Hi Folks,

Another day and another question yet again! Hopefully I'm not becoming too much a nuisance with all these questions

With tapered wings, is right to assume that because the tips are smaller than the wing root, there will be less wingtip vortices produced compared to a wing of the same area and span? Is it also safe to assume that due to the smaller tip area, that it contributes less to lift than the rest of the wing?

Secondly, I have seen graphs which show the CL to wingspan distribution of a tapered wing, and it tends to show that the wingtips have a higher local CL than the rest of the wing, which leads to the common explanation that it suffers higher aerodynamic loading and hence will stall first there, all things remaining constant. Why does it have a higher local CL and suffer higher aerodynamic loading at the tips?

Cheers again for any input!

Gidday

Almost every discussion on aircraft design contains many instances of the word 'compromise'. The most obvious solution to the spillage of air around the wing tips is to have smaller wing tips and therefore less opportunity for air to flow. Taper allows the inboard section of the wing to have a large area as well as added strength. However, taper also results in a tendency for the wingtip to stall first. This can be overcome by twisting the wing so as to have a smaller angle of incidence at the tip - washout. A higher local CL at the tip helps to compensate for the reduced angle of incidence. This allows the wing tip to still contribute to the total lift envelope while at the same time, the smaller tip reduces the induced drag.

Note that it isn't always the case that the tip section will have a higher CL than the root. In the case of the Cessna 152, the wing section changes from cambered at the inboard section to symmetrical at the wing tip. As is so often the case, the designer's constant need to compromise makes it very difficult for people like us to look at a wing design and come up with a simple single-sentence explanation for why he's chosen to do what he did.

Thanks Bob.

So what causes the wingtip to actually stall first on a tapered wing if everything remains constant i.e. no washout etc?

When people say that a tapered wingtip is more aerodynmically loaded, does that mean, that although the wingtip produces less lift overall compared to the rest of the wing, for each unit of wing area, the tip contributes more lift due to the higher local CL, the exception being something like the 152 you described?