basic terminology associated with rotorcraft

1.advance ratio,μ=V/ΩR typically μ<=4
V:forward flight speed
Ω:angular speed of the rotor
R:rotor radius
2.blade azimuth ψ
the angle that the blade makes with the horizontal axis
3.the advancing blade side
rotor blade moves in the same direction as the forward flight speed
4.the retreating blade side
the blade moves in a direction opposite to the direction of flight
5.trim
the process of balancing the forces and moments
6.cyclic pitch
the angle of attack of the blades on the advancing and retreating sides must be adjusted periodically throughout each blade rotation cycle so that there is a balance of rolling moment
7.trimmed
after cyclic pitch the rotor is said to be trimmed
8.collective pitch
a control in which the angle of attack of each of the blades is increased simultaneously to achieve a higher lift;for a hovering rotor,an increse of the collective pitch,for example,results in climb
9.form drag
that part of the drag on an aerofoil which arises from its shape. It varies according to the angle of attack and can be decreased by streamlining
10.viscous drag
That part of the rearward force on an aircraft that results from the aircraft carrying air forward with it through viscous adherence
11.induced drag
in situations where loads are generated by three-dimensional vortex systems,the pressure drag is usually called induced drag
12.BVI
blade vortex interaction
13.coefficients
the major design parameters for the helicopter are the dimensionless coefficients related to thrust andpower
thrust coefficient Ct
torque coefficient Cq
power coefficient Cp
figure of merit FM