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On some aircraft, the tip airfoil is symmetrical, while others carry their root foil all the way through the tip. It would seem an aerodynamic disadvantage to have a non-symmetric airfoil at the tip since it is not making much (any?) lift.

It doesn't seem to be simply for manufacturing purposes since it is on planes with tapered wings as well as straight wings.

Why is it incorporated into wing design?

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Camber shifts the airfoil's section of lowest drag of the drag polar to higher lift coefficients. In order to create the least amount of drag in level flight, an airplane wing benefits from moderate camber. Most of the lift is created in the mid section, but enough lift is left towards the tips to justify camber there, too. In case of elliptical or tapered wings, the design lift coefficient for lowest drag at a given lift will be equal over the whole span (elliptic wing) or even peak near the tip (highly tapered and untwisted wing with no regard given to stall behavior or spar mass).

Normally the tips carry less load than the inner wing, details depending on wing taper and twist. This helps to prevent the tip section stalling first at high angle of attack. Good aileron effectiveness also requires an airfoil which equally produces positive and negative lift at low drag.

One example would be the Me-262. When Ludwig Bölkow designed the wingtip, very little was known about transsonic effects and a thin, symmetric airfoil with an elliptic nose was chosen because it showed a late onset of transsonic effects in wind tunnel tests.

When North American later designed the F-86, the outer wing design of the 262 was copied over because it had worked well in the German design.

Many Horten flying wings used symmetric tip airfoils because the bell-shaped lift distribution needed for stability resulted in a slightly negative lift at the tips at low angle of attack and very little positive lift at high angle of attack.

With some designs I a sceptical that a symmetric airfoil has been used even if it is claimed so in David Lednicer's outstanding collection. The Lockheed P-3 is there listed with NACA 0014 at the root and NACA 0012 at the tip - no, the Lockheed engineers 60 years ago knew better than that!

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  • $\begingroup$ Thank you for the response. I should have been more clear in my question. I understand the use of symmetrical airfoils at the tips, just not for cambered airfoils. Could you please elaborate as to why positive camber at the wingtips is beneficial aerodynamically? $\endgroup$ – casousa Dec 8 '17 at 7:12
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Generally you want a slightly less effective AOA at the tip to keep the ailerons working near stall. A symmetrical section would do this if the root were flat bottomed. You wouldn’t lose as much cruise speed compared to washout.

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Symmetrical airfoils do not cause lift at all, because there is no pressure difference.They lift just because of the angle of attack.They are profitable on private jets because there is enough speed and the weight isn't large, so, symmetrical airfoils is enough.That's maybe not right, but it's my opinion.

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