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#230 - Tajfun 2 L2

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#228 - Tajfun 2 Elec.

#227 - Zip Line

#226 - DIY Barometer

#225 - Air Pressure Exp.

#224 - Tajfun 2

#221 - Horizon Deploy

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#193 - Coming Soon

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#188 - Skittles Part #2

#187 - Skittles Part #1

#186 - Level 1 HPR

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#184 - More Axion G6

#183 - Axion G6

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#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.
Click on an image to view a larger image, and click the browser's BACK button to return back to the page.

Day 41 - Successful 2 Stage Flights (Acceleron IIIb & Tachyon)
Filling the booster. Each segment was filled with 1.5L for a total of 4.5L.
The sustainer air supply on the left and the pressure switch (TDD) on the right.
Sustainer was filled with 800mL of water and bubble bath mix.
Programming and Arming the sustainer flight computer needs balance.
Looks like we are doing a little voodoo dance ... probably just deep in thought.
Off to set a personal altitude record.
Just after separation. The booster is off to the left.
Our cars on the left, and the team on the right. The black square on the tarmac was used to calculate altitude. It is 33m wide.
Apogee. Yup those are the Blue Mountains on the horizon.

~ 177m (580')

Parachute starts to open.
Fully open parachute.
Descending under parachute. Look back towards Penrith.
More trees and buildings near the launch site.
Assessing the booster for damage during landing. It was just fine.
More water. We add the food colouring for better photos.
Some kind of very technical discussions .... probably what we are going to have for lunch.
A fuzzy image taken from video showing the start of the air pulse.
Just after separation the white line is the sustainer foam trail. White dot in the middle is the booster.
Booster coming in for a safe landing.
More water of course. The grass was well watered after three launches.
Locking the sustainer into place with special hooks.
The step ladder comes in handy when launching water rockets. Ground to tip is 2.36m.
Dad took this photo as he pulled the string.
Acceleron IIIb hits top speed as the water runs out.
... and back to Earth safely.
Date: 29th July 2007   10:30am - 1:00 pm
Quakers Hill
Cool and partly cloudy, calm winds. 14 degrees C.
(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, PK, AK, IK, HK, Jordan K, John K and Paul K.

Today was an fantastic launch day with very little wind and mild temperatures. We had the whole family come out and watch and give us a hand as we were going to fly the new Acceleron IIIb booster and Tachyon sustainer for the first time.

We ended up flying the booster and sustainer three times. It takes about an hour to set up camp and get ready for the first launch and then it is around 30 minutes to get the next launch ready again. We were really happy with the performance of the rocket as it did exactly what it was suppose to do.

Flight Day Events

  • The day started off really well until on the way to the launch site dad's engine oil light came on. It looked like we needed to scrap the launch day, but after a few checks and a top up with oil, he nursed it to the launch site. We had two cars full of equipment.
  • From previous experience we knew that setting up a big launch you tend to forget things, and so this time we came prepared with a page long check list that needed to be followed before each launch. This proved very useful and made sure we had all the right bits attached and set as needed.

    We also brought a small step ladder so that we could reach the flight computer on the sustainer. The fully assembled rocket is 2.36m (~8 feet) tall.

Flight 1

  • We used only about 100psi on the first launch, to make sure the bottles wouldn't fail. We wanted to get at least one launch under our belt so we took minimal risks. The parachute delay on the booster was set at 2.75 seconds after second stage release. Due to the lower pressure and longer delay, the booster's parachute fully opened only about 1 meter above the ground, but it was enough to stop the booster from suffering any damage.

    The take off was nice and slow and mostly vertical, it looked like it was taking forever to release the second stage, but it finally did and it flew off very nicely. It took 34.5 seconds for it to land.

  • We also attached an upward facing camera to the side of the booster so that it could film the second stage separating. However, when we got home, I noticed it did not record anything. This was disappointing, and now I am really considering getting a new camera that can record longer that the 30 seconds. It wasn't a complete loss as we had two hand held digital cameras filming as well.
  • The only other hiccup was a stuck return valve in the sustainer air supply which started draining the sustainer into the booster when we locked it down. This was quickly fixed, but it meant we had to refill the sustainer with water and foam again.

Flight 2

  • We weren't going to fly any more cameras on the day, but a last minute decision was made to swap the mirror used on the booster camera and put it on the second camera. Since the sustainer wasn't designed to carry a camera, we simply taped the camera to the mid section of the rocket. This adds about 10% more weight to the rocket, as well as adding considerable drag to the rocket.

    We also set the deploy delay for the booster parachute to 2 seconds to open a little sooner.
  • This time we pressurised the rocket to 110psi and launched it. You could see and hear that it had more power than the previous launch and took off faster. The rocket flew mostly vertical and again the second stage released right on queue. (That TDD works a treat Trevor!)
  • The second stage took off like a bullet and headed almost vertical. We used a 7mm nozzle on the sustainer for all flights. The in-flight video shows how it steered itself vertically. Using the in-flight video The best estimate of altitude came to 177m (580 feet). [See altitude estimates below] The sustainer took 40.64 seconds to reach the ground. This was our highest altitude to date.
  • The booster's chute opened at a nice altitude and so it landed well again.
  • Unfortunately the onboard video only has 30 seconds of record time 15 of which was taken up while still on the ground, but shows the entire ascent, the chute deploying and descent under parachute for a few seconds. The launch was covered by two hand held DV cameras and one static pad video camera.

