NavList:

Brian Villmoare you wrote:  How much does the fluid change the ability of the bubble to move around when you tilt it slightly? One would assume that a bubble less inclined to move when tilted slightly would make for a less accurate reading. In my case, I am hopeful that the sealing material can withstand alcohol. I used blue silicon gasket sealant for the removed (lower) window, leaving the upper, curved, window intact.

Brian
Good, for a bubble chamber, it’s the curve and the fluid that matter.  The bubble is just small bundle of almost nothing.  It’s important to differentiate between static tilt and acceleration.  With static tilt, the fluid remains subject to gravity alone.  It’s just that the sextant bubble isn’t in the centre of the bubble chamber.  With for and aft static tilt, once steady in the new position, the star should have followed the bubble (Except I’ve never seen it happen perfectly with my A12).  With joggling around on the ground and turning or speed change in flight, the fluid is subject to gravity plus any additional accelerations applied, so the bubble indicates a false vertical.
The hydrostatics of why a bubble tries to align itself with the apparent vertical in a fluid and the hydrodynamics of how it gets there requires a bigger brain than mine to work out, so I’ll leave that to the experts. It’s something to do with the weight of the fluid displaced by the bubble; and weight of course is the sum of the various accelerations including gravity applied to the fluid.  Viscous friction within the fluid and at the bubble glass surface is going to affect how fast the bubble moves.  There are undoubtedly PhDs concerning this gathering dust all over the place if you could but find them. DaveP