NSL-60

Maximum Altitude: 43128.6 m (141498 ft) above sea level

Unpowered glide distance traveled: 140 km (86.7 miles)

Maximum speed: 218 m/s (488 mph) at 32 km altitude
(speed of sound at that altitude is ~303 m/s)

Flight duration: 5 hours 5 minutes

With the winter jet stream encroaching upon North Carolina, it was time for one last, long-duration flight for the year. We can fly in the winter, but it usually involves more planning and looong drives times for recovery.

NSL-60 was flown on the morning of Oct 7, 2017. This was a re-flight of Paul L's NSL-49 gear with a tweak to the cameras. The foam glider from NSL-49 was loaded with an AP510 tracker and 4200mAh LiPo. Again, this was just a simple $10 toy glider with no flight controls; subject to the winds like a parachute. The cameras were swapped, so that this time the Mate808 camera was embedded into the rear stabilizer of the plane -- looking forward. It was connected to the same big LiPo as the tracker. The 808 #16 Lens B camera was mounted inside of the craft, pointing out a hole in the bottom. This camera was set to take still photos and was powered by its own small 1000mAh LiPo. All these parts were secured with toothpick struts and copious amounts of black electrical tape (to absorb solar heating). The entire craft and its 3m tow line came to 350g. It was hauled up with a 1600g cell with 900g of lift.

Ascent images from the 808 #16 camera looking through the bottom of the nose-up plane -- note the setting moon.

This was scheduled as a five hour flight, so the chase crew had plenty of time to get ready and head out to the landing area. Getting actual and projected flight plans that agree can be challenging on these long missions. The gas fill and measurement have tighter tolerances. A difference in a liter of lift gas can dramatically change the low ascent rate and make quite a change in the final altitude and path. Even an extra zip-tie can make a difference. Add to that the challenge in modeling the descent of a glider that could descend at 1m/s or 8m/s depending upon the trim and balance.

At burst, the huge balloon shredded in about three 1/30sec video frames!

After the violence of burst (the payload was only 3m from the HUGE balloon), the craft tipped over and began to descend, nose first. The tow line disconnected as designed. The payload nosed in, going faster and faster, finally reaching 218m/s (488mph) ! During this rush, at 70% the local speed of sound, the craft oscillated, producing a loud hum in the video. The video and still images showed this vibration as well.

The payload then slowly pulled up and entered a very steady glide, with little of the bucking or stalling seen on previous flights. It also did not spiral much, but kept a true heading northeast. Robert and Paul followed along below in the chase car.

As the payload slowly descended, it entered into the frigid upper troposphere. On typical HAB flights, this period only lasts a few minutes, on this flight it was over an hour. The temperature inside the payload dropped and this caused the battery voltage to decrease as well. The 808 #16, which acts like a heater, shut down when its battery fell below 3.7V. The Mate808 and AP510 can run a bit lower, but would die at 3.4V. Would there be enough power to keep the tracker going, or would it be lost in the swamps of eastern NC?

Paul was feeling as gloomy as the approaching weather as the APRS telemetry told of an on-board temperature of -13C and a battery voltage falling to 3.5V. But, then the temperature started to slowly rise! Over the second hour of descent, the temperature increased almost 40C and the voltage returned to 3.75V.

As the payload descended to the cloud tops, the remaining working camera started to be saturated with the high amount of bright white light in the field of view. It's simple exposure levels just couldn't go dark enough.

In the final minutes of the flight, the payload hovered above a storm cloud, riding the updraft. It eventually drifted around the edge of the updraft and entered the cloud. The view of cloud tops was replaced by a solid gray and the sound of strong rain. A rain drop obscured much of the tiny lens on the tail camera, but a nice open landing area soon loomed out of the mist. It skidded to a stop in tall grass -- a perfect, gentle landing.

At recovery it was discovered that the video camera was still running! We finally have video of an entire 5 hour flight of over 246km (153miles).

And Robert got in a lot of hours of driving on his learner's permit!