Design Assistance

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.

If there is anyone in this newsgroup that can point me in the right
direction it would be appreciated. It costs way too much to build these
things to lose another one.

FYI, I just finished my first trip down under recovering a Blackhawk off
Fiji for the Royal Australian Navy. I'm going back after Easter for some
work off the west coast near Perth. Great place.

C. Newport

"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)

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)

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
Remove the 2x to reply



"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)

I've been using Rocksim for years but I'm entering a flight regime that this
program was not designed for. I have several others as well such as John
Wickman's "Flight," Aerolab, etc. I suppose I'm looking for an application
that is in between Rocksim and what people are using for commercial
sub-orbital simulations (as their software is probably out of my price
range). One of the posters was correct is that even if stability looks good
at ignition and burnout, it's the in between time I'm worried about.

C. Newport

C. Newport wrote:
There were, shall we say, some stability issues, and
the rocket came apart at about 5 seconds into the flight.

Was that was the spiraling one you sent us the video of? That was an
engine mount failure, wasn't it?


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.


Would any of these help?

Subject: Nasa interactive websites list
Hypersonic aerodynamics: http://www.grc.nasa.gov/WWW/BGH/shorth.html
Aerodynamics: http://www.grc.nasa.gov/WWW/K-12/airplane/short.html
Compressible aerodynamics:
http://www.grc.nasa.gov/WWW/K-12/airplane/shortc.html
Propulsion: http://www.grc.nasa.gov/WWW/K-12/airplane/shortp.html
Rockets: http://exploration.grc.nasa.gov/educ...et/shortr.html

Free softwa
Virtual wind tunnel: http://www.grc.nasa.gov/WWW/K-12/FoilSim/index.html
Jet engine simulator and range test for aircraft:
http://www.grc.nasa.gov/WWW/K-12/Enginesim/index.htm
Interactive rocket modeler, gas behavior, kite design, atmosphere
modeler: http://www.grc.nasa.gov/WWW/K-12/Int...rogs/index.htm

Beginner's guides:
Aerodynamics: http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html
Propulsion: http://www.grc.nasa.gov/WWW/K-12/airplane/bgp.html
Model rockets: http://exploration.grc.nasa.gov/educ...cket/bgmr.html
Compressible aerodynamics:
http://www.grc.nasa.gov/WWW/K-12/airplane/bgc.html
Kites: http://www.grc.nasa.gov/WWW/K-12/airplane/bgk.html
Hypersonics: http://www.grc.nasa.gov/WWW/BGH/bgh.html

Undergraduate level simulators (Mach/speed of sound, jet engine
simulator, wind tunnel, sound wave, isentropic flows, rocket nozzle
design, shock waves, multiple shock waves):
http://www.grc.nasa.gov/WWW/K-12/Und...rogs/index.htm


Pat

The Apogee website has links to other pubs discussing stability--perhaps one
of them would be of help
http://www.apogeerockets.com/educati..._stability.asp


--
David Stribling
Remove the 2x to reply


"C. Newport" wrote in message
. ..
I've been using Rocksim for years but I'm entering a flight regime that
this program was not designed for. I have several others as well such as
John Wickman's "Flight," Aerolab, etc. I suppose I'm looking for an
application that is in between Rocksim and what people are using for
commercial sub-orbital simulations (as their software is probably out of
my price range). One of the posters was correct is that even if stability
looks good at ignition and burnout, it's the in between time I'm worried
about.

C. Newport

Jeff Findley wrote:
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.


I think he's concerned about CP shift when it goes supersonic, as well
as the effects of supersonic shockwaves on its stability.
i.e.- What effect does the formation of the nose shockwave have on the
fin's ability to keep it stable?
Me, I'd stick a chunk of lead in a Really Pointy Nose and give it Really
Big Fins. :-D

Pat

C. Newport wrote:
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.


To me, the video looked like the motor had become misaligned, or one of
the fins had suffered some sort of structural failure in flight, that
caused it to generate excessive drag on one side of the vehicle; say
coming free at the forward end and having that part bend sideways from
the airflow going over it. I think misalignment would just cause it to
start spinning on its axis more that doing the spiraling motion visible
in the video.

Pat

On Fri, 30 Mar 2007 10:24:28 -0400, "C. Newport"
wrote:

FYI, I just finished my first trip down under recovering a Blackhawk off
Fiji for the Royal Australian Navy.

....To be dramatized in the upcoming adventure film, "Black Hawk
Drowned" :-)

OM
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