Yaw frequency - where does it come from?

[barnabie]

If someone could explain what factors affect yaw frequency - why it can be 30 Hz in one finned projectile and 2 Hz in another not-so-different (perhaps fatter) projectile, etc - or just offer a basic discussion of the parameter, I'd be grateful.

I'm a mechanical engineer by training, so use small words

 

[GregLocock]

The frequency comes from

(yaw gain/polar moment of inertia)^.5

yaw gain is the restoring torque per unit of yaw.

Well, that's how it works in the vehicle dynamics world anyway.

In the case of a projectile that restoring couple will be a function of the area of the fin and its distance from the centre of gravity of the projectile, some complex function depending on the shape of the body, and the speed and density of the surrounding fluid.

From this I'd expect the frequency to vary with speed.



Cheers

Greg Locock