Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Date:  3^rd May 2008 (7:45am - 2pm)
Location: Doonside
Conditions: Temp: 18 degrees C, wind speed 10-15km/h SW gusting around midday, cloud cover 0/8
Team Members at Event: GK, PK, Paul K + Members of NSWRA and spectators.

After the NSWRA launch event was postponed last week due to bad weather we were eager to try the new Polaron V rocket with the bigger boosters. The weather was great this week with an occasional stronger gust but the wind was at least in a favourable direction - away from the big rocket eating trees.

Before we get to launch day events here are a few details about the rocket itself:

Polaron V

The Polaron V rocket basically remains in the same configuration as the Polaron IV rocket with the exception of an extra 2L bottle in the stack. This gives the rocket a capacity of 10L.

The Gluon boosters have had their capacity also increased by 1.25L each, giving them a total of 3.35L. The boosters are attached the same way to the main stage as described earlier. Due to the extra length of the boosters we wanted to support them as high as possible up the main stage so that aerodynamic forces could not pull them off. There was a major problem though in attaching them further up since the top bottle on the booster has to be removed in order for the lower spliced pair to be filled with water on the launch pad. This prevented us from permanently gluing the pin to the top bottle. Instead, we made essentially a large rubber band from an old bicycle tire and the base of the pin was made into a comb shape that allowed the rubber band to be threaded through.

This allows us to place the lower portion of the booster on the pad, fill it with water and then screw on the Tornado coupling and into the other side of the coupling we screw in the upper bottle. When it’s all tightened up, we adjust the pin and rubber band so that the pin fits inside the upper tube on the main stage. The rubber band is quite tight on the bottle so there is virtually no movement from the pin.

Because the boosters are now getting quite heavy, we have added a small parachute to each of them. In order to keep things simple, there is a small flap of PET plastic that is attached to the top of the lower booster section. The parachute is simply tucked in behind this. There are no springs or rubber bands to eject the parachute, it just slides off. The flap is kept closed with a piano hinge type arrangement and the hinge pin is just a piece of wire attached to the main stage. As the booster drops away the wire is pulled out of the hinge and the flap springs open releasing the parachute. Since the booster is still traveling quite quickly when that happens we have used stronger string and an extra couple of loops of the string around the chute in order for the parachute to take a little extra time to open.

Tornado Couplings

After last weeks development of a tornado coupling made of common irrigation parts we discovered during further testing that they held only a little more than 130psi before springing a leak. This was marginal for what we wanted to do with them, so we started looking for alternatives.

During the tests we also found that at the higher pressures, over 100psi on occasion there was a small leak between the cap and the bottle. This was easily fixed with a BS119 o-ring around the bottle that just fit under the cap of the coupling.

Trevor sent us a couple of tornado couplings about 6 months ago that he had re-threaded from standard ¾” polypropylene BSP sockets. We tested these couplings and they worked really well. Requiring just two o-rings to seal them up.

We would have liked more like it but unfortunately our little lathe couldn’t cut such a coarse thread, at least it didn’t appear on any of the thread cutting gear ratios charts.

Dad again came to the rescue and figured out what gear ratio would be needed and luckily we had the right gears in the box, but they did not fit on the gear brackets. (Probably why it was not listed) So dad modified the brackets on the lathe and got them to fit. He then proceeded to machine up coupling out of a solid piece of PVC. Yee haa.. we were back in business. Being able to cut bottle threads opens up the capability to make other types of couplings, staging mechanisms, one piece nozzles etc.

We tested the new coupling to 130psi without any sign of stress or leaks. Being one-component construction makes them ideal. These also use the BS119 o-rings against the bottle to seal them.

These couplings are even better because of their full bore 22mm hole that is almost twice the cross sectional area of the 15mm ones we made last week. When compared to the 8mm Robinson coupling these Tornado couplings have a cross-sectional area of 7.6 times bigger than the Robinson couplings we have been using. This should translate to better efficiency of water and air flow between the rocket segments. The new Gluon II boosters use these couplings.

