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Photo by:
Sam Gibbs

Date: 26th January 2013
Location: Doonside, NSW, Australia
Conditions:  Overcast, light winds < 10km/h
Team Members at Event:  GK, PK, Paul K and John K.

Launch Day

This was a bit of a mixed day with some good successes, but also some failures. We first started off the year again by helping to mow the grass at the Doonside launch site as it tends to grow more over summer.

It was also great to meet Sam Gibbs (http://www.facebook.com/aerospacedu) at the launch and chat about rockets. Thanks also for all the help on the day Sam!

Shadow II

We had prepared the Shadow II rocket earlier in the week to get it ready for launch. There really wasn't much that needed to be done, but the deployment ejection piston was re-greased with silicone, and the deployment system was tested again. We decided to include the AltimeterOne altimeter on the rocket as there was empty space for it in the payload bay. It was a backup in case the zLog altimeter failed to record the flight. The AltimeterOne will shut down after about 1 hour of inactivity, so we simply turned it on and then attached the payload bay to the rocket. There was no need to drill another hole to turn it on. It was located in exactly same section of rocket as the zLog, because we wanted to see how close the two are.

The target launch pressure was 440psi (30.3bar) for this flight, but just as we got past 420psi, the launcher popped an o-ring on the quick connector. With the small, but significant leak going we decided to quickly launch. Because the parachute deployment is time based if the pressure drops too far, there is a danger the rocket would start falling sooner and we could have a high speed deploy. From the video it looked like the pressure was just about 420psi (29bar) when it launched.

The flight was perfect, and straight up. The rocket just kept going and going with the 9 second delay it seemed to hang in the air for a long time. The rocket drifted past the rocket eating trees and landed on the AeroClub's mowed section. The altimeter on the AltimeterOne read 1256 feet (383m), and the zLog gave a peak altitude of 1241 feet (378m). This was difference of 15 feet which means they agreed on the altitude within around 1%. So for this flight we are averaging the two readings which gives us: 1248 feet (380m). This is very much comparable to the last flight flown at 420psi.

Unfortunately the on-board video camera failed to record the flight. :( I'm not sure why that was, the camera has worked well on numerous other flights, and I am "pretty sure" I had turned it on. There just weren't any files on the SD card. Perhaps the acceleration or the landing somehow jarred it and it stopped recording? I tried to record on the camera in the workshop and it recorded just fine. Oh well it was a cloudy day anyway.

From the altimeter we also get a flight duration of 72.5 seconds and ground video also shows 72 seconds.

John said that the rocket was easy to launch, so the arm extension on the launch leaver had done it's job.

We checked the launcher for why the o-ring popped, and it looks like the quick adaptor wasn't screwed all the way into the base and must have left a tiny crack. We tightened it and it should be good to go for the next flight.

Inverter Rocket

We switched over the release head on the launcher and set it up for the Inverter rocket. Setup was straight forward and it was put on the launcher dry. We then removed the PVC air manifold and filled it up with approximately 6.5 liters of water. This was just below the launch tube in the top bottle.

We strapped a camera to the top bottle looking down over the parachute. We also taped an AltimeterOne altimeter to the side of the rocket so we could get an idea of the performance.

Everything was armed and running, and as I was walking away from the rocket, I thought I'd double check the release mechanism. I had forgotten to set the mode to the break wire trigger, and because the timer was mounted sideways the G-switch wouldn't have worked. So I quickly switched to the correct mode. Simulations said this was going to be a very slow launch and so we decided to go with the break-wire.

We pressurised it to 120psi and tried to launch, but the rocket did not take off. The collar was dropping down correctly but it looked like the nozzle was wedged in the release head. We depressurised the rocket and had a closer look. Everything had been greased so that wasn't the problem. We rotated the release head in relation to the nozzle hoping that it was something about the location of the locking tabs on the nozzle.

We pressurised it again to 120psi, and this time it launched without problems. The take off up the launch tube was very slow with the rocket and water weighing around 8Kg. As soon as it cleared the launch tube the rocket accelerated nicely. The rocket looked nice and stable on the way up, and just as it passed through Max-Q the parachute slipped out from under the door, opened, and promptly shredded all but two of the shroud lines. The rocket continued to power skyward but with the high drag of the flapping parachute it soon tipped over and headed toward the ground. Luckily it didn't hit at full speed and so only the top 6 bottles were damaged. All the payload had survived, and even the PVC air manifold had survived. Only one of the cap retaining rings broke loose, so that will be glued back on.

At first we weren't sure what caused the early deploy, but the on-board video showed clearly what happened. The air pressure on the parachute probably coupled with the burst of acceleration during the air pulse simply caused the parachute to slide out. The parachute bottom wasn't resting on anything and the friction between the parachute and the plywood brace just wasn't enough. I had wanted to use two rubber bands on the door for stronger support but I suspect even that wouldn't have been enough. This is an easy fix and so that will be done before the next launch.

The altimeter read 245 feet (75m) which isn't surprising with all the extra drag, and the big hit to upwards velocity the rocket would have received when the chute opened. Two of the knots on the nylon shock cord were actually fused by the opening. It sounded great though on the way up. :)

We've already stripped the rocket down and have started repairs. Because of the impact on the manifold we will re-test it to 130psi. Stay tuned to the rebuild progress on the Inverter build log.

Here is a highlights video from the day:

Other Flights

After the Inverter flight we swapped the release head on the launcher once again to the 9mm one and launched the Axion II a couple of times. Both flights went well. Paul also launched his Thunderbee Hero on a 1/2A3-4. The rocket lost it's streamer, but because it is so light no damage was done.

Shaped Bottle Splicing

Recently we were asked if it was possible to splice those shaped coke bottles that don't have straight sides and have all sorts of protrusions. We had a go using the same narrow sleeve asymmetric splice technique we normally use on the straight wall bottles, with one additional step in the procedure.

We let the splice cure for 3 days, and did the burst test. The splice held 170psi before it burst. That's about 20psi shy of the normal burst pressure of the bottles. The splice would work fine for the regular un-reinforced bottles that are launched at 130psi. (same as the straight walled splices). After the burst test we inspected the splice and it had pulled apart at the glue line, but we noticed that the glue was still a little soft. It looks like it hadn't fully cured yet. We'll try another splice and let it cure for a full week.

We'll add the extra step into the splicing procedure for those who wish to use the shaped bottles in their rockets.

Flight Details