Medusa Multi Orifice Nozzles

Elapid · May 20, 2004

I was looking at the RCS (www.rocketmotorparts.com) website and saw these units. has anyone here used them?
i imagine that they would lower chamber pressure, resulting in a loss of thrust, but boy howdy! i think it would be cool to have the cluster-type exhaust without the problems of igniting clusters of AP motors.

https://www.rocketmotorparts.com/engdrawings/rcs_01700_nozzle_dwg.pdf

EXcuse me for veering into the Forbidden Zone...
(methinks we need a new forum section password protected for EXtremely curious individuals who need EXtra information...)

Ryan S. · May 20, 2004

they dont lowe chamber pressure, you only drill out a certian number of holes for different motors. For a short motor you would only drill out one, for longer motors more, therfore keeping the KN about the same.

The purpose of the Medusa nozzle is to save material. By making lots of little holes your nozzle does not have to be as long and you use less plastic

Todd Knight · May 20, 2004

I have used them in the Stock 54mm AT motors. The previous post really says it all, smaller nozzles. I did read an article somewhere (I think ROL Info Central). THey do seem to work well enough. Check out some of the EX pages as I assume they cover this in more detail.

Elapid · May 20, 2004

doesn't save material. from what i can find,
https://www.ukra.org.uk/faq/faq2_2_12.shtml
"The Medusa nozzle allowed the exhaust to be spread out and enabled a larger flame to be produced. "

the effective nozzle diameter determines chamber pressure/thrust. more nozzles means that the flow(s) of each nozzle must be taken into account to find total flow. the nozzles can be enlarged to varying extents to custom-tailor thrust levels and total output of the motor.

here's a spreadsheet to calculate Kn (kN?) for the medusa nozzles.

if higher pressures produce more thrust/power then more (bigger) holes = less power

AlexNUMB · May 20, 2004

Originally posted by Elapid
doesn't save material. from what i can find,
https://www.ukra.org.uk/faq/faq2_2_12.shtml
"The Medusa nozzle allowed the exhaust to be spread out and enabled a larger flame to be produced. "

The flame might be more pronounced as a side effect, but that is not the primary reason they are used.

As someone mentioned earlier, you can use a 1/2" long medusa style nozzle in place of a 2" solid graphite AMW/Kosdon type nozzle. This allows more propellant to be packed into a given volume. With single throat nozzles, you need to have a long expansion cone section. With several smaller nozzles, you can run shorter expansion cone sections and reduce the overall length of the nozzle.

Note that Aerotech is now replacing the medusa style nozzles for standard single throat nozzles on some of the 54mm Redline type motors.

the effective nozzle diameter determines chamber pressure/thrust.

The area of the nozzle's throat is one factor in that equation. One also has to consider the surface area of the propellant in the given motor, the burn rate exponent, and the burn rate coefficient.

The exponent and coefficient remain static while the motor maker can adjust the throat diameter and propellant surface areas. Determining a propellant's exponent/coefficient is beyond the scope of this discussion.

more nozzles means that the flow(s) of each nozzle must be taken into account to find total flow. the nozzles can be enlarged to varying extents to custom-tailor thrust levels and total output of the motor.

More correctly, additional throats can be drilled or left plugged to suit the needs of the motor being made. Example of this is like a K1100 w/ all ports open vs a K550 w/ 4 ports open. Same volume of propellant, different propellant characteristics, different nozzle size.

<snip>

if higher pressures produce more thrust/power then more (bigger) holes = less power

Higher pressure does not neccessarily = more power. However, propellant burned at higher pressure has a tendency to be more efficient, thus increasing the power delivered by the same amount of propellant. Folks like Jeff Taylor like to run their motors around 1000psi... I keep mine around 500-750psi. Different Strokes....

--Alex