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Touring Motor Gliders Association (TMGA)
edwalker

Is your cabin a bit drafty? I now know why...

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edwalker

Eric and I were flying a few weeks ago in my Phoenix fairly high in the Cascade mountains, and we both noticed how much cold air was coming into the plane from around our hips and through the center console. Last week Eric did some experiments in his plane and found the same thing, but tied it, correctly, to flaperon position, with neutral to positive flaps creating the biggest breeze. He hypothesized that the baggage area was being pressurized, but we were unable to figure out how the air was getting into that area. I think I now understand what's happening.

The increased pressure under the wings has two routes into the baggage compartment on each side. As the control rods pass out into the wing through the side of the fuselage there is a circular passage that allows their unimpeded movement. This communicates with an open area in the rear part of the wing just in front of the rear spar. What stumped me is how so much air could get into that space since the spar appears to seal it off and the wing joints are taped. On closer examination I found two routes. The first is the flaperon actuator which passes through the spar and allows the control rod move the surface. There's a hole about 2 inches in diameter there. Next there is a passage right at the outboard end of the spar which, even if you tape the wing extensions, is still allowing air to pressurize the area between the end of the wing and the wing extension. It looks like there is about a half inch or more of space between the end of the wing and the wing extension when the spar pin is tightened (your nav light wires utilize this space to cross over the top of the main spar extension), and the air does an end run around the backside of the rear spar into that space which communicates with the chamber in front of the spar to pressurize it, running straight into the baggage compartment. Taping the seam does not seal this passage. Multiply this by 2 since the other side of the plane is doing the same thing, and there is more than enough open area to do the trick.

Not sure how we can remedy this without sealing the control rod passage at the fuselage wall.

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TeriStar

I know the original post is 4 years old, but I had this draft problem happen in a big way today.  I was on a flight doing both power on and off, then when I was back on power and at 4000 ft when we got a lot of cold air coming into the cockpit from the pitch trim lever opening.  It had pretty good velocity and scared me that something must be wrong.  I landed immediately to check out the exterior.  Found nothing.  Took back off, had the draft for the first part of the climb, leveled off and it just suddenly went away.  I don't understand it.  If any Phoenix user has an understanding of this, I would appreciate info.  It feels more like some gap seal is opening at random.

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