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    MB-water-rockets




    Flight day 5 - stability investigation


    Date: 21.11.2009 (11:30 - 13:00)

    Weather conditions: partly sunny, 13C, light winds

    During the last launches we observed the tendency of Antares Ia to fly in a slight arc. Always in the same direction. We blamed slight instability for this behaviour and scheduled two launches for investigating it.

    Launch #1: This was the reference launch with Antares Ia, 1000 ml of water and a pressure of 9 bar.
    At 8 bar the nozzle sprang a leak so we launched ad hoc. Unfortunately the camera did not work and we didn't get any footage of that launch. The flight was similar to the ones last week: a slight arc to the west. The flight duration was  26.5 seconds. Antares Ia touched the ground approx 25 meters west of the launcher. Recorded altitude was 86.6 meters.

    Altimeter data of launch #1. Servo activity can be easily detected by a dip in the recorded on board voltage.

    Launch #2: In order to make Antares more stable we added much bigger fins. Still 1000 ml of water and a pressure of 9 bar were used.
    Just before launch we noticed that the trigger mechanism didn't work. A little steel ring was broken. We decided to fix the problem without de-pressurizing the rocket. This was only possible because we didn't have to touch pressurized parts.
    Antares Ib was aligned to the east but went to the west when it was released from the launcher. The flight was pretty high this time. Ejection of the parachute was clearly visible but it failed to deploy. The flight time was approx.10 seconds. Antares Ib crashed into the ground 25 meters west of the  launcher. Recorded altitude was 95 meters.

    Launch #2

    Altimeter data of launch #2. It is not totally clear why recording stopped before the impact. Probably the write cycle of the last values could not be completed before the voltage broke down.

    Antares Ib after crashdown. The parachute had been ejected but failed to open. During descent it was visible as a small yellow ball flying alongside with the rocket.

    The parachute failed to open because one cord looped around the others when packing the parachute.

    The payload section had been completely destroyed. There was no chance for the thin plastic to withstand an impact with a speed of more than 30 m/s.

    Luckily servo and altimeter survived....

    Since there were shorts on the PCB of the deployment timer the servo was still running when the recovery crew arrived at the impact zone.

    The deployment timer survived with minor damage. Some components were bent some lines on the PCB were broken. The reed switch was broken too (front corner on the image).

    Lessons learned:
    The direction Anteres is flying to is very reproducible (4 launches in a row!)
    Very big fins do not change this tendency which might indicate that it is not a stability issue.
    The simulated height was again lower than the actual height. This is most likely due to the poor calibration of the pressure gauge.

    Next steps:
    Repair Antares
    Further investigate the root cause of the not optimal trajectory of Antares
    Calibrate the pressure gauge