Model Forum / Radio Controlled / Helicopters / November 2004

I'll have a go. I am not an expert in these matters however

Yes it is working correctly. Because on my Sceadu it is the same.

The reason I think it can work like this is because most of the cyclic input
is actually sent through the fly bar which you can plainly see is at 90
degrees to the main blades and therefore the precession is accounted for.
The best way to see this in action is to take the main blades off and spin
the head by hand while putting the inputs in. You should be able to see that
you get large amounts of deflection in the stabilizer paddles while the
blade grips change in pitch is alot less.

I think this explains why flybar-less heads handle like dogs (going on what
I've read, never flown one).

If any of this is wrong someone pease correct me, I would be very interested
in the correct answer as well.

Thanks

Andy

Hi RP,

This is not an uncommon misconception.

Precession (aka gyroscopic precession) is a process that's related to any
spinning object, like our main rotor systems.  Basically, gyroscopic
precession is defined as, "Any force applied to a spinning object, that
tried to change the 'plane of rotation' of that spinning object, will be
reacted to at a point, 90 degrees in the direction of rotation."

So what did I just say?  First, setup the controls on your Raptor as the
directions state.  Then tilt the swashplate hard over in the starboard
direction and make sure that there is no for/aft control inputs at this
time.  Now slowly turn the rotor system a full 360 degrees and watch the
main rotor blades while they move around the circle.  When the main blades
are situated at a point that is perpendicular (90 degrees) to the
longitudinal axis of the fuselage (the tail boom is a perfect reference)
you'll see that the  pitch attitude of the main rotor blades is the same.
From that point on, as you rotate the rotor system around, the blade moving
toward the tail rotor will be increasing in pitch and the rotor blade moving
toward the nose of the fuse will be decreasing in pitch.  This increase and
decrease in blade pitch will reach it's maximum  when the rotor blades are
parallel to the longitudinal axis (tail boom) of the helicopter.  After
that, the blade over the tail boom will start decreasing it's pitch angle
and the blade over the nose will increase it's pitch angle until they both
hit the equal point back at the position perpendicular to the long axis of
the models fuse.

The end result of all this long winded explanation is that the rotor blades
will be producing maximum lift over the tail boom and minimum lift over the
nose with the end result being (as described in the definition in the first
paragraph) that the model will roll toward it's starboard side.  I look at
it this way.  The main rotor blades are spinning at a high right of speed
while in flight.  Because of this, they have a large inertia in the
direction of their rotation.  Even though, as in the above example, the
blades are making maximum lift over the tail boom and minimum lift over the
nose, they don't react at those exact points and change direction "right
there."  Because of their inertia in the direction of main rotor rotation,
it takes 90 degrees of rotation for the blades to fully react to the lift
differential between the front and back halves of the rotor disk.  That's
why, for all intents and purposes, all cyclic control inputs on our model
helicopter main rotor systems are made 90 degree "ahead" of the point where
we "really" want it to go.  Full size helicopters do exactly the same thing.
Take a good look at a Jet Ranger the next time you get to see one up close.
It's setup the same way.  :-)

Hope this makes sense!
Fly Safe,
Steve R.