The Comstock Autopilot
Over the course of several decades, I developed a series of balloon autopilots, beginning with a crude analog version and culminating in the good digital version that I developed for Steve Fossett to use in his solo round the world balloon flight attempts. With this autopilot, which he named the "Comstock Autopilot", Steve did complete the first solo non-stop balloon flight around the world in 2002. In early 2016, Russian Fedor Konyukhov used this autopilot when he duplicated Steve's flight, but several days faster. Many other solo world records and ohterwise epic flights have been made with the help of this device.
The accompanying video shows Fedor preparing for his round-the-world flight. He and the others in the basket of a hot air balloon are being flown by the Comstock Autopilot that Fedor subsequently used on his rtw flight. Fedor's son and project manager Oscar reported that the autopilot flew the balloon level for an hour within "a few feet" of the selected altitude, and that the ascent and descent "almost to landing" were done using the autopilot's constant rate ascent/descent feature.
The photo at the bottom shows Fedor in the capsule before the rtw flight, with the autopilot atop the center of the instrument panel. Fedor used the autopilot during his successful rtw flight to keep the balloon at a constant altitude while he slept.
After the flight Oscar commented: "Hi Bruce, thank you! Your autopilot is just fantastic! You should be getting a Nobel Prize for that!". As of Fedor's flight, all solo round-the-world balloon flight attempts have used this autopilot.
Video credit: Oscar Konyukhov