Launch Day Events

• We turned up early at the launch site because we knew it was going to take a while to set up the rocket. There are a lot of things that need to get configured with this rocket. It took about 40 minutes to set up camp and get the launchers assembled.
• On this day we were going to test the new control panel on its first official dual pressure launch. We have been using the panel now for all pressure testing for the last few weeks.
  
  As we brought up the pressure on the main stage we closed off the main stage valve and continued pressurising the boosters. We were pretty much ready to launch when one of the boosters took off unexpectedly by itself. Surprisingly it went straight up although not designed for stable flight. Its parachute opened right around burnout, so it was a pretty violent stop, but floated back down undamaged. Upon closer inspection of what went wrong we noticed that the pins on the booster basically ripped the full length of the plastic tubes they were in. These tubes are made out of plastic ball point pens so we would have expected them to be quite strong. (See photos on left). We continue to be amazed at the strength of the PL premium glue and the fact that it held to the pins and the tube.
  
  We are still puzzled why the tubes failed. We would have expected them to be able to hold much more than that. With the pressure that was in the boosters at the time there would have been perhaps 6 Kg of force on each of the pins. The top tube was also ripped its full length. What is even more interesting is that the pin on the top of the booster is essentially only attached by a large rubber band! Perhaps there was a small movement in the booster that made the pins hit the edge of the tubes rather than just pressing against them? Perhaps there was a small crack in one of the tubes that weakened them and that could have started it? We really don't know at this stage.
• We considered launching the main stage with just the two boosters, but that could have ended badly especially with other people and cars around. So we decided to remove the boosters and just launch the rocket by itself. We filled it up with water rather than with foam, since we needed the initial thrust to get up to speed.
• The rocket went up well and landed without fuss under parachute. Without the boosters it only reached 251 feet (76 m).
• Next we set up Acceleron IV with the Tachyon III sustainer. We fitted the camera in the nosecone again, but a lot more streamlined this time. We filled the booster with water to its full 2L capacity. Our limiting factor is the length of the fill tube since the air inlet holes have to be above water level.
  
  2L per segment is about what the simulator recommends for this rocket. Despite this recommendation on the last launch day we only put 1.5L in each in order to reduce the overall weight near the tail, to keep the Cg a bit more forward, although we knew we would not get maximum altitude with less water.
  
  The rocket was filled to 130psi and launched. Because of the extra water the boost lasted visibly longer. The second stage separated right on cue and continued vertically with a deploy just a few feet before apogee (as seen from onboard video). The booster, however, failed to open its parachute and slammed nose first into the ground with a beautiful thud. We took a nice core sample with the staging mechanism and I'm pretty sure that at least a few ants on the nearby anthill had a great view of a "dinosaur extinction type event".
• The payload section was pretty much destroyed, but the electronics survived unharmed, and the two servos popped open but are fixable with a little epoxy. While it's always disappointing to have to do a rebuild, it won't be so bad since most of the components survived and we know how to rebuild it. We will attempt to make the whole mechanism lighter as the old one weighed over 400 grams.

  The central aluminium pipe was bent slightly and some of the bottles on the booster were a little buckled, but don't look like they will need to be replaced.

  On a positive note though, the second stage flew to 617' (188 m) which is our highest directly measured altitude to date. The flight time was also our longest to date and stands at 56.3 seconds.

  Looking at the altimeter data and ground video for timing, we know that water ran out at T+0.92 seconds at an altitude of 48' (14.6m) and staging occurred at T+ 1.96 seconds at an altitude of 144' (43.9m). Peak velocity for the second stage was ~190’/sec = 58m/s = 208 km/h at ~220’ (67m).

  Our only other higher flight based only on estimates was 630' last year but had a much greater degree of error.

• The last two launches of the day were carried out by J4 IV since we were running out of rockets fast. Both launches went well and both had good landings.

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Flight Details