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Date:  15th April 2009 (8am - 12:30pm)
Location: Doonside, NSW, Australia
Conditions: Clear early, with cloud increasing, 22 C, wind 15-20km/h with gusts up to 35km/h
Team Members at Event: GK, AK, Paul K and John K

This week we went out to Doonside with only a couple of smaller rockets. One of them was designed by Paul and we built it together. It's maiden flight had been delayed a couple of times so this time it was going to be the first one off the pad. The payload was a handful of Lego "astronauts" and the rocket even had its own R2 unit. The weather was nice and mild, but the strong wind was a problem.

Stabilising Descent Video Experiment

This week we were going to try at changing the way we attach a parachute to the rocket in order to get more stable descent video. Normally when the rocket is tethered by a single line, the rocket is free to roll from side to side and also pitches more freely around this pivot point especially if the rocket is attached close to the center of gravity.

We attached the strings either side of the rocket to stop it from rolling, and attached them near the nose and tail to swing slower. The parachute shroud lines were connected as close to these strings as possible rather than to a long main line in order to reduce the swinging further.

We have also attached the strings in such a way that one of the fins points directly down, and the other two form a V to help stabilise the rocket as well.

For this set up the camera was pointed to the side rather than looking down the axis of the rocket so that it could film the ground directly below the rocket on the way down.

The strings were attached at either end by a loop with a scaffold knot and the loose end of each string was then tied together with a reef knot. This allows the string to be loosened for removing the parachute and then tightened again to secure it back in place. The reef knot is on the bottom of the rocket and prevents the two loops from sliding around to the top of the rocket. With the two separate lines there is also a level of redundancy should one fail. (see photos at left)

The experiment did not go exactly according to plan.

Flight Day Events

• We set up the medium launcher with the 2m guide rail extensions because of the wind, to help the rocket keep straight as it gets up to speed. We launched Paul's Pod 1 at around 95 psi, as the bottles it uses are old and showed a little stretching around the neck area. The entire rocket was constructed from retired rocket bits lying around the workshop. The parachute opened well and the rocket did not drift too far from the pad.

• We then had about an hour break waiting for the wind to die down. A lot of the other rocketeers were also reluctant to launch in the high wind conditions. Since the wind continued blowing we prepped and launched the boys' small pyro rockets on small motors (1/2A3-2's), and since they use streamer recovery they didn't drift far.
  
  There were a number of pyro rockets lost on the day somewhere in the adjoining suburb.

• I replaced the 9mm release head on the launcher with a 15mm one with a long launch tube and loaded up the Axion rocket. This flight was intended to test the alternate parachute attachment for stable descent video. We normally get pretty shaky video on the way down as the rocket pitches from side to side. This was going to be an attempt to reduce some of that.

• The rocket was launched at 130psi and flew straight up reaching 501' (152m). The parachute opened well after apogee and deployed correctly suspending the rocket as designed. I used a small piece of tape to hold the lines to the side of the rocket during ascent to prevent them from getting tangled in the launcher or fins. The tape easily lets go as the parachute opens.
  
  As Murphy would have it the on-board video stopped recording on the way up so we never got to see the descent video. I was able to watch and film the rocket from the ground and the one thing that was obvious was that the rocket and parachute were in a slow spin about a common center. This would have resulted in quite a dizzying video. We will need to add a second smaller parachute to the tail of the rocket to stop this flat spin. Otherwise the rocket did not look like it was rocking. We will fly this rocket again in this configuration at the next opportunity to see if it actually makes a difference or not.
  
  The rocket drifted about 320m downrange. I managed to step on an ant nest while retrieving it and then spent 5 minutes brushing them off as they started biting.

• I'm not sure why the camera cut out. It was fully charged the night before and recorded fine for 2 minutes before launch. At the time that it cut out the rocket was travelling quite slowly and there was no evidence of an event that could have interrupted the power. The camera powered up fine after recovery.

• We called it a day after that launch. We have learned from past experience that it is better to try again during more favourable conditions than loose a rocket.

Acceleron V Development

Over the last several weeks we have been redesigning the Acceleron V booster in order to be able to launch bigger payloads. There were two primary reasons for the configuration changes:

1. The booster/sustainer combination was getting too long making it more difficult to fit bigger sustainers to the booster without putting too much stress on the staging mechanism. Lack of sufficient longitudinal support for the sustainer meant there was a real danger of the sustainer bending over under high G-loads and either sending the rocket off course or snapping the staging mechanism.

2. Due to the larger weight of the rocket, more thrust is necessary to get the rocket to stable flight fast enough. Until now all Acceleron rockets used 10mm nozzles for each of the booster segments. We needed to switch to larger nozzles for more thrust. The 13mm nozzles used on the drop away boosters of the Polaron rockets were already made and so we decided to use them.

In order to accommodate the bigger nozzles we would have needed to manufacture new nozzle seats for the old Acceleron launcher. Instead of machining new nozzle seats we decided to use the drop-away booster launcher for the Acceleron rocket. The old Acceleron rockets used a spear gun release mechanism, so we are replacing this with custom made aluminium Gardena nozzle mounted on the base-plate that holds the cluster together. This nozzle will fit into the existing Gardena central release head on the launcher. The entire rocket is held down by this release head.

Because this launcher's minimum nozzle spacing does not allow the three segments to be up against each other like in the old Acceleron rocket, we are separating the cluster segments further from each other. This requires a new base-plate for the cluster. This again will be made from aluminium and reinforced with carbon fibre.

By separating the cluster segments we will be able to lower the staging mechanism further down in between the segments allowing the second stage to also sit lower in the booster addressing point 1 above. By lowering the sustainer between the segments, we can use the segments themselves as guide rails. This will allow us to build a sustainer around the length of a Hyperon or Axion rocket. With long rockets like these, it should also be feasible to add a third stage in the future.

Other changes

• Recovery - The dual parachutes will now be located in the space between the spliced pairs in the segments instead of the pod. These will most likely be deployed using servo motors.
• Pressure switch - The old Acceleron booster used a mechanical pressure switch (TDD) built by Trevor that detected when pressure inside the booster dropped during the air pulse phase. This was used to initiate the staging mechanism. We will be replacing this switch with a simpler switch (TDD2 http://groups.yahoo.com/group/water-rockets/photos/album/930791471/pic/list), also of Trevor's design that uses a simple micro switch directly attached to the cap. The switch will be located at the top of one of the segments.
  
  I noticed this week that Nick over at DotRocket is also using Trevor's design so it will be good to see how that goes. http://www.fisk.me.uk/blog/2009/03/22/pressure-switch-part-4/
• Redundancy - The staging and parachute deployment will be controlled by dual independent V1.6 flight computers. I'll cover the full details of the staging and deployment mechanisms in future updates.
• Dual Air supply -With the new configuration and by using the booster launcher we will be able to fill the booster and sustainer to different pressures. This was not possible with the previous configuration, as the air supply to the sustainer came from the top of one of the boosters. We will be able to build reinforced sustainers allowing them to be pressurised to higher pressures while leaving the booster at lower pressures.

All up Acceleron V has three segments in the cluster and each segment uses 3 x 2L spliced pairs giving a total volume of almost 33 liters. Including the second stage, the total lift-off weight is now going to be approaching 16 kilos (35 lbs).

With the sustainer now supported by the segments, it can have a boat tail for better drag efficiency.

We've been modelling Acceleron V to scale in 3DS Max in order to figure out the spatial relationships of the new release mechanism, clearances for fins and the positioning of the staging mechanism. Included are some pictures of the various designs. We have all the materials now for design option #2, and have started construction. The next update will contain the construction progress photos.

Flight Details