SOV-4-20 part-2

Because the test flights of SOV-4-20 were a success I decided to increase the launch pressure the next flight. The test flights were at 60 psi so the goal for the next flight was 80 psi and if all went well then I would try 90 psi.
Weather conditions were perfect, it was a beautiful summer evening with no wind. When arrived at launch site everything was setup within 10 minutes, the rocket was filled with 600 ml water and placed on the launcher. I pressurized the rocket with the bicycle pump, at 40 psi I listened an watched for leaks, there were none so I got on with pressurizing. Just before reaching 80 psi I heard a sudden "BANG!", I looked up and watched the rocket tumble through the air, it tumbled because it hadn't any fins on it, they were still on the launcher along with the lower bottle, the join between the bottles didn't hold the pressure. 

When I got home I watched the video and tried to imagine what exactly happened. At first I thought the cap wasn't tight enough but then I found a formula to calculate the forces that act to the join (yes, I know I'd better done that before building the rocket) and I was very surprised by the results, the bottles tried to separate from each other at a force of 780 N or almost 80 kgf which, I think, was way too much for the cap to hold. I still thought it would be possible to make the rocket hold higher pressures, it just needed a way to reduce the force on the caps. 

A couple of weeks later I got an idea that could work. The idea was to tie 2 cords at the nozzle, lead the cords over the top of the rocket back to the nozzle again creating 4 lines along the side of the rocket, then when the rocket stretches by pressurizing, the cords would tension and so take over some force from the caps. I had some old lines in the shed, left over from my "power kiting" hobby, rated at 125 kg they were a little overdone but for testing they would do the job. While adding the lines I realized that the rocket had to stretch somewhat to make a good seal between the cap and the washer so I added rubber rings, cut from a bicycle inner tube, in the lines. 

In the pictures below you can see the lines along the side of the rocket. At the top of the pressure vessel is a piece of another bottle that keeps the lines in place. 

It all seemed to work well when testing on the launcher, at 50 psi there already was a lot of tension on the lines so it was time to test it in the field. I decided to start at 90 psi for the first launch and, if there were no issues, increase pressure to 100 psi for the second. Will it work?

Launch 1

Launch 2

It worked!...

SOV-4-20 part-1 building and first test flights

The idea:

At the beginning of spring 2011 I found a very thick 0.5 liter bottle, I thought if I could splice a couple of these bottles it would make a great water rocket that could hold up to maybe 200+ psi. The bottles have no straight sides so it wasn't an option to glue the bottles together and I didn't want the disadvantage of airflow restriction with a robinson coupling, so I thought of another way of splicing the bottles. The idea was to cut a hole in the bottom of one bottle, insert a cap in it and put the neck of the next bottle through the hole and secure this with the cap that has a hole in it to let the air pass through.

Building:

I first tested this method with a single splice and it held up to 90 psi, this was the highest I could get with the cheap bicycle pump.

The rocket itself was made out of 4 of these bottles so the total volume would be somewhere around 2 liters. Building the pressure vessel was quite easy but at the first pressure test a problem showed up, when the pressure got higher the rocket started to bend. To solve this problem I added a sleeve over the pressure vessel all the way from the nose to the tail to align the bottles, this solved the bending problem and made the rocket more streamlined but it also made the rocket somewhat heavier then planned. The total weight of the rocket was about 250 grams including the nosecone with parachute and airflap release mechanism. 

The fins of the rocket were made of 2 layers of cardboard glued together and then laminated. I glued the fins directly onto the pressure vessel.

Test flights:

The first test flights were made June 2011 and looked very promising the rocket was tested at a launch pressure of 60 psi, it flew nice and straight without spinning to much. The airflap recovery worked properly releasing the parachute right at apogee, although the parachute failed to fully inflate at the second flight the rocket was slowed down enough to keep the rocket intact. Below is a (shaky) video of the 2 test flights, unfortunately the onboard camera wasn't properly fixed.

Here's another onboard video of a flight that I made a few weeks later. The camera was fixed to the side of the rocket with tape. It was already getting dark so the video is a little underexposed.

Altogether the test flights were a success but would the rocket hold higher pressures...?

My first water rocket

after seeing the first water rocket videos it didn't take long before i started to make my own water rocket.

This first rocket was made of a single 1.5 liter bottle with the top of another bottle as a nosecone, at first there was no recovery system on this rocket, later i added a parachute that was supposed to deploy at apogee using NOAA (Nosecone Of At Apogee) but the nosecone hardly ever came of at all or fell of just after thrust phase. 

I used a cork with a bicycle valve and a bicycle pump to launch the rocket (no release system), this way it's always hard to know when the rocket launches and you miss half of the flight because the rocket is already near apogee when you're aware that it was launched. So i made a release system to launch the rocket when i wanted it to. This release system was a U-pin that held the bottle behind the collar. Then, when the rocket was pressurized, the pin was pulled out and the rocket was launched.

 

We had great fun with this rocket, but i wanted more...

Welcome

Welcome to the N-B Water Rocket blog. At this blog i will post launch reports and updates about the progress of my water rocket build projects.

It was September 2010 when i first saw a video of a water rocket and was immediately interested. One of the things i like about water rocketry is that you can build a water rocket from scrap, things you would otherwise throw in the trash suddenly become potential rocket parts. Another interesting thing is speed, a water rocket can easily reach a velocity of 250 km/h. That said, i recommend you to read the water rocket safety rules before you start launching your own rockets.

I hope you'll have fun reading this blog and feel free to ask questions or leave a comment.