Corkscrew in Takeoff

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Brian Pernell - 31 Jan 2005 02:41 GMT

Hi,
I am new to building rockets from scratch. I built a 18 inch rocket out of
Phenolic Tubing fins out of Carbon fiber. The fins were on straight as an
arrow. I designed it in Rocksim and it was stable by all methods. However
when I shot it off I get a bad corkscrew type motion. It was first launched
on E-9 motors the second Time Aerotech F-39 motors.

any Help

Brian

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Gary - 31 Jan 2005 06:30 GMT

> Hi,
> I am new to building rockets from scratch. I built a 18 inch rocket out of
[quoted text clipped - 6 lines]
>
> Brian

Difficult to guess at without seeing the design.

I've corrected corkscrews which seemed (was a process of elimination)
to have been caused by:

Flexing fins - stiffened with a laminate.

Flexing airframe - abandoned super-rocs

Asymmetrical airflow(?) - had a hi-perf model corkscrew years ago until
someone here, IIRC, suggested ANOTHER set of launch lugs 180 degrees
from the existing set. (I didn't have a tower back then.) It worked.
That
model had small fins, minimal stability margins, and long lugs.

What's the stability margin and weight of the model? Is it a
"traditional"
shape? Are the fins symmetric in shape and location? NC symmetric?

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Gary Bolles

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Jerry Irvine - 31 Jan 2005 13:30 GMT

> Asymmetrical airflow(?) - had a hi-perf model corkscrew years ago until
> someone here, IIRC, suggested ANOTHER set of launch lugs 180 degrees
> from the existing set. (I didn't have a tower back then.) It worked.

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Jerry Irvine, Box 1242, Claremont, California 91711 USA
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Model Forum / General / Rockets / January 2005

Corkscrew in Takeoff