Basic Flaps

[BaldEagl]

Originally posted by Yarbles
I thought that the surface area on top of a wing is greater by virtue of the shape and therefore the air flow is faster over  the top of the wing and the air pressure is therefore reduced. Lower pressure on top of the wing ='s lift.

Correct.

Do flaps infact when lowered below fully up increase this lift further but at the expense of increasing drag?

Correct.

Is that what flaps are all about in which case I can understand why a plane would turn in a shorter radius with flaps lowered so to speak.

Flaps are all about improving lift at low speeds.  The reason they make you turn better is that they allow you to slow down while keeping your nose in the air.

I think when new to flying properly grasping the principles or to put it another way the forces involved could be helpfull. Intuitively I see lowerered flaps as increasing the speed of air under the wing and reducing lift. I get this idea from the ailerons which dip on the wing that is dipping and rise on the wing that is rising. Can someone confirm that this is not what is going on.

The speed of the air under the wing doesn't change.  It hits the lowered flap causing a simultaneous braking and a lifting effect.  The more flaps you deploy the greater the effect.

Ailerons work the opposite of what you describe above.  Aileron up on the lowering wing and down on the rising wing.  The air then hits the aileron forcing the roll.


Several factors go into achieving flight.  The wing profile creates lift as you surmised above.  The faster the plane goes the more lift that is produced by this.

Angle of attack (the angle at which the wing is to straight flight) also creates lift to a point.  For this and other reasons most tricycle gear craft raise the nose wheel once a certain amount of ground speed has been achived on take off.  Beyond a critical point, too much angle of attack will cause a stall.

Flaps also add lift as air hits them.  The trade-off is speed and, as seen in my prior post, speed has a greater effect on lift than flaps.  That said, when landing or in a slow fight, flaps reduce stall speed by adding lift to the wing which it can't create through it's own profile at those speeds.

Hope that helps.

[Traveler]

Originally posted by BaldEagl
Edited from aerospaceweb.org:

assuming all other variables are constant

That's a mighty big assumption, where in the formual is drag?  or did they leave drag a constant.  As you add flaps drag go up.

[BaldEagl]

Originally posted by Traveler
That's a mighty big assumption, where in the formual is drag?  or did they leave drag a constant.  As you add flaps drag go up.

Good point.  They must have left it as a constant.  Note that while they talk about weight it's also not represented in the formula.

[Yarbles]

Originally posted by Krusty
Please do. I get enough sociopathic watermelon from 3 specific people on the forums as it is. They follow me around and reply to whatever I say with crap like that. I don't know if you're just joking or if I should make that "4" now...


EDIT: I just noticed something in your reply. I posted my original reply with all intent to be helpful. Was it not received as so?

Look mate the fact that you bother to try and help people makes you one of the very best of the best in my book,  I just used this opportunity to remind EVERYONE that we are all still learning but at different levels or stages

[Krusty]

Originally posted by BaldEagl
Ailerons work the opposite of what you describe above.  Aileron up on the lowering wing and down on the rising wing.  The air then hits the aileron forcing the roll.

This is purely academic, and basically a discussion in semantics, but I've heard it another way.

The aileron down on the one wing acts like a flap, and increases lift, while the aileron up on the other wing spoils the airflow, disrupting lift. Rather than simply pushing the wing around, surplus lift is given to one wingtip and lift is removed from another, causing the craft to roll.

That's how one book described it, but it could have just been creative with the terminology.


EDIT: Yarbles, no worries

[GooseAW]

another way I remember discussing it in ground school was that the flap down increases the distance that the air over the top of the wing has to travel to rejoin the air under the wing at the trailing edge. The higher velocity at which the air has to travel over the top of the wing creates more vacuum on the top of the wing (lift). This would presumeably be aided by the deflection against the underside of the flap as well I guess.

Not tryin to go all Einstein on anyone here. This thought process just helped me visualize the principal more clearly.