PITCH DAMPING OF PROPULSIVE JETS

When gases flow at high speed inside jet or rocket engines at the same time as the ve­hicle is rotating in pitch or yaw, they react against the walls of the ducts with a force perpendicular to their velocity vector (the Coriolis force). This reaction can result in a pitching moment proportional to q, that is, in a contribution to Cmq, (and similarly to Cn). An analysis of this effect is given in Sec. 7.9 of Etkin (1972).

For jet airplanes in cruising flight this contribution to Cmq is usually negligible. Only at high values of CT, and when the Cmq of the rest of the airplane is small, would it be significant. On the other hand, a rocket booster at lift-off, when the speed is low, has practically zero external aerodynamic damping and the jet damping be­comes very important.

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