One of the pillars of the U.S. helicopter industry, Charles Kaman, passed away on January 31, 2011. He began Kaman Aircraft Corporation in 1945 to cash in on the popular enthusiasm for helicopters that was then sweeping the United States as a suggestion of postwar prosperity. The hoped for halcyon days never did appear for the fledgling American helicopter industry, but Kaman’s company was one of the few survivors of this era to make it to the present day, and his preferred intermeshing rotor configuration and servo flap control systems are still in use. Though always a niche manufacturer, Charles Kaman supervised the development of many innovative rotorcraft technologies.
After receiving an aeronautical engineering degree at Catholic University in 1940 under the famed aerodynamicist Max Munk, Kaman went to work for Hamilton Standard, a sister company of Vought-Sikorsky, near where Igor Sikorsky was flying the first practical American helicopter. Kaman was enthralled by the new technology but developed what he thought was a much simpler approach to controlling the helicopter.
Kaman’s idea was to use “servo flaps” (similar to an aileron on an airplane), instead of Sikorsky’s swashplate system that would become the standard for most helicopters. His superiors did not appreciate his advice on Sikorsky’s work, and by 1945 Kaman had decided to strike out on his own and build his own servo-flap controlled helicopter. He thought the tail rotor was an inefficient waste of power. He saw that two side-by-side rotors angled outward that “intermeshed” (like an eggbeater), but without hitting each other, could provide lift and stability with better efficiency. Contrary to some claims, there is no evidence that Kaman borrowed this idea from Anton Flettner, whose own intermeshing helicopters, then known as “synchropters” must number amongst the first “practical” helicopters in the world.
Kaman’s first helicopters were simple designs that lacked the polish of his competitors. Forgoing cabins, the pilot and passenger of the K-125, K-190 and K-225 (so designated because of the horsepower of their powerplants) rode in the open with intermeshing rotors whirling uncomfortably overhead. By the late 1940s, Kaman had eked out a few sales for agricultural dusting (for which the chaotic downwash of the intermeshing system was ideally suited). Like the other successful American helicopter manufacturers – Bell, Hiller, Piasecki and Sikorsky – Kaman soon realized that only the military could sustain his company with sufficient orders for the foreseeable future. Fortunately for him, the outbreak of the Korean War led to expanded military interest in helicopter development. An initial order by the U.S. Navy and Coast Guard for three open-cockpit K-225s soon led to an additional order for a new closed-cockpit training variant. The HTK-1, as it was designated, was a docile, stable platform that the Navy thought was well-suited to novice rotorcraft pilots. The ensuing orders began to put Kaman on a sound financial footing.
Ultimately, the HTK-1 was not a particularly successful training helicopter as it was too easy to fly and did not perform like most operational helicopters, but a slightly upgraded version was selected by the U.S. Marine Corps as its primary medical evacuation helicopter at the end of the Korean War to replace its underpowered Sikorsky HO5S-1s. This model, the HOK-1, soon evolved into the H-43 for the Air Force where it was soon mated with a the Lycoming T53 gas turbine to produce the H-43B, the U.S. Air Force’s preferred crash and recovery helicopter for much of the Vietnam War era.
Kaman is often best remembered in the rotorcraft community for being the first to apply a gas turbine to a conventional helicopter gearbox (France’s Sud Ouest was the first to successfully fly a turbine powered helicopter, though it drove a compressor that supplied tip-jets). Kaman launched this new era when one of the Navy’s K-225s was re-engined in late 1951 with a Boeing 502-2 turbine. Kaman soon followed this up in March 1954 with the first twin-turbine helicopter – modification of a HOK-1 (also with 502-2s).
Kaman Aircraft did well in the 1950s and ‘60s with groundbreaking research and development programs, including a rotary wing delivery system for nuclear weapons and perhaps most significantly for the present-day, the first remotely-piloted full-scale helicopter. In August 1952, Kaman received a contract from the Office of Naval Research to develop this technology, and by April 1956 an HOK-1 was flying a full-flight profile by remote control. Today, Kaman is still at the forefront of this technology with examples of an unmanned K-1200 preparing for operational evaluation with the U.S. Marine Corps.
1956 marked something of a departure for Kaman Aircraft as it competed for a new U.S. Navy utility and search and rescue helicopter. Kaman discarded the intermeshing rotors that had become a proprietary signature in favor of the conventional single main rotor and auxiliary anti-torque tail rotor, though the new design, the HU2K-1 retained the servo flap control system. Later to become the SH-2, this aircraft became a mainstay of U.S. naval aviation through the 1990s, and proved to be well adapted for the anti-submarine warfare mission though it often operated in the shadow of the Sikorsky SH-3, which performed a similar mission. The SH-2 enjoyed some foreign sales with use by Australia, New Zealand, Egypt and Poland. In the 1960s and ‘70s, Kaman used the SH-2 as a basis for another advanced ONR program – the Circulation Control Rotor. Though this boundary layer system proved to offer improved rotor efficiencies, it complexity and manufacturing challenges have prevented its realization in practical form.
Kaman’s product line is still moving forward with the K-1200, an intermeshing “synchropter” that represents a gradual evolution from a design that first flew in 1947. The K-Max, as it is known, is one of the most unusual aircraft on the market, designed exclusively as a single-seat external load platform. Charles Kaman’s professional interests extended well beyond aircraft. He founded a number of subsidiaries, including Ovation Guitars. An avid musician, he observed that the techniques required to eliminate vibration from rotor blades were also useful in making better-sounding acoustic guitars and he produced the first practical electrically amplified acoustic guitars. He founded Fidelco Guide Dog Foundation for the blind and police along with his second wife, Roberta Hallock Kaman.