Problems with rocket nozzle

[bobes]

Hi, I want to make a nozzle for my rocket and I have problems with defining the diameter of the critical cross section of the nozzle.

Normaly it is calculated from the area ratio, I know that the value of the area ratio for fast burning rockets is between 100 - 200.

But ... it seems to me to much because with this value of area ratio, the critical cross section should have only 3 mm.

I don´t know what to do.

 

Thanks

[Enthalpy]

You have to compute the density of the ejected matter, its speed, and then the mass flow per second gives you the section. At the throat or at the exit - just take the local conditions.

 

Density results from pressure, temperature, composition, and these are not really accessible to hand computation. Take a rocket computation software like CPropepShell or RPA.

 

200 looks much for a rocket in the atmosphere.