was not limited by rotor considerations, but the maximum power of the engine. Adding separate engines for additional forward thrust was expected to allow speeds as high as . During the early 1960s the company also outlined several production designs, most using twin rotors, the largest of these was the Bo 310. This design would be powered by two T55 or T64 engines, each of which drove both a Derschmidt rotor and a forward-facing propeller for additional forward thrust. The engines would be on the ends of an aerofoil section to reduce the rotor loading. Several versions of the Bo 310 were modelled, mostly passenger transports, but also attack helicopter versions. The Bo 310 would have a cruise speed of . Initial test flights of the Bo 46 with the rotors locked started in the autumn of 1963. In testing a series of unexpected new types of dynamic loads were encountered, which led to dangerous oscillations in the rotor. These did not appear to be inherent to the design itself, but they could only be cured through additional complexity in the rotor. During the same period, rotor design was moving to composite blades that were much stronger than the older spar-and-stringer designs, which eliminated the need for the complex bearing system that relieved loads. Although the Derschmidt rotor still improved performance, it appeared the added complexity was not worthwhile. Interest in the system waned, but research flights continued. The Bo 46 was eventually equipped with two Turboméca Marboré engines, allowing a speed of 400 km/h. The fibreglass bladed rotor proved to be workable however, and would go on to see wide service in the Bölkow Bo 105. Logbook Entries of Test Pilot The flight test pilot of the Bo 46 was Wilfried von Engelhardt. His log book entries are as follows: February 14, 1964: first attempt to lift off October 27, 1964: four successful hovers, duration in total 3 minutes October 28, 1964: four successful hovers. Duration in total 18 minutes. Note that the helicopter can be controlled but is sluggish October 29, 1964: two landings from higher than 3 Meters. In total 13 minutes of flight time. Aircraft on display A preserved example of the Bo 46 is on public display at the Hubschrauber Museum, Bückeburg. Specifications (Bo 46) See also Sikorsky S-69 Advancing Blade Concept References Notes Bibliography Hans Derschmidt (Derschmidt 1955), "US Patent 3,107,733: Rotary Blade System