On 08/04/2012 07:03 PM, Fred Klein wrote:
> Apropos the recent thread on this topic, I found an old posting by John
> Lawton which may be enlightening:
Thanks Fred!
>> and the trim tabs when they are deflected. This equalization causes
>> drag, a lot of drag. So, the idea behind seals, both flap gap and
>> positive seals on ailerons (and rudder and trim tabs), is to prevent
>> this pressure equalization.
I never understood why these seals are not standard on the Europa. I
have seen them on other brands of homebuilts. Not only do they enhance
the performance, but they are also esthetically more attractive than
just a (often uneven) gap or a hinge line.
>> On N245E I used PVC weather-strip to create the flap gap seal. The
>> size will depend on how big your gap is between the leading edge of
>> the flap and the flap closeout when retracted. Choose a foam that is
>> slightly thicker than the widest spot in the gap you have. The XS flap
>> closeout looks as if it were designed to be sealed, given the flat
>> area at the bottom rear of the closeout.
How much air is going to this gap with the flaps extended? Is it
possible to make the underside of the wing flush with the flaps when the
flaps are retracted? This would reduce the size of the gap with the
flaps extended, does this have consequences?
>> According to Bruce Carmichael, renowned Aerodynamicist who wrote a
>> book on drag reduction in homebuilts, the wing root/fuselage
>> junction is another area of high drag on most airplanes. Sealing it
>> up helps, too.
Especially on the Europa, where both the wing and fuselage have a very
low pressure area at the same datum, the only good solution is to fill
in this area, like with Fred Klein's wing root fairings.
Another important thing here is to seal the doors properly. Otherwise
the suction will cause the doors to bulge out, releasing massive amounts
of turbulent air.
>> Aileron seals are a bit more tricky to employ. Some folks apply Mylar
>> strips over the hinge lines and think they've sealed their ailerons.
>> This /is not/ true. Mylar /is not/ a seal, but rather is applied to
>> help the boundary flow stay attached over the hinge line. Mylar is
>> also somewhat cosmetic in that it hides the hinge line. At high speeds
>> the Mylar will lift up off the wing due to the pressure equalization,
What if you seal both surfaces of the ailerons? The seal where the
highest pressure is (most likely the one at the underside of the wing)
will be pushed snug against the surface, blocking any leakage.
I have seals on the flaps and aileron and haven't observed any lifting
of the seals during flight.
>> For sealing ailerons you need to install what are known as positive
>> seals. These seals go from the leading edge of the aileron to the rear
>> of the closeout.
I find this a bit tricky. I can imagine that with such seals, inside the
closeout, can deform, get loose, wrap up, bulge out, and somehow jam the
ailerons. With standard Mylar seals applied on the outside you can't
think of any serious failure. If they get loose, they will just fly away.
>> In power planes
>> this translates to faster cruise, better climb rates and better fuel
>> economy.
I think many of us have invested more time and money for less
performance gain...
Frans
|