Glue part 2

The fact that I didn't know how much force it would take to get the tube of the bottle, was constantly on my mind so I did some more testing today. I took the luggage scale again and made a pulley system so I could easily pull with more force. The scale went 1,5 times around (which would be around 50kg force on the tube) when the rope broke again. I really wanted to know what it would take to get it of, so it was time for some brute force.

This is just the last part of the video, there where more than 10 hits preceded.

Finally the tube is off but was it the glue that gave up?

a layer of pet has been pulled off

No, probably not, looking at the bottle it looks like a layer of pet has been pulled off.

Difficult to see in the picture but there's a very thin (shiny) layer of pet still stuck on the glue.

So I still don't know how much force in kg it would take, but I know for sure that this glue bonds very well to pet, in fact it's stronger than pet. I'm definitely going to use this glue to make the drop away boosters...

Glue

It's been a while since my last post but I'm back in water rocketry again.

I'm planning to build some drop away boosters for the last rocket I made. I want to build the boosters out of spliced pairs so I needed to find a strong glue that will stick to pet. There's a glue called PL Premium that's often used for splicing but unfortunately it's not available here in Holland. I've looked in several stores for other PU glues (PL Premium is also a PU glue) with the same specifications as PL Premium but didn't find a match. So I just bought a glue named "Tangit M400" a PU glue that looked promising to me. I made a asymmetric splice out of 2 coke bottles and the next day I did a hydro pressure test, unexpectedly it held up to 100 psi and there was no sign of any leaks, I could not test at higher pressures because I'm still stuck with the old bicycle pump, I'll probably get a new one soon so I can do a real burst test on the splice.

The test splice, next time I'll use a little less glue.

For the drop away booster system there need to be tubes at the sustainer and pins at the boosters. I tested 3 glues to attach tubes to a pet bottle; Tangit M400, Pattex PL600 and Pattex Power Fix. The PL600 is also a PU glue and the Power Fix is a polymer based glue.

The 3 tubes glued to a bottle. from left to right: Tangit M400, Pattex PL600 and Pattex Power Fix.

The wires you see in the picture were used to attach a luggage scale with a bucket underneath, when testing the bucket was slowly filled with water to increase the force on the tubes.

the test setup. not pretty but it works.

At first i tested the Power Fix glue, it held up to ~6 kg.
The PL600 gave up at ~7 kg.
With the Tangit M400 I filled the whole bucket with water and it was still holding, I pulled the bucket down until the scale was at 14 kg but still no sign of the tube coming loose, I removed the bucket and and hung a loop of rope to the hook of the scale and placed my foot in the loop, at 27 kg the rope broke!

Pattex Power Fix: 6 kg

Pattex PL600: 7 kg

Tangit M400: 27 kg

  















The pictures above are coming from a video I made during the test, they all are the last frame before the tubes came loose or the rope broke.

I still don't know how much it would hold but I'm pretty sure the M400 glue is strong enough both for splicing and for the tubes and pins of the boosters...

15 January 2012

At the 15th of January the new rocket made its maiden flight, it was a beautiful day to launch a water rocket.

Weather data of sunday 15 January 2012

•  partly cloudy
•  Temperature:     2.5°C
•  Wind:     2.7m/s = 2Bft      87° = East
•  Air pressure:     1026.6 hPa
•  Humidity:     87%

We arrived at launch site at 15:45, after setting up the launcher and rocket I wanted to set up the launch trigger mechanism and  then I realised I just forgot to mount the springs on the gardena quick connector, they were still in the shed. In spite of the risks related I decided to launch the rocket manually.

Launch pressure for the first launch was 90 psi, and the tommy timer was set at approximately 5 seconds. The 808 key cam was attached to the side of the rocket and pointing downwards.  
Pressurization went very well with no audible leaks.The rocket took off pretty fast and flew straight up, there was quite a lot of spin but that was expected because the fins are not properly lined out. The tommy timer side deployment did his job and the chute came out just after apogee but the chute itself failed to open until about 10 meters above the ground, probably because I had it lying around folded. Because the batteries of the digital dv cam gave up there's no ground footage of this flight.


