NSL-41

Launched the morning of Sept 19, 2015, this was another test flight of the "cheap Styrofoam glider" set-up like flight NSL-39. The glider was completely uncontrolled. The wings simply acted as a replacement for the parachute used on typical flights. Compared to NSL-39, this flight had the glider attached to the balloon via a hook in the nose and the center of gravity was moved about 1.5cm towards the tail.

The payload was a 1.2m foam glider ($9.99) with an AP510 APRS transmitter and an 808 #16 lens D camera. A piece of plastic coat hanger was embedded into the nose to act as a hook for attaching the balloon. It all totaled about 330g. A 2.5m piece of string ran from the 600g hydrogen balloon to a small keyring. The keyring simply slid onto the hook. A hole was carved into the foam for the AP510 (mounted at a 45 degree angle) and the 808 camera (bare circuit board mounted vertically). The 808 is a good source of heat, so it was placed next to the batteries. Its 120 degree lens was then tilted to look out the port side; the view captured the nose back to the port wingtip. The area around the electronics was darkened with black tape and a Sharpie to help with solar heating.

The morning was clear and pleasant. Set up at Lake Benson went quickly. Paul and Matthew dumped what was left in their hydrogen tank (about 95 cu ft) into the balloon. Chris acted as Capcom / PAO, The goal was to reach 18km and see how the front hook and flight stability worked out. The prediction was that the flight would hang around southern Wake County in large loops. Strong jet winds were to arrive later in the weekend, so it was decided to launch around 0930 before it got too hot. Throughout the course of the flight, the temperature increased and puffy clouds started appearing.

The payload was VERY stable as it climbed. There was no darting around like on NSL-39 and very little spin. There were apparently no consistent winds up to 20km as payload just stayed over Lake Benson. None of us has ever witnessed such a calm flight !

As the balloon passed 20km, winds started tossing it about. At times the entire balloon and payload would tumble end over end. Then at 20,730m the glider landed against the expanding balloon. The plastic hook caught on the latex and it tore. Unlike a typical violent burst at altitude, the balloon deflated over a second or two.

After a few seconds, the torn balloon balled itself up and fell faster than the glider. The glider detached as expected (audio clearly picks up the keyring sliding down the plastic hanger) and began its nosedive. As it gained speed, it began slightly bucking as it tried to pull up and then stalled.

As the glider fell into thicker air, its descent rate decreased. Its bucking turned into slow stalls, and then, eventually loops! They were not graceful loops; but more of stalls, with the nose pointing straight-up, where the glider continued to roll forward. There were brief periods when the glider simply hung motionless in the air. On its way down, the flight path followed the gentle air currents just like in ascent. At no time did the video show consistent, tight spinning as seen on most parachute flights. [Once we get this down to a science, we should get some wonderful video from this from this system!]

The story of this flight was the ground track. The payload went to 20km and landed only 3.4km (2 miles) from the launch site. The recovery crew was in the neighborhood, but due to a laptop crash, they were two blocks away and missed seeing the landing.

The flight ended at a golf course near the launch site -- a big, wide-open golf course. As is seemingly the case in most flights, it landed in a tree.. on the edge of this golf course. The nice landowner offered the use of a ladder and a broom to ease the recovery.

Notes:

• Sadly the 808 camera cut out on descent. We missed video of the landing. There appeared to be plenty of battery left. Upon opening the payload, the small power connector was found detached from the camera. Was this due to cold temperatures and too many loops? Or simply popped off upon impact with the tree? There have been many failures recently that may be due to write failures to the microSD chips. That may have happened here. Still, the surviving video met the flight goals.

[UPDATE 11/18/2015: Paul has discovered that several of his cheap microSD chips are actually bogus and the source of the recent camera failures. They are listed as 32GB units, but are forgeries with only about 8GB of valid space. Use a program called 'h2testw' to test your chips.]

• A wide angle 808 (#16 lens D) was used for this flight to capture as much of the area around the glider as possible. Please use caution when flying these 'lens D' units. Some of them go out of focus at high altitudes - some work fine. Perhaps it's due to the cold or maybe internal atmospheric pressure on the lens. This particular camera was known to go out of focus, but that was okay for the flight goals.
  *** 808 cameras are cheap in every way. But they are only $40 and mass only 10g !
  

• The glider was just slightly tail heavy -- perhaps the CG was 0.5cm too far back. It kept pulling up into a stall. This may actually be what we want though. The stalls end up dumping speed similar to the roll-reversals that the shuttles used to employ. If it was cleanly gliding it may have come in at a too high ground speed.
  

• How do we reduce the chances of a glider impact with the payload? A short 2.5m bridle was used to reduce the chances of a wing tangle and also accidental pre-release due to a whipping bridle. Perhaps try a 4m string next time.