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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 />

Rotors in practice 119<br />

Fig. 4.2 (a) A representative rotor head in which <strong>the</strong> flapping and dragging hinges are coincident but with <strong>the</strong><br />

fea<strong>the</strong>ring hinge situated outboard. (b) Offset flapping hinges allow a couple to be transferred to <strong>the</strong> head when<br />

<strong>the</strong> tip path plane is not orthogonal to <strong>the</strong> shaft axis.<br />

4.3.2 <strong>The</strong> tip path axis<br />

<strong>The</strong> axis at right angles to <strong>the</strong> tip path plane is generally called <strong>the</strong> tip path axis or disc<br />

axis. <strong>The</strong> resultant thrust <strong>of</strong> <strong>the</strong> rotor aligns within about a degree <strong>of</strong> <strong>the</strong> tip path axis,<br />

and for most purposes <strong>the</strong>y can be considered to be coincident. <strong>The</strong> tip path axis is also<br />

called <strong>the</strong> axis-<strong>of</strong>-no-flapping in some texts, although this term is not strictly correct<br />

because <strong>the</strong> existence <strong>of</strong> harmonics in <strong>the</strong> blade motion cause <strong>the</strong> blades to flap slightly<br />

with respect to <strong>the</strong> tip path axis. By <strong>the</strong> same token <strong>the</strong> tip path plane is not strictly a<br />

plane.

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