Gyro PRECESSION

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On Jan 21, 1:14 am, "Steve R." wrote:
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On Jan 20, 6:12 pm, "Steve R." wrote:
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As to helicopters, I know they morphed out of autogyros thanks to the
rotor head development of Cierva. But I don't understand how
gyroscopic precession can enter into the control of the helicopter
rotor plane when there is so much imput coming from the pilot. That
would mean his controls would be set in precession so a move to right
is really an input on the bottom of the rotor plane?

If I'm reading you correctly, you're uncertain why the control inputs are
applied to the rotor blades ahead of where you really want the rotor to
react? Maybe I'm not following you on this but with regards to gyroscopic
precession, I'll offer this.

First of all, as a spinning object, the rotor system, be it on a
helicopter
or gyroplane, is a gyroscope. As such, it acts like one. One of the
properties of a gyroscope is the property of rigidity in space. That is,
it
wants to maintain it's plane of rotation and resists deviating from that
plane. If a force is applied to the gyroscope that is strong enough to
force it out of it's plane of rotation, that force will be reacted to at a
point 90 degrees in the direction of rotation from the point where the
force
was applied. That is the definition of gyroscopic precession.

In a rotorcraft, all cyclic blade movements that are used to change the
attitude of the rotor disk in pitch or roll, must be applied 90 degrees
ahead of where the pilot really wants the rotor to move. If the rotor is
spinning clockwise as viewed from above, or moving from the pilots left to
right as seen from the cockpit, and the pilot wants to roll the aircraft
to
the left, the actual cyclic movement applied to the rotor blades should
have
each blade reach it's maximum pitch straight ahead and minimum pitch back
over the tail. The rotor will react to this at a point, 90 degrees in the
direction of rotation. That will have the forward blade climb to it's
maximum point on the right side of the bird, and the rearward blade
descend
to it's minimum point on the left side of the bird and she rolls left.
However the cyclic pitch movements are achieved, the result is the same.

I hope that makes sense! :-)

Steve R.

Hey, thanks. I'm begining to get the right idea.
I found this tid bit to add to it:
" . . . the control rigging in the helicopter compensates for
gyroscopic precession. In helicopters, the controls are rigged is such
a way that when forward cyclic is applied, the helicopter moves
forward, likewise for aft, etc. To accomplish this, the pitch horn is
offset 90º to the rotor blade. The controls still tilt the swashplate
in the same direction as the control input is made, but due to the
pitch horn placement, the input to the blade occurs 90º earlier in the
plane of rotation . . . "
So as the pilot pushes the stick left the input is really hitting the
swash plate 90 degrees before left or at the top. (if the blades are
rotating counter clock wise).
right?


Yes, sounds right, although I don't think I would have worded it quite like
that. I wouldn't say that the control rigging "compensates" for gyroscopic
precession, rather, I'd say the control rigging simply allows for gyrocopic
precession. That may be just a matter of semantics but in my mind, the word
"compensate" implies countering the effect (gyrocopic precession) and that's
not what's really going on. At least not the way I like to think about it.
:-) The 90 degree offset is built into the design of the rotor system and
the control links that run from the swashplate up to the rotor blade pitch
control arms. If you watch the swashplate tilt when the pilot moves the
cyclic control, you'll see that the swashplate actually tilts in the same
direction that the pilot moves the control. If the pilot moves it forward,
the swashplate tilts forward. Backward and the swashplate tilts backwards.
Likewise for left and right control movements and everything in between.
The main rotor system will follow in the direction that the swashplate
tilts. Everything that happens from the swashplate up, happens
automatically and the 90 degree lead is, as the man said, built into the
control rigging.

Steve R.