To: Rotorque and SPS
You stated,” I have always been under the impression that there has been flapback on the tailrotor in forward flight, most of which is cancelled by the delta hinge but there is always a slight angle of incidence compared to the relative airflow. Nut over that one!!”.
If you are addressing a two blade tail rotor such as that used on the Bell or the Robinson you can use the term “flapback” if you wish but what is happening is that the advancing blade has a greater degree of lift than the retreating blade. The advancing blade will flap inward and in doing so the delta hinge removes pitch and at the same time the retreating blade because it is mechanically attached will flap outward and the delta hinge will add pitch. In performing this flapping the delta hinge effect will equalize the lift across the tail rotor disc and this keeps the tail rotor from flying off due to the fatigue on the tail rotor gear box quill shaft. You get the same effect on a two-blade main rotor. If the advancing blade is caused to lift then the retreating blade will drop. The delta hinge effect will remove pitch from the advancing blade and increase the pitch in the retreating blade thus restoring the symmetry of lift across the disc. If the perturbing force continues “blowback”(flap back) will result.
On a multi blade tail rotor where the blades a free to individually flap only the advancing blade will flap and the delta hinge effect will reduce the pitch on that blade. The remaining blades will maintain their position in the disc track and only move when those blades become the advancing blade. On very large tail rotors where the individual blades are free to flap those blades are attached to the tail rotor head by a composite hinge that allows leading and lagging as well as flapping.
------------------
The Cat