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.

We had an excellent day of launches this weekend. The weather was ideal with very little wind and well behaved rockets. On this day we were able to finally fly multiple flights to compare foam and water-only using altimeter data.

Flight Day Events

• The newly rebuilt J4 IV was first off the pad with a couple of water-only missions. The rocket flew nice and straight and had nice deploys on both occasions. We kept all the rocket parameters the same between all of the comparison flights so that we could get good relative data.
• Next we launched J4 IV three times with added foam and configured it to use Jet Foaming. The first flight pitched over quite a bit and the rocket powered through a long arc. It landed well, but due to the non-vertical flight the altitude data could not be used for comparison. The last two foam flights were a lot more vertical and could be used.
• J4 IV flew two more missions after that at higher pressures and foam but this time with a downward facing camera attached to the side. The highlights video contains the footage from these flights.
• The last mission of the day was the Graviton rocket again with a gravity payload. We wanted to fly this last mission with foam to see if there was any difference in the experiment with a more gradual transition from thrust to coast. Unfortunately by the time launch took place all the water had drained to the lowest bottle and as a result Jet foaming was not achieved and the launch was mostly a water-only launch. The video from inside the rocket was similar to the previous zero-G flights, except this time we replaced the M&Ms with small non-melting Lego blocks.
• We were very happy with the rockets performance on the day and were happy to not have to spend the next week doing repairs.
•  

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

Foam vs. Water-Only

Here are the results of the comparison flights for the day. The data was exported from the altimeter software and imported into Excel where the data was aligned in time and altitude offsets adjusted. The only difference between the flights was that bubble bath was added to the water for the foam flights. The pressure, capacity, nozzle size and weight all remained the same.

The rocket parameters:

Observations

While these tests are by no means conclusive, we did learn a couple of interesting things.

• Water-only altitudes were 338 and 308 feet, although on video review of  the second water-only flight it didn't go quite as vertical so the average between the two is closer to 330 feet.
• The two valid foam flights were 316 and 326 feet and both were quite vertical. The average was 321 feet.
• This means that foam resulted in 2-3% less altitude.
• The simulation predicted altitude for water only was 320 feet (Taking a guess at the drag coefficient and nozzle efficiency values).
• This implies that foam has less performance, however, after the last foam launch I capped the rocket so the residue foam would not leak out in the car. Hours later when the residue foam condensed back into water I was surprised to find that there was approximately 80ml of water in the rocket. That is at least another 80 grams that had to be carried to that altitude.
  
  This amount does not include all the water that drained out of the rocket on the way down and when we carried it back to the launch pad. There may have been perhaps just as much or more water still left in the rocket when it reached apogee that did not contribute to the thrust as a reactive mass!
• This means that the foam powered rocket lofted another perhaps ~150 grams. This represents ~12% total water mass! Simulations predict a water-only rocket with 150 grams more should achieve only ~ 246 feet compared to 321' foam flight. (23% more)
• The question now is how do we make use of all that dead weight during the thrust phase?
• From previous thrust measurements we found that foam had 14% less total impulse, however, this only resulted in 2-3% less altitude. Most of this is likely due to the reduced drag on the rocket because it travels slower for longer.
  
  If we can improve the total impulse for foam, and utilise the extra dead weight we are likely to be able to improve the altitude ... more experiments needed we think.
• The noise in the altimeter data on descent is likely due to the parachute door flapping near the altimeter port hole.

Flight Computer Progress

Development on the new flight computers is also progressing well with most of the design now finished. And software still needing to be completed. The new flight computer will have a remote control for setting and arming so that no one needs to be near the rocket. It will also completely control the altimeter's recording. Supporting two separate RC servos it can control staging and parachute deployment, or a drogue/main parachute combination. A small speaker is included to provide audible computer state information.

We will publish full details again once this is complete and flight tested.

