V-22 Rotor Question

sorry...dis SYMMETRY that is...aduhhh

Bob

Definition of Coriolis Effect ~ Rotor blades will accelerate when its CG
moves closer to the center of rotation and will decelerate when it moves
farther. Rotor blades accelerate and decelerate accompanied with the rotor
blades flapping.
__________________________

Bob you are correct when discussing a conventional teetering rotor or a
flapping rotor. The above definition supports your statement, but, the
"center of rotation" it is referring to is that of the mast. On a gimballed
rotor, the teetering does not causes the blades to move closer or further
from the "center of rotation" (tilted axis) of the teetered rotorhub.

It must be noted that the rotor blades of a teetering rotor are connected to
the mast via a Hooke's (Universal) joint. In this arraignment, the mast
will turn at a constant velocity but the rotor will accelerate and
decelerate. This effect can be equally well explained by the cyclical
Coriolis effect or by the Hooke's joint effect.

By replacing the Hooke's joint with a Constant Velocity joint the rotation
of the teetered rotor hub will now be constant. In other words, the blades
will no longer lead/lag in respect to the axis of the rotorhub AND will no
longer lead/lag in respect to the axis of the mast.

Dave J


"Bob" wrote in message
...
Coriolis effect has to do with dissimetry of lift (advancing blade vs.
retreating blade) not blade velocity. On an articulated rotor head,
lead/lag
will remain, so CV joints are moot in that regard.

Bob

I believe I stated that the "moot" application is and articulated rotor head
and should have said a Fully articulated rotor head.

Agreed. The subject is rotor with three or more blades. I used the
teetering rotor as the example because it is easier to understand, and the
out-of-plane flapping and teetering hinges are functionally very similar.

Researchers have been looking into the possibility of a soft-in-plane rotor
for the tilt-rotor, to reduce the strength and weight of the current rotor.
This implies, of course, that there is lead/lag activity in the V-22 rotor
and the question is one of what activities are causing this lead/lag.

Excluding lesser activities such as drag, a Constant Velocity joint will
cause the rotor hub to tilt and have the same plane as the tip-path-plane.
This will mean that the hub and blade roots will rotate at a constant
velocity. There are patents for rotor head CV joints, but the original
question asks if a CV joint has actually been implemented.

The use of a CV joint in the V-22 should imply that it could also be
implemented in conventional rotorcraft and result in simpler smoother
rotors. http://www.SynchroLite.com/1301.html and its associated pages is
the reason for originally asking the question.

Dave J




"Bob" wrote in message
...
I believe I stated that the "moot" application is and articulated rotor
head
and should have said a Fully articulated rotor head.

Dave,
I am following your idea of the tetering rotor hub i.e. the Bell 206, and I
must state clearly that the blades on such a hub never change the angular
relationship with respect to one another. The angular relationship from the
trailing edge of one blade to the leading edge of the other blade NEVER
changes. There is no mechanism in the rotor head that could possibly allow
that to happen. positions on the head are FIXED PERIOD.

The reason the head teters os to provide for equal lift on the advancing
blade side of the rotor disk and the retreating blade side of the rotor
disk. The higest point of the teter is over the nose and the lowest point
is over the tailboom.

Coriolis will ALWAYS accelerate a blade whose center of gravity moves toward
the axis of rotation. Lift being agreed now equal all around, and blade
angular relationships never changing, therefore velocity with respect to one
another never changing, where does coriolis effect enter into this
discussion at all??? Forgive me, but even after 20 years of strictly
helicopter maintenance of All shapes and sizes I am at a loss to see the
merit in your discussion.

On a V-22 the same physics apply. For coriolis to enter the picture, it
would necessarily be induced only by lead/lag of the blades and a hinge or
mechanism to allow that to happen. I'm certainly not a V-22 guru but on ALL
helicopters thae same things will happen for the same reasons. Now I'm
sitting here asking myself where this might be going.

Bob

Hi Bob,

The intent of the original post in this thread was for me to get a clear
understanding of exactly what is taking place in the V-22 rotor.
Specifically, to find out if it is only a gimbaled hub or it is in fact a CV
hub.

I believe we agree on what the Coriolis effect is.

We probably both agree that if a rotor mast is vertical and its TEETERING
rotor disk is tilted 10-degrees down at the front, then the two blades, in
unison, will be experiencing a two/rev. acceleration and deceleration, as
they move toward and away from the axis of rotation. This rotational
vibration is absorbed in the mast.

In addition, we probably both agree that if a rotor mast is vertical and its
FLAPPING rotor disk is tilted 10-degrees down at the front, then the blades
will be experiencing a two/rev. acceleration and deceleration, as they move
toward and away from the axis of rotation. This rotational vibration is
absorbed in the lead/lag hinges.

Now lets tilt the masts in both examples 10-degrees forward, so that the
masts are now normal to the disks. I think that we will agree that in both
examples the blades will no longer experience a two/rev acceleration and
deceleration. There is no Coriolis effect about this tilted mast.

This is where the CV joint differs from all existing rotor heads. The CV
joint takes the constant rotational velocity of the vertical mast and
delivers a constant rotational velocity to the axis of the tilted rotor
disk. The blades are now rotating about tilted axis of the rotor disk and
when viewed along this axis there is no Coriolis.

Hope this explains my original question.

Dave J.



"Bob" wrote in message
...
Dave,
I am following your idea of the tetering rotor hub i.e. the Bell 206, and
I
must state clearly that the blades on such a hub never change the angular
relationship with respect to one another. The angular relationship from
the
trailing edge of one blade to the leading edge of the other blade NEVER
changes. There is no mechanism in the rotor head that could possibly
allow
that to happen. positions on the head are FIXED PERIOD.

The reason the head teters os to provide for equal lift on the advancing
blade side of the rotor disk and the retreating blade side of the rotor
disk. The higest point of the teter is over the nose and the lowest
point
is over the tailboom.

Coriolis will ALWAYS accelerate a blade whose center of gravity moves
toward
the axis of rotation. Lift being agreed now equal all around, and blade
angular relationships never changing, therefore velocity with respect to
one
another never changing, where does coriolis effect enter into this
discussion at all??? Forgive me, but even after 20 years of strictly
helicopter maintenance of All shapes and sizes I am at a loss to see the
merit in your discussion.

On a V-22 the same physics apply. For coriolis to enter the picture, it
would necessarily be induced only by lead/lag of the blades and a hinge or
mechanism to allow that to happen. I'm certainly not a V-22 guru but on
ALL
helicopters thae same things will happen for the same reasons. Now I'm
sitting here asking myself where this might be going.

Bob

Yes Dave. That does explain your original question.