Wing root seals

As I was peeling the dead glue off from where the old wing-root seals had been stuck on by the previous owner, I got to wondering about something (one's mind being prone to wandering while picking off old contact cement)...

Wing root seals, as I understand them, are used to seal off the openings where the control linkages pass from the fuselage into the wing, while allowing the control linkage to move. They're a kind of plastic bellows or cone that is tightly attached to the linkage and the edges of the opening at the wing root, so the linkage can move but air can't bleed through. Apparently the purpose of this is to keep air from flowing from the fuselage out along the wing and out into the airflow through the spoiler caps (if the spoiler boxes aren't airtight) or (more commonly) through the openings where the control surface actuators emerge from the wing. I gather that air bleeding out through these points can create very significant amounts of drag (Johnson's flight tests show major changes in the polar when the 'wing root seals' are missing, and I assume he's talking about the same seals).

So, as I was pondering all of this and staring at the inside end of my wing root, I noticed that I was looking at the inboard end of the flap. To accomodate the leading edge of the flap, the main wing ends in a box: there's a vertical wall ahead of the flap, and the upper and lower surfaces of the wing are continued aft of the wall for a short distance. The flap is hinged on the lower surface, and as it deflects up and down its curved upper surface 'rolls' in and out of the extended upper surface of the wing. This particular flap does have a seal along the lower surface to prevent air bleeding through from bottom to top.

This 'box' around the L.E. of the flap extends all the way to the wing root. Where, of course, it sits next to the fuselage, a few tenths of an inch clear of the fuselage side. There's gap tape above and below, of course, but there's an air volume at the wing root between the upper and lower gap tapes, and air can flow from the fuselage out into this 'gap volume' and from there into the flap box (if I can call it that) - which must create a huge air leak along the entire upper edge of the flap!

If that's the case, I can't imagine that preventing air leaks through the aileron control linkage matters at all!

Am I right? Am I wrong? If I'm right, any suggestions for how to seal that 'flap box'? A simple seal won't work, because the flap comes all the way to the wing root, so the moving flap end is in the plane where the seal would go and would wear away a simple plastic seal. (Wish I could draw this.)

The flap/fuselage junction area is just plain difficult to seal on lots of gliders. Which is a pity, because you do need to get a good seal there in order to make the wing/fuselage fillet function properly.

Chances are good that someone with a ship just like yours might have already figured out the best way of sealing the area for that glider type. I'd suggest you find a type-centric forum to ask your question on.

Getting a good seal there is why you see that the flaps on some newer 15-meter racers don't go all the way to the fuselage. Instead, there's a short (50 mm or so spanwise) unflapped section that butts against the fuselage. Taping around the perimeter of the wing/fuselage junction creates an airtight seal between the fuselage and the wing. The LS-6 is a good example of this, and I'll be doing something similar on the HP-24.

Bob K.

Hello,

I went through exactly the same pondering when refinishing the wing root seals on my Mosquito. It sounds like the ship you are flying is identical with regard to flap setup, is it a Ventus B or Mini Nimbus?

Anyway, I fabricated a couple of 'rods' from soft cell foam, wrapped them in cellophane to make them air tight, which the foam is not in itself. You then insert these rods into the 'flap box', and you have a seal that will (if nothing else, in your mind prevent the air from flowing. A couple of notes: - You should experiment with the size (I used foam of about 40 cm. in length, and 3 x 4 centimeters thick) and flexibility of the foam. Very soft, very flexible seems to be the best, as it will not impair flap movement at all. - When doing something like this, off course you must make absolutely sure that whatever you put into your wings could never shift around and impair control movement. - The foam/cellophane loses its flexibility over time, so I replace these seals about once a year, which is quite manageably, compared to the other costs of soaring

Have fun, Lars Peder