Aeordynamic Q's

[BRIGADEAVIATOR]

Ok so here's what i have to find out... 1)Why is it that one aileron deflects up farther than the down deflected aileron? 2)Atleast on a Cessna 172s why is it that when an aileron is deflected up there is a portion of the aileron that protrudes on the bottom side of the wing? any help appreciated

Raul

 

[legaleagle]

Look at where it is hinged. It is either at the top or bottom depending on the aircraft, not in the center. Thus if a aileron is hinged at the top of the wing, it will extend past the wing surface more when deflected up, than when deflected down.

 

[BRIGADEAVIATOR]

thanks, i understand that part, but why is it that way. or what purpose does it serve aerodynamic wise?

 

[Flymach2]

There are primarily two types of aileron designs in GA airplanes. The first type you mentioned is the "differential" type where the up aileron has a greater displacement than the down aileron. The other type you referred to is known as "Frise" type ailerons. Both accomplish the same thing but in different ways.
As you know, when entering a turn you have to use coordinated rudder input. What happens if you don't use rudder? That's right, the nose of the airplane wants to move in the direction opposite the turn. This phenomena is commonly referred to as "adverse yaw". So to assist in correcting for adverse yaw, designers implement these two aileron types.
On the first type, the differential, the "up" aileron moves up farther than the "down" aileron moves down. When the "down" aileron moves down, it changes the chord of the wing and effectivley increases lift. This increase in lift also causes an increase in drag and the nose of the airplane wants to move in the direction opposite the turn. So, the up aileron causes some drag on that wing and helps, along with rudder, to keep the turn coordinated.
The "frise" type accomplish the same thing, but instead the leading edge of the "up" aileron drops below the bottom of the airfoil into the free stream of air and causes the drag which helps correct for adverse yaw. Good luck!

Regards

 

[BRIGADEAVIATOR]

Flymach2 thank you very much for you input...greatly appreciated!!

 

[Tinstaafl]

There's a reason for the above: To raise & lower opposite wings during a roll the lift must be increased on the upgoing wing and decreased on the downgoing wing.

A consequence of increasing Lift is increased Drag for that part of the wing. Conversely, reduced Lift will result in reduced Drag. The increased Drag on the upgoing wing will cause the a/c to yaw towards the upgoing wing ie 'away' from the roll/direction of turn.

There are a couple of common solutions to this: Reduce the amount of increased drag on the upgoing wing, or increase the drag on the downgoing wing.

Drag on the upgoing wing can be reduced by using Frise ailerons. This design uses differential cams to cause the 'down' aileron' on the upgoing wing to move down less than the 'up' aileron on the downgoing wing moves upwards. The effect is to increase the lift on the upgoing wing less than the lift is reduced on the downgoing wing. This, in turn, causes a differential change in drag between the two wings. Not as much of an increase in drag on the upgoing wing, and not as much of a drag reduction on the downgoing wing when the two are compared to each other, or the S&L case.

End result is not as much adverse yaw ie the nose swinging away from the intended turn during the roll in to the turn.

The other common method is to hinge the ailerons so that the upgoing aileron (ie the downgoing wing) protrudes its leading edge below the wing. This increases the drag on the downgoing wing, countering the increased lift - and drag - on the upgoing wing.

Another method is to have a spring interconnect between the ailerons & rudder. Applying aileron causes the rudder to move, countering the adverse yaw. This doesn't really reduce the underlying aerodynamic effect. It only substitutes for what a competent pilot should be doing with his/her feet anyway.

 

[Flymach2]

You're very welcome, Brigade. Good luck to you.

Regards