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Date:  4th July 2009 (8am - 1:30pm)
Location: Doonside, NSW, Australia
Conditions: Clear skies, 17 degrees C, wind < 5km/h
Team Members at Event: PK, GK, HK, AK, Paul K and John K.

After the long wait for the weather to clear and the launch site becoming accessible we finally had a chance to launch the Acceleron V booster with the Axion IV sustainer. The conditions turned out to be ideal. The previous week we went out to the launch site to help with mowing and clear an area for the launch pads. Since we haven't done an update for a while I though I'd include a little bit of what we have been doing as well.

Acceleron V work

On the left are images of the ring brace used to hold the booster segments apart to give enough clearance for the sustainer fins. The ring was wrapped with fiberglass to give it the needed rigidity for surviving a landing. We glued 6 mounting brackets that align each of the booster segments.

We tested each of the bottle pairs to 130psi and held them there for 2 minutes. Out of 18 spliced pairs we made, only 10 were without any leaks at that pressure. 9 of these were fitted to the booster and we had one spare in case we needed to swap it over.

We then assembled each booster segment with the Tornado couplings and tested each segment individually to 100psi to check for leaks.

We then pressure tested the base plate and retention mechanism to the full operating pressure to make sure it did not buckle with all the booster segments pressing up at the ends. Only 3 small ball bearings hold down the force of the entire rocket.

Nozzles

During earlier testing we found that a couple of the 13mm nozzles leaked slightly when the rocket was unpressurised. We are only talking a few drops of water. The o-ring grooves were fractionally too deep, and with the narrow o-rings this is more of an issue. When the boosters were pressurised the o-rings would seal properly. Dad decided to fix the issue and machined up a whole new set of nozzles.

We also decided against a guide rail for this rocket as there was no convenient place to secure it. We could have attached it to the outside of one of the boosters, but it could have caused more harm than good due to the potential uneven drag on that side of the rocket. The nozzles are quite long ~40mm and the fill tubes were quite a tight fit, so in the absence of a guide rail, the rocket straying from vertical could potentially wedge one of the nozzles on the fill tube causing all sorts of chaos.

We machined out the top 30mm of the nozzle to be about 15mm in diameter and the nozzle hole itself by another 0.5mm. This allows the nozzle to pivot more without seizing on the fill tube. The 0.5mm increase to the nozzle gives about 8% more cross sectional area so we get a little more thrust on take-off.

Fill tubes

Each booster segment was supposed to be filled with 3.4L of water, however, we found out that these particular spliced pairs only held ~3.3L as opposed to the 3.6L that some of our earlier ones had. The problem was that the fill tubes were very close to the top of the water level and the air outlet holes would have been under the water level. (The holes have to be above the water level). The holes are normally on the side of the fill tubes to stop water going down into the air manifold when the boosters are being filled. We plugged these up and drilled new holes in the top to get that extra couple of cm to get the right amount of water into the booster.

In order to stop the tubes now being filled with water we used a long funnel that filled the boosters from the bottom. It turns out we had to use 3.2L of water instead of 3.4L to stay below the fill tube holes.

FlycamOne Cameras

I spent a bit of time looking into why the Flycamone2 stops recording after a few minutes/seconds. Many online forums have discussed this issue and it seems to be power related. Apparently the LiPo battery (220mAh) is only marginal for what the camera needs and if it is a little cold and the battery is a little old then it just does not have enough power and will stop recording.

Of the two cameras, one records for a few minutes on a full charge, and each subsequent recording will be shorter and shorter.  The other cam was okay. I attached the bad camera to its mounting bracket and then connected a 4.8V battery - (four AAA 900mA NiMH batteries from Jaycar) to the bracket connector.

On a full charge of the external batteries the camera then recorded fine for 16 minutes at which point I stopped the test. We mounted the batteries and flycam to the booster. The sustainer camera was going to use the internal battery.

Flight Day Events

• We set up the launch pad in the area we cleared a week earlier, well away from everyone. It took about an hour to set up everything as there are many things we must do to get it ready. We now always use a checklist so that we don't miss anything.

• This was going to be the first test flight of the rocket and since there was a lot of firsts for us on it we really did not know how well it was going to go.

