8
$\begingroup$

I'm trying to analyse the relationship between the angle of attack and lift coefficient of a wing profile I tested. However, I am finding that the data shows that the wing hasn't stalled by the time it reaches an angle of 25 degrees, whereas I am under the impression that a wing usually stalls around 15 degrees. I cannot recall where I have heard it, but I am under the impression that one of the reasons the F-18 is capable of high AoA flight is because of the "surfaces" around the cockpit:

Is that correct? Is high AoA associated with smaller wing width and high chord length?

Also, this is the data I've gathered. I tested the same wing at three different airspeeds. Sorry about the text being in Danish.

$\endgroup$
  • $\begingroup$ Assuming you mean leading edge root extensions (LERX), LEX fences, and vortices. The answers to this question may be helpful, also this article. $\endgroup$ – mins Dec 16 '16 at 16:06
  • $\begingroup$ You may also have a look here. It is not the airfoil, but the kind of flow which is provoked by the extended wing roots. The wing is indeed stalled at 25°. And - no excuse needed for adding Danish plots. $\endgroup$ – Peter Kämpf Dec 16 '16 at 17:31
8
$\begingroup$

You're correct that the leading edge extension (LEX) plays an important part in increasing the maximum angle of attack of the Hornet/Super Hornet. The LEX basically forms a vortex above the main wing, which improves the high angle of attack capabilities by delaying separation. See this question about vortex lift and also another related question.

You can see the LEXs forming vortices over the wing in the following image.

F-18

An F/A-18E Super Hornet assigned to Strike Fighter Squadron (VFA) 81 maneuvers over the Nimitz-class aircraft carrier USS Carl Vinson (CVN 70) during an air power demonstration. (U.S. Navy photo by Mass Communication Specialist 2nd Class James R. Evans/Released)

Is high AoA associated with smaller wing width and high chord length?

There is no simple way to answer this question because what matters is not the aspect ratio of the wing per se, but the way the lift is created. In case the wings have high sweepback, the method of lift generation is by vortex lift, which operates in higher angle of attack compared to the normal (moderately swept) wings.

In other cases where the wing sweepback is less, the lift generation will be by conventional means and consequently, the high angle of attack performance will suffer, though this can be remedied by the use of canards, thrust vectoring etc.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.