INERTIAL COUPLING

Although little can be done to influence the aerodynamic coupling, the inertial coupling is amenable to control by design. If the elevator mass center is on the hinge line, ee = 0 and one coupling term vanishes—i. e. acceleration in the z direction will then not tend to induce motion of the control. With reference to Fig. 11.5, we can calculate Pex as follows

(11.3,14)

For Pex and ee both to be zero, we would require

(11.3,15)

This condition cannot be met if Л = 0, but in principle can be if Л Ф 0 by the addition of suitable balance weights. When both Pex and ee are zero we have complete dynamic balance of the elevator, and rigid body motion of the vehicle does not induce motion of the control.

The problem of reducing inertia coupling when aeroelastic flutter is the issue is similar to, but not the same as, that discussed here. The relevant product of inertia would in general be a different one [see (11.3,24)].