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

A better quality version is available here (37Mb)
Also available on MySpace here.

Flight 3

  • As we prepared for the third launch, we kind of winged it and forgot to follow the check list procedure. We only realised once we started pressurising the rocket that the booster wasn't locked into the launcher. At about 30-40psi the rocket popped up out of the launcher about an inch and proceeded to spray the booster water everywhere. Due to the launcher setup the rocket did not tip over and the guides kept it in place.

    The sustainer computer was already armed and the little pop up was enough for it to detect "launch" and popped the parachute about 8 seconds later. The booster computer was not armed and therefore did not release the sustainer when the pressure dropped to zero. We have to arm the booster flight computer after it has about 40 psi in it, enough for the pressure switch to be securely deactivated.

    The problem was that we had a partially pressurised sustainer on the launch pad and a deployed parachute. We could have manually launched it but we weren't sure what would happen. So instead we disconnected the non return valve and let the sustainer drain through the air supply line.
  • We refilled everything, locked it down and launched it a third time with no cameras and again at 110psi. The booster and sustainer again performed really well, and the sustainer took 50.36! seconds to come back to earth. The estimated altitude was:

     ~192 meters (630 feet). [See altitude estimates below]
  • This flight set two new personal records for flight time and altitude. 

Altitude Estimates

Without an altimeter we have to try to calculate how high our rockets go. (I know, I know we have to get one). Normally we don't publish how high they go in our updates unless we have some reasonable way of measuring the altitude.

On board video gives us this ability and on today's flight #2 the camera took a picture of a large area of asphalt (old runway) directly below the rocket as it was approaching apogee. We measured the asphalt to be 33m wide. We then used a calibration image taken from the same camera and using the similar triangles method we calculated the altitude for the second flight to be ~ 177m. (580 feet).

The third flight altitude estimate has a greater margin of error because there was no camera.  However, we were still able to get a reasonable estimate of altitude.  This is how we arrived at the altitude estimation: 

Flight 2 and 3 both used the same launch pressure, same parachute deployment setting and the same amount of water in the booster and sustainer.

We used ground based video to get timing information for total flight time and time to separation, from launch.  In flights 2 and 3 the time to separation was the same at 2.24 seconds.  This led us to believe that the ascent profiles were relatively similar.

The one big difference between flight 2 and 3 was the extra ~10 seconds of flight time.  Since most of the extra flight time would have been under parachute, we needed to know the rocket's descent rate. 

This was calculated from flight #2. The average descent rate was calculated by figuring out how long the rocket fell under parachute and over what altitude.  Since it took 7.36 seconds to reach apogee - timing we got from the onboard video. Also from the video we know it took a further 2.4 seconds before the parachute opened. Subtracting these from the total flight time we know that the rocket fell under parachute for ~31 seconds.  But before the parachute opened, the rocket was in free fall from apogee for 2.4 seconds.  Using simple acceleration due to gravity calculation, we work out that the rocket fell by ~28 meters in the 2.4 seconds. We neglect drag as this was relatively low velocity. 

Therefore, the altitude lost during parachute descent was 177 - 28 = 149 meters. This makes the descent rate 149 / 31 = ~4.8 m/s.

Now since the the rocket on flight 3 took 10 seconds longer to land, and assuming that most of this 10 seconds was under parachute, this gives us an extra altitude of about 48 meters.  This, however, is highly unlikely and we need to take into account potential updrafts and slightly lower descent rate due to the lower weight of the rocket, as well as a little extra time to go that little bit higher.

All things being equal the simulator predicted that due to the lower weight and drag (no camera), we should have gained an extra 10 meters in altitude.  Therefore, instead of the extra 48 meters we considered only a gain of 15 meters for this flight giving a total of 192 meters (630 feet).  This is our best estimate of the altitude and is probably within +/-10 meters of the actual value.

Flight Record

Launch Rocket Pressure (PSI) Notes
1 Tachyon II and Acceleron IIIb 100 Sustainer: FC setting 'b' 7mm nozzle and 800ml Foam and water mix.
FC setting '3'. 1.5L per segment. Camera on booster.
Slow take off, mostly vertical with a great release of second stage. Both landed well.
2 Tachyon II and Acceleron IIIb 110 Sustainer: FC setting 'b' 7mm nozzle and 800ml Foam and water mix. Camera on sustainer.
FC setting '0'. 1.5L per segment.
Excellent flight. Good deploys all around.
3 Tachyon II and Acceleron IIIb 110 Sustainer: FC setting 'b' 7mm nozzle and 800ml Foam and water mix. Booster: FC setting '0'. 1.5L per segment.
Excellent flight again. Great deploys, and our highest altitude to date at ~192 meters. Flight time 50.36 seconds.


  • This two stage rocket has been in development for about seven months with progressive complexity introduced along the way and lots of trial flights. The booster and sustainer together now have around 400 individual components. We are likely to put further development on the back burner for now and concentrate on a few other developments and experiments we have been considering for a while but haven't had time to do them.
  • When we fly this rocket again, it will likely be a little lighter and also be launched at 120psi, and hopefully with a real altimeter.
  • Write your checklists, and FOLLOW them.


Many thanks go to our family who have supported and helped us along the way in this fun hobby.

Also thanks goes to all the water rocketeers out there that have contributed with materials, design issues and insights into how these things work.

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