Aircraft Flight Controls: Flaperons and More

Movable Wing Slats

• Movable wing slats are used during landing or maneuvers that approach the stall, but are retracted in normal flight to minimize drag.
• Types of wing slats include:
  • Automatic: extend as the angle of attack (AOA) increases.
  • Fixed: permanently extended, often used on specialist low-speed aircraft or for simplicity.
  • Powered: controlled by the pilot, commonly used on airliners.

Leading Edge Flaps/Krueger Flaps

• Hinged flaps that fold out from under the wing's leading edge, increasing camber and thickness.
• Invented by Werner Krüger in 1943 and evaluated in Goettingen.
• Found on many modern swept wing airliners.
• Often used in conjunction with trailing edge flaps to reduce nose-down pitching.
• As flaps are extended, drag increases at a greater rate than lift.

Aircraft Flight Controls

• Unusual/dual purpose controls include:
  • Ruddervators
  • Elevons
  • Flaperons
  • Stabilator

Ruddervators

• A movable airfoil at the trailing edge of a V-tail airplane.
• Performs functions of both a rudder and an elevator.
• For elevator control, both moving surfaces move up and down in the same direction.
• For rudder control, both moving surfaces move in opposite directions.
• As elevator, pulling the control stick/yoke causes the tail to move downward, pitching the nose up.
• As elevator, pushing the control stick/yoke causes the tail to move upward, pitching the nose down.
• As rudder, pressing the right rudder pedal causes the tail to move to the left, yawing to the right.
• As rudder, pressing the left rudder pedal causes the tail to move to the right, yawing to the left.

Elevons

• Combine functions of elevator and aileron.
• Frequently used on tailless aircraft like flying wings/Delta wings.
• Installed on each side of the aircraft at the trailing edge of the wing.
• Turning the control yoke/stick to the left causes the left flaperon to move up and right flaperon down, making the plane roll to the left.

Flaperons

• Pilot controls for lowering or raising the flaperons are separate from those controlling the aileron function.
• A mixer is incorporated in the design to combine the two pilot inputs appropriately.

Secondary Flight Controls

• Wing Flaps
• Leading Edge Devices
• Spoilers
• Trim Systems

Flaps

• Devices used to improve lift characteristics of a wing.
• Mounted on the trailing edges of the wings of a fixed-wing aircraft.
• Reduce the speed at which the aircraft can be safely flown and increase the angle of descent for landing.
• Shorten takeoff and landing distances.
• When used during takeoff, flaps trade runway distance for climb rate.
• The amount of flap used on takeoff is specific to each type of aircraft.
• Flaps may be fully extended for landing to give the aircraft a lower stall speed, allowing for a slower approach and shorter landing distance.