Re: Precession effect on helicopter - Why 90 degrees?
- From: tadchem <tadchem@xxxxxxxxxxx>
- Date: Sun, 29 Jun 2008 08:01:25 -0700 (PDT)
On Jun 29, 6:55 am, Sammuel <samko...@xxxxxxxxx> wrote:
"Gyroscopic precession also plays a large role in the flight controls on
helicopters. Since the driving force behind helicopters is the rotor
disk (which rotates), gyroscopic precession comes into play. If the
rotor disk is to be tilted forward (to gain forward velocity), its
rotation requires that the downward net force on the blade be applied
roughly 90 degrees (depending on blade configuration) before, or when
the blade is to one side of the pilot and rotating forward." (Wikipedia)
You may find it from here:http://en.wikipedia.org/wiki/Precession#Torque-induced
n...@xxxxxxx wrote:
On Jun 29, 2:05 am, Sammuel <samko...@xxxxxxxxx> wrote:
Hi, I am reading some notes of the precession effect on helicopter, and
it said the left of main blade is 90 degrees ahead of spin.
But why is it '90 degrees' and is 'ahead'???
Where did you find these notes? Seen from above, which way are the
blades spinning?
Mark L. Fergerson
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:official&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
.
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