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Date:   29^th March 2008 (8am - 2pm)
Location: Doonside
Conditions: Temp: 25 degrees C, wind speed < 5km/h gusting in afternoon cloud cover 3/8
Team Members at Event: GK, PK, John K, Paul K, AK, HK + Members of NSWRA and spectators.

It was another great weekend at the NSWRA launch event this month. The weather conditions were perfect, although the ground was a little wet and there was plenty of mud everywhere. People brought some very impressive rockets that are always fun to see. I have included a video of the last months pyro rocket highlights here.

Before we get into the events on the day I'll cover some development topics leading up to the launch day.

Acceleron IV

We finished rebuilding the Acceleron IV booster a few days earlier. The main difference being Acceleron's lower capacity of around 18L compared to the previous 24L. Each of the booster segments are now attached by 3 strips of Velcro which makes it much easier to get them on and off for servicing.

During full operational pressure tests we discovered that the rocket wasn't sealing well at all. Further inspection revealed that we forgot to put in washers into 3 Robinson couplings. Doh! We had test assembled the rocket 2 weeks earlier, and forgot we hadn't gone back to put the seals in. 5 minutes later all the seals were back in and we ran the rocket up to ~100psi since the neighbours were out in their back yard, and having had this rocket fail a pressure test in the past, we didn't want to push it. We did have the video camera recording though just in case. The rocket will most likely get launched at 120psi on the day. The rocket theoretically should hold up to around 140psi operational pressure, with a burst pressure of around 180psi.

We hooked up all the electronics and made sure the staging still worked when the pressure in the rocket dropped. We replaced the sustainer in the test with a small bottle full of water that fired as expected.

We replaced the rubber bands in the staging mechanism as keeping them stretched all this time in storage caused them to deteriorate quite badly. The same went for the wide rubber bands that held the fins on.

The launcher has also had an upgrade with new longer fill tubes that allow us to use the spliced pairs of bottles on the bottom of each segment. We simply slipped new thin-walled aluminium tubes over the existing ones and epoxied them down.

Tachyon III Sustainer Work

The altimeter has been moved into the space between the bottles that help to protect it. The altimeter is attached to the inter-bottle ring and having its own power supply allows us to swap it between rockets. The payload section now also has the FlycamOne2 camera built in.

We also made a couple of rocket carriers that help us transport and protect the rockets. They also help prevent the rockets from sagging in warm conditions.

Control Panel

Dad surprised me on my birthday last week with a control panel he made for the rocket launchers. We can use it with all our launchers and especially the dual air supply ones. See photo on left. The panel has a pressure regulator, two valves for the lines, a bleed valve and four gauges that show the tank pressure, the regulated pressure coming out of the regulator and then the two line pressures. It comes with foldable legs, so it stands up all by itself. Virtually all of the internal fittings he made on the lathe that connected everything up. It has a great looking retro look. I am looking forward to using it next time.

Okay now back to the launch day.

Launch Day Events

• We first set up Polaron IV on the pad. It was flying in the same configuration as the previous month, but with the wind conditions being so calm we wanted to see what difference it makes to altitude. The previous month we had really strong winds and the rocket fish-tailed quite a bit.
• As the pressure reached around 90psi, the main stage nozzle sprung a leak. We could have launched, but I had the deploy timer set on a longer delay expecting the long boost. If the rocket had not reached a high enough altitude there was the danger that the parachute would open too late. Over the last 2 years we have learnt that if everything is not 100% correct just before launch, it is much better to abort and try again later.
• We were glad that we had the bleed valves in the launcher, and we safely released the pressure from both the main stage and the boosters.
• The seal probably wasn't sitting properly which sometimes happens, but on removal we noticed that there were also some small aluminium shavings in it. I am not sure of the source but perhaps when the nozzle was left out in the workshop. We washed them out, reconnected the nozzle and all was fine.
• We pressurised to 120psi and let the rocket go. The boosters again behaved as predicted and the flight was almost completely vertical. Altimeter gave us an altitude of 510'. The in-flight video also turned out well.
• Bizarre Flow: Both the ground video and a still photo showed our first mach diamonds. Well not really mach diamonds as such but it was quite a bizarre flow from one of the boosters. There were definite pulses visible in the water flow, but only one of them showed this. The video shows there were two distinct pulsing events before water ran out.
• We have not seen this before in any of our launches. So far we have no idea how they originated. Perhaps some sort of cavitation effects caused it? You can see the column of normal flow before the pulses start. You can also see that the booster (red one) is nowhere near its air pulse as there is still quite a bit of water left in it. It didn't seem to affect performance as far as we could see, so we will not try to do anything about it, but will keep an eye out on future launches to see if it happens again. The boosters are numbered so we will be able to track it down if a particular one causes it.
• Next off the pad was the newly rebuilt Acceleron IV booster with the Tachyon III sustainer. Again we were struck by a minor fault that caused us to abort the launch. This time it was the fact that the rocket wasn't locked down all the way. It was locked down earlier in the checklist, but somehow we must have caught on the string during preparation and unlocked it. This has happened once previously and is a reason why it is on the checklist. We now know to double check prior to pressurization.
  
  As we reached about 20psi, the booster started hopping up and down a few centimetres as it started venting the water. The guide rails did their job preventing the rocket from tipping over. As the water drained we ended up with a small air pulse and the pressure drop was detected by the flight computer and deployed the sustainer. The sustainer had just enough pressure to lift off perhaps 10cm and clear the booster. As it did so, it sprayed foamy water all over the electronics pod and the side of the booster. The sustainer luckily fell on its tail and suffered no damage. On board video and altimeter captured the whole sequence.
  
  We cleaned up the mess, dried off what we could and refilled everything again. This time the rocket was locked down properly. We turned everything on again and filled it to 120psi.
• The launch was very good and mostly vertical. Staging happened right on cue and the sustainer proceeded to fly to 160m (525') according to the altimeter.
• Both parachutes also opened, but the sustainer's parachute tangled and the rocket hit the ground at a less than ideal velocity. Thankfully the parachute was out and causing some drag, and the ground was soft with tall grass, heavy damage was done to the nosecone. The altimeter was ok, and all the electronics and camera survived well. The camera did not record any footage that we could recover. I noticed that the SD card had popped out of the camera on impact. It was either this or a power spike that caused the camera to stop recording or corrupt the file.
• For Acceleron's last flight of the day we fixed the sustainer by replacing the nosecone section from the Hyperon rocket we had along as standby. The altimeter ring was simply reused, but the Hyperon nosecone did not have a bay for the new video camera so we just taped it to the side with duck (gaffer) tape. This was less than ideal aerodynamically, but we weren't after altitude, but the footage. The rocket reached 153m (503'). The parachute opened well on the sustainer and it landed close to the tallest trees in the field. The booster's parachute opened very late, apparently only a couple of meters above the ground. I couldn't see it as I was tracking the sustainer.

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