Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Team Members at Event:  GK, PK

We have been spent the last two weeks catching up mostly on non-rocket related stuff, but we are now getting back into development again. We have been working on a number of different projects.

Current Developments

Acceleron IIIb

The booster has been inspected and cleaned after the last set of launches. We will likely fly it again when we buy a logging altimeter since we would like to know how high its sustainer can fly. We want to use the altimeter to give us feedback on various design changes we make. It is too difficult to evaluate performance when you can't see the rocket well, and total flight time only gives us a rough idea.

We also spent time analysing the video footage from different cameras to see how the two stage rocket performed:

1. It looks as if the stage separation was taking place a little later than we would have liked. The booster was already slowing down when the release happened. This can be seen at the top of the flight path as the booster starts pitching over. Since the release sequence is initiated by the pressure switch, we will need to make the pressure switch activate at slightly higher pressure. We can adjust the tension on the spring of the TDD, or alternatively add slightly less water to that segment with the pressure switch. Less water means that the segment will stop producing thrust slightly sooner compared to the other two segments that are still accelerating the rocket.
2. We now have a better idea of the time it takes to get to apogee and hence can set the parachute deploy delay for the sustainer appropriately. The parachute deployed about 2.5 seconds after passing through apogee from the videos.
3. The parachute deploy delay for the booster will be shortened as even the minimum setting allowed by the software on the day wasn't quite enough. This is just a software upgrade.
4. After release the booster looks like it falls more like a back-gliding rocket. It actually saved us a whole lot of work after the first launch since the parachute deployed so late. This flight profile was visible in all three flights before the chute opened. This is actually a favourable feature because if the parachute fails the rocket should land at a lower speed than if it was going nose first.

New Flight Computers

We continue to incrementally develop the flight computer. With this latest iteration V1.3.2 we have tried reducing the footprint and weight, as it is still a little too large for our liking.  The flight computer including the actuating servo now weighs 29 grams (excluding battery).

After investigations into suitable batteries a few weeks back, I have bought a number of CR123A's. These are lithium batteries with a great power rating of 1300mAh which is more than we need (twice that of a 9V battery), but need two of them to make up 6V. The two batteries still only weigh 32 grams compared to 46 grams for a 9V that we have been using recently. The increased power capacity means we will be able to also power from the same batteries other experiments we are planning. With normal usage the batteries should also last longer compared to the 9V ones.

They each cost around AUD$3 online in Australia, but I picked up a pack of 12 on e-bay for AUD$1.38 each including delivery.

The new flight computers are smaller in size and so can be mounted horizontally in the nosecone. This allows us to shorten the length of the nosecone section further reducing weight.

The flight computers also have a new launch detect switch which allows it to work in two dimensions. This allows you to mount the PCB in a range of orientations. (See photo on left)

The spring is the compressed type which prevents it from oscillating while you are handling the rocket or there is slight vibration on the launch pad after the system has been armed.

These types of springs can be found in various equipment such as old tape players, printers, CD players and the like. We use a little bit of solder wrapped around the end of it to provide a weight.

The other end of the spring is just clamped to a piece of a connector and that is soldered to the PCB to provide both mechanical and electrical contact.

The activation force can be adjusted by varying the length of the spring, the weight on the end, and the size of the loop of wire (the other contact).

Full details of the flight computer are now available here.

J4II Upgrade

J4II is having an upgrade done to its parachute deployment system. Until now it has used the NOAA technique, but with limited success and more often than not the parachute has been deploying too early. J4II is now being fitted with a similar deployment system to that of Tachyon, but with version 1.3.2 of the flight computer. The total weight of rocket will remain roughly the same.

The fins have also been replaced with new ones held down by large rubber bands. The last set of fins had become misaligned over time. Since they were taped on, and likely had contributed some of the less predictable flight paths.

New Hyperon Standardised Platform

We are going to be doing a number of experiments and needed a modular rocket with standardised components so we can change them depending on the experiment. The platform is based on 1.25L 90mm diameter bottles. These are easy to get everywhere, can hold a reasonable pressure and are easy to work with. The rocket can have bottles added or removed easily to change the capacity. 

This modular design allows the rocket components to also be interchanged between other rockets should they become damaged.

A 5L rocket (Hyperon) has been constructed this week that adheres to this standardised model. Most of the components for it came from other rockets so it was relatively easy to put together. (The Tachyon sustainer also adheres to this standard.)

Hyperon uses the removable fin assembly design to allow for easy modification.

Upcoming Experiments

Some of the upcoming experiments to be done with the Hyperon platform are:

• Baffle flights. A few months back we static tested a baffle on the lowest coupling to prevent the blow through effect, but haven't evaluated its performance in flight yet.
• Nozzle tests. We want to fly a 15mm nozzle on a larger rocket.
• A new booster design - A simplified booster design for smaller rockets. We spliced together a number of bottle pairs this weekend that will serve as a basis for this booster design.
• A new compact and lightweight staging mechanism has been designed that is not based on the Gardena or Crushing Sleeve methods. It is based on a different principle altogether. If the design works, it should enable simple construction of multistage rockets.
• We currently have about another 10 engineering and science experiments in various stages of development that we will cover in future updates.

Construction Details

Over the last few months we have had a number of requests asking about how we make various components for our rockets. So we are going to start making a number of videos that show how we do things as it is much easier then trying to describe them in words. The first one this week is of our Robinson coupling:

Making a water rocket bottle coupling

(If the video does not play, try the latest Flash player from Macromedia)