With the first launch being a success ,apart from the chute, I decided to launch the rocket at 100 psi with the tommy timer set to 6 seconds, this would give the rocket some more time to speed up before the chute comes out in order it would catch more wind and open quicker. It was a nice flight again, the chute opened very fast and the rocket descended back to earth slowly. The onboard view shows a lot of spin again and also that the fins "flapped" at top speed, this could be because the fins are just to thin or because they tend to "hinge" were they are glued to the bottle. The ground footage of this flight was taken by a 7 year old girl an shot with a mobile phone, good job!

The fins need some adjustments but I'm very happy with the results of this first flights...

New launcher

To launch the new rocket I definitely needed to build a new launcher because the other one was way to small for this rocket and you couldn't really call it a "launcher".
The new launcher should contain the gardena quick release and a launch rod to guide the rocket. I wanted to make it a tripod so it would be stable on uneven surfaces. Beneath is an image I made with Blender (a free open source 3D creation program) just to see what it would look like.

I had some leftover plywood which would function as a base for the launcher. For the launch rod I used 2 pieces of 10mm glass fibre rod fitted over a piece of 8mm carbon fibre rod, this makes the rod easy to transport because it can be divided into two parts. The legs of 50cm length where sawed from a mounting rail and are mounted on the base with bolts and nuts, so they can easily be removed for transport. The gardena quick release is pulled down by a pair of springs, during pressurization the quick release is held in the locked position by a piece of wood. At launch this is pulled out, the springs pull the collar down and the rocket is released.

Ready to launch some rockets!.... or isn't it...

 

Proven techniques

After the disappointing results of the last few launches I decided to build a new rocket. I just wanted a rocket that worked so I chose to use common techniques and materials that have been proven to work.
I Chose to use a "Robinson coupling" to splice the bottles, this is probably the easiest way to connect bottles. A Robinson coupling consists of a hollow threaded tube that joins the bottles together, the hollow thread allows water or air to pass from one bottle into another. "HHWRSA" has a great video on how to make a Robinson coupling: http://wrocket.hampson.net.au/?p=1081  and that is exactly the way I did it.

The recovery system is based on the side deployment mechanism from Air command water rockets but without the electronic timer and the servo, instead of them I used a so called "tommy timer" which I've taken out of a cheap wind-up toy. At the launch pad the gears of the timer are jammed by a piece of plastic wire, at liftoff the wire is pulled out and the timer starts.

The pressure vessel consists of three 1.5 liter (labeled) bottles, so the total volume will be around 4.7 liters, and it is equipped with a 9 mm gardena nozzle.

The rocket will use a 1.6 meter long external guide rod to keep it stable during the first part of the flight, by the time it leaves the guide rod the rocket should go fast enough for the fins to keep it stable. The fins will be made and attached the same way as on the sov-4-20 rocket (see:SOV-4-20 part-1). 

With the great videos of the side deployment mechanism and the robinson coupling building the rocket was pretty much straightforward. 

I'm looking forward to launch this rocket, but a bigger rocket needs a bigger launch pad...

SOV-4-9

This is actually the same rocket as in the 2 previous posts but with a 9 mm gardena nozzle. the reason I added this 9 mm nozzle is that I wanted the rocket to have a longer thrust phase and fly slower. I made the nozzle from a soap dispenser cap and a gardena quick connector, the reason that I used this cap is that it has a longer thread so there's enough space to hold the connector and a washer, and it already has a hole in it to put the nozzle through. 

It had been a cold and wet summer but there were a couple of good days at the beginning of the fall so I made some time to launch the rocket again.
After a 10 minute drive and a 5 minute walk we arrived at launch site. I assembled the launcher, prepared the rocket and another 10 minutes later we were ready for the first launch. The plan was to launch the rocket at 100 psi again but (as always) things didn't go as planned. The rocket took off spontaneous at 60 psi leaving the nozzle and his adapters on the launcher. We got the rocket back and reassembled it but the second launch it had the same problem again, we tried a third time again with the same results. Probably the stress from previous launches had made some cracks in the thread of the cap so it couldn't hold the pressure anymore. I had no tools and materials to fix this in the field so we went home a little discouraged by the failed launches. 

Well, at least there's a nice onboard video that shows the kids had fun...