Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Date:  22nd October 2009
Location: All over the place.
Conditions:  Pleasant
Team Members at Events: GK and PK

We haven't done any flights since the last update mostly due to catching up on non-rocket related activities. Development progress has, however, been continuing on a number of different projects which I'll discuss below. It's a bit of a long write-up so you may want to skip some sections.

• Parachute Release Mod

• Crestwood Fair

• Beauty and The Geek - Australia TV show

• New Splice Testing

• Miscellaneous

Parachute Release Mod

We have made a slight improvement in the side deployment mechanism we use by eliminating of the door's pin, string and latch. The servo horn now directly holds a rubber band attached to the door. When it is time to open the parachute door, the servo simply releases the rubber band.

Advantages

• Much simpler construction - Eliminates the need to make the matching latch components, the pin, and tying the string to the correct length. This saves on construction time.
• Eliminates a metal component - the pin.
• A smaller servo can be used as there is no force required to overcome the frictional forces when pulling the pin.

Disadvantages

• Uses a rubber band which can deteriorate over time and may need to be replaced.
• Slightly less secure door. The pin and latch made the door sit better against the bottle, but a stronger rubber band can be used.

We have been using this technique on the Acceleron V booster to release the primary and secondary parachutes, but have now started using this technique on all new rocket deployment mechanisms.

The servo horn "V" configuration ensures the rubber band can't slip over the servo's axel and prevent it from releasing.

Crestwood Fair

Last month I spent a whole day helping to man NSW Rocketry Association's stall at the Crestwood fair. David and Neville did a great job of organizing the stall and getting all the display materials together. We had all sorts of rockets on display, and I even brought along a couple of water rockets including the Acceleron V to sit in the corner. It was a fun day talking with people about rockets both water and pyro.

Quite a few interested people stopped by for a chat. We gave out close to 50 fliers on the day, so we'll see how many people turn up to the Doonside launches.

The worst part of the day was the strong wind. We had to tie everything down, and rockets on display had to be pointed into the wind. I saw two other tents go flying at the fair.

Beauty and The Geek - Australia - TV Show

During the last month I had an interesting opportunity to help out in one of the challenges on Channel 7's Beauty and the Geek Australia. The challenge for the 'beauties' was to build a simple rocket and launch it. The first to launch it over a rope suspended about 5 meters above them would win the challenge. The rocket challenge was shown in Episode 3. (22nd October 2009).

The task producer had contacted me several weeks before the challenge about providing assistance with the rockets and so I met with him, another producer, and their safety guy at North Sydney oval. We discussed what options there were for the challenge in terms of rockets and what to expect. We spent about two hours discussing and testing a couple of different prototypes I made for them including a water rocket and at their request a vinegar/bi-carb soda (baking soda) rocket and launcher. We had the tables and rope set up as well at the park. We used a couple of the water rocket launchers from Jaycar to test the water rockets.

The requirements for the challenge were quite different to what we are normally used to. Unfortunately the challenge was more about entertainment for the viewer rather than about rocketry. The show's requirements were such that the rocket build had to happen within 3-5 minutes and the contestants had to be standing next to the rocket when it went off. The altitude the rocket had to reach was only about 5m.

The build length was short because they wanted to capture the rushed competitiveness between the contestants to make it more dramatic rather then allowing them say an hour to build it and then edit the footage down to the required time.

The producers also indicated that they did not necessarily need the rocket launches to be 100% reliable to add to the excitement of the challenge. With the water rockets using commercial launchers, it was pretty much a certainty that once the rocket was loaded into the launcher that it would be capable of launching over the rope. The fast reacting bi-carb soda/vinegar combination was a little more unpredictable as to when it would launch and so they went with that.

About 10 days prior to the challenge I attended the rehearsal on location, but after a couple of hours waiting for the rain to stop we called it a day. So instead I made a video for them of a prototype being built and launched so they could get an idea of the entire process:

The rockets

Initially they had asked if I could build them the rocket kits, but in the end they bought about 15 rocket & launcher kits from the US. I am glad they did because it would have been a lot of work to get them all made in time, and would have been more expensive. The rockets they got were pretty simple, consisting of a 1L bottle, two moulded plastic sides with adhesive strips and a rounded Styrofoam nose. The fins were made of thin balsa wood and simply slotted into the moulded plastic sides.

The launcher consisted of a tube, attached to a rubber stopper and the stopper was attached to a small foot that would keep it upright. You fill the tube with bi-carb soda, and the rocket with vinegar. You then insert the tube and jam it all the way in up to the stopper, shake and stand the rocket up on its fins. When enough pressure builds the stopper and tube is ejected and the rocket flies off.

The Challenge

I attended on the day of the challenge in a safety guy / technical advisory role.

On the day of the shoot I discussed with the task producer some of the possible safety issues there would be with the rockets they purchased such as the thin and weak balsa fins the rocket had to stand up on and the possibility of the rockets tipping over. The fins were simply pushed into pretty flimsy slots on the rocket. This ended up by far the biggest problem with these rockets.

A brief assembly demo was given by the task producer to the contestants prior to start of the challenge. I made sure he mentioned the possible safety issues. They did not want the contestants to spend too much time asking assembly questions to make the challenge a bit more ... you know ... challenging. The contestants had a full set of instructions on the table and were given a minute to read them before starting.

Also prior to the start of the actual challenge, both the task producer and their safety guy made the contestants individually aware of pointing the rockets straight up and not at any other contestants.

Because of their proximity to the launching rockets they all wore safety goggles, and even the other contestants standing 3 meters behind them had safety goggles. Some members of the film crew also wore safety glasses.

