(remember the adds for the differential flaps on the "T" Bird and the "flys better in the wind" airfoil for the Smoothy).
What hasn't been addressed is does the polywog airfoil have any advantages? In the post on Hi Johnsons "Stuka", Hi seems to think that it performs as good or close enough to a flapped symmetrical design without the hookup complication (on his version of the Stuka with the double angle TE the full flaps would be a challenge). In an article on the sidemount Barnstormer, Dave Cook indicated that Lew Andrews also thought that the flat flap with square edges gave performance that matched the flapped ships. Now the question is if it works well with fixed TE flap does it work better or worst with movable flaps?
A few comments that are illustrated in other threads and mentioned often enough...
1) Just a FWIW: I don't remember anyone mentioning the airfoil of the "Smoothie" in the windy weather ads. Although the term airfoil technically refers to an actual wing, we are used to using it in place of "wing section", and since we're talking about the chief's section, I assume this was meant. My impression has always been that the planview shape of the "Smoothie's" wing was given the credit for windy weather advantages. I can see this, since it approximates an elliptical wing. The MAC of an elliptical wing is about 42% of the half span out, which is farther inboard than any other shape not approaching a delta or triangular wing. This concentrates the lateral upset forces inboard, where they don't have as much unbalanced leverage. So I wouldn't think in those terms regarding airfoils - pollywog or not.
2) I think that the polywog shape would be a disadvantage with flaps, since like Al Rabe and Igor Burger say, it should be better to ease the transition at the hinge line by making the aft section, before the flaps, a bit convex.
3) I agree that the polywog, perhaps with the concave surface concentrated a bit further back, would be advantageous for flapless wings though, since it would be a smoother approximation of the ordinary section with flat stationary flaps - like the Flite Streak. As I posted, NACA tested at full size and found this to be a more efficient wing at zero flap deflection than one with the flaps as part of the "airfoiled" wing section. XFOIL agreed, when I had it test such a wing vs. the NACA 00xx section of the same % thickness.
4) Whether a plane flies better with or without flaps is a function of the following:
a) The tail moment available to overcome the wing's negative pitching moment tendency from deflected flaps. The PDQ "Super Clown", Sterling
Yak-9 and P-51 come to mind as too short-coupled to show a definite advantage.
b) The relative deflection of flaps and elevator.
c) Personal preference.
I think that the polywog airfoil might be quite good on a flapless plane, but cannot imagine it being any kind of advantage on a flapped plane. From what I've read, the squared-off t.e. flap has advantages - what used to be termed the Kamm effect on race cars. Probably a tapered flap, like 1/4" -> 1/8", with sharply edged trailing edge would allow the air to rejoin down stream, giving the effect of an area increase. Again, amount of flap used vs. total wing area is the consideration.
Edit: The last question...I'd think that the flat moveable flap, or a tapered thin one as described above would be better than one incorporated in a classic airfoil shape. I
think that Al found this to be true in his famous experiments.
SK
Topic: The why behind Hi's Polywog airfoil. (Read 15827 times)
