Re: Sometimes physics is fun

["John S. Denker" <jsd@AV8N.COM>]

On 10/29/2003 12:09 PM, Gary Turner wrote:
> This is all correct, but has some logistical problems.

Logistical problems can be overcome.  Indeed there are
standard techniques for overcoming the problems mentioned.
This isn't very complicated.  It's not brain surgery;  it's
just rocket science.

> The main reason that simple pressure rockets tend to outperform
> chemical rockets over short distance is the ignition delay.  Over
> such a short distance, this whole thing is going to be over in a
> fairly small fraction of a second - most chemical engines will still
> be sitting on the start line waiting for a fuel ignition.

So, the claim is that it necessarily takes a significant
fraction of a second to ignite a chemical rocket.
How do you know that?  How sure are you of that?

When you pull the trigger of a gun, do you expect to hear
a "click" as the firing pin hits, followed a significant
fraction of a second later by the actual shot?

What is the propagation velocity of typical pyrotechnic
substances?  How many *thousand* meters per second?  At
that rate, assuming I can start the reaction at at least
one point, how long does it take to spread throughout
a 10cm reaction chamber?

> As an extreme, you could always strap a
> stick of dynamite to the back,

That's been my main point since day one.  This whole
exercise is a performance/safety tradeoff, with the
biggest advantage to the most reckless participant.