On 08/06/2018 07:28 PM, Troy Prideaux wrote:
When I was using pre-heaters, I used KClO4+Epoxy grains--fairly thing slices. No kablooeys as a result.
Also worth noting: Paul Kelly was looking for an N2O hybrid preheater grain propellant that utilised an oxidizer he could make himself easily. I suggested NaClO3+Epoxy as an option as it was shortly after I went through testing that stuff in solids and I had an old electrolysis cell to offer to get him started.
After a few amazingly spectacular casing->shrapnel conversions, it was soon abundantly clear that the amount of propellant required for the preheater grain was only a small fraction of what we required for APCP as the exponent really kicked in with a U/C valve N2O hybrid ignition - well beyond our expectations.
Troy
*From:*arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] *On Behalf Of *Troy Prideaux
*Sent:* Tuesday, 7 August 2018 8:58 AM
*To:* arocket@xxxxxxxxxxxxx
*Subject:* [AR] Re: Cheap Solids? Amonium Nitrate: catalysis vs sensitization
Mark,
I didn’t really have a problem with the tiny grains – or at least in the boiler plate motors I tested them in. Well, I cracked a few graphite nozzles from over pressuring but can’t remember experiencing anything significant until I started scaling up – which was also accompanied by more adventurous fuel experimentation – a methodology and practice doomed for nasty surprises.
I agree that the exponent is manageable **IF** you’re really disciplined with the development. The margins for experimenting with different fuels or additives or processing techniques than what you’ve already proven is a lot lot tighter than a typical APCP. Issues with porosity or binder wetting or structural integrity with the propellant will be magnified exponentially.
Which is not to suggest there’s no place for trying different fuels or whatever – just that you need to be extra careful about thorough characterization 1^st with tight controls on maintaining what’s been characterized to be workable when scaling up.
Troy
*From:*arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx>[mailto:arocket-bounce@xxxxxxxxxxxxx] *On Behalf Of *Mark C Spiegl
*Sent:* Saturday, 4 August 2018 1:10 AM
*To:* arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: Cheap Solids? Amonium Nitrate: catalysis vs sensitization
>> The exponent is the issue with these oxidizers.
I remember the same thing. I think I measured the exponent around 0.65, which is high, but not impossible to handle in hobby motors which can be designed with huge safety margins. Part of your problem may have been the small size. 18mm is unforgiving. I made 2.5" J motors. They worked fine. It was an interesting experiment.
--MCS
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