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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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120 <strong>The</strong> <strong>Art</strong> <strong>of</strong> <strong>the</strong> <strong>Helicopter</strong><br />

(a)<br />

(b) (c)<br />

Fig. 4.3 (a) A helicopter in steady forward flight requires a combination <strong>of</strong> forward and lateral cyclic inputs<br />

to neutralize flapback and inflow/coning roll. Note <strong>the</strong> tip path axis that is very nearly aligned with <strong>the</strong> rotor<br />

thrust, <strong>the</strong> control axis, and <strong>the</strong> shaft axis that are generally not coincident. When observed with respect to <strong>the</strong><br />

control axis, <strong>the</strong> blades do not fea<strong>the</strong>r, but instead appear to flap. Note that even a hingeless rotor with rigid<br />

blades can flap with respect to <strong>the</strong> control axis. (b) If <strong>the</strong> pitch control rods are parallel to <strong>the</strong> shaft and 90 ◦<br />

from <strong>the</strong> fea<strong>the</strong>ring axes, <strong>the</strong>n <strong>the</strong> axis <strong>of</strong> <strong>the</strong> swashplate is identical to that <strong>of</strong> <strong>the</strong> control axis. (c) <strong>The</strong> angular<br />

difference between <strong>the</strong> tip path and control axes is equal to <strong>the</strong> amount <strong>of</strong> flapping observed with respect to<br />

<strong>the</strong> control axis and to <strong>the</strong> amount <strong>of</strong> fea<strong>the</strong>ring observed with respect to <strong>the</strong> tip path axis.

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