Each flight log entry usually represents a launch or test day, and describes the events that took place.
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13mm nozzles in the front and the nozzle seats they fit into behind. There will be a launch tube sticking out of each of the launch seats.

Two air hoses heading off to the left are for the main stage and booster manifold.

This week we tried a new launch site that is a little bigger than where we normally launch. We arrived at the George Kendall Reserve at 9am, for a later start than normal as we brought the whole family along, and had further to drive. It was overcast but there was only a slight breeze. The only minor issue were the patches of standing water from the previous day's rain. We also met up with David and Darren from the Forum for Australian Rocketry and they brought their pyro rockets along. We really enjoyed the day.

Flight Day Events

• We launched J4 IV three times first up with the altimeter, camera and foam. All the flights were mostly straight up and the parachute deployed well just past apogee. Having the laptop along allowed us to fly the camera on all missions. We only get 30 seconds of video so downloading between missions is essential.
• One issue that cropped up after the first flight was that the altimeter suffered a malfunction. It is powered from the same battery as the flight computer, and turns on when the flight computer is turned on. The power LED lit on the unit, but the LCD did not display anything. It was going to take a little time to swap it out, so we decided to leave it in place and fly it non-operational. After we had a break for about an hour and I was going to investigate what was happening, the altimeter came good again. We flew the altimeter on the last two missions of the day with it in working order.
• Because the larger field was available to us, we also increased the pressure in the rocket to 130 psi for a number of flights. With the added weight and drag of the camera and the added weight of the padded nosecone the rocket only went up to 397' on the first flight.
• After the three flights we went over to see David's and Darren's pyro rockets launched at a somewhat dryer part of the park. It was great to see the different rockets and how they were prepared. The kids helped retrieve them for which they are now trained, but had to be cautioned that the tail end of the rocket would be hot just after landing.
  
  This is an interesting contrast to a water rocket as our rockets tend to be colder than ambient (due to the expanding gasses) after landing.
  
  The other interesting point I learned was that wet ground conditions can have adverse effects on the cardboard bodies of smaller rockets. Water rockets tend to be quite water proof because of all the splashing that happens during launch.
• One interesting rocket flown by Darren looked like a cross between a frisbee and a UFO. With the motor mounted centrally it remained very stable on the way up and tipped upside down at apogee and the body acted as a airbrake on the way down.
  
  If you are interested in pyro rockets Darren runs: http://www.suburbanrocketry.com/. There are lots of cool things to buy.
• One of David's interesting rockets was a small triangular bodied rocket which also flew very well. His other rocket was also a blast to see.
• The last pyro launch of the day was Darren's Canadian arrow. We decided to tape our camera to the side of the rocket. We weren't quite sure what to expect because the camera is a significant fraction of the weight of the rocket and causes considerable drag on the one side. The rocket actually flew quite straight to around the 400' level and the video was also pretty good.
• Later in the afternoon we flew J4 two more times. We noticed after pressurizing the rocket that the nosecone was slightly bent to one side. This was likely due to the black plastic tape stretching in the heat of the day. We had been using the strapping tape up to this point without problems so I think we will go back to that. The heat may also have effected the bonding strength of the tape glue.
  
  The bent nosecone caused the rocket to pitch over quite significantly on takeoff. Of course Murphy stepped in and made sure the rocket flew the shortest path towards the river. Luckily the parachute opened before it ever got that far, but if it hadn't, it would have been close.
• The camera did not record the last flight. We will have to investigate. Flight #4 landed on the bitumen path, so that may have had something to do with it.
• From the altimeter data we get a descent rate for J4 of 6.3 m/s which is pretty high. We are going to need to switch to a larger chute to bring that back to about 5 m/s. The chute ejection mechanism can accommodate this larger parachute.

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

Polaron IV development

We have been focusing development on Polaron IV over the last few weeks. There is a lot to get done because the rocket yet again requires a new launcher. We have now done the final technical drawings of the components we need to make and have started manufacturing them. We pretty much have all the materials on hand and are looking forward to getting this thing up and flying.

Payload Section

The entire rocket will now be placed dry onto the launcher. This is because it will take a little time to align and be seat everything properly. Because the boosters can be filled from the top there was no issue, but the main stage was normally filled through the nozzle. The rocket will now be configured so that it can be filled from the top as well. Filling it from the top poses a problem, because the payload section is in the way. So we have made the payload detachable allowing us to fill the stage with water, capping it and then locking the payload into place.

Main stage

The main stage parachute will be upgraded to the one used by Acceleron II. The smaller 42cm parachute isn't enough to bring this heavier rocket down. We have flown a rocket of this size with twin chutes, but the single larger chute is simpler.

Because we are using the 2 liter bottles for this stage, we have decided to use the reinforcement technique discussed on day 49 to reinforce the base only. On about 3 occasions we have had failures at the coupling hole, and this reinforcement attempts to prevent that from happening. We have slightly amended the procedure discussed previously and now pressurize the bottle to about 10psi while shrinking the outer sleeve.

Launcher

This launcher will again be a universal launcher that will enable rockets of various sizes with three boosters and a main stage to be launched simultaneously. Single stage rockets may also be launched from the launcher.

Dad made up the necessary air supply system for the launcher with a number of gauges, valves, a pressure regulator, check valves and bleed valves. All these are mounted on the side of the ground transportation vehicle for now, before we fit them in a nicer self contained box. The new pressure regulator also allows us to go to about 25 bar (360psi), almost double that what the previous one could do. This new air supply system allows us to use a scuba tank to supply differing pressures to the boosters and to the main stage.

Flight Details