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Flight Log Updates

#230 - Tajfun 2 L2

#229 - Mac Uni AON

#228 - Tajfun 2 Elec.

#227 - Zip Line

#226 - DIY Barometer

#225 - Air Pressure Exp.

#224 - Tajfun 2

#221 - Horizon Deploy

#215 - Deployable Boom

#205 - Tall Tripod

#204 - Horizon Deploy

#203 - Thunda 2

#202 - Horizon Launcher

#201 - Flour Rockets

#197 - Dark Shadow II

#196 - Coming Soon

#195 - 3D Printed Rocket

#194 - TP Roll Drop

#193 - Coming Soon

#192 - Stager Tests

#191 - Horizon

#190 - Polaron G3

#189 - Casual Flights

#188 - Skittles Part #2

#187 - Skittles Part #1

#186 - Level 1 HPR

#185 - Liquids in Zero-G

#184 - More Axion G6

#183 - Axion G6

#182 - Casual Flights

#181 - Acoustic Apogee 2

#180 - Light Shadow

#179 - Stratologger

#178 - Acoustic Apogee 1

#177 - Reefing Chutes

#176 - 10 Years

#175 - NSWRA Events

#174 - Mullaley Launch

#173 - Oobleck Rocket

#172 - Coming Soon

#171 - Measuring Altitude

#170 - How Much Water?

#169 - Windy

#168 - Casual Flights 2

#167 - Casual Flights

#166 - Dark Shadow II

#165 - Liquid Density 2

#164 - Liquid Density 1

#163 - Channel 7 News

#162 - Axion and Polaron

#161 - Fog and Boom

#1 to #160 (Updates)



Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Day 40 - Acceleron III Rebuilt and Burst Tests
Preparing to test a 2L bottle.
We submerged the bottles under test to contain the noise.
Two 2L Robinson coupled bottles failed at 165psi.
The coupling still retained some of the plastic from the failed bottle.
A typical 2 L bottle failure. Splits down the side.
Stress fractures in the base of a 2L bottle after being subjected to 140psi.
1.5m diameter parachute for Acceleron IIIb.
We finished assembling the rocket at about 7:30pm so that's why its so dark.
Acceleron IIIb booster with Tachyon II sustainer on top.
Closer detail of the sustainer mated to the payload pod.
The Acceleron IIIb payload pod.
The parachute is stored on the other side of the pod.
The booster is locked into the launch pad.
Bottom up view of the two stages.
Top down view. Photo had to be taken from the first story.
Sustainer nozzle locked into the Gardena staging mechanism.
The white triangle is the staging mechanism latch. You can also see the swivel on the latch cable. This allows us to disconnect it.
Detail of how the sustainer fits into the staging mechanism.
Tachyon II's new fins.
Tachyon II ready for flight.
Component diagram for Acceleron IIIb.
Date: 22nd July 2007  
Workshop and pool
Cool and sunny.
(click the name for rocket details)
Name Capacity Notes
Acceleron IIIb 24 L A newly rebuilt rocket after Acceleron III exploded on the launch pad during a full system test.
Tachyon II 2.5 L An upgraded sustainer that provides better support during liftoff.

Team Members at Event: GK and PK

After a couple of weeks work, we have rebuilt the Acceleron III booster now designated Acceleron IIIb. During the rebuild we have also made the following upgrades to it:

  • All the neck to base couplings had the lids replaced with the long threaded lids. They now also have reinforcing rings around them to stop them deforming when they are tightened.
  • All couplings have new seals.
  • The inter bottle separating rings have been replaced with continuous ones. These are made from 2.25L bottles.
  • The capacity of the booster was decreased 0.75L because we used 2 L bottles for all booster segments. Acceleron III had three 2.25L bottles in the stack.
  • The nozzle lids have been reinforced.
  • The sustainer now is better supported to withstand take-off forces.
  • The sustainer fins have been replaced by a different arrangement to allow the sustainer to be supported by the booster.
  • The coupling holes in the bottles have been heat treated to reduce the risk of hairline cracks developing under pressure.
  • The flight software has been upgraded to better reflect the state of the computer. Flight computer V1.4 details are now available.

The rocket gallery now includes a diagram with descriptions of the Acceleron IIIb booster components.

Burst Tests

We performed a number of burst tests to get a sense of how these particular 2L bottles perform. The results of these tests can be found in the burst test section results.

This time we tested the bottles under water so that they wouldn't produce such a big bang and any flying debris would also be contained. The bottles being filled with water and being submerged simply make a relatively low thud and some bubbles. The outside pressure of the water is less that 0.5psi so it really does not effect the burst pressure.

We also tested two bottles coupled together using the same coupling that Acceleron III uses. One of the bottles burst at around 165psi and it looks like the crack propagated from the bottle outside diameter to the coupling hole. This then fanned out in multiple directions from the hole. One thing it did teach us about the coupling is that it can hold up the burst pressure of the bottles.

A while back while testing reinforcing of bottles the Gardena  nozzle attachment kept flying off and so for these tests we made a permanent connection to the lid. The lid was also secured with a pipe clamp.

The upshot of the tests is that we will be pressurising only to 110psi instead of the 120psi as originally planned. Although 120psi is still feasible, the first flights will be at the lower pressure. Once we have a few good flights under our belt, we may increase the pressure a little, and later we will have a go at reinforcing the bottles.


We have also finished making the parachute. Originally we wanted to make the parachute from a flat hexagonal sheet of Ripstop nylon. We even bought the material and cut it out, but decided to go with the material from one of those large golf umbrellas instead. The shape is more correct for a parachute than a flat sheet, and it has already been properly edged. I actually found it on the way home on the side of the road still attached to a destroyed umbrella, after the last set of Sydney storms. The parachute is 1500mm in diameter and weighs 120 grams.

We sewed reinforcing ribbon to the shroud line attachment points and used some heat shrink tubing over the knots to stop them from unravelling. There are two main parachute lines for redundancy, should one of them snap during a deploy, the other should still bring the booster to a gentler landing, although at a less optimal attitude. The booster is designed to fall sideways under the parachute to increase the drag of the rocket on the way down.


  • I called the local manufacturer of the 2L bottles to see if I could by a small batch but they said they do not deal with orders smaller than 100,000! But they suggested I call the local distributor. They said they can do smaller lots, but only by the palette which contained just over 500 bottles at 38c each. That was still a little too much so we are just buying them off the shelf in a supermarket. Aldi sells them for 99c each with lemonade. Franklins sells them for $1.09.
  • We have also tested mounting the hand held DV camera to a wooden boom to steady it when filming zoomed in at a distance. Since a tripod makes it very difficult to track a rocket quickly, the shoulder mounted boom seemed to do a reasonable job at reducing the shake. We will make slight adjustments to it and we will use it to film the sustainer at a distance.
  • The sustainer's removable fin assembly has been removed (now being used on a new rocket under construction) and was replaced by a new skirt that helps support the sustainer during takeoff. The fins are permanently attached to the skirt. For strength the skirt is glued to the sustainer body with PL premium.
  • There are still a few minor things to finish and we should be able to do all the tests again very soon. And hopefully fly as soon as possible after that.

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