# Aerospace Ramjet Topic!

1. Aug 9, 2006

### Jet-designer

Hello,
I'm Arman, new user here. I'm a jet-engine designer and I'm really interested in building and running different types of jet engines.

I have quetion now: Some amount of air enters a cone shaped pipe with a minimum diameter of 6 cm and a maximum diameter of 10 cm, and a length of 7 cm at 30 m/s. We know that beacuase of the increased volume, the air slows down. can you tell me how much does the air slow down and what changes are made in the pressure of air?

Thanks,
-Arman

2. Aug 9, 2006

### Astronuc

Staff Emeritus
Here is a page on ramjet propulsion -
http://www.grc.nasa.gov/WWW/K-12/airplane/ramth.html
http://www.grc.nasa.gov/WWW/K-12/airplane/ramjet.html

I don't know if you'll find the specific calculation in which you are interested. One must solve the simultaneous continuity (mass), momentum and energy equations to obtain the correct state point (pressure, temperature, momentum/velocity) in the flow.

from the propulsion page -
http://www.grc.nasa.gov/WWW/K-12/airplane/shortp.html

Here is some basic information on rocket propulsion - http://exploration.grc.nasa.gov/education/rocket/shortr.html

3. Aug 9, 2006

### FredGarvin

Not to be a stick in the mud here, but you're a jet engine designer and you're asking how to calculate the pressure rise in a diffuser?

4. Aug 9, 2006

### Jet-designer

Any Problem? I'm not a Ramjet designer and that's why I'm not that professional in designing ramjets...

5. Aug 9, 2006

### FredGarvin

Just asking. As you must know, you described a diffuser which a very common element in jet engines, not just ramjets.

6. Aug 9, 2006

### Danger

That sounds a tad peculiar to me too, Fred.
Jet, what exactly is your education in this field? It's a lot easier to help if we know what level we're dealing with.

7. Aug 9, 2006

### Clausius2

:rofl: :rofl: :rofl: Jet, I'm NOT a Ramjet designer, neither every of us. But yeah, we know the answer, it belongs to "general culture" for an engineer. The answer is: who knows. You are only specifying one of the three variables (v,P,T) needed for solving the thermofluid-dynamic state of a gas.

8. Aug 9, 2006

### 3trQN

Hey, id like to get involved in making my own designs, and simple propulsion models, as a hobby. Any advice from anyone thats done somthing similar? i.e. with hobby models and small scale experiments.

Im currently trying to further my understanding of Thermodynamics, mechanics and fluid mechanics, and my maths also. I think a project would help keep me motivated & focused.

9. Aug 9, 2006

### FredGarvin

There are some pretty cool kits out there as well as a lot of homebuilt websites. Do some surfing to see what's out there. You can get into it pretty cheaply by getting into the CNG powered burners. I remember seeing a web site that had a guy in New Zeland that used a homemade turbine to cool his beer in his garage.

10. Aug 9, 2006

### Staff: Mentor

I think what he meant to say is that he would like to become a jet engine designer...

Be sure to check out the homepage he lists in his bio for more information:

http://air.blogfa.com/

EDIT -- There are even some turbojet and ramjet drawings mid-way down that home page....

Last edited: Aug 9, 2006
11. Aug 9, 2006

### Jet-designer

Yeah, I'm not a real jet engine designer, I'm an analyst in aviation science and my homepage is a lovely and really enthusiastic weblog in Iran, and I'm a writer for a lot of country-published aviation magazines and the question I've made was about a new project I'm working just for fun. Thank you all...

12. Aug 10, 2006

### Jet-designer

Hi,
I'm quite disappointed now, because no one gave me what I exactly wanted.
Tell me what variables are needed to calculate and solve the problem I talked about?

13. Aug 10, 2006

### FredGarvin

14. Aug 10, 2006

### Jet-designer

Dear Fred, I've already read that, can you offer me a simple solution to solve the problem?

15. Aug 10, 2006

### Mech_Engineer

<SIGH>

16. Aug 10, 2006

### Hawknc

http://www.grc.nasa.gov/WWW/K-12/airplane/mass.html

Look at the fluid dynamics section. That, at least, will explain how to obtain velocity. From that, since it's a nice slow air flow, you could use simple incompressible flow equations to find pressure which pretty much every flight/fluid textbook/website ever invented has.

17. Aug 10, 2006

### Astronuc

Staff Emeritus
18. Aug 10, 2006

### Hawknc

Sure, if you want to be all complicated about it. :p Things get a whole lot more interesting with compressible flow.

19. Aug 10, 2006

### Astronuc

Staff Emeritus
:rofl: I suppose with the parameters given in the OP, the compression will be very little. Then one only needs to employ the continuity equation, which is NBD.

Besides, 30 m/s (~100 ft/s) isn't much of a ramjet.

Last edited: Aug 10, 2006
20. Aug 10, 2006

### FredGarvin

Do you have an english version of your blog? I would be interested in reading it, especially from the viewpoint of someone who lives in Iran.