Here is what Jim Barrowman had to say about supersonic CP
http://www.geocities.com/rocketguy10...s/ssfincna.pdf

Subsonic CP can be calculated using a program such as Rocksim available from
Apogee Rockets
http://www.apogeerockets.com/rocksim.asp


--
David Stribling
NAR 18402 SR
But it _is_ rocket science!
Get yer Barrowmans at http://www.geocities.com/rocketguy101/index.html
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"C. Newport" wrote in message
. ..
Jeff:

Thanks for the advice but the problem is that the center of pressure
changes based upon the velocity, especially when passing through Mach 1.
I think it also shifts around through Mach 2 but not as much. In reality,
I figure that if I make the rocket just barely stable at ignition, by the
time it leaves the rail it will be stable in flight as the fuel burns off.
However, I really need to make sure that this new design will be stable
through the entire envelope. At LDRS, the rocket had several problems. It
was over stable and one fin was slightly misaligned (I think) which caused
pitch-roll coupling and the eventual breakup. I cannot afford to lose too
many of these things hence this effort to do a higher fidelity dynamic
analysis.

C. Newport





"Jeff Findley" wrote in message
...

"C. Newport" wrote in message
. ..
I know that this is off topic but where else can you find such a group of
individuals interested in space and rocketry?

As some of you may or may not know, in addition to the underwater stuff,
I also dabble in amateur rocketry. I am well past the Estes stage, you
could say. My last design was about 12 feet long with a launch weight of
130 lbs. and should have reached about 30,000 feet and close to Mach 2
(it was launched at LDRS 2006). There were, shall we say, some stability
issues, and the rocket came apart at about 5 seconds into the flight.
This particular design was a modification of an existing rocket.

I am now working on a new design and have been trying to find some
simulation software that can do a decent dynamic stability analysis
through Mach 3 but have so far been unsuccessful. While I am shooting
for about one caliber of stability at launch (one caliber between the
static CG and Center of Pressure), I know this is going to change as the
vehicle accelerates. Consequently, I need the right software (or someone
who can do this kind of analysis) to ensure that this next design is
stable through it expected burn-out velocity.

I think what you want to do is determine the CG and CP at both launch and
at burn out. You ought to be able to find the CG with an empty/spent
engine, right? I don't think any software is needed, unless you already
have software that you're using to estimate the CG of a design.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)