TABLE OF CONTENTS 12.1 The pitching moment that a rotor can generate is directly limited by attenuations caused by unsteady aerodynamic considerations. Expressions for the rotor pitching moment, including unsteady aerodynamic effects, can be obtained using both the Loewy/Miller lift-deficiency function (for harmonic airloads) and the air mass dynamics theory in the preceding chapter (Section 11.5).
Derive expressions for the ratio of rotor pitch damping (with unsteady aerodynamic effects) to that using only the quasi-steady assumption using i) the Loewy/Miller lift-deficiency function and ii) air mass dynamics, respectively.
Explain any differences obtained using each of the two unsteady aerodynamic formulations considered in part a.
12.2 Consider the tail rotor of a helicopter in yawing (hovering) flight at sea level (see Problem 4.1). In this maneuver the (two-bladed) tail rotor develops once per rev (1 P) flapping responses as a result of the gyroscopic excitations. A properly designed tail rotor must account for these responses with regard to determining an appropriate setting of the flapping limit stops. The 1 P excitations created by the gyroscopics are equilibrated by the aerodynamic loads, which are necessarily unsteady. The rotor and flight condition specifications are as follows:
Using the Loewy/Miller lift-deficiency function for harmonic airloads, estimate the percent loss in first harmonic aerodynamic effectivity for respective helicopter yaw rates ? z of 100 deg/s.
Using the results of part a and the blade properties given in Problem 4.1, calculate the maximum teetering angles expected in this yaw maneuver. Note...
