I understand that the delta hinge acts like a flapping spring by creating an aerodynamic force on the blade proportional to the flapping angle thereby altering the flapping frequency away from the rotational frequency which reduces the overall amount of flapping and prevents the possibility of the flapping going resonant and destroying the tail rotor. And that it probably doesn't matter whether it's positive or negative. But it still looks wrong to me to see the blade pitch increase with flapping on negative delta3 rather than decrease like with the more conventional positive delta3.
But I am curious if anyone on here can give any good reasons why either positive or negative delta 3 on a tail rotor would have any advantages or disadvantages over the other? The main difference that I could see is that it would change the direction of flapping, this could have an advantage of adding tail structure clearance from the blades. However it doesn't seem to me that any clearance is gained by using the negative delta 3 on 212/412 designs. Although it looks like it might provide for a slight gain on the 407.