Dash 8 Achieving Strong Sales

From the starting point of a twin engined version of the Dash 7, several changes were made to produce a more up-market product for an increasingly sophisticated commuter industry. Competition from entirely new designs such as the Embraer Brasilia and the Saab Fairchild SF340 showed that more speed and better fuel economy would be required. The extreme short field capabilities of the Dash 7 were traded for other more saleable characteristics. New engines of greater power replaced the PT6’s giving higher cruise speed and lower specific fuel consumption. With the higher speeds it became necessary to reprofile the nose and cockpit window area to reduce both drag and interior noise. The high wing layout was retained to give good propeller clearance and easy loading and unloading. Let us look at the result in more detail.

The airframe relies more on good conventional engineering practices than exotic materials. The primary structure is aluminium, although featuring extensive metal-to-metal bonding. Composites are used more for secondary structures to ease construction and save weight. Whilst the structure is a little heavier than that of some of its competitors it should prove extremely durable in service. The airframe is designed to be crack free for 40,000 hours or 80,000 flights and to have an economic life of at least 80,000 hours or 160,000 landings. The high wing. T-tail configuration has almost become a company trade mark on recent designs. but is well suited to commuter operations to sparsely equipped airports.

The wings feature large single-slotted flaps which provide sprightly if not STOL runway performance. Roll control is shared between rather short span outboard ailerons and differentially operated outboard spoilers. Once on the ground these outboard spoilers revert to a lift dump/speed brake function, augmented by four additional ground spoilers inboard. Pitch control is achieved through manually operated elevators, with aerodynamic assistance from a spring tab. The rudder, however, is hydraulically powered and features two serially hinged panels operating much in the manner of those on the Boeing 747SP or DC-10. Any displacement from the central position on the forward rudder panel produces a larger displacement in the same direction on the rear panel, giving very powerful rudder response. Pneumatic-powered de-icing boots are fitted to the leading edges of the wings and the horizontal stabilizer.

On the standard Dash 8-100 series, power is provided by two Pratt & Whitney Canada PW120 turboprop engines of 2000 shaft horsepower driving 13 foot diameter four bladed Hamilton Standard propellers. The three-shaft PW120 engine features two centrifugal compressor stages, each driven by an individual single stage turbine. A two stage free power turbine drives the propeller through a reduction gearbox giving a propeller speed of 1200rpm for takeoff and climb and 1050rpm for cruise, resulting in commendably low noise levels, both inside and out. The constant-speed propellers are capable of both full feathering and beta (reverse) pitch operation. The underslung engine nacelles house the main landing gear when retracted and the thru-flow exhausts are mounted above the rear of these nacelles to further reduce ground noise. A standard fuel capacity of 825 US gallons is housed in integral wing tanks between the front and rear spars outboard of the engines. Optional long-range tanks containing an additional 692 US gallons may be fitted onboard of the standard tanks. Engine fire detection and extinguishing systems are fitted as standard.

Electrical power is provided by two 28v DC starter/generators augmented by two transformer rectifier units powered from AC generators driven from the propeller reduction gearbox on each engine. These AC generators also provide AC power for propeller and windshield de-icing and for fuel pumps and fans. Two separate hydraulic systems are provided, each with its own engine driven pump and standby electric pump. Hydraulic power operates the spoilers, rudder, flaps, wheel brakes, undercarriage extension and