Gurney Flaps

Question 1

Name the two mechanisms by which GFs increase lift.

Answer 1

1) Increase dumping velocity
2) Increase effective camber

Question 2

How do GFs increase dumping velocity?

Answer 2

They lower base pressure, which increases the dumping velocity and therefore, the circulation on the aerofoil.

Question 3

How do GFs increase effective camber?

Answer 3

The difference in size of the vortices at the GF base alters the streamlines, increasing the camber.

Question 4

How can GFs help avoid TE separation?

Answer 4

By increasing the dumping velocity, thereby decreasing the adverse pressure gradient.

Question 5

How can the change in camber due to GFs be visualised?

Answer 5

By drawing a line between the two base vortices, which will have more angle than the camber of the aerofoil.

Question 6

What effect do upward angled base vortices have?

Answer 6

They increase upward momentum, which increases downward momentum on the wing due to N2.

Question 7

What effect do GFs have on the CoP?

Answer 7

GFs move the CoP RWD.

Question 8

When are GFs inappropriate?

Answer 8

If a wing has a very flat pressure surface, and therefore is trying to achieve a laminar flow.

Question 9

Draw the effect that Gurney Flaps have on the flowfield.

Answer 9

Stagnation point moves counter to circulation.
Effective AoA increases.
Circulation region in-front of GF rotating CW.
Circulation region rolling around top of GF to base.
Circulation region rolling around TE to base.
The Kutta Condition is moved RWD, extending the effective chord.