter radius. An example of this was illustrated in one article that I read
detailing dimples and center punch marks on the port floor to give the air
something to hang onto as it turned the port.

Back to the canard. With this in mind, I can see how the surface roughness of
the elevator well could indeed enhance the effectiveness of the elevator by
getting the airflow to turn over the top of the elevators over a wider range
of speeds.

The point I wish to ponder here involves the fact that prior to this
knowledge, I had gone to great pains to sand this area down quite smooth. If
Alan, Mark or Duane verify what I have outlined here to be true, I would like
to "roughen up" the surface again. 

US Paint, the makers of the 545 primer that Alan likes, is primarily a
supplier of boat paints. In their catalog they list a paint that goes on the
deck to prevent slippage by the crew. I imagine it would be a lot like a
rough, textured, gritty epoxy much like wing walk material. I think that a
layer of this or something like it applied in the elevator well, out to about
maybe the midpoint of the elevator hinge area, may be enough to slow the
airflow down to the point of doing some good.

Any thoughts?

Dale Alexander
173 RGE