直升机教员手册 Helicopter Instructor’s Handbook
时间：2014-11-10 08:35来源：FAA 作者：直升机翻译 点击：次
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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Coaxial rotors reduce the effects of dissymmetry of lift through the use of two rotors turning in opposite directions, causing blades to advance on either side at the same time. One other benefit arising from a coaxial design include increased payload for the same engine power. A tail rotor typically wastes some of the power that would otherwise be devoted to lift and thrust; all of the available engine power in a coaxial rotor design is devoted to lift and thrust. Reduced noise is a second advantage of the configuration. Part of the loud slapping noise associated with conventional helicopters arises from interaction between the airflows from the main and tail rotors, which in the case of some designs can be severe. Also, helicopters using coaxial rotors tend to be more compact (occupying a smaller ‘footprint’ on the ground) and consequently have uses in areas where space is at a premium. Another benefit is increased safety on the ground; by eliminating the tail rotor, the major source of injuries and fatalities to ground crews and bystanders is eliminated. The coaxial rotor system has the following disadvantages: 1. Mechanical complexity. 2. Poor hover performance characteristics of the smaller rotor disk in higher altitudes and warmer climates. 3. Heavier, stiffer blades required to prevent the blades from flexing into the other rotor rotating in the opposite direction. 4. Heavier rotor head and hub components to control and retain the heavier blades. Swashplate Assembly Explain to the student that the rotating swashplate couples stationary cyclic motion with rotating cyclic control movements. The drive link ensures that the rotating swashplate stays synchronized with the main rotor as it turns. The antidrive link and lever are attached to the aft side of the inner ring and swashplate support, preventing rotation of the inner ring. Point out to the student where these controls are connected. Also, point out (if installed) the stationary swashplate, rotating swashplate, pushrods, antidrive link, uniball, and pitch horns. [Figure 5-16] During preflight inspect for obvious damage, condition, and security of all components. Explain to the student that there are several different mechanisms for transmitting cyclic and collective inputs to the main rotor system. The Robinson R22 and R44 have the swashplate mounted on a monoball. This allows the entire swashplate to slide up and down on the rotor mast (for collective inputs) and tilt (for cyclic inputs). Figure shows how the swashplate slides up and down to transmit a collective pitch change. Figures and should be used by the instructor as references. Demonstrating to the student the actual movements on the helicopter is a better option, if available. Figure depicts how collective inputs affect the swashplate assembly. The red arrow is pointing to the bottom of the swashplate (A), B shows the entire swashplate has moved up the mast. Note the effect on the pitch links. Small hashed lines show that in B, the pitch link has moved up along with the swashplate (compare the top of the pitch link and the left-hand coning hinge bolt in the two pictures). Since the entire swashplate has moved up without changing its tilt, the pitch links have all moved up a set amount, but continue to move up and down during rotation in response to the tilt of the swashplate. Figure depicts how the cyclic inputs affect the swashplate assembly. Notice that the swashplate in A is basically level, while in B it has been tilted. The tilt forces the pitch link to move up as it travels to the right-hand side of the picture, and move back down as it travels to the left- hand side of the picture. As it moves up and down, the blade pitch increases and decreases. NOTE: On some helicopters, the control rods were routed internally up through the main rotor mast to protect them. On those helicopters, the cyclic inputs come down from the top of the mast and the swashplate is under the transmission, where it is all covered and protected from wires (Enstrom). Antitorque Systems Tail Rotor Explain to the student that the tail rotor is required on a single rotor helicopter to overcome the torque effect. This torque effect is the result of the fuselage turning in the opposite direction of the main rotor system. Figure depicts the main rotor blades turning counterclockwise and the fuselage (torque direction) turning clockwise in order to compensate for the unwanted torque of the fuselage. On a static aircraft, show the student how the inputs of antitorque pedals effect the pitch change in the tail rotor. Discuss with the student the emergency procedures for loss of tail rotor authority, loss of tail rotor thrust, loss of tail rotor components (forward CG shift), a break in the tail rotor drive system, and fixed pitch settings. Point out to the student the different parts of the tail rotor (if installed), including the pitch change tube, pitch change link, and the cross head assembly. [Figure 5-20] The Bell model 427 tail rotor assembly shown in Figure has an internal control rod which is designed this way for protection. Demonstrate that as the crosshead assembly moves in and out, it will change the pitch angle of the tail rotor blades via the pitch change link and pitch horns. When left pedal is applied, control tubes are moved and the lever assembly retracts the control tube. As the control tube retracts, the crosshead moves closer to the yoke assembly; tail rotor blade pitch is increased. Show how the tail rotor is much like the main rotor, except it is turned on its side and provides thrust instead of lift. Another way to describe the tail rotor is to compare it to an airplane propeller which also generates thrust and does not provide lift. Reinforce to the student the importance of keeping the antitorque pedals free of obstructions and having full range of movement. Emphasize that if a loose object fell during flight and were not retrieved, it could jam the pedals and reduce aircraft controllability. |
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