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#186 - Level 1 HPR

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#182 - Casual Flights

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#163 - Channel 7 News

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#156 - Foam Flights

#155 - Down The Barrel

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#1 to #150 (Updates)

 

FLIGHT LOG

Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Day 19 - Repaired J4Y test flights.
Repaired J4Y pressurised to 135 psi.
J4Y coming in to a safe landing.
Frankovka III performing an angled take-off.
Recovering it from a less than desirable landing.
Rocket on launcher detail.
J4Y hit the launcher on its way down from around 80 meters.
Frankovka III drifting in the light breeze.
Date: 2nd December 2006   7:15am - 8:30 am.

Location: Denzil Joyce Oval. (launch site #4)
Where exactly is that? Click the above link to see a Google Earth place mark. What is Google Earth?

Conditions: Overcast with occasional light shower, very light breeze.

Rockets:

Name Capacity Notes
J4Y 3.75 L This is a new rocket made out of three 1.25L bottles. It is our tallest rocket to date. Parachute deployment is achieved using the nose-cone-off-at-apogee technique. Rocket is typically filled with 1.1 liters of water.
Frankovka III 4 L This is an older rocket designed to carry a video camera and a flight computer. On this day, it was flown with the camera and the flight computer for the first time. This is a 2 x 2L rocket. Typical fill is 1.25L of water.

Team Members at Launch Event: PK, GK, Paul K and John K.

Number of launches: 9

It's only been a couple of days since the last launch day, but we were keen to fly the newly repaired J4Y rocket. It wasn't a perfect day for flying because there was the occasional light shower, but at least the air was fairly still.

Flight Day Events

  • J4Y was first up with a 9mm nozzle, filled to 110psi without any more leaks. The flight was excellent, with a parachute deployment right near apogee.
  • J4Y was flown 5 times on the day with pressures up to 135 psi with no issues on the pressurisation side of things, however, parachute deployment was a little off. The parachute tended to deploy too early on the rocket, but thanks to the strong main chute line and the hole in the parachute, crashes were avoided.
  • Frankovka III was flown 4 times, once with a video camera. The flight looked great, and we were looking forward to the video footage, but when we tried to download it from the camera, the computer said the file was corrupt. We could see that the file wasn't full length but all our attempts to read it failed. What we believe happened was that the impact with the ground, even though it was a parachute landing, was too great and it either jarred the camera switch or likely the power was briefly interrupted. This would have certainly corrupted the file mid recording.

    On the previous day when we recorded in flight video, the video too was cut short on landing. but we were able to recover the file without problem. We will attempt to address this issue in three ways. More padding for the camera, bigger chute and have the rocket land tail first to try to reduce the shock from the landing.
  • Frankovka III has been flying really well, but we have noticed on a number of occasions the rocket tilts significantly just after takeoff (see picture on the left), and then tends to reverse the direction just before the air-pulse. After that the rocket appears to fly quite straight, and not spiralling, which leads us to believe that it isn't the aerodynamics of the rocket. At first we thought perhaps a fin was bending under acceleration, but this would be less likely to happen within the first 5 meters of take-off when speeds are still comparatively low. A faulty misaligned nozzle could cause this as we have seen it in the past, but the in those instances the rocket tended to continue to turn in the same direction for the entire boost phase.

    We suspect it is caused by the water creating a wave inside the bottle, as others have mentioned on various forums. Perhaps as the rocket is leaning slightly to one side on the launch pad, there is more water on one side of the bottle, as the rocket accelerates, the acceleration forces the water level to become perpendicular to the water flow from the nozzle creating a wave. This movement of water could explain the sudden shift in direction just after takeoff. It could also explain the reason why the rocket looks like it reverses the direction of tilt before the water runs out. This could be caused by the wave reflecting off the other side of the bottle. When the water runs out there is no more instability issue and the rocket flies straight. We will try some experiments to see if this is the cause.

    Potential ways of reducing this effect would be to make sure the rocket is perfectly vertical on the launch pad, and perhaps some kind of baffles to stop the water from sloshing around inside. Probably the first test will be to use detergent to create foam inside the bottle to reduce the wave action. Foam inside of water rockets isn't anything new, and Antigravity research have used it on their world record attempts.
     

Flight Record

Launch Rocket Pressure (PSI) Notes
1 J4Y 110 9mm nozzle. Excellent flight, with parachute deploying right near apogee.
2 J4Y 120 7mm nozzle. Straight flight, slow take off.
3 Frankovka III 130 Flown with video camera, rocket went straight up. Computer was set at the 4.5 second deploy setting. Video footage was corrupted on landing.
4 Frankovka III 135 No video camera, 4.75 second deploy setting on FC. The rocket angled considerably on take off before proceeding to fly long and straight although be it at an angle. The rocket landed in some trees, but was easily shaken down.
5 J4Y 130 9mm nozzle, Take off was straight up, but the parachute deployed way too early, the momentum of the nosecone, ripped it off from where it was attached to the rocket. Rocket landed safely.
6 J4Y 130 9mm nozzle, Good straight take off, but the parachute opened too early again. The rocket drifted back to the launch site and actually hit the launcher when it landed.
7 Frankovka III 135 9mm nozzle. The rocket angled quite a bit on take-off. The parachute looked like it took a little too long to deploy. Perhaps it took a while to open.
8 Frankovka III 135 Perfect flight straight up. The rocket looked like it drifted for quite a long time. Flight time was 29 seconds.
9 J4Y 135 Good flight, but the parachute opened way too early again.

Design and Development

  • When using the nosecone off at apogee (or any time in between launch and lawndart) technique we find we have to do a certain amount of tuning to get it just right. We will now be building the next iteration of the flight computer (FC) for the J4Y rocket. The aim is to have the FC lighter and smaller for a good fit into the 90mm rocket diameter.
  • Since a rocket finally got stuck in a tree, we have been thinking of ways to get them down. Some ideas were: have the FC cut the chute line; have the FC release a long string with a weight to the ground so it can be pulled down; or my favourite - have the parachute on a very long line, that way the rocket dangles lower to the ground where it is easier to reach.
     

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