My current wheel fairings are dimensioned exactly as you have described,
plus a 3:1 L:D ratio.
The result is good , but I think alot of the result comes from having a
vertical split, which allows both a much closer fit around the wheel and no
protuberances forward of the 50% chord position (which is where the vertical
split is positioned and is slightly aft of maximum thickness point at 40%).
By way of comparison, my Mk I set of wheel fairings were very similar,
except with a 2.5:1 L:D. The speed increase was identical (as best I could
measure), the 'poorer' L:D being offset by the lower surface area. All in
accordance with the theory for bodies-of-revolution as described by NACA
following experiments on buoyant 'dolphins'.
But a lot of work making moulds etc just to get to that point!
Duncan McF
>
> I was the one suggesting laminar flow wheel pants. A theoretical,
> laminar-flow shape is not fully rounded at the front, but more pointy as
> on the Europa wing. It's fattest part is around 40-50% back. Toward
> the tail end of the fairing, it is concave, IOW, squished inward at the
> back, meaning then the tail is not pointy, but like a vertical fin.
> This means also that the sides are more flattish than rounded when
> viewed from the front. Also true might be the manufacturer of this
> thing doesn't have a wind tunnel, so what they claim in sales literature
> is based on whatever crude method used to test it if they did. On a
> "fat" airfoil like this, maintaining flow attachment gets tricky.
>
> When we add a fairing to a necessarily smaller tire, we're adding
> significant pressure drag (looking at the thing from the front, and
> friction drag (wetted area). Hoerner's text, e..g, documents the drag
> of exposed wheels and fat faring shapes, and in the chapter on wheel
> fairings (not of laminar flow type), he suggests a drag reduction of
> less than one-half that of a tire in the breeze, even with a "hubcap."
> He does document, however, much greater drag reduction if a round gear
> leg is faired, and that fairings are placed where the leg meets the
> fairing and up at the fuselage junction (eliminate interference drag).
>
> An example of this are the fairings on the Grumman AA-5, which they
> claim as only 2 MPH boost and which I can't really see when they're on
> or off. Too small, and thus requiring controlled testing. These are
> not laminar flow, but classic airfoil shape, and they did little to
> clean up the turbulent mess around the brake caliper, nor the
> interference drag at the gear-leg junction.
>
> Reg,
> Fred F.
>
>
>
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