Virgin Oceanic team has over the summer done a half dozen more test dives learning about the sub’s behavior.
Things like locking in the buoyancy seem simple, but were vexing and the team would have trouble initiating a descent, then in the same dive be heavy and have a challenge returning to the surface without dropping the “neutral” ballast because the sub was heavy. Sometimes adding another 10 pounds of weight would make the difference – in a 8,000 pound vessel. Unintended variable buoyancy is the bane of a submariner’s existence!
The team also started chasing “trapped air” and got this problem under control. Air that was still bubbling out of course made the sub heavier over time, and the truly trapped air shrinks under pressure when descending. In the end, the team attacked the sub with a drill and hole saw to ventilate every space that could hold air, big and small. Now buoyancy has become a fixed figure, which is a relief!
The life support has been settled in too. Both, the primary systems and the rebreather backup are going well now. It is reassuring to have these systems working well and predictably. Sorting the life support system mainly means making sure the sensors are giving the right information and avoiding any air or oxygen leaks. A human uses about 5 Liter/minute, so even a small O2 leak in the cabin will affect the available O2.
To delve into the details for the tech hungry, the cabin air makeup is monitored directly via sensors for the O2 percentage and cabin pressure; falling cabin pressure or O2 levels in turn mean turning the O2 flow rate up to maintain the environment. There is a natural change in cabin pressure right after closing due to the heat load coming through the dome, and a slight change due to heat from the pilot and the CO2 scrubbers.
„ For more details for techies, the testing has revealed which systems have weaknesses, which we in turn beef up. It is gratifying to be working through these teething issues with the resources of home base rather than far away with only shipboard capabilities. Typical is a problem with the thruster motor controllers which were subject to heat induced failures; a trip to see the original designer revealed they have engineered several upgrades and added software based thermal protection to later models, so we are retrofitting those upgraded controllers. The devil is in the details too; the heat sinks on the controllers are dependent upon near perfect heat transmission to larger aluminum heat sink plates, and things as small as not countersinking the first millimeters of aluminum thread can interfere with a good, broad heat bond and in turn lead to a failure”, said Co-Founder and a Pilot of Virgin Oceanic, Chris Welsh.
He added: “Flight testing is a certain amount of building pilot confidence as well. In a sub, you are at the mercy of your crew for launch and recovery, and it’s not always comfortable. You can’t see much of what they are seeing, or why they’ve stopped at a particular moment. We radio communicate about some of these things during the handling of the sub, but they are busy and not always able to tell me what’s up. And through it all, you learn to relax and let them proceed (easier said then done for the kind of dive into it personality that goes with being a sub pilot). There is confidence to be gained too around the behavior of the sub, and especially operating in bad visibility. How fast is too fast? What is it like to run into something? It turns out the sub can take a pretty good hit into the bottom – I’ve done it, inadvertently at half speed when the sub was heavy, and finally, on purpose to break through the fear barrier of worrying about it.”
[mappress] November 21, 2012