On Sept 10th, 2016 we flew another fun glider flight. It was a nice day for a chase, so we decided to see how long a glider could stay airborne.
We took the NSL-47 glider and added an additional camera to it. A new ($25) Mate808 with an extended wide angle lens and its own 1000mAh battery was fitted into the fuselage. Its lens was cabled to the underside of the craft and oriented so that it would capture an upright image while ascending under the balloon. Like NSL-47, an 808 #16-D camera was mounted inside with its lens extended to the vertical stabilizer. Copper shielding was added to the lens cables to try to rule out noise issues.
115,256 feet as seen from the two on-board cameras
Only a small piece of balloon neck remained on the end of the tow line.
At burst, the balloon disintegrated; the glider nosed over and began to dive. The tow line then detached as planned. This flight used a 6m cotton string and a nose-hook ring made of biodegradable cardboard.
Diving after burst from the two cameras
Ascent to 35km took 113 minutes. Even with an initial dive of over 140m/s, it took 108 minutes to land. This is by far the longest descent duration of any of our flights.
The glide path as seen from the landing site
This long glide tested the patients of the chase crew. At a height of 21km, the glider began to stall; diving at 40m/s and then pulling up to a standstill. Sometimes even gaining altitude (position recorded every 5 sec). By 16km, it began to smoothly glide in 1km circles. At that height, it was only falling at 5m/s; as fast as a typical parachute payload at landing. Below 9km, the descent rate dropped to a very slow 2m/s ! It seemed to just hang above Siler City for an hour. Eventually it came to rest in a thicket of thorns on the edge of a field (recovery involved some nasty blood letting).
This flight tested the new Mate808 wide-angle camera. Lens construction appears different from the 808 #16 lens-D, but as feared, both went out of focus in middle altitudes. Apparently the cold causes the lens elements to slowly deform. This is noticeable in the Youtube video above. Once solar heating took place in the stratosphere, the black camera lenses came back into focus. The Mate808 lasted over 150 minutes on a cold 1000mAh battery. I wonder how it would behave if it was covered in an additional insulating shell? Could I make a plastic cover that was clear enough to see through?
The 808 #16 was expected to provide video over the entire flight, but it shutdown as the glider plunged back to earth. The cold lowered the lipo voltage towards the 3.7V cutoff. After shutdown, without the camera's additional heat, the electronics compartment got very cold. But without the camera's current draw, the lipo voltage jumped up a bit.