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Last modified: 0 4 / 20 /1 9
II.E. Airplane Flight Controls
Objectives The student should develop knowledge of the elements related to primary flight controls, trim control, and wing flaps. Key Elements Primary flight controls—airflow and pressure distribution Trim relieves control pressures Flaps increase lift and induced drag Elements Primary flight controls Trim controls Wing flaps Schedule 1. Discuss objectives
- Review material
- Development
- Conclusion Equipment White board Markers References Instructor’s Actions
- Discuss lesson objectives
- Present lecture
- Questions
- Homework Student’s Actions Participate in discussion Take notes Completion Standards The student can explain the primary flight controls, their function, and how they do what they do. The student understands how trim works and can more effectively use it, and understands the different types of flaps and their differing characteristics.
Last modified: 0 4 / 20 /1 9 References FAA-H- 8083 - 25B, Pilot’s Handbook of Aeronautical Knowledge (Chapter 6 )
Last modified: 0 4 / 20 /1 9 Slot forms, air flows smoothly over low aileron, more effective at high AOA. Adverse yaw is not eliminated—coordinated rudder is still required. 172RG: Differential and Frise-type; down 20°—up 15° Elevator Control pitch about the lateral axis. Operated through steel push rods. Pulling controls backwards deflects the trailing edge up—decreases the camber of the elevator, creates downward aerodynamic force— tail moves down, nose moves up about CG. Moving controls forward deflects trailing edge down, increasing the camber, creating more lift, moving the tail upward and pitching the nose down. Strength determined by distance between CG and horizontal tail surface. Types of elevators T-tail: elevator above most effects of downwash from the propeller and airflow around the fuselage and wings in normal flight— consistent control movements in most flight regimes. Slow speeds—elevator must be moved through a larger number of degrees to raise the nose a given amount, since it doesn’t have the downwash to assist in raising the nose. Stabilator: movable horizontal surface, combines horizontal stabilizer and the elevator. Controls pulled back—stabilator’s trailing edge raises, rotates nose up. Pushing forward—lowers trailing edge and pitches the nose down. Anti-servo tabs incorporated on trailing edge to decrease sensitivity. Move in the same direction of the trailing edge. Movement of antiservo tab causes it to be deflected into the slipstream, providing a resistance so that the pilot does not overcontrol the airplane. Rudder Controls yaw around the vertical axis. Operated through cables.
Last modified: 0 4 / 20 /1 9 When the rudder is deflected, it exerts a horizontal force in the opposite direction. Pushing the left pedal moves the rudder left, altering the airflow around the vertical stabilizer, creating a sideward lift—moves the tail right, yaws the nose to the left. Effectiveness increases with speed. Any slipstream flowing over the rudder increases effectiveness. Primary purpose is to counteract adverse yaw and provide directional control and coordination. Trim controls Used to relieve the need to maintain constant pressure on the flight controls. Usually consist of cockpit controls and small hinged devices attached to the trailing edge of primary control surfaces. Minimize workload by aerodynamically assisting movement/position of controls. Trim tabs Most common installation. Single trim tab attached to the trailing edge of the elevator. Operated manually through control wheel/crank. Moves in opposite direction of elevator surface—placing the trim in full nose-down moves the tab to its full up position. Tab up, into airstream, airflow over the tail forces the elevator down, causing the tail to move up, resulting in a nose-down pitch change. Tab down, air flowing under the tail hits the tab forcing the elevator up, reduces elevator’s AOA, causing the tail to move down, resulting in a nose-up pitch change. Balance tabs Look/function like trim tabs, but they are attached to the control surface rod. When controls are deflected, the tab automatically moves in the opposite direction, easing the load. If the linkage is adjustable from the cockpit, the tab acts as both a trim and balance tab. Antiservo tabs Serve to decrease sensitivity and also as trim devices to relieve and maintain control pressure. When the trailing edge of the stabilator moves up, the trailing edge of the tab moves up. Works the same way as the balance tab, but moves in the same direction. Ground adjustable tabs Metal trim tab on the rudder bent in either direction while on the ground to apply a trim force. Displacement found through trial and error. Flaps Most common high lift devices. Attached to the trailing edge of each wing to increase lift and induced drag for any given AOA.
Last modified: 0 4 / 20 /1 9 Can also assist in turning the plane if needed to increase bank. Autopilot Pilot relieve modes. Reduces pilot’s workload. Can maintain direction and altitude, accounts for the wind. Conflicting signals or unusual attitudes might disengage the autopilot. Canard Make attaining a higher AOA harder, but increases maneuverability when there and can maintain higher AOA better. May provide lift after the main wing has stopped providing lift.
Last modified: 0 4 / 20 /1 9 Conclusion Brief review of main points. Airplane’s attitude controlled by deflection of primary flight controls. Trim controls relieve necessary control pressures. Flaps increase lift and induced drag, creating compromise between high cruise speed and low landing speed.
