# 6.16 Is there a way to increase the stability of a model with near neutral stability?

## Description

This article is from the Model Rockets
FAQ, by Wolfram von Kiparski with numerous contributions by
others.

# 6.16 Is there a way to increase the stability of a model with near neutral stability?

From: Peter "My views are not to be confused with those

of a rabbit librarian" Alway (petealway@aol.com)

Sounding rockets that are aerodynamically stable are often spun at a

slower rate that insures that any off-axis thrust will cause the

rocket to corkscrew, rather than follow an arc. The corkscrew may

be subtle--but it beats an equally subtle arc. A sounding rocket

that naturally describes an arc with a 20-mile radius due to its

asymmetries cannot reach higher than 20 miles. But if the rocket

is spun through 360 degrees every few hundred feet, the

20-mile-radius arc turns into a very suble corkscrew.

Imagine the modeler puts a very slight misallignment between the

forward and rear fins of a sidewinder. Suppose it's just one degree.

also suppose the fins are 1 foot apart. the rocket will naturally

arc in a circle with a 360-foot circumference and a 57-foot radius.

That's instant doom! make the error half as bad and you are in

trouble. But if the rocket spins every 10 feet, the path will be

a generally upward corkscrew, less than ideal performance, but

a safe flight.

So with model rockets, a spin on ascent is a good way to make a

marginal or asymmetrical model safe. Estes used to sell a space

shuttle orbiter kit that had a spin tab for this reason, and the

old Astron Space Plane had spin tabs as well.

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