[Ref The Pilot’s Manual PM2 Ground School Page 51]
Adverse yaw is aileron drag that the tendency for an aircraft to yaw out of a turn due to the increased drag produced by the down-going aileron (the up-going wing)
How the adverse yaw induced?
For example, to make the plane bank clockwise (use pilot view as reference). The Port side aileron should deflect downward in order to causes an effective increase in the camber of that wing section to increase the effective AoA (angle of attack). As a result, the lift from that wing increases, but unfortunately so does the drag.
Meanwhile, the starboard aileron rises, the effective camber of that wing section is decreased and its angle of attack is less, therefore lift as well as drag from that wing are decreased.
The differing lift causes the airplane to bank one way, but the differential aileron drag also causes it to yaw.
This is known as adverse yaw effect, or aileron drag, or adverse aileron yaw. Whatever you call this effect, it is mainly a low airspeed problem that you would most notice during a turn entry at low speed shortly after takeoff or on final approach.
Adverse yaw is opposite the direction of the bank;
Adverse yaw effect become more significant at low airspeed condition – during take-off and final approach ;
Adverse yaw effect is also more significant in aircraft with long wing spans.
How to improve or reduce the adverse yaw effect?
Adverse yaw effect can be reduced by various design:
- interconnecting the rudder to the ailerons
- differential ailerons
- Frise-type ailerons
Rudder is used to minimize the adverse yaw effect. It is the most simply way and we should have learned from the basic maneuver lessons.
Interconnected Ailerons and Rudder cause the rudder to move automatically and yaw the airplane into the bank. As a student pilot, we should learn the features of the plane at first feel lesson. Knowing the stability, maneuverability and controllability is important.
Differential Ailerons and Frise-type Ailerons cannot eliminate adverse yaw completely;
However, Spoilers can eliminate adverse yaw.
Notes: For those high speed aircraft, such as jet aircraft, they are equipped with spoilers to solve the aileron adverse yaw effect.
Differential Ailerons design aims to increase the drag on the down-going wing. This is achieved by deflecting the upward aileron (on the descending wing) through a greater angle (distance) than the down-going aileron (on the up-going wing). The greater aileron deflection means that drag is increased on the down-going wing, reducing (but not eliminating) the adverse yaw.
Frise-Type Ailerons is a design to make the leading edge of the down-going wing (when aileron deflecting upward) protrudes into the airstream beneath the wing causing increased drag on the downgoing wing while the leading edge of the up-going wing (when aileron deflecting downward) does not protrude into the airstream, causing no extra drag. In addition, frise-type aileron also forms a slot so air flows smoothly over the lowered aileron, making it more effective at high AoA.
Flaperons is simply combining both aspects of flaps and ailerons. It can be lowered to function much the same as a dedicated set of flaps.
Read More –
What’s a flaperon? (Ref ABC.net.au)
A flaperon combines aspects of both flaps and ailerons — hence the name.
On the 777, the flaperon sits behind the engine between two sets of trailing edge flaps. Passengers at a window seat behind the wing can clearly see the flaperon move as an aircraft comes in to land.