Zero-velocity exhaust

Re: Zero-velocity exhaust

Postby lavalamp » Tue Jun 21, 2011 9:38 am

Interesting that the phase 1 burnout occured higher and faster than you anticipated, but by the time it got to 3.2 km it was travelling significantly slower than predicted. From that it seems as though thrust was much higher than anticipated, but so was drag.

Since you ignite phase 2 at 3200m, I assume the fairly long coast period is by design, what's the rationale there? For instance, would it not perform better if the coast was much shorter, but the phase 1 thrust were lower? Gravity drag would be a bit higher, but it seems as though it's the aero drag killing you.
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Re: Zero-velocity exhaust

Postby rick m » Fri Jun 24, 2011 10:13 am

Preliminary analysis shows the vehicle experienced roll pitch coupling causing the increased drag and vehicle break up. We are looking at balance issues with placement of the avionics. We were fortunate to recover the data intact after the avionics experienced free fall when the chutes ripped off during breakup.

I have continued to improve the propellant with each new test thus increasing thrust and performance of the motor. This was our first completely successful motor test in a flight.

The reason for the delay between first and second motor firing is to coast through the denser lower atmosphere and fire the forward motor later when higher up. Our sim shows this gains the highest altitude for our vehicle/propellant. Since the Isp of sugar is low, we have to design for the maximum weight reduction that puts us on the cutting edge of performance.
Hard work is good for you, try it.
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Re: Zero-velocity exhaust

Postby pauldear » Sat Jul 02, 2011 6:08 pm

lavalamp wrote:You cannot expel a mass out of a barrel with a velocity higher than the speed of sound in the expanding gasses. .


Aha - I knew that I must have overlooked something!

Question to the panel - how do high-velocity gas-guns (some of which have been proposed as "space cannon") work?
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Re: Zero-velocity exhaust

Postby lavalamp » Mon Jul 04, 2011 7:04 pm

In a light gas gun it's done by getting a light gas very hot, the lighter and hotter the better, this results in a higher speed of sound.

In a combusion light gas gun, I believe they compromise on the mass (they include some oxygen!), which allows them to put even more energy into it and get a still higher speed of sound.

There is another type of gun that relies on the projectile compressing a combustible mixture of gasses between the barrel of the gun and itself and riding the pressure wave, essentially like an aircraft engine.
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Re: Zero-velocity exhaust

Postby SANEAlex » Mon Jul 04, 2011 9:43 pm

pauldear wrote:Question to the panel - how do high-velocity gas-guns (some of which have been proposed as "space cannon") work?



Their is a brief description of how they work in this article on a proposed version
http://www.popsci.com/technology/articl ... lies-space

I think i once had a link to a better description but cant find it now its basically brute force and ignorance lots of brute force proportional to low levels of ignorance as if you get the calcs wrong your libel to lose more than your eyebrows ;) :twisted:
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