# . Calculate Tail Rotor Thrust

(Note the inclusion of the blockage factor BT for the tail rotor.)

The determination of the induced velocity of the tail rotor is the next part of the calculation. The advanced ratio components together with the thrust coefficient of the tail rotor are now required:

 V mxT = VTT (A. 16) mZT = q (A. 17)

The tail rotor is only required to develop a thrust, normal to the helicopter’s centreline, so has no need for any disc tilt; in consequence the disc plane is assumed parallel to the flight path.

A.3.2.2 Calculate Tail Rotor Downwash

Using the same iterative method, the tail rotor downwash, 1iT, is then calculated.

A.3.2.3 Assemble Tail Rotor Powers

The tail rotor power components are now calculated. Induced: PiT — kix ■ TT ■ Vtt ■ liT   Profile:

Total:

Ptott — PiT + Ppt (A. 20)

(Note that there is no parasite power for the tail rotor as the main rotor is assumed to be responsible for overcoming the parasite drag of the aircraft.)

A.3.3 Complete Aircraft

The total power required is now – calculated by summing the total powers for the main and tail rotors together, to which is added the power necessary to drive any auxiliary services (PAUX) such as oil pumps and electrical generators. It is to be expected that some losses will occur in the transmission and, to account for this, a factor is applied giving the power required from the engines as follows.