newbie question: blade flapping & pitch links?

[MachThree]

I have a question about rotorheads. I'm thinking of a two bladed teetering rotor, though I suspect this might be applicable to other rotor types as well.

 

As a blade flaps up, it will (I think) pull the pitch horn farther away from the rotating swash plate (and as the blade flaps down, the pitch horn will come closer to the swash plate). Since the pitch links are attached both to the pitch horn and to the swash plate, when the blade flaps up, does this (in and of itself) cause the pitch of the blade to be lowered somewhat? Does the blade flapping down likewise cause the pitch of the blade to be increased somewhat? Or will the blade flapping action not cause the pitch of the blade to be adjusted in any way?

[delorean]

Flapping does not change the angle of attack MECHANICALLY.

 

By flapping up, it changes the angle of attack by just that, flapping up. Since it now has a [upward] vertical vector, the AOA is reduced. At the same time, as the other blade flaps down, the downward vector takes a bigger bite of the air, increasing AOA.

 

Makes a lot more sense drawn out on the white board. Sorry.

[Eric Hunt]

The pitch rods attach 90 degrees (approx) forward of the blade,in line with the flapping hinge, so when it flaps up, the pitch is not affected. Go look at a real rotor head to confirm it.

 

However, the tail rotor is different - as it flaps out or in, the pitch rods change the pitch to reduce the flapping - via the Delta 3 hinge.

[Tom22]

Here is some more literature, it’s the Army training manual. Chapter 1 might be insightful.

 

http://www.everyspec.com/ARMY/FM+-+Field+M...3-04-203_11773/

[crashed_05]

Check out Principles of Helicopter Flight by W.J. Wagtendonk, Pg 96, 97. The offset pitch horn reduces the angle of attack as the blade flaps up, reducing the amount of flap required to eliminate dissymmetry of lift. Does the same job as the Delta hinge.

[Trans Lift]

As the blade flaps up or down, the induced flow over the blade is changed. This is what causes the change in the Angle of Attack. It is not mechanical, as said above.

 

The delta 3 system on a tail rotor works in the way you are suggesting. As the blade flaps, the angle of attack is reduced due to the pitch links influence. Therefore reducing the amount of flapping by the tail rotor.

[Guest pokey]

I think the delta 3 hinge was used on the M/R of some early helicopters. It is basically a mechanical means of changing the pitch of the blade as it flaps. It does this by utilizing an offset of the pitch horn in relation to the axis on which the blade flaps. A good analogy of this is to think of a rear motorcycle swing arm with a chain drive. NO delta hinge effect would put the front sprocket exactly on the swing arm pivot, and IF the swing arm were to rotate a full 360 degrees?--the chain tension would remain the same ( no pitch change) However if the sprocket were offset ( which most are) as the swing arm rotates up & down, the chain tension is constantly changing.