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Flaperon Control System

The flaperon control system, shown in figure 9-10, is an example of lateral control provided by an electrohydraulic-mechanical flaperon system. The system includes an inboard and outboard flaperon for each wing and three actuators (a single flaperon autopilot actuator and a flaperon power actuator in each wing).

Control stick movement, left or right, raises the respective two flaperons, while the opposite two remain flush with the wing. Full throw of the control stick by the pilot causes the inboard flaperon to rise 49 1/2 degrees and the outboard flaperon to rise 53 degrees. In flight, the flaperon can also be positioned by the AFCS. Control stick movements are transferred through the pushrod and bell crank system to the flaperon autopilot actuator. Mechanical outputs from this actuator are conveyed to a gearing mechanism, at which point linkage to the left and right wing flaperon power actuators separates. The gearing mechanism transmits movement to the left or right flaperon, while the opposite flaperon is

Figure 9-10.—Flaperon control system.

 maintained flush with the wing. When the flaperon pop-up cylinder is actuated, the gearing mechanism transmits pop-up motion to each wing flaperon power actuator.

The semiautomatic flaperon pop-up device aids in reducing ground roll during landing. The pop-up system is activated by the pilot placing the flaperon pop-up switch in the ARM position. All flaperons (four) will then automatically pop up approximately 41 degrees when the aircraft weight is on the landing gear and the throttles are retarded.

A mechanical interlock device prevents damage to the flaperons during folding of the wings. When the wings are folding, the flaperons cannot be extended. In addition, the folding operation cannot start unless the flaperons are flush with the wings. A wing-fold interlock prevents flaperon pop-up after the wings are folded. A fail-safe spring returns the flaperons to the flush position in case the combined hydraulic system or electrical system should fail.

The eddy current damper links mechanically to a bell crank in the flaperon control linkage. See figure 9-11. It dampens any rapid left or right control stick movement by producing an opposing force proportional to the speed at which the stick is moved. The damper contains permanent magnets, a rotating copper disc, a gear train, and a clutch assembly. Control stick motion rotates the clutch and gear train, which, in turn, rotates the copper disc. The copper disc is sandwiched in the air gap between the six permanent magnets and a flux plate. As the copper disc revolves, the magnetic field between the magnets and the flux plate is disturbed, causing an opposing force (eddy currents) that tries to stop the disc. The opposing force is proportional to the speed of the rotating disc and to the speed of stick movement. The clutch will slip at a force of 275 to 325 inch-pounds to prevent control stick binding if the damper jams.

Figure 9-11.—Eddy current damper.

 Figure 9-12 illustrates a representative flaperon control system. The flaperon autopilot actuator is powered by the flight hydraulic system and transmits mechanical movement to the flaperon power actuators. The flaperon power actuators are tandem type and powered by the combined and flight hydraulic systems. They are capable of operating on only one system if one system should fail. The artificial-feel bungee provides an initial control stick preload and increased force feel over the full range of stick displacement. The electro-mechanical actuator provides lateral trim, which varies the neutral position of the artificial-feel bungee. Trim is set by the switch on the control stick grip. The pilot may read the mechanical flaperon trim indicator on the control stick. See figure 9-10.


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