rotational stability

[dandandawildman]

I am building a model flying saucer and need to know for any given diameter and mass the required angular velocity necessary to sufficiently stabilize the craft in flight without ground effect.

 

[Fabrico]

Additional things that have considerable effect:

1) The requirements for hovering are not the same as those during lateral movement.

2) Aside from amount of mass, is placement of mass and any gyroscopic effects.

3) How and where upward and forward thrusts are applied is a factor.

 

[JimCasey]

Gyroscopic effects DE-stabize a helicopter-because precession causes the rotor disc not to oppose a destabilizing force, but to tilt at 90 degrees from it.

That is the beauty of the Bell and Hiller rotor systems-these enabled helicopters became stable enough to correct for momentary interruptions without spiraling out of control.

For a flying saucer, you have to be stable in hover( helicopter technology) and I presume you also wish to transition and fly through the air with some speed(aircraft technology) , so the hull would need to be aerodymically stable. This does interesting things like making it necessary to balance the hull not at its center but at a point corresponding to 25% of the mean aerodynamic chord in the direction of travel. Otherwise it will be like a cheap frisbee and just roll over and crash.

 

[JStephen]

I think Fabrico hit the pertinent points.

Consider that if the disk is just flung through outer space, there should be zero tendency to flip out of the plane (assuming you throw it straight). So you can assume that ALL the forces causing it to rotate out of the level are due to aerodynamic forces. If you know those forces, great, you can specify a maximum tilt angle, whip out the ol' dynamics textbook, and see what it takes to resist those forces. But in the more likely case where you don't know those forces, you also don't have any basis for figuring a stabilizing speed.

From past experience flinging Frisbees and other disks, you do need a fair bit of the weight near the rim to stabilize it adequately.