PARIS pops down to QinetiQ
Vital hypobaric chamber test proves... interesting
Well, that worked a treat. As the pressure dropped, the plunger slid smoothly out, according to our prediction. In fact, it turned out we needed only 15cc of air for the thing to work, and a pressure sensor test on the syringe revealed that a pressure of just 8mm of mercury (official QinetiQ standard for these matters) was required to move the plunger.
So, we set up the syringe again in our initial test configuration, with 15cc of air, and took it up at 1,000 feet per minute.
Once again, nothing, at which point we realised what was going on: after the first failed test, we'd increased the rate of climb on subsequent runs to speed up the process.
In fact, a rate of climb of at least 2,000 feet per minute was required for the contraption to work - in excess of the predicted balloon ascent rate.
A further pressure sensor hook-up demonstrated that the pressure inside the syringe at 1,000 feet per minute was just 2mm of mercury, which indicated a leak. It appears that if the rate of ascent was too low, the air had time to sneakily escape between the ground glass plunger and the syringe interior wall.
So there you have: a sound plan thwarted by unforeseen factors. All is not lost, though, since the QinetiQ chaps did quickly put together another possible pressure-based system, which looks promising. We'll report back on that as soon as we have some new kit ready for testing.
It just remains to say ta very much to QinetiQ for their hospitality and enthusiasm, and to note that'll we'll be posting a video of the test on our YouTube channel in due course. ®