Mike wrote:

In both cases I'd only considered cowl flaps that were hinged with piano hinge
across the bottom of the cowl. Now I've had a different idea. Refer to the
attached (poor quality) cross section view. The venetian blind sections are
rotated about a pivot point anchored at each end to the exit duct walls. The
sections are made from hot-wired blue foam and vacuum bagged with fiberglass or
carbon or whatever. Pretty easy to knock these out quickly, and with the airfoil
shape they are extremely rigid and still very light. I've made model airplane
wings like this for years. What's your opinion?

Paul Lamar replied:

Looks cool. Use carbon fiber as you could see as much as 0.7 psi on them at 200
MPH. 12 inch span 5 inch cord 60 square inches 0.7 psi ..... 42 pounds each.

Except that presumably half of the chord is shielded from the airstream by virtue of
being "inside" the cowl.  0.7 lbs / 1 sq.in. * 12 in * (5 in. / 2 [dimensionless]) =
21 lbs.

That 21 lbs (very approximate) works to both bow the flap as well as rotate it
(towards closed).  There's likely to be a pretty serious torque applied to the
pinion; make certain it is firmly attached to the flap.

And finally, depending on the angle of attack relative to the cowl line that the
flaps are in, only the first flap will see that (very approximate) 21 lbs of force.
The following flaps are "downwind" from the first, and so do not see the full brunt
of the airstream.

Russell Kent

Good work Russell. When I die or become completely senile you are 
going to take over :-)

Paul Lamar
 
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