Polymer Bearings Survive Altitude Test

67 year-old Indian aviator Dr Vijaypat Singhania recently flew to 21,291m and set a new world altitude record for a hot air balloon. UK expert Flying Pictures Space managed the project from design concept to manufacture, pilot training, launch and recovery. Igus injection moulded polymer bearings were used in the balloon's pressurised capsule, which was vital to reach these heights. Atmospheric conditions at 21,000m are hostile: exposure at this altitude would cause instant death. The cylindrical pressurised capsule design had to contain life-support systems, telemetry and communications systems. One of the major challenges was to keep its huge burners going in an atmosphere virtually devoid of oxygen. Andy Elson, Project Director at Flying Pictures, and his team tested a series of designs in a custom-built altitude chamber over 12 months to overcome the altitude issues. A conventional hot air balloon has a large fabric valve in the top. This parachute valve is normally opened by the pilot pulling a string when he requires the balloon to descend. This mechanism was designed into the pressurised capsule by building two hand wheels either side of the pilot's seat. These connected to a drum on the outside of the capsule via a shaft mounted in Iglidur polymer plain bearings from Igus. The string to operate the parachute valve was wound onto the drum. By winding the hand wheels, the pilot could open or close the parachute valve and control the descent rate of the balloon. The balloon envelope was approximately ten times bigger than the average passenger balloon, meaning the descent system was absolutely crucial. Iglidur bearings were also used in the main and escape hatch operating levers. Although these were all mounted inside the capsule and not subjected to extreme temperatures, they still had to be extremely light and completely reliable. The bearings enabled a simple lightweight sliding seat support to be built, which could absorb the bulk of the load resulting from a heavy landing when integrated with a pair of variable rate gas struts. This reduced the likelihood of pilot injury. On the day, the pilot was able to make a good landing despite difficult conditions and the shock absorbing system was not called into play. However, this was imperative as a backup safety feature. At 21,000m, the temperature was expected to be -60C, and temperatures of +38C were expected in the shade on the ground. These temperatures were no problem for the high performance polymer bearings. Elson says: 'We needed bearings that were totally reliable, very lightweight and able to cope with the temperature range, as well as the dirt and dust expected during take off and landing in fields in India'.