Dual Thrust Water Rocket static tests

These are the static tests of a dual thrust water rocket. For a full explanation please visit: www.AirCommandRockets.com/day1...
To see the dual thrust water rocket in flight please see:
• Dual Thrust water rock...

[@peterhub1]

What is the design of the release mechanism at the bottom?

[@nic12344]

The vacuum is caused by the venturi effect. When the dynamic pressure (velocity) of the jet increases, the static pressure drops! To reduce the effect of the jet punching a hole and letting air escape, you could try to use a conic tube "floating" between the restricted nozzle and the full-bore nozzle. With the small opening pointing up, as the jet would go through, it would push the water instead of the air. I should just be large enough so that after the booster stage is empty, the jet can pass through without being affected..

[@AirCommandRockets]

+Nicholas R.M. Interesting. Thanks for the comment.

[@BrendaEM]

Can you make a coaxial nozzle?
In other words, looking at the bottom of the nozzle, the boost flow would come from an annular ring which surrounds the sustainer nozzle oriface. This ring would be mostly a circular ring, with a few remaining supports for a central nozzle. A tube would extend from the sustainer volume--through the boost volume--to the center of the nozzle. This way, the sustainer flow would not be disturbed as much. Perhaps, the central sustainer nozzle could be threaded and interchangeable, to adjust the impulse time. A larger launch release would encompass both nozzles.
I wonder if pilot valves could be helpful for internal staging. When the pressure drops, they could open--like gangbusters.

[@AirCommandRockets]

Kind of like this?: ua-cam.com/video/uZ_p25VoswQ/v-deo.html

[@noway2831]

Could you run the two phases separately? Perhaps it'd give 2 more recognisable curves - perhaps differently sized besel curves?

[@ReptiglorandRockets]

This is very interesting on why there is a brief Vacuum inside the rocket. Just wondering, isn't this what T-nozzles are for, to do the same thing?

[@AirCommandRockets]

Hi Randy, yup T-nozzles are based on a similar principle, but they only work for the duration of the launch tube. When the rocket reaches the end of the launch tube it switches to the smaller nozzle. With the dual thrust rocket it's like having a two stage rocket without dropping the booster. The boost phase last much longer and has it's own water and air phases.

[@michaelwni]

I was inspired by this video so created my own with a similar setup ... the result is the rocket took off very slow then didn’t have enough thrust to maintain vertical flight. The rocket tipped over and kept firing off while horizontal and got stuck in the mangroves. I made a nice video you can see on my channel.

[@ruthdoyle9085]

Have you tried liquid propane and water? LPG is 149 psi at 90° temp (ambient) and can replace the air pocket with a liquid that expands as a the air would but should maintain pressure until all the water is gone... possibly allowing you to use more water...

[@AirCommandRockets]

We have thought about this previously, but have not done any experiments with it as yet.

[@danielreardon6453]

jeezus thats soo much thrust.... sustained thrust = above 500 newtons which equals 51 kgs

[@zishkii7249]

I am zish. not josh!!