I also discovered a design issue with the existing flight computers when powering them from 6V. The voltage regulator voltage wasn't being regulated to the desired level because the input voltage was not high enough. When powered by a 9V battery there was no issue. Instead of the 5V we were getting only 4.35V which was still enough to power everything but meant the servo wasn't achieving its full power potential. This issue has now been resolved.

Crushing Nosecone

After destroying a number of payloads over the last few months, we wanted to redesign the nosecone and payload section so that if a parachute failed to open, the payload would have a reasonable chance at surviving the impact. On the water rocket forum Richard and Cliff had some good suggestions how to go about it. Speeds of 150-200km/h are typical on impact.

The shock absorbing nosecone design we finally settled on is an extension that tapes onto an existing payload nosecone. It consists of a aerodynamic sleeve made from a PET bottle with half a ping pong ball at the top to give it the proper streamlined shape. It is filled with a block of soft foam. The sleeve has a number of long slots cut along its length to allow it to open up during impact. The foam inside the sleeve is designed to compress against the existing nosecone. Because the nosecone extension can move it will also compress the air inside it against the existing nosecone further helping to absorb the shock. When that reaches its limit the existing payload nosecone will also crush further absorbing the shock.

On impact there will still be significant damage to the nosecone, but the payload components should be reasonably well protected. The altimeter is also housed in its own foam padding.

This nosecone extension weighs 37grams and can be easily removed when flying high performance missions, and put back when doing tests or other experiments.

We have now flown 7 missions with this nosecone extension, but thankfully we haven't needed to use it yet.

The layout within payload section has also been redesigned, with the battery now in the middle of the bulkhead "V" behind the parachute and the RC servo is now mounted sideways just above the flight computer. Both are much more securely attached.

The parachute attachment point has also been moved further up the rocket so that it always lands tail first. This reduces the risk of damage to the payload section when landing under parachute.

Bottle Reinforcing

During the week we had another go at reinforcing bottles to take higher pressures. We have tried this technique before but the last tests were only for a single bottle and due to problems with the pressure test setup we didn't quite achieve what we wanted. There was also a slight issue with one of the outer sleeves sliding off.

This time around we have improved how the sleeves fit and can no longer slide off. This test also included joining together two reinforced bottles with a Robinson coupling, because ultimately we want to build higher pressure multi-bottle rockets.

We did a hydrostatic pressure test on the two joined bottles up to 200psi. We held it there for about 20 seconds and let the pressure out. There were no leaks and upon close inspection we found that there were no visible stress marks around the bases or necks of the bottles. This was very encouraging as it means that the bottles could have probably held at least 230psi+. It also means a launch pressure of at least 200psi can be used.

Detailed steps of the reinforcing procedure are now in the construction section.

Misc

We have expanded the ground support equipment we bring to the launch site. Dad made a portable sun shade that goes up quickly, and we now also bring a fold up camping table. The table makes it easier to work on rockets.

I also purchased a new laptop last week so that we can have a computer at the launch site for downloading videos from the in-flight cameras, and downloading & viewing altimeter data as well. Eventually we will be able to make flight computer software changes in the field. The computer can run simulations on the spot so we know what to expect with rocket configuration changes before launch.

Normally these really aren't an issue when launching at the local park, but as we plan on launching more powerful rockets, we will need to go a lot further from home and launch events will take up most of a day instead of one or two hours.

Goals

Our goal in the medium term is to develop a fleet of 4 or 5 different rockets and corresponding spare parts so that we can continue to do experiments when weather allows instead of loosing good launch days to repairs.

A longer term goal is to move to the higher power rockets and do experiments in the higher performance range. At this point in time it looks like the NSWRA (NSW Rocketry Association) is re-forming and getting access to great launch sites as well as the proper permissions from authorities. When everything is sorted we hope to join in the new year. Having local contact with experienced pyro rocketeers will be a great benefit as many materials, payloads and recovery systems are very similar in both rocket disciplines.

Flight Details