The Explorer sailplane was a Schweizer SGS 2-32 all-metal sailplane sold on July 12, 1966, to Explorer Research Corp (ERC), a non-profit corporation, whose members were associated with the Explorers Club. The sailplane was manufactured by Schweizer Aircraft of Elmira, New York expressly for the ERC, with modifications for high altitude and cold temperature flights. The FAA designated tail number of the sailplane was N9929J. Here we will refer to it as Explorer or simply the sailplane. The members of ERC were sailplane pilots and they wanted to promote research within the Explorers Club. Joachim Kuettner was one of the individuals involved in the purchase of the Explorer as a member of the board of advisor of ERC. Kuettner¹ was a lifelong advocate for the use of sailplanes in atmospheric research.

Not long after the purchase by ERC, Explorer was instrumented to investigate Clear Air Turbulence (CAT) in lee waves with scientific measurements which were recorded on a strip chart recorder of airspeed, altitude, temperature, rate of climb, three-axis accelerometers, and an experimental IR radiometer to detect turbulence ahead of the sailplane. It was first flown for ERC research during Oct – Dec 1967 in lee waves near Mt. Washington, New Hampshire. In early 1968 Explorer was ferried to Jefferson County Airport and hangered in NCAR’s Aviation Facility hangar near Broomfield, Colorado so that ERC could participate in studies of CAT in lee waves over the Rockies near Boulder, Colorado. This effort was collaborative between ERC, the Environment Science Services Administration (ESSA) and NCAR in a project led by Joachim Kuettner of ESSA and Douglas Lilly of NCAR (Kuettner and Lilly, 1968). Kuettner was at that time Director of the Advanced Research Projects of ESSA in Boulder.

In 1968 members of the ERC realized that the continued research use of Explorer along with instrument improvements would require a continuing source of funding most likely available through government agencies. The prospect of upgrading the instrumentation on Explorer and using it in a cooperative CAT field program planned for 1970, organized by Doug Lilly at NCAR, appealed to ERC as consistent with their goals for its use and of benefit to their organization. The donation by ERC of Explorer to ESSA on February 25, 1969 was prompted by the presence and active participation of Kuettner at ESSA, J. Doyne Sartor, leader of the Cloud Physics Program at NCAR, and the availability of Willem (aka Vim) Toutenhoofd to be pilot/scientist. ESSA would maintain ownership of Explorer, but NCAR would have stewardship and operations responsibilities of the sailplane with the understanding that it would remain actively used in research. It was donated to ESSA rather than directly to NCAR because at that time Congressional approval was required for NCAR to acquire a new aircraft. ESSA was abolished on October 3, 1970, and was replaced by NOAA as a branch of the Department of Commerce. Thereafter it was often referred to as the NOAA/NCAR or the NCAR/NOAA sailplane.

The choice of NCAR as the operating institution for Explorer, with Toutenhoofd as the pilot, apparently was due to a convergence of several factors. ERC wanted a long-term solution to keep Explorer active in research. Kuettner, a life-long advocate for the use of sailplanes in atmospheric research, was on the board of directors of ERC and now a director of the Advanced Research Projects within ESSA in Boulder Colorado. Doyne Sartor who came to NCAR from the RAND corporation was active in cloud physics research and was building a cloud physics program at NCAR with the intent of conducting airborne cloud physics research. Kuettner and Sartor knew each other as both had done research on thunderstorm electrification. Toutenhoofd, an accomplished sailplane pilot and scientist with a Ph.D from Australia was now a post-doctoral fellow at NCAR interested in non-linear modeling of waves and analysis of aircraft data obtained in the 1970 lee wave experiment. Kuettner and Toutenhoofd knew of each other through accomplishments in the glider organization Organisation Scientific et Technique Internationale du Vol à Voile (OSTIV). And finally, the Boulder area has both lee wave clouds and building cumulus clouds which can be investigated using a sailplane as a platform and were topics of much interest and possible research in the meteorological community.

¹A description of Dr. Kuettner’s career can be found at: https://ostiv.org/about/in-memoriam/obituary/joachim-p-k%C3%BCttner-february-24-2011.html