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Old 3rd September 2002 | 09:37
  #29 (permalink)  
Q max
 
Joined: Jun 2002
Posts: 62
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From: UK
Basic physics a bit off

Nick GLS and vorticey (but especially Nick)

Respectfully I say: you are wrong (close but wrong)

For simplicity first consider only a pendulous type rotor head:

In the horizontal plane the disc must create a force equal and opposite to the t/r force - or you'll translate (right, right?)
(NO fuselage roll required yet)

In the lateral vertical plane an additional couple is created if the t/r is not in the same plane as the disc - the couple which opposes this the cg/vertical thrust couple. This is created by the cg 'stepping out' from under the point of suspension. I.E.:Fuselage is rolled by an ammount to the left.

(consequenses of this are odd: ie disc will be 'tilted to the left' but fuselage will tilt either left if t/r is below plane of rotation or right if t/r is above plane of rotation (no-one's made one like that tho') , zero FUSELAGE tilt if t/r in plane of rotation)

It is absoloutely not a function of t/r thrust height w.r.t. cg UNLESS you look at the INERTIAL scenario (ie accelerations - for instance if 'weightless' when t/r thrust above/below cg WOULD definately created a roll acceleration). This does not apply in the steady state hover. Cg 'height' does have a bearing on degree of roll since the 'restoring force' will be greater per degree of tilt for a cg which is further away from the disc.

So to answer the question: Yes you can make the fuselage level by messing around with the cg position - but the disc has still "gotta do what a disc's gotta do" ie tilt left.

Now consider the other rotor heads (breifly).
They all make a direct rolling moment on the fuselage (if there's a differance between disc plane and head plane) - so if the disc is tilted there is the additional consideration of how much that will tilt the fuselage BUT but a disc has still "gotta do what a disc's gotta do" ie tilt left.



(left/right when viewed from behind, terminology watered down for readability, some simplifications)
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