Delta-3 & Phase Lag

[Dave_Jackson]

heedm,

You appear to be going into phase angle much deep than I am capably of going. You may also be bringing in variables that are not necessary to understand the actions of delta three.

The following is a simplistic description; but it does describe the activity.

Let's say that we want 10º of flap at 180º azimuth. To get this we must input 10º into the swashplate. For simplicity, when the cyclic stick inputs this 10º, it is done instantly. In addition, let's say that the phase angle is 72º in both examples.

1/ ~ Offset flapping hinge causes a faster flap to position, so the input of 10º from the cyclic stick can be done later than it would need to be done in a basic teetering rotor. In approximately 72º of rotation we have the desired 10º flap.

2/ ~ Delta-3 is located between the swashplate and the blade pitch. In addition, as the blade flaps, delta-3 removes some of the pitch that is input from the swashplate. This means that when the blade gets to 180º azimuth the flap is not 10º. The flap is the swashplate's 10º input minus the delta-3 reduction. The blade has not flapped faster, it has flapped a smaller angle, and, it has done this in 72º of rotation.

Now remember that the swashplate is still asking for 10º of flap at 180º azimuth. So the rotor must go around again to get the flap closer to 10º. After half a dozen rotations, the flap eventually get to 10º.

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The summation is that the offset flapping hinge only needs 72º because it travels the flapping angle faster. Delta-3 only needs 72º because it travels a smaller flapping angle.


Summation added.