> Hello John;
> I am interested by your information concerning laminar
> flow. What is your idea to reduce drag?
>
> bientt,
>
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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