43 years ago on this day, the De Havilland Canada DHC-7 (Dash 7) entered service with Wardair Canada Ltd. The initial development for the Dash 7 started in 1972 and the first flight was on the 27th of March 1975. The heritage of the aircraft goes back to the 1960s, with other STOL aircraft from the De Havilland Canada factory, namely the DHC-2 Beaver and the DHC-6 Twin Otter.
Other aircraft manufacturers offered (for the time) high-performance turboprops to the airlines, what was lacking, from the point of view of De Havilland Canada, was Short Take-Off and Landing (STOL) capability. Besides the STOL capability also the noise footprint of aircraft became more and more important in the 70s, especially in the envisaged STOL roll which would bring the aircraft into smaller airports close to or inside city boundaries The original specifications for the aircraft were for a 40 seat aircraft operating from 2000ft (610 m) runways.
The amount of thrust from the propellor depends on the combination of several factors like blade length, blade chord, angle of attack and rotational speed. The amount the noise a propellor produces for a big part is originating from the tip that can be operating close to the speed of sound. To counter this the Dash 7 was fitted with oversized geared propellors that would rotate and a low rpm, to keep the noise from the propellors down. The constant speed props of the Dash 7 normally operated in a 900 rpm (landing) to 1200 rpm (take off) range. The Dash 7 is based on the Twin Otter, although with 2 additional engines, a circular fuselage, larger tail section retractable gear etc, it looked completely different.
To get the most out of the STOL capabilities of the Dash 7 the ailerons were shortened to enable larger flap panels to be fitted, to keep roll control at an acceptable level, roll spoilers are fitted.
Depending on the speed of the aircraft only the outboard spoilers operate ( < 130 kts) or both inboard and outboard spoilers operate ( > 130 kts). The double slotted Fowler flaps create the huge amount of lift required for take-off and landing. The normal flap setting for landing was 45 degrees giving the aircraft a Vref between 70 and 85 knots. When the weight on wheels is sensed on landing the flaps will automatically retract to 25 degrees. The initial development for the Dash 7 started in 1972 and the first flight was on the 27th of March 1975. A total of 14 different versions were produced, for both civil as military use. Aircraft specifications:
Capacity: 50 passengers
Length: 80 ft 7.75 in (24.5809 m)
Wingspan: 93 ft 0 in (28.35 m)
Height: 26 ft 2 in (7.98 m)
Wing area: 860 sq ft (80 m2)
Empty weight: 27,690 lb (12,560 kg)
Max takeoff weight: 44,000 lb (19,958 kg)
Powerplant: 4 × Pratt & Whitney Canada PT6A-50 turboprop engines, 1,120 shp (840 kW) each Maximum speed: 231 kn (266 mph, 428 km/h)
Range: 690 nmi (790 mi, 1,280 km) (with 50 passengers and baggage)
Service ceiling: 21,000 ft (6,400 m) (25,000 ft (7,620 m) without passengers)
Rate of climb: 1,120 ft/min (5.7 m/s) (en-route, flaps and landing gear up)