Wing root fairings

Robert Ehrlich wrote in message ...
Bert Willing wrote:

The Calif A21 has a pretty elaborate wing root fairing (I own one, so I
should know).

--
Bert Willing

ASW20 "TW"

"Slingsby" a écrit dans le message de
om...

For the sake of the discussion, why have an upper wing root fillet at
all? The Caproni A 21 wing blends into the top of the fuselage. What
are the advantages/disadvantages to this type of design?

A better example of a wing root without fillet is the LS1f. But the manufacturer
added them to the LS4. Another example is the Janus B (just had a look on our
Janus now disassembeld in the workshop).

I have done extensive dye flow testing on the wing root area of my
Janus C. The Janus has no fairing--the wing just butts into the
fuselage. Where the leading edge of the wing meets the fuselage, the
fuselage boundary layer is rolled up by the wing boundary later,
forming a horshoe vortex that trails back over and under the wing
root. This is caused by the velocity gradient in the fuselage boundary
layer. The flow just above the surface overruns the flow below, but
when it runs into the stagnation at wing leading edge, it doubles back
along the surface.

At hight angles of attack, the dye tests show a clear stagnation point
on the fuselage in front of the leading edge (about 10cm), and
reversed flow from the leading edge forward to the stagnation point.
They also show the vortex is attached to the fuselage above the wing,
where any dye that enters the vortex is scrubbed out at an upward
tilted angle relative to the flow. A thick line of dye marks the upper
edge of the attached vortex. The vortex separates from the fuselage
near the point of maximum wing thickess (where the fuselage also
begins to taper sharply), briefly attaches to the wing upper surface,
and then trails off into the flow. If you imagine bending one of those
pool toy "noodles" in half over the leading edge of the wing root,
then straight back on both sides, you would get a pretty good picture
of what is going on.

BTW, the interesting finding from the Maughmer wing root study was
that a concave fairing was actually worse than no fairing at all. He
got the best results from a straight 45 degree angle fairing. Perhaps
the concave fairing supports the vortex while the 45 degree fairing
does not?