Re: Air Scoops

[aegerter@dataway.ch (Simon Aegerter)]

>I think if someone did the pressure distribution analysis (hello, Velocity)
>you would find that the pressure above and below the wing near the trailing
>edge (and presumably also the strake) would be pretty much the same.

Al:
Depends what you mean by "pretty much". The 173 wing has a wing loading of
17 pounds per square foot, which is exactly the avarage pressure
differential. If I understand the system right a sqft has about 144 sqin,
so that translates to 0.12 psi, or 0.26". That is equivalent to the ram
pressure at about 120 kt (if I remember my pitot calibration procedure
correctly).

So, even taking the fact into account that the pressure differential tapers
off just about like the wing does, it cannot be neglected. The arm pit
scoops are placed on the better side of the wing and they have another
advantage: You can cut them at an angle of about 20 deg from the vertical
which makes them act like an automatic cowl flap. In slow flight, at high
angles of attack, the opening becomes bigger, in cruise it is smaller
thereby reducing drag.

Following these arguments and my experience flying my plenum cooled
Franklin engine I'll stick to the arm pit scoops. They work. My CHTs are,
if anything, too low. I have never seen a CHT above 320F. The hottest
cylinders are #1 and #2, the ones closest to the firewall. To me this
signifies that dynamic effects (air speed and momentum) are stronger than
static effects (pressure drop). In other words, we have adequate air flow.

In concluding this (sorry - lengthy) note I would like to second HYTEC's
plea that flying Velocitites should continue to share their experience on
the reflector.

Best
Simon

Simon Aegerter, Winterthur, Switzerland