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The Art of the Helicopter John Watkinson - Karatunov.net

The Art of the Helicopter John Watkinson - Karatunov.net

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(a)<br />

(b)<br />

Engines and transmissions 195<br />

Fig. 6.2 (a)Drive train arrangement for a light turbine-engine helicopter; <strong>the</strong> Bell 206. (b)Drive train for<br />

twin-turbine helicopter. Each engine has its own one-way clutch so one can fail leaving <strong>the</strong> o<strong>the</strong>r to power <strong>the</strong><br />

machine. <strong>The</strong> tail rotor will be driven from <strong>the</strong> main rotor transmission.<br />

two constant velocity joints to allow relative motion <strong>of</strong> <strong>the</strong> gearbox and <strong>the</strong> engine. In<br />

some machines <strong>the</strong> turbine drives only <strong>the</strong> main transmission as in Figure 6.2(b). In<br />

many machines twin engines are installed. In this case a pair <strong>of</strong> autorotation clutches<br />

is needed, one for each engine. <strong>The</strong>n ei<strong>the</strong>r engine can fail and <strong>the</strong> remaining engine<br />

drives <strong>the</strong> transmission. <strong>The</strong> tail rotor drive must also come from <strong>the</strong> transmission.<br />

6.5 Correlators and governors<br />

<strong>The</strong> RRPM determines <strong>the</strong> rate <strong>of</strong> response to <strong>the</strong> controls and must be kept constant.<br />

It was shown in Chapter 3 that <strong>the</strong> power needed to drive <strong>the</strong> rotors at constant speed<br />

varies considerably with <strong>the</strong> attitude and flight regime. Governors and correlators are<br />

devices intended to make control <strong>of</strong> <strong>the</strong> throttle more or less automatic so that <strong>the</strong> pilot<br />

has less to do. <strong>The</strong> governor is a system using negative feedback to adapt <strong>the</strong> power

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