Russian-born Igor Bensen is probably the world's leading exponent of the lightweight, home-built rotorcraft. After working for many years with General Electric and later with the Kaman Aircraft Corporation on rotorcraft research, he formed the Bensen Aircraft Corporation in 1953. Its first product was the single-seat, ramjet-powered Mid-jet, tested in 1954, and this was followed in 1955 by the B-4 Sky-Scooter which was powered by a 40hp Nelson engine and could carry a pilot and one passenger. Bensen's current range of do-it-yourself helicopters and autogyros stem from the B-5 Gyro-Glider of 1954, which was a single-seat rotor-kite towed into the air at around 30km/h and obtained its lift by the flow of air over its autorotating rotor. From this factory-built prototype, Bensen evolved the B-6 and B-7, and from these has come the standard production model the B-8. This has a somewhat more sturdy construction and is available as a factory-built machine or in kit form for amateur construction. Two water-borne versions of the B-8 are also available: the B-8B Gyro-Boat which has a boat-type hull and twin outrigged stabilising floats, and the B-8W Hydro-Glider mounted on twin floats.
Powered autogyro versions of the auto-kites have been developed simultaneously, the first of these being the B-7M which flew for the first time on 6 December 1955. This was followed on 8 July 1957 by the first B-8M (M = motorised) and by the first production B-8M on 9 October 1957. The B-8M is normally powered by a 72hp McCulloch piston engine. Optional features include a 90hp McCulloch engine and a mechanical rotor drive enabling the autogyro to make jump starts. A float version of the B-8M is known as the Hydro-Copter. In recent years Igor Bensen has developed a multi-engined version of the B-8M known as the B-11. The original B-11 of 1964 has now been superseded by the B-11M Kopter-Kart. This has a generally similar airframe to the B-8M, but is powered by six 10hp McCulloch MC75 go-kart engines mounted in two rows of three behind the pilot's seat and driving vertical propellers in addition to the 2-blade rotor. The engines can be controlled separately or collectively and level flight can be maintained with only four engines operating.
In addition to the autogyros, Bensen has also produced two helicopter designs, the first of these being the B-9 Little Zipster, a light-weight single-seater with a 60 or 70hp Mercury engine and twin 2-blade coaxial rotors. This has now been superseded by the B-13, flown for the first time (N4625S) on 4 March 1963. This has a single two-blade main rotor, driven by a 70hp Mercury engine, and an anti-torque tail rotor driven by two 10hp West Bend piston engines. Two VTOL lifting platform designs have also appeared in recent years. The B-10 Prop-Copter was flown in prototype form (N56U) on 6 August 1958 and was powered by two 72hp McCullochs, each driving a horizontal propeller. It has since been abandoned in favour of the B-12 Sky-Mat, which flew for the first time on 2 November 1961. In its latest form the Sky-Mat consists of a trellis-like open metal framework with ten small 2-blade rotors, each driven by a 10hp West Bend engine, and a pilot's position in the centre. The Sky-Mat is fundamentally a ground effect machine, being designed for an agricultural role with a normal operating height of only 1m from the ground, although it can rise to clear obstacles up to 5m.
While development of the B-11M, B-12 and B-13 continues, main output of the Bensen Aircraft Corporation continues to be the powered and unpowered versions of the B-8, many thousands of which have been sold in factory-built or kit form in the United States and other parts of the world.
K.Munson "Helicopters And Other Rotorcraft Since 1907", 1968