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

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.