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Date:  21st December 2008 (7:00am to 9:00am)
Location: Denzil Joyce Oval  
Conditions: Calm, 20 degrees C, perfect flying conditions
Team Members at Event: GK and PK

FTC Flights

Since we could not make it to the last NSWRA launch day, and then the cancelling of the NSWRA picnic due to bad weather we haven't been able to test fly our first FTC rocket. This Sunday, however, the weather was perfect with no wind, mild temperatures and dry ground, and so we went to our old launch area at Denzil Joyce oval. We wanted to see how well all the systems on the rocket were going to perform since we hadn't built a rocket like this before. The aim was to reduce the launch pressure to keep the rocket within the park.

We also brought along some of our other rockets as backups in case the FTC rocket lasted only one launch. All in all it was a great day for flying rockets, and all rockets performed well and landed without damage.

We also tested for the first time the Assemtech G-switches as well as our RCA plug G-switches. The Assemtech G-switch will be an optional component for V1.6 of the FC.

Launch Day Events

• We arrived at the oval just before 7am, and the set up time was quick since we didn't need to bring any cover, chairs or tables. The launcher was also easier to set up since the guide rails weren't needed for the FTC rocket (and Axion II) as the launch tube acts as the guide rail.
• For the first FTC flight we set the deploy time delay to around 4 seconds and only pressurised the rocket to 100psi since we had no idea what the rocket would do or if the parachute deploy mechanism would fail under the G forces. The rocket went up very well and straight and the parachute opened well past apogee. It only reached 198' (60m).
  
  We were happy that the split nosecone deployment mechanism worked well, and dad even managed to catch the rocket on the way down. No breeze meant it landed close to the launch pad.
• Encouraged by good flight and proximity of the landing to the launch pad, we left the time setting as it was and pressurised the rocket again but this time to 160 psi. The rocket again went up nice and straight and this time reached 341' (104) m. The parachute deployment happened closer to apogee this time. Dad managed to catch the rocket again before it landed.
• On the third flight we increased the pressure to 180 psi and also added more water as that was what the simulator was predicting as the optimum. The rocket took off nice and fast and what appeared fairly straight. This time the parachute opened right around apogee so we had the timing set correctly. The rocket reached 370' ( 113m ).
• As we started pressurising the rocket for the fourth flight it popped up ever so slightly in the release head - perhaps a couple of mm, but that was enough to trigger the launch detect G-switch and the parachute popped off. It's nice having the safety abort pressure relief valve for these instances. We repacked the parachute and pressurised it to about 20 psi before arming again. The little bit of pressure ensures that the rocket is full up against its stops so there is no vertical movement.
• The fourth flight was almost identical to the previous one reaching an altitude of 373' ( 114m ). The parachute deployed around apogee, but it looked like it became tangled on the way down. It finally fully opened at around 130 feet AGL. We will need to see if there is a better way to pack the parachutes and lines. We did learn that the payload and parachute attachment points as well as the thin Kevlar cord are strong enough to handle the higher speed deploys.
  
  All in all we were very happy with the FTC flights.
• We then decided to launch some of the smaller rockets for the kids. We used our original small launcher as that's all that is needed for the small rockets. We launched the Neutrino rocket as well as Clifford. We hadn't launched the Clifford rocket for almost 2 years so it was fun to do a bit of retro rocketing. The rockets survived well, and kids got enjoyment out of seeing them fly.
• The only other two notable flights were of the reinforced Tachyon IVb and Axion II.
  
  Tachyon IVb was launched with foam and at 140 psi. The rocket used one of our new G-switches so it was a good test for it. The rocket flew well and went pretty high but landed fairly close to the road, so we set that one aside. Foam is always unpredictable.
  
  The Axion rocket uses a 15mm nozzle and the launch tube. We removed one of the spliced pair sections to reduce its volume and only filled it to 100psi, again to keep it in the park. The rocket flew very straight and very high. It would have been close to the 110-120m mark but without an altimeter that's only a guess. The rocket landed without incident. It also used our new RCA G-switch so we are confident that it is working well.
• We packed up and were off the oval by 9am. It was nice to be able to get 9 launches in in a two hour window. We would normally only achieve half of that in a whole day at Doonside due to the necessary launch windows when so many people fly at the same location.

Observations

• The Assemtech G-switch seems to be working well for the FTC rocket. We still need to test it for lower velocity bottle rockets with small nozzles.
• The FTC rocket's altitude differed significantly from simulator predictions. We will have to investigate why this is the case, but as can be seen in one of the photographs and a video as well, the rocket bent quite significantly on takeoff.  The rocket is not very stiff so we didn't find this surprising. This bending is most likely inducing significant amount of drag and hence lower altitude. At 180 psi we are still below the burst pressure of the naked FTC tubing, so we should be able to push the pressure beyond the 200psi mark with the strapping tape reinforcement. We had only done pressure tests to 180 psi of the assembled rocket before launching it so we did not want to go above that pressure on launch day. We will now test it to higher pressures before launching again. But we will take it to Doonside to do the higher pressure launches.
  
  Judging from these flights we will not be able to push the upper altitude of the rocket much higher in its current configuration. The small volume of the rocket is quite restrictive. And while we could further reduce the weight by perhaps 50 grams, reduce the fin size and reduce overall drag, I would expect only another 100 feet or so in altitude at the pressures the rocket could handle. Switching to T-12 FTC with better reinforcing is really the only option for significantly improving performance and allowing higher pressures. 
  
  These were definitely our highest velocity launches to date. Simulator suggests around 230km/h 0.1 seconds after take off. Peak G-forces are around 70G.
• Despite lubricating the release mechanism and nozzle with silicone grease the release mechanism was a little stiff on launch. This may be due to the higher pressures involved. We may need to add a longer lever to the mechanism to have enough force to easily release it.
• During the NSWRA open day Phil had suggested that we should use a swivel on the parachute line. We didn't have one handy and so we left it out, but it turns out we should have followed his instructions. After the second flight the main line was quite twisted and it took us a couple of minuted to untwist it.

Misc

Now that we have a couple of weeks holiday, in the short term we will be focusing on finishing V1.6 of the FC as well as completing the initial release of the recovery guide. There are still many links and cross references to add to it so it will take a few more days. We will also continue work on the new Acceleron as there is a lot of pressure testing to be done. Looking further forward into 2009 we would like to continue with the static tests where we left off a couple of months ago, more work will be done on the multi-stage rockets with larger boosters, learning to make lightweight fibreglass body tubes as well as finally implementing a couple of projects that have been in the design phase for at least half a year. These FTC flights are a part of the that development cycle. In there somewhere we also need to find time to work on the new workshop space that we are adding under the house.

Flight Details