Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Date: 31st August 2013
Location: Doonside, NSW, Australia
Conditions:  Overcast, light winds  5km/h early, 15km/h later, 22C
Team Members at Event:  PK, GK, Paul K, and John K.

Over the last several weeks we've been continuing with the Polaron G2 phase 2 development. This is a project that has dragged on for a long time (since September 2010), so we are keen to get it finished. A lot of work still needs to be done, but we now have a way forward with one of the main issues and that was holding us up and that was how to attach the boosters at higher pressures. The glued pins and tubes work well for lower pressures, but would not be sufficient for high pressures. To test how well a part of this retention mechanism would work we tried it on our Axion G4 rocket this week.

For more details of the booster clamp see the Polaron G2 build log.

zLog Altimeters

We also purchased a couple more zLog altimeters from Hexpert Systems. These are the newer Mod 6 (Z6R) versions that have a neat USB connector  that allows you to directly plug it into your computer and download the data without the need for a cable. The one thing we really like about these altimeters is that you can start them recording on the ground. Some commercial altimeters have specific launch detect criteria that work well for model rockets, but with some of our slow foam launches, these often fall outside the criteria and would fail to detect launch. These altimeters are also very thin and can run from a single LiPo battery.

Launch Day

The main aim for the day was to get at least a couple of flights in of the Axion G4 rocket. We wanted to test the following:

• Flying a high pressure rocket with a small nozzle to get a nice long burn.
• Booster clamp with thrust ring as a proof of concept for the Polaron G2.
• New zLog altimeters

We ended up using the old Gluon boosters since they were already made and sitting in storage. They also already had their recovery systems so that made it even easier. Since we have never tried a higher pressure main stage before we weren't sure what was going to happen. We decided for a conservative 200psi on these launches. (This rocket has flown at 245psi previously.)

Rocket and launcher setup took about 45 minutes because you have to assemble the whole rocket on the pad.
The assembly procedure is as follows:

1. Boosters go on the pad first
2. The main stage is threaded onto the boosters and locked down
3. The guide rail is threaded onto the rocket and attached to the legs.
4. Boosters are filled with water from top and capped.
5. Main stage is filled with water and foam from top and capped.
6. Nosecone is attached.
7. Booster parachutes are packed and parachute doors are locked with wire connected to main stage.
8. Main parachute is packed and stowed in the nosecone.
9. Deployment mechanism is armed, camera and altimeter started.
10. Rocket is ready to be pressurised for launch.

Nozzle

The nozzle has a 7mm internal diameter and uses a standard Gardena launcher. We made this nozzle a few years back, but haven't really used it. We have mostly used it's plastic brother on low pressure launches. We decided to use the brass version because of greater pressures were used in the main stage, but especially because this nozzle also had to hold down not only the rocket, but also the 3 boosters. That is a combined force of around 70 kgf (690N, or 155 lbf) The entire nozzle is held down by 3 ball bearings in the release head, and if we had used plastic the ball bearings would have made neat little grooves in the nozzle.

7mm brass nozzle used on the Axion G4, next to a standard 9mm Gardena nozzle.

Because the boosters are not reinforced we had to use our dual pressure panel where we can supply different pressures to the main stage and the boosters. We have to run two separate hoses to the launcher for this. We fill each of the boosters with a different colour. Not only does it look better on video, but it lets us see if there is a specific leak as to which part is responsible. It also helps us to identify booster problems during flight. We also have matching coloured tape on each booster nozzle so that we can check for nozzle seal issues post flight if we see unusual flow from a booster,

Dual pressure control panel

1L into each booster

Packing booster parachutes

Filling main stage

Gauges marked with target pressures

Ready to go.

Flight #1

Because it is difficult to simulate these flights due to the use of foam we chose 6 seconds as the deployment delay. The boosters were pressurised to 120psi but as the main stage passed about 120psi a leak developed near the nozzle. It was spraying quite considerably so we quickly decided to launch as 120psi was sufficient pressure. The actual launch pressure was somewhere between 120-150psi as could be heard dad calling the pressure out from the video. The rocket took off nicely and the boosters all separated at the same time. The rocket had a nice slow and long burn, but it had a bit of a roll and ended up spiralling upwards. The rocket reached 623 feet (189m) and it looked like the parachute opened just a little bit prior to apogee. So a good flight overall despite the leak. The burn time was around 5.5 seconds.

Rocket landed nice and close...

...about 1m next to me.

Prior to apogee

The rocket landed only 1m away from me so that made it easy to retrieve. The only damage done was that one of the fin can leaves slipped out from under the booster clamp when the fin hit the ground. We just loosened the clamp and slipped it back under.

Here is the flight #1 altimeter plot from the zLog

Flight #2

We weren't quite sure why the nozzle leaked, but it was a non-standard nozzle that we don't normally use. We attached the nozzle to just a single bottle and pressurised it to 120psi without any trouble and released it. So we re-attached it to the rocket for another go. The most likely cause was an improperly seated seal.

After the rocket was put on the pad and filled with water we noticed that we forgot to put the reinforcing ring around the nozzle cap. We had it in place for the first flight. The reinforcing ring helps hold the cap on the bottle at higher pressures. We had a bit of fun lifting up the rocket out of the launcher without loosing too much water and slipping the ring back on. It took 3 of us to get all the pins and tubes aligned again. We topped off the main stage with another 100mL of water to cover the stuff we lost. We had already added 100mL extra to the rocket just in case we had another leak.

This time pressurisation went smoothly and we got the main stage up to the target 200psi. The launcher released the rocket easily and the rocket went up again fairly straight. The boosters separated from the rocket simultaneously again. You could visibly see and hear how much longer the burn was and the rocket kept going and going spiralling it's way up to apogee. The parachute delay this time was set to 7 seconds, but from the on-board video you could see that it was just a little too early again. This time the rocket went up to 760 feet ( 231m ).  It would be interesting to see how this rocket would go at 245psi like was used on the Axion G2 flight. The burn time was over 7 seconds.

Boosters separate simultaneously

 

 

Flight line

Approaching apogee

Parachute opens just before apogee

Turning off camera and altimeter

Back to civilization

Here is the altimeter plot from the zLog for flight #2

When comparing the altimeter plots we noticed that the descent rate was quite different for the two flights which was quite strange. It was the same weight rocket with the same size parachute. Both descent rates looked constant so it was unlikely it was caused by a thermal. The only thing I can think of is if the rocket had a different attitude hanging under the parachute. In both instances we can see that the parachute had opened cleanly. The rocket also may have spiralled more under the parachute which could increase the descent rate because the canopy is at an angle.

Flight #1 had a descent rate of 18.2 feet/s and flight 2 had 25.4 feet/s That's a difference of 7.2 feet/s!

We were quite happy with the performance of the booster clamp and thrust ring and we did not see any damage after the two flights We're now going to go ahead and make a bigger version of the clamp for the G2. The zLog altimeter also worked great. It was a lot of fun seeing the very long burn on the second flight. I'm really looking forward to the 10+ second burn of the G2.

The next step will be to make similar clamps for each booster, but with the loops replaced with the pins made from folded sheet metal. The thrust rings will also be glued to the boosters, but under the clamp rather than on top of it.

Highlights video

Other Flights

We also flew the Axion rocket by itself with water. We tried yellow food colouring this time, but it looks way too much like urine! :) I think we'll be sticking to the other colours next time. The rocket launched at 120psi went up well and landed without problems as well.

Rocket uses 1L of water

Only using one of the pressures.

Draining water back down

 

120psi launch

Sun halo.

Flight Details