Water Rocket Forum

Oh, doesn't it put too much stress on the interstage?

So, will there be instructions on how to build such a staging mechanism on instructables? It seems to me like this is a very efficient and fairly easy way to have multi-stage rockets.

Astrofox wrote:So, will there be instructions on how to build such a staging mechanism on instructables? It seems to me like this is a very efficient and fairly easy way to have multi-stage rockets.

One day! :-)

I know how it works

But I don't know how to send pictures in the Forum

So any videos of this stager with successful flight?

Braaainz wrote: ↑Sun Jul 29, 2018 9:59 pm So any videos of this stager with successful flight?

I did a trial in 2016.. I haven't an opportunity to do again since then.. Worked fine in principle.

kitestring wrote: ↑Sun Jul 29, 2018 10:54 pm

Braaainz wrote: ↑Sun Jul 29, 2018 9:59 pm So any videos of this stager with successful flight?

I did a trial in 2016.. I haven't an opportunity to do again since then.. Worked fine in principle.

Where do you think your leaks were coming from?

Braaainz wrote: ↑Mon Jul 30, 2018 3:57 am

kitestring wrote: ↑Sun Jul 29, 2018 10:54 pm

Braaainz wrote: ↑Sun Jul 29, 2018 9:59 pm So any videos of this stager with successful flight?

I did a trial in 2016.. I haven't an opportunity to do again since then.. Worked fine in principle.

Where do you think your leaks were coming from?

From a launcher issue, not the rocket

I recently started experimenting with a similar concept like this thread. It is a fully 3d printed release mechanism with an internal non-return system (holds pressure in one direction but slowly bleeds it off if 2nd stage fires prematurely). Here is a test video. First step was to depressurize the first stage to test the non-return valve. Then I manually triggered the air-flap on my tommy-timer system. The timer releases a radial deploy sleeve (Thanks USWR!) which takes the pressure off of three claw-arms that hold the 2nd stage. A parachute would be tucked in there as well. The hinges on the claws are also 3D printed. The system just needs two o-rings, a washer, and a 1/4" rubber ball bearing. I printed a 3D section view of the mechanism which I can post if anyone wants to see how the non-return system work. I have not launched this yet.

Here is a section rendering of the device (video in last post). The Non-return valve rubber ball bearing is dropped into the device during the printing and the system continues to print around the bearing. The hinge pins are also 3D printed. This version uses 3 claws to hold the second stage which allows just enough room for a first stage parachute.

I am eagerly awaiting to hear about the launch.

I think the time delay would make for a higher height than a crushing sleeve, thoughts?

Times like this, I wish I had a computer for simulator use. I only have a smartphone. Anyone know of a simulation that run on an Android phone?

Awesome!

Braaainz wrote: ↑Wed Aug 29, 2018 6:07 pm I think the time delay would make for a higher height than a crushing sleeve, thoughts?

Answer is "it depends." Generally you get more altitude by increasing max velocity (as in, no delay), rather than by letting the rocket slow down before the second stage fires.

However, increasing velocity also increases drag (which goes up as the square of velocity), which might mean that the energy used to overcome that drag is wasted when it could have been used to accelerate the rocket from a slower speed by adding a delay. There may be an optimum delay time, greater than zero, but less than waiting for first stage apogee before firing the second stage. I don't know but I suspect the answer is closer to zero delay.

I can modify my simulator to test some scenarios.

OK, I was wrong, it helps to have a small delay before firing the second stage. Here are some simulations. Arbitrarily, I set:

• 2L bottle for each stage
• each stage filled with 0.5L of water
• no flow restriction on each stage, standard 22mm nozzle diameter
• 200g of ballast (instruments, staging mechanism, fins, etc.), reducing to 100g when first stage falls away
• 200 mm launch tube on first stage
• drag coefficient of 0.2

Test 1: no delay - second stage fires when first stage runs out of water
Velocity and altitude on second stage firing: 24.4 m/s, 0.92 m
Final altitude: 134 m

Test 2: small delay - 0.5 sec delay from launch to fire second stage
Velocity and altitude on second stage firing: 23.2 m/s, 12 m
Final altitude: 143 m

Test 3: medium delay - 1 sec delay from launch to fire second stage
Velocity and altitude on second stage firing: 18 m/s, 22.3 m
Final altitude: 147 m

Test 4: large delay - 2 sec delay from launch (almost to apogee of 2-stage assembly with 2nd stage still full)
Velocity and altitude on second stage firing: 7.9 m/s, 35.3 m
Final altitude: 146 m

Conclusion: For the tested configuration, a small delay before firing the second stage achieves some additional altitude, by about 10% over firing the second stage immediately after the water is exhausted from the first stage. Optimal delay is about 1 second from launch. Any delay more than 2 seconds risks firing the second stage after reaching apogee from first stage.