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He means DaCrezthchs
I know that but if he gets to +1 postcount with spam questions then I get to +1 postcount with spam answers. :p
Let say I had a steady flow of propane gas at a pressure of 1 psi, leading to a de laval nozzle which in turn will be ignited. Will the nozzle create "push" with just the 1 psi?

Thanks!

Futher discusion: chefkrohn@ g ma il
The exhaust velocity depends on the energy of the reaction and the geometry of the nozzle, not really the pressure of the propellent flow (at least not directly). So the answer is no, it won't be 1 psi unless the setup coincidentally produces that.
Can a convergent/divergent nozzle convert 1psi of gas to 2 or more when ignited?
Yes, but typically the pressure drops as it exits the nozzle as the pressure is converted to velocity, which is much more important than pressure.
 
OK, well if you want to burn propane gas, you'll need some air at ~9.5 times the volume of propane. Here's a page that talks about the theory of that. Then you're looking at the pressure of the combustion gases.

I'm still not so sure what you mean about "1psi of gas" but that by itself is not enough to generate flow in the de Laval nozzle considering ambient pressure is like 15psi. So it comes down to your combustion products which may or may not be enough for the job.

So my initial impression is that you're barking up the wrong tree but if you are talking in terms of gauge pressure as hobbsyoyo believes then you're on the right track, I guess, sort of.
 
How would you burn propane without air oxygen? :>

Pure oxygen is dangerous buuut if our friend here doesn't mind the imminent risk of catastrophic failure then he may have at it.
 
How would you burn propane without air oxygen? :>

Pure oxygen is dangerous buuut if our friend here doesn't mind the imminent risk of catastrophic failure then he may have at it.
I meant I assumed he was going with pure oxygen of some form. I guess he could rig up some sort of air-burning scheme but then he's either got to bottle the air (and drag along useless N2) or figure out a way to make an open reaction chamber that works with 1psi NG and that alos doesn't sturctually compromise the rocket with air intakes. I just don't see it working to be honest....
 
Gauge pressure is the pressure you read on the gauge, which typically aren't 'zeroed' out. When measuring pressure, gauges don't usually account for the pressure of the air. So let's say you have a gauge attached to your car tire and it reads 18psi. That means the pressure in the tire is 18psi above air pressure, which (IIRC) is ~14.7psi) so the actual pressure in the tire is 18psi + 14.7psi = 32.7psi. 32.7psi is the absolute pressure, because it measures from zero pressure, while 18psi is the gauge pressure, because it measures with the 'zero' taken to be the ambient air pressure.

In this case, it would be silly to use 1psi absolute pressure as it would mean the tank is in partial vacuum and would require some serious plumbing to get the gas out of it (or air would back up into the tank and make the rocket inoperable). However, there was so little information in the question that I had to ask.

:wallbash:

Of course.

This means that I've been screwing up ALL of my mental estimates of truck weights for the past 10ish years. See, I do this thing where I look at the footprint of a truck tire, estimate the surface area, multiply by the number of tires, multiply by the nominal fill-pressure *which is, I now believe, GAUGE, NOT ABSOLUTE* - and estimate the mass of the vehicle.

Fun while riding a bike.

But not fun if I'm off by a factor of 15^2!!
 
Would you consider defecting the Democratic People's Republic of Korea? We have rocket program, aimed at moon and mars, you could join and help humans for science. We also have lots of girls in uniforms to choose from. As socially dysfunctional engineer - as seen on "Big Banga Theory" - you must appreciate this, yes?
 
I meant I assumed he was going with pure oxygen of some form. I guess he could rig up some sort of air-burning scheme but then he's either got to bottle the air (and drag along useless N2) or figure out a way to make an open reaction chamber that works with 1psi NG and that alos doesn't sturctually compromise the rocket with air intakes. I just don't see it working to be honest....

A homemade rocket with propane and pure oxygen is a recipe for failure if you're stuck on the nozzle geometry...
 
Would you consider defecting the Democratic People's Republic of Korea? We have rocket program, aimed at moon and mars, you could join and help humans for science. We also have lots of girls in uniforms to choose from. As socially dysfunctional engineer - as seen on "Big Banga Theory" - you must appreciate this, yes?

Traffic girls, so sexist. And sexy. But sexist.
 
Would you consider defecting the Democratic People's Republic of Korea? We have rocket program, aimed at moon and mars, you could join and help humans for science. We also have lots of girls in uniforms to choose from. As socially dysfunctional engineer - as seen on "Big Banga Theory" - you must appreciate this, yes?
The most important question to get right when you interview for an aerospace job is, 'Are you a secret Chinese Communist Infiltrator who hates America? Are you sure?'
A homemade rocket with propane and pure oxygen is a recipe for failure if you're stuck on the nozzle geometry...
Point taken.
 
hobbsyoyo said:
The most important question to get right when you interview for an aerospace job is, 'Are you a secret Chinese Communist Infiltrator who hates America? Are you sure?'

You'd pass then, comrade.
 
My answer to that question: No, of course not. :)
(Next question)Do you have any disabilities that require special accommodation?
Yes, I have severe 'dyslexia' that requires that I be given time after work in a private room with your hard drives to ensure I complete my 'assignments'.:scan:
 
At least with regards to the first question, you wouldn't be lying.

Easier solution: just work late.
 
At least with regards to the first question, you wouldn't be lying.

Easier solution: just work late.

Huh?
The bad joke was that I would make up a disability to get ahold of their hardrives to copy all the data off of them so that I may sell it to my Chinese masters.
 
hobbsyoyo said:

They asked if you worked for China, you would however be working for the Democratic Republic of Korea. Thus there would be no need to lie.

hobbsyoyo said:
The bad joke was that I would make up a disability to get ahold of their hardrives to copy all the data off of them so that I may sell it to my Chinese masters.
We wouldn't ask you to do that comrade. Instead, you could just work late!
 
How do ICBMs work?

*

I have binders full of women prepared to send over. Can you please tell me your fax address?
 
I love you, Masada.
 
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