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(photo: Todd Kennedy)

Date:  31st May 2008 (7:45am - 2pm)
Location: Doonside
Conditions: Foggy early with 7 degrees C early, warming to 20 degrees by midday. Wind speed 0-5km/h W, cloud cover 0/8
Team Members at Event: GK, PK, AK, Paul K, John K + Members of NSWRA and spectators.

We had another good launch day with NSWRA. The weather was a little foggy early on, but then it turned out to be an almost ideal day for rockets with mild conditions, no clouds and very little breeze. We got to launch our upgraded Polaron rocket and set a personal best altitude in the process. Before we get into the day's events here is a little info about two new rockets flown on the day.

Polaron VI

About a week before the launch day while inspecting the Polaron V main stage I noticed that some of the bottles were showing quite severe stress marks around the bottle necks. We decided to play it safe and replace the bottles. We had a number of the 2L spliced pairs (3.6L capacity) ready to go, and with having the 22mm Tornado couplings on hand we decided to screw together 3 of the spliced pairs. We kept the lowest 2L bottle from the Polaron V rocket as it had all the booster retention tubes, fins and guide rail lug already attached. This was also convenient since the bottle also had a Robinson coupling which we wanted to use for Jet Foaming.

During the week we pressure tested the three sections to 130psi - the launch pressure.  One section sprung a very small leak, but we decided to change it for a new one as we imagined the "tiny crack in the dam" scenario. In the process we managed to increase the volume of the rocket by almost 3 liters while only gaining an extra 15 grams! With the exception of the one Robinson coupling both the main stage and boosters were all spliced and Tornado coupled together.

Axion

Axion is a new rocket based on the 90mm body diameter size. The rocket is entirely made up of spliced pairs joined with the 22mm Tornado couplings. We will eventually use this rocket to do experiments with larger nozzles and long launch tubes. The removable fin section was taken from the Hyperon rocket, as was the nosecone and deployment mechanism. When it was assembled, we realised that the little white parachutes we have been using are just too small for a rocket of this size. We made a quick parachute out of the lightweight rip-stop nylon we bought a few months ago. One of the nice things about the material is that it packs very small and we were able to fit the bigger parachute in the same space as the smaller one. 

We have found that the spliced pairs and couplings can make pretty straight rockets without much effort. If you construct rockets this way an easy way to check your alignment is to look down the nozzle and you can easily see if the other joins are aligned or not. All the couplings should look concentric. The couplings also allow us to unscrew the rocket half way along which makes transportation and storage much easier.

Launch Day Events

• We arrived at the launch site just before 8am and found that there was quite a heavy fog at the launch area. We figured we'd set up slowly and wait until it burned off. But soon we realised that this was a unique opportunity to launch a rocket with a video camera to see if we could get above the fog. So we quickened the pace to get the launch in.
• As we assembled our old medium launcher and were blowing water out of the hose (because I forgot to purge it after the last pressure test) I noticed that the brass riser tube under the release head was blowing bubbles out the side. There was a hairline crack in the tube. I guess after 1.5 years or so in service and perhaps a couple of hundred launches under its belt, it must have just work hardened and finally cracked under the repeated pressurisation cycles. We will replace it with a stronger copper pipe to stop that from happening again.
• We thought we might miss the fog launch opportunity as the only other launcher we had was the Polaron launcher, but the problem was the it uses a different guide rail system. So we quickly decided to adapt the guide rails from the medium launcher to the Polaron launcher and secured them with a few wood screws and some wire. We had to use the guide rail extensions because Axion stands at almost 2 meters tall.

• We weighed up the launch pressure as we wanted to go high enough to get above the fog, but not too high since there was a serious danger of it drifting out of sight in the fog. Settling on 125psi which we guessed would give the rocket about 400 feet, we launched it and it promptly disappeared in the fog. A short time later we heard the parachute pop sound so we knew it was under parachute, but could not see the rocket. We were looking in all directions until it was spotted descending perhaps 30 meters away. We quickly downloaded the video and altimeter data to see if the rocket made it. The video clearly showed the rocket was flying above the fog. It was a fun experiment to do, but if we ever get the opportunity to do it again then we will need to have a siren on it to help us locate it.
• Pretty soon after that the fog had lifted and we converted the Polaron launcher back to the ... well Polaron launcher. It took us about 30 minutes to set up the Polaron VI rocket on the pad and fill it, secure the boosters, and all the parachutes.
• The launch and flight were pretty close to ideal. The boosters separated right on cue and simultaneously and the rocket just continued to power up and up. With the higher capacity we had 2.4Liters of water and foam mix in it and trying to get it all out through a 7mm nozzle takes a while. The foam trail extended all the way to apogee. The only couple of minor issues were that the rocket had a bit of a spin, which didn't really affect the flight but made for a more dizzy video. The other issue was that the parachute deployed a tad too early while the rocket was still ascending, and pointing vertically, although judging by the onboard video, the rocket would not have gone much higher.
  
  The downloaded altimeter data showed an ideal curve with a peak at 637 feet! (194m). This was our new personal best and directly measured altitude. This was 20 feet higher than the Acceleron + Tachyon 2 stage rocket. It was also over 125 feet higher that with the smaller Polaron IV rocket. Both the Acceleron and Polaron rockets still have plenty of room for improvement so it will be interesting which combination ends up being better.

   

• The last flight of the day for us was the Polaron VI rocket again with the same setup as the previous launch. This time the rocket took off vertically, but just before booster separation the rocket started pitching over and continued to do so. We reviewed the video frame by frame to see if we could spot what had happened but there was nothing obvious as a stuck booster. the rocket looked like it was pitching over even before separation. Our only plausible explanation at this stage is that the rocket was marginally stable. With so much water in the tail section of the rocket it may have had the Cg too far back for too long.
  
  In any case the rocket now being pointed towards the ground kept accelerating until impact. The parachute deployment delay was just set for too long.
  
  On a good note, all the electronics survived well, however, the camera did not record the flight. On impact there may have been an interrupted power supply so the data would not had been finalised and therefore the file was not accessible. The altimeter data was recovered although it did record a -7000 foot drop sample on impact.
  
  All the 2L spliced pairs were damaged beyond repair, and the nosecone needs to be rebuilt, but otherwise the entire fin tail section with all the tubes and nozzle survived well and will be reused. We can also reuse all the tornado couplings. So ultimately  the repair bill will be the PL glue used to glue the new recycled 2L bottles together.

• The other important lessons learned from this day were:
  - The new spliced pairs, both 1.25L and 2L are working well with the Tornado couplings.
  - The parachute deployment mechanisms on the boosters also worked well.
  - The thin walled brass booster retainer tubes were up to the job.
  - The rubber band attachment points at the top of the boosters worked well.
  - Axion's new simple parachute worked as designed.

Flight Details