![]() Changes included the addition of cabin pressurization (requiring a switch to a fuselage with a circular cross-section), landing gear that folded forward into the inner engine nacelles, and a large T-tail intended to keep the elevator clear of the propwash during take-off (the Twin Otter's empennage was a cruciform arrangement). In other respects, the new DHC-7 was essentially a larger, four-engine version of the Twin Otter: the general layout remained similar, with a high aspect ratio, high-mounted wing, and similar details of the cockpit and nose profile. The Dash 7 often landed at only 900 rpm, and took off at only 1,210 rpm. In reducing the speed, this noise is reduced substantially. By using oversize propeller blades, no need exists to have the blade tip reach near the speed of sound, and the rotating speed can therefore be reduced without sacrificing thrust. Much of the problem sound from a typical propeller is generated at the tips of the blades which are rotating at or just beneath the speed of sound. To meet these new regulations, the new design used much larger (oversized) propellers geared to rotate at a slower speed than is normally designed. Propeller noise is a factor of blade length and chord and the speed at which it rotates. With new noise restrictions coming into effect throughout the 1970s, an aircraft tailored for this role would also have to be very quiet. The original specification called for a 40-passenger aircraft with a fairly short range of 200 statute miles, operating from runways only 2,000 ft long (610 m). With their excellent STOL performance, their designs could fly into smaller airports located in city centres and smaller, outlying, more austere airports having runways that the other aircraft could not easily use (unpaved, unimproved). The de Havilland Canada company personnel felt they could compete with these designs in a roundabout way. However, these aircraft were generally fairly small and served outlying routes, as opposed to the busier regional airliner routes which were already well served by larger, higher-performance turboprop aircraft such as the Fokker F27, Fairchild F-27, Convair 580, Convair 600, and Hawker Siddeley 748. In the 1960s, de Havilland Canada was already well known worldwide for their series of high-performance STOL aircraft, notably the very popular DHC-2 Beaver and DHC-6 Twin Otter. ![]() In 2006 Bombardier sold the type certificate for the aircraft design to Victoria-based manufacturer Viking Air. It first flew in 1975 and remained in production until 1988 when the parent company, de Havilland Canada, was purchased by Boeing in 1986 and later sold to Bombardier. ![]() The de Havilland Canada DHC-7, popularly known as the Dash 7, is a turboprop-powered regional airliner with short take-off and landing (STOL) performance. ![]()
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