2 replies to this topic

[Odin]

I have heard about the "Kn factor" for calculating the internal diameter of nozzles for both core and end burning rockets. Does anyone know how it works?

[bigtonyicu]

I have heard about the "Kn factor" for calculating the internal diameter of nozzles for both core and end burning rockets. Does anyone know how it works?

The full explanation, including the formulas in well explained By Richard Nakka, on his web page

http://members.aol.c...dx/design1.html

But in itself the Kn number isn't of any use, it's simply a ratio. Unless someone has a range of acceptable value to use with BP motors. The grain strength, casing rigidity, operating pressure, those have a much greater importance then the Ratio of surface area to nozzle throat; because a very strong case an nozzle will be able to have a greater surface area and hence improve the ISP (fuel efficiency) because of the increase in exhaust temperature.

I wish it could be a simple as keeping the Kn in a given range but there is many more factors that come into play. However, the range would give you a star at value to begin testing if you don’t want to do the math. Keep in mind that as the motor burns the Kn value changes especially in core burners due to the outward grain regression, so for core burner the final Kn value is much more important then the initial one.

Edited by bigtonyicu, 19 June 2008 - 01:23 PM.

[Odin]

The full explanation, including the formulas in well explained By Richard Nakka, on his web page

http://members.aol.c...dx/design1.html

But in itself the Kn number isn't of any use, it's simply a ratio. Unless someone has a range of acceptable value to use with BP motors. The grain strength, casing rigidity, operating pressure, those have a much greater importance then the Ratio of surface area to nozzle throat; because a very strong case an nozzle will be able to have a greater surface area and hence improve the ISP (fuel efficiency) because of the increase in exhaust temperature.

I wish it could be a simple as keeping the Kn in a given range but there is many more factors that come into play. However, the range would give you a star at value to begin testing if you don’t want to do the math. Keep in mind that as the motor burns the Kn value changes especially in core burners due to the outward grain regression, so for core burner the final Kn value is much more important then the initial one.

Bigtonyicu,

Thanks for the advice and the website address