Airplane Description

The de Havilland Canada DHC-7 ("Dash 7") was the first STOL Airplane certified according to FAR25 criteria for transport-category aircraft. It first flew on March 27th, 1975 and the first airplane was delivered to Rocky Mountain Airways on February 3rd, 1978. After delivery of the 100th airplane in 1984 further sales were slow and after de Havilland was taken over by Boeing production ceased. Many small airlines found a four-engined airliner too costly to operate and the "little sister" Dash 8 could fly most of the routes faster and more economically. City center STOLports did not materialise as expected and there simply were not enough routes to remote airfields with short runways that would still generate enough traffic to justify use of a 50-seater. The last Dash 7 (S/N 113) was delivered to Tyrolean Airways in 1989 and the programme was closed with a loss of about 145 million Euro. In recent times a number of Dash 7s were completely overhauled, re-engined and converted to O-5A, EO-5B and RC-7B surveillance planes for the US Army. 

Construction and technical Details

To achieve optimum short take-off and landing performance the aerodynamics of the airplane have to be optimised for maximum lift at minimum airspeed. If a reasonable cruising speed is desired as well, this requires sophisticated wing flaps. De Havilland developed a system of dual fowler flaps for the Dash 7. The flaps cover 75% of the trailing edge of the wing. Up to 25° they extend together and for 45° the rear part of the flaps is extended a further 20° by hydraulic jacks. At touch-down hydraulic pressure is dumped allowing the slipstream to retract the flaps to 25°, thus reducing lift and increasing brake efficiency. The same happens if the power levers are advanced beyond 50% during a go-around. Drag is reduced and the loss in lift is more than compensated by increased power. 
To achieve sufficient roll control despite the small ailerons two roll spoilers on each wing extend together with the aileron. By reducing lift and increasing drag on the inside wing in a turn they augment roll control. With all three landing gear on the ground and the power levers below 50% the spoilers extend to kill lift and increase drag on landing or aborted take-off. For the same purpose two extra ground spoilers on each wing extend on mainwheel touchdown. 

Further aerodynamic "tricks" include different wing profiles for the outboard and inboard wing, a drooped leading edge, and a multitude of small fences, fins and "teeth" to energize and control airflow. 

Four engines leave the airplane with 75% of total power and less pronounced asymmetric thrust in case of an engine failure. This reduces Vmc which in turn allows lower take-off speeds and shorter take-off runs. 

The slipstream of the propellers covers a large portion of the wing, further increasing lift. This is also valid in the opposite direction with sudden power reductions during the landing flare killing a lot of lift rather abruptly, causing "firm" arrivals and light bruises to the pilot's ego. This effect is enhanced by the adjustment of the propellers which produce drag rather than thrust at flight idle. This de Havilland technology allows precise glidepath control by rapidly varying total drag/thrust without any aerodynamic devices. (Flaps 45° and flight idle result in about -20° pitch at Vfe45). With only 1200 RPM for take-off and as little as 900RPM in cruise the Dash 7 is a good neighbour at airports in the middle of built-up areas. Props are reversible for deceleration on ground but most of the braking is performed with anti-skid equipped wheel brakes (nosewheel brakes were optional). On a maximum performance landing the airplane will be stopped before the engines even reach maximum reverse thrust. 

The Dash 7 can be certified for ILS approaches up to 7.5° - a normal ILS having 3° - and CAT 2 approaches down to 100ft/30m decision height and 300m/1000ft RVR. 

Despite all this aerodynamical tricks the Dash 7 is no thoroughbred in cruise. Cruising altitudes above 17.000ft are advisable on cool days only, with the climb rate above FL100 solidly below 1000ft/min and a maximum cruising speed of about 215KTAS. 

Take-off and landing is where the Dash 7 shines. Maximum Vr (rotation speed) is 85kts with an empty plane lifting off at 70kts. With maximum flaps Vr (speed over threshold) is a leisurly 83kts at max landing weight and 70kts for an almost empty plane. This allows for a landing roll of as little as 125m/400ft; rumour has it, that Dash 7s have turned off at by-pass intersections 70m/230ft beyond the threshold..... Spoilers, anti-skid and reverse make all this feel a lot more solid than light aircraft with comparable performance (e.g. C210, C340). 


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Technical Data
Wingspan  28,35m 93ft 
Length 24,58m 80ft 7.7" 
Height 7.98m 26ft 2" 
Wing Area 79,9m2 860sq.ft 
Wing Loading 247kg/m2 50.6 lb./sq.ft 

Operating Weight 13.2t 29.000lb. 
Maximum Take-Off Weight 19.96t 44.000lb. 
Maximum Landing Weight 19.05t 42.000lb. 
Maximum Zero Fuel Weight 17.69t 39.000lb. 

Maximum Passenger Capacity 54 Tyrolean: 48 
Maximum Fuel Capacity (Jet-A) 4.5t 9.926lb. 

Engines 4 Pratt & Whitney PT6A-50 
Maximum Take-Off Power 1120 SHP 
Maximum Continuous Power 973 SHP 
Maximum Climb/Cruise Power 900 SHP 


maximum cruising speed 231 KTAS @ 8.000ft 
  227 KTAS @ 15.000ft 
Maximum Operating Altitude with passengers 20.400ft 
Maximum Operating Altitude w/o passengers 25.000ft 
Take-Off Distance (FAR25/ISA/sea level) 689m 
Landing Distance (STOL/ISA/sea level) 594m 


