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  #21  
Old 11-10-2013, 03:45 PM
Jerry Irvine's Avatar
Jerry Irvine Jerry Irvine is offline
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Originally Posted by Jerry Irvine
The entrapped air is about 0.000001% of the deal and the eroded paper is about 10% of the deal.
Tech Jerry
I want to augment my comments on this. Just as when there is vacant space inside a firecracker, its performance increases as a result of the ability of the chemicals to trigger their burning rate exponent vs pressure "feature", a tandem benefits from a small plenum between the booster motor burn thru (chunks) having a space to react and expand physically.

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  #22  
Old 11-10-2013, 10:06 PM
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blackshire blackshire is offline
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Originally Posted by Solomoriah
Um. Black powder already contains an optimal amount of oxidizer; adding oxygen doesn't help matters, though one might argue that it would support burning out more of the casing.
Yup--that's why I prefaced all of the comments with "*if* the black powder is fuel-rich," as I didn't know if it was or not (it may be possible to compound black powder that is either fuel-rich or oxidizer-rich, as the three types of black powder used in model rocket motors definitely have different burning characteristics). Also, ducted rockets (which use composite propellant--they are related to solid-fuel ramjets) use fuel-rich propellant, which burns with oxygen from the air to achieve an optimum fuel/oxidizer ratio.
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Last edited by blackshire : 11-10-2013 at 10:11 PM. Reason: This ol' hoss done forgot somethin'.
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  #23  
Old 11-10-2013, 10:23 PM
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blackshire blackshire is offline
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Quote:
Originally Posted by Jerry Irvine
I want to augment my comments on this. Just as when there is vacant space inside a firecracker, its performance increases as a result of the ability of the chemicals to trigger their burning rate exponent vs pressure "feature", a tandem benefits from a small plenum between the booster motor burn thru (chunks) having a space to react and expand physically.

Uber Tech Jerry
Indeed--the plenum gives the reactants time to react fully within the motor. The "evaporating fuel" paraffin hybrid rockets (in which the paraffin fuel vaporizes and mixes with the oxidizer above the solid fuel's surface, just as occurs near and in the wick of a paraffin candle) also benefit from having enough open volume for thorough fuel & oxidizer mixing and combustion to occur inside the motor, as any combustion that occurs behind the nozzle--as cool as it looks to spectators--isn't helping to push the rocket upward! :-)
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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

Last edited by blackshire : 11-10-2013 at 10:24 PM. Reason: This ol' hoss done forgot somethin'.
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