Natural Science Forum / Physics / General Physics / June 2008

For the rotational direction is anti-clockwise, view from top view.

You could look up some articles on the gyroscopic
effect but these are likely to use vector calculus,
which you may not be familliar with.

One way to look at the rotor, which at least makes the
gyroscopic effect look plausible is to say that if you
want to make the front of the rotor move down it is no
use applying a downward force to the blade when it is
at the front - that is too late, by the time the force
translates into a change in position, the blade has
moved on.  If you want to make the front of the rotor
move down you need to apply the force to the blade
before it gets to the front.

Martin Hogbin

I believe what they are talking about is this: when a torque is
applied to the axis of a rotating object ( as is done to tilt the
rotor to convert some of the lift into thrust), gyroscopic precession
will apply a force perpendicular to the applied torque.

This is the basis of the classic demonstration using a pivoting chair
and a bicycle wheel:
http://video.google.com/videosearch?client=firefox-a&rls=org.mozilla:en-US:offic
ial&channel=s&hl=en&q=bicycle%20wheel%20gyroscope&um=1&ie=UTF-8&sa=N&tab=wv#

The demonstrator hold the axle of a bicycle wheel that is spinning in
the vertical plane. The demonstrator applies a torque to the axle
(force perpendicular to the axis), raising one side and lowering the
other (i.e. the torque is in a vertical plane).  Precession then
applies a force of its own against the experimenter's hands
*horizontally*, depending on the direction the demonstrator tries to
rotate the axis (clockwise, counterclockwise).

Horizontal vs vertical = 90°.

Tom Davidson
Richmond, VA

 OK. I'll give you a more visual answer than the others (so far).
Ignore gyroscopic precession, torque, all that terminology for a
moment. Just look at the rotation axis of the rotor and see it as a
vertical line, centered in the complicated joint on top of the
helicopter, with a built-in twist. Now, "tilt the rotor disk forward
from the vertical" means "rotate the line a little bit around that
joint on top of the chopper", yes? Now visualize another line running
from side to side through the joint on top of the chopper; that's the
axis you're going to have to twist the rotor axis around. Notice that
it's exactly like the axis of the rotor in that it's a line with a
built-in twist.

 Here's the tricky bit; the twist of the rotational axis of the rotor
will try to line up with the twist of the side-to-side axis you're
trying to rotate it around.

 You say the rotor disk rotates right-handed as seen from above, so
tilting the disk forward means twisting the axis right-handed as seen
from the right side of the chopper. The disk will try to turn to the
chopper's right so as to line up the twists.

 Did that help?

 Mark L. Fergerson