04-18-2009, 06:31 PM
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Craftsman
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Join Date: Apr 2009
Location: Canon City, CO
Posts: 100
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Quote:
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Originally Posted by shockwaveriderz
Mike. what do you think of a BP re-loadable.
I understand that there would be at least 1 initial detriments:
CPSC would not recognize this as a model rocket because of the metal casing; therefore only adults could purchase and use. Ok so Estes makes a product for adult only.
It sems to me that Estes could use its current investemnet in its Mabel technologies:
you just press a propellant grain/delay/smoke train/ejection charge/clay containg cap into a smaller length and diameter paper casing.
Using a metal casing would allow you to burn the BP propellant at much higher chamber pressures resulting in much higher Isp's.
Nozzles could be single use or multi-use perhaps and replaceable.
looking forward to your responses.
terry dean
what advantages/disadvantages pros/cons do you see to such a product?
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Terry - first of all pressed black powder only increases a couple clicks in ISP by increasing the chamber pressure to as much as 1,000 psi.. You might get lucky to get ~95 out of it at those pressures. Estes BP motors run typcally down around ~80 ISP at 50psi. Black powder as a propellant for re-loadables simply does not merit the effort. This was the whole purpose for introducing the composites with ISPs typically in the ~180 range into model rocketery.
Then there is the problem of pressing the re-loadable BP grains. It would be a mess. You would either press into a very thin tube to act as the exterior inhibiror, or press into a solid un-inhibeted grain. The latter is going to burn on all surfaces making it a high thrust short burn motor. The inhibeted grain will be an end-burner with either one or both ends burning. Remember, BP burns right at 1" per second no matter the chanber pressure, so you can get out your calculator to see that the options you have for grain design versus burn time is very limited. And then consider having these solid grains of BP rolling around in your flight box. A 1" diameter uninhibited grain is going to totally burn in .5 second if you accidently light it up. A typical AP composite grain will burn at .25" per second with the exterior almost always inhibeted. You'll have a far greater time getting out of the way of a burning composite grain than the BP grain. Give that some thought.
Next, I would estimate that to press re-loadable BP grains would end up to be very nearly the same cost as pressing an entire motor. And then you need to now purchase and maintain the re-loadable metallic casings to drop them into. Black powder is a terrible corrosive burning propellant. Have you noticed how nasty and ugly your blast delector gets from using BP motors? That's what it will do to the inside of your metallics. And the exhaust is also very abrasive. While a black powder motor is running, the internal gas flow is chewing out the paper just in front of the clay nozzle. That's what will happen over time in a re-loadable casing unless you also drop in a heavy liner.
Terry - there are in my opinion simply no pros in opting for a re-loadable BP motor. There are far more design and manufacturing issues than with the composites. Sorry.
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