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Rotor 89
T/T ∞
1.3
1.2
1.1
1.0
Hayden
Rabbott
Cerbe
Cheeseman
Zbrozek
0.9
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
z/R
Figure 11-2. Ground-effect models (hover).
11-4.2 Rotor Forces
Cheeseman & Bennett
Cheeseman & Bennett (BE)
Law
Hayden
Zbrozek
Direct control of the rotor thrust magnitude is used, so the rotor collective pitch angle θ0 must be
calculated from the thrust CT /σ. If the commanded variable were the collective pitch angle, then it
would be necessary to calculate the rotor thrust, resulting in a more complicated solution procedure;
in particular, an iteration between thrust and inflow would be needed. There may be flight states
where the commanded thrust can not be produced by the rotor, even with stall neglected in the section
aerodynamics. This condition will manifest as an inability to solve for the collective pitch given the
thrust. In this circumstance the trim method should be changed so the required or specified thrust is an
achievable value.
Cyclic control consists of tip-path plane command, requiring calculation of the rotor cyclic pitch
angles from the flapping; or no-feathering plane command, requiring calculation of the tip-path plane tilt
from the cyclic control angles. The longitudinal tip-path plane tilt is βc (positive forward) and the lateral
tilt is βs (positive toward retreating side). The longitudinal cyclic pitch angle is θs (positive aft), and the
lateral cyclic pitch angle is θc (positive toward retreating side). Tip-path plane command is appropriate
for main rotors. For rotors with no cyclic pitch, no-feathering plane command must be used.