[SS-Propellant] Launch of the Propellant Development phase ofSS2S

[dormans]

Richards, Paul Kelly's and Near's  motors that are cited as exhibiting the
triangular thrust curve  when using Sorbitol all used bates grains that were
presumably prepared in the same way.  A casting tube filled from the top
with molten propellant and allowed to cool.  Is it possible that the KN,
being heavier, is settling a bit from the top and leaving a thin layer of
fuel rich propellant at the top?  So that it's not the space between the
grains causing the ignition delay, but that half of the grain ends have this
layer of fuel rich propellant that is delaying ignition.  The use of an
ignition primer or pyrogen ignition would not necessarily help if this is
the case.  Has this already been considered?  It's an easy theory to test,
just trim a thin layer off the tops of all the grains after curing or maybe
it would be easier to top off the grains during casting with a thin layer of
KN rich propellant or KN/SU as Tony has suggested. 

Randy

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From: ss-propellant-bounces at exrocketry.net
[mailto:ss-propellant-bounces at exrocketry.net] On Behalf Of Rich Nakka
Sent: Sunday, November 13, 2005 5:28 PM
To: ss-propellant at exrocketry.net
Cc: Antoon Vyverman; william colburn
Subject: Re: [SS-Propellant] Launch of the Propellant Development phase
ofSS2S

 

dormans wrote:



 Hi all,

It sounds like we have a lot of work/fun ahead of us.  I think that a mix of
SB/SU as Miraglia has suggested, or KN/SU applied only to the ends of the
grain to as Tony suggests are definitely worth investigation.  I used to use
a 50/50 mix of SB/SU mainly as a means of reducing the cost of the Sorbitol.
I always thought of it as a performing like Dextrose.  Unfortunately I
wasn't doing a lot of static testing at the time, but in the static testing
that I did the SB/SU mix produced a thrust curve that closely matched the
predicted.  I suspect that a ratio with more Sorbitol and less Sucrose would
give similar results.  The motor tested in the attached gif was an
unrestricted J-class motor; propellant was 60/40 OX/fuel and 50/50 SB/SU and
gave a healthy isp of 122.

That thrust curve certainly shows no sign of the dreaded "triangular" shape.
I wonder if this is because of the 50/50 SB/SU mix, or because the grain is
unrestricted? Could it be that only BATES suffer from this? Perhaps due to
non-normal burning at the segment ends?




The thrust curve for NEAR's first firing of the Phenix motor was fairly
triangular , but the thrust curve from the 2nd firing was much closer to the
predicted (not nearly as triangular).  Does any one know what the difference
was between the two tests?  I can't find the report on their site, but I
think that I have a printed copy some where.

You're right, Randy, the 2nd firing was much improved. I'll contact a fellow
at NEAR and see if I can get any info as to the possible reasons.




I read that many commercial/military motors use an oxidizer having a mixture
of particle sizes (multi-modal mixtures) as opposed to uni-modal mixtures
mostly as a means to lower the viscosity thereby making the propellant
easier to process.  Something I think we should look into to help with the
large grains.

I would think that for large grains, viscosity would be less of an issue
than for small grains. From my own experience, though, particle size of the
KN makes a HUGE difference in the viscosity of the molten slurry.




I would be happy to do some testing also; Peter and I will hopefully, in
addition to the BEM, also be firing a 4inch diameter N-class Sorbitol motor
soon.

Awesome. Looking forward to hearing about the N-motor results...good luck
with it.

Richard



 





 

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