I was given permission to step in in case I perceived there was a potential problem or diffuse a rocket that might be pressurised but did not launch. The contestants were also made aware of this and were told to ask me if they thought there was a problem with their rocket.

The challenge was actually legitimate and the girl who won managed to get the rocket over the rope first. (max altitude was about 6 or 7 meters) The sequence was then re-shot several times to get different camera angles and close ups of the contestants making the rockets. At one stage the winners' table was replaced with a glass topped table with a camera guy underneath, and the rocket was set up and launched again by the winner.

All in all, it was a fun day and pretty interesting to see how a reality TV segment that takes 10 minutes of the show take about 5 hours to shoot.

In the end, it was good that they went with the low power of bi-carb soda and vinegar considering there were a lot of people (~40) standing around including cast and crew, and the rockets weren't always pointing vertically when they went off.

They did pay me for my time and materials, so now we can spend it on more rockets of course. :)

New Splice Testing

This week we have been investigating ways of improving the way we make our splices. We have been using the same symmetrical splice technique (#1 in Figure 1. below) on our 2L bottles for a couple of years now, but I have never been quite happy with it. We have had quite a few failures along the way, and the no-leak yield hasn't been as high as we would like. This meant a lot of wasted bottles and wasted time. The other issue has been the relatively low pressure the spliced pairs could hold. 130psi has been the limit we could practically push them to. 

Figure 1. Splice variations

We have been using PL premium almost exclusively for our splices, but due to its porosity leaks were common. To try to stop the leaks we have been using a different but weaker glue (Sikaflex 11FC) to do the sealing in the joint and PL to hold the splice together but this made the assembly more complicated and we still ended up with leaks although less often. (Splice #2 in Fig. 1.)

We used to use 2.25L bottles as the sleeve since they fit well over the 2L bottles and no shrinking was required. But recently we have found that some of the 2.25L bottles don't fit as well anymore.

So we decided to explore what other options we had in terms of splicing techniques.

Now that we have a reliable process for shrinking the bottle down to the right diameter to fit into another bottle (as opposed to shrinking the sleeve to fit) we are revisiting the classic asymmetric splice (#3).

The main reason for this approach is to take advantage of the tighter fit where the bottles meet each other at the edge of the shrink region. This is where the two bottles have the same diameter. Compare this against the relatively uneven join between the curled edges in a symmetrical splice.

Because we are inserting one bottle into another we are reducing the internal volume compared to the symmetrical splice, so the smaller the overlap the better. If the overlap is too small then there isn't enough glue to hold the splice together at higher pressures.

To help overcome this problem we are adding an external sleeve to help hold the splice together. The overlap then only needs to be about half the amount if the sleeve is gripping the outside of the bottle by the same amount. (#4)

We are using a split sleeve since it would be very difficult to slide a sleeve over the bottles of the spliced pair. The sleeve does not necessarily need to seal well since the seal is provided by the overlap. A small section of another sleeve can be used to overlap the split in the sleeve to provide better sleeve strength.

Some other improvements over what we have been doing up to this point:

Neck Reinforcing

We have previously reinforced the necks of the spliced-pair with rings made out of other bottles, but it only strengthened the necks not the rest of the bottle. This time we are using Richard Wayman's bottle-on-bottle (jacketing) technique to not only strengthen the neck but also a significant portion of the rest of the bottle. The jacket is not held down by glue but rather a couple of wraps of the fibreglass strapping tape. This allows them to be removed and used on other bottles should the splice leak.

Bottle Type

We are now using a single type of bottle for the entire spliced pair. This makes it much easier to apply this technique to different types of bottles, and you are not required to find a well matching sleeve diameter from another bottle.

Bottle Count

Our previous spliced-pairs, used 5 bottles each. 2 for the main bottles, 1 for the sleeve, and 2 for the neck reinforcements. The new spliced pairs are only made from 4 bottles. The sleeve is made from sections of the 2 reinforcing bottles.

Reusability

With the reinforcing bottles now no longer glued to the main bottles, they can be reused on other spliced pairs if the splice leaks. We used to throw away the whole spliced-pair if a leak developed as they are very difficult to fix.

Also if the splice leaks, the main bottles can be converted to reinforcing bottles for later use. This saves a significant amount of bottles when making up a lot of spliced-pairs for clustered rockets.

There are of course a whole range of other splice variants that may be worthwhile exploring if these tests aren't successful. I've only covered the ones we have been experimenting with.

Tests

So far we have tested splice #4 with only PL premium. Although the splice held well, a small leak developed at 130 psi and so the test was aborted. This was a little disappointing, but the reinforcing held well and there were no visible stress marks on the bottles. The spliced-pair had a 3.15L capacity and weighed 139 grams. The leak may have also occurred due to insufficient cure time. I left it only for 4 days to cure.

A second splice has been prepared based on splice #5, using Araldite Super Strength epoxy in the overlap to provide the seal and PL for the sleeve. We are giving this splice a full week to cure before testing.

The epoxy was chosen after the standard 1cm x 1cm tests showed it holds well to PET.

If this test also fails, then we will try a more flexible glue like the sikaflex in the overlap for the seal.

Miscellaneous

The new workshop construction is going really well. All the walls and ceiling are up and it is about half painted. We still need to make a door and then fit-out the workshop. This has taken up a lot of our free time.

The new website extension is also coming along well. There is just a lot of typing to do and I'm already a couple of weeks behind where I would like to have been by now. I don't want to publish it before it is ready as I really dislike "Under Construction" websites.