• We pressurised the rocket to 130psi and launched.

• The rocket took off slowly at first and started pitching over. It was flying horizontally by the time the second stage fired. The separation looked quite clean but the sustainer performed a giant S manoeuvre before heading towards the ground.

• The booster managed to open the secondary parachute before landing and so the rocket landed on the soft grass sideways without any damage.

• The sustainer hit the ground fairly hard, smashing the Flycam into a few pieces, and bucking the top two bottles. The flight computer and the altimeter were okay. The camera may be repairable.

• We debated over whether we try to launch it again as the damage to the sustainer could have been repaired. We had spare bottles and new nosecone. In the end we decided against it since we weren't so sure what had happened at that stage, and the wind started to pick up a little bit.

• We also launched Paul's "POD 2" (Praetor) pyro rocket a couple of times on a C6-5. The rocket was very stable during flight and had a good recovery on both occasions. We also flew his Thunderbee rocket on a 1/2A3-2. It was a good flight, but broke a fin on landing.

Analysis of the Flight

Booster

On review of the launch videos we noticed that the column of water coming out of the green nozzle showed very nice laminar flow as would be expected. The flow out of the other two nozzles was more turbulent. The more turbulent flow usually results in slightly lower thrust. So that may have contributed to why the rocket tilted in that direction.

The other interesting thing revealed on the video was that the blue water column appeared to not be flowing inline with the rocket. This was pretty unusual and the resultant thrust vector also looks like it was pushing the rocket in the direction it was pitching over.

We inspected the nozzles after the flight, and the only possible cause may have been the rubber washer that seals the nozzle. The red and blue nozzles had about 1 - 1.5mm overlap of the washer into the water stream. I can understand that could have perhaps resulted in the turbulent flow. It is less clear how the blue nozzle thrust was directed away from the centerline, unless somehow the water was being deflected off the inner wall of the nozzle. The green nozzle that had the nice laminar flow showed no sign of the protruding washer upon inspection.

The washer may have distorted when the nozzle was tightened against the bottle and stretched into the opening.

I checked the nozzle alignment with a tight fitting dowel and it was still lined up well. We are currently treating the washer issue as the leading cause of the pitch over manoeuvre. The rocket is also a little tail heavy at lift off so overall rocket stability may have contributed to the problem.

We are not considering uneven booster segment pressure as the cause as the air pulse from all three nozzles occurred at the same time.

It appears that the pressure switch failed to trigger at the right time on the primary computer. From the staging timing (2.08 seconds after launch) and the secondary parachute emerging first, it appears that the backup secondary computer saved the day, by releasing the second stage and parachute before landing. From the video it is evident that the primary parachute had deployed before landing, but did not fully open before the landing. The primary staging servo was in the release position when inspected after landing probably indicating that it had triggered but late into the flight.

Sustainer

It appears that the sustainer separated cleanly from the booster, however, we are putting it's wayward flight path down to two issues.

1. Rocket was unstable due to: A combination of small fins, small nozzle, a lot of water and use of foam. The last three points make the rocket tail heavy for a longer time during the flight.

2. The booster also may have executed a classic "pit manoeuvre" on the sustainer as it was pitching over towards the ground. As the sustainer was emerging from the booster the tail may have been swung around by the descending nose of the booster. That would help explain why the sustainer flew upwards.

It is also unclear how the water was distributed within the sustainer after a horizontal coast period. The water may have sloshed around inside the rocket during staging upsetting the balance further. Something that would be unlikely to happen if it was going vertical.

The sustainer hit the ground 6.8 seconds after lift-off which was about 1.7 seconds before the parachute was due to deploy. It actually landed before the booster.

Conclusions

All in all we consider the test flight a success. There were many firsts for us on this flight and we learned a great deal about what worked and what didn't.

Things we tried for the first time:

• New small pressure switch. This does not appear to have worked well, although it did activate in a later part of the flight.

• Dual independent systems. Worked well together for backup. Saved the day in the end.

• Staging mechanism worked well to release the rocket.

• Ring brace and booster segments used for sustainer support. Worked well to support the sustainer even during a pitch manoeuvre. Ring brace survived the landing well.

• The booster was stable in flight after all the water had gone.

• Acceleration was high enough for the G-switch to trigger.

• This was our highest capacity rocket to date.

• This was our highest lift-off weight to date.

• Our most complex rocket with the most number of individual components.

• New baseplate design for holding down the entire rocket by a common point. This worked well.

• New parachute deployment servo configuration. These servos release the door directly without the use of thread and pin. This worked well.

• Removable large fins. These were taped to the rocket and held up well to flight and landing conditions.

Changes for Next Flight

We will attempt to fly the rocket again at the next NSWRA launch event. The following changes will be made to the rocket and launcher before the next flight:

• Narrower washers to seal the nozzles so that they do not intrude into the water stream.

• New 15mm nozzles. We will use the old nozzles with the o-ring groove removed giving us a larger nozzle. This should yield a faster take off.

• Create new nozzle seats and fill tubes for the launcher. These will seal the nozzles from the inside rather than from the outside. This will actually result in less required hold down force.

• We will add a guide rail to the launcher.

• Use less water in the booster. Perhaps ~2.5L to reduce the amount of time the rocket is tail heavy. With the larger nozzles this will also empty faster.

• Mount the camera further down in the sustainer.

• Rebuild the sustainer and increase the surface area of the fins.

• Reduce the amount of water in the sustainer, perhaps down to 1.3 liters. This again should help reduce the amount of time the rocket spends with a heavy tail.

• Switch to the old pressure switch we used on the earlier Acceleron rockets.

Some of the information below is more for our reference, as we also use these web pages as our technical journal and refer back during upcoming flights.

Flight Timeline

Launch Checklist

This is the check list we use for launching Acceleron V.

1. Grease booster nozzles
2. Grease central nozzle, staging mechanism and sustainer nozzle
3. Grease launch tubes and release head
4. Lock booster onto pad – DOUBLE CHECK
5. Fill booster segments with water
6. Cap segments and tighten caps
7. Connect pressure switch to connector
8. Cover pressure switch
9. Pack sustainer parachute
10. Fill sustainer with foam and water
11. Load sustainer into first stage
12. Lock into position with lever arm
13. Pack booster parachutes
14. Turn on primary flight computer
15. Turn on secondary flight computer
16. Turn on sustainer flight computer
17. Verify parachute servos and staging servos are in default positions
18. CLEAR AREA
19. Pressurize to 20 psi
20. Verify SAFE-TO-ARM light is ON
21. Check for leaks, check air flowing to sustainer through non-return valve
22. Level launcher if rocket is not vertical
23. Turn on altimeter in sustainer and start recording
24. Turn on altimeter in booster and start recording
25. Turn on camera in sustainer and start recording
26. Turn on camera in booster and start recording
27. Start ground cameras and get photography people ready
28. Arm sustainer computer
29. Arm primary computer
30. Arm secondary computer
31. Pressurize to 130 psi
32. Launch
33. Cheer / Run for cover
     

Flight Details

Miscellaneous

Casio Exilim FC-100 Camera

We couldn't resist the temptation and finally bought the Casio Exilim FC-100 two weeks ago from Porta Gadgets Australia: (http://www.portagadgets.com/australia/product.php?productid=29644&cat=0&page=1)

They had one of the cheapest ones available on the net. We also bought the 8Gb Ultra II card to go with it from them. I think they must import it from Japan. The printed manual was only in Japanese, but a CD with the English version was included. They also included a universal to Australian power adapter for the charger. The camera was approximately half the cost of some other Australian retailers.

The whole camera is pretty slim which was very surprising for what it does. We first tried the camera on some static tests to see how well it would work:

As expected the 1000fps is pretty useless due to its frame size, but the 210 and 420fps are quite good. You also need lots of light for the high-speed shots otherwise the image is grainy.

We also used the camera to film some of the launches during the NSWRA launch day at Doonside.

One of the nice things of the slow motion is that camera shake is vastly improved because it looks like slow panning.

Camera Handle

Dad made a great handle with a mounting bracket for our DV camera and the new Casio camera.  It is aligned so that both cameras point in the same direction. This allows us to capture high speed video as well as realtime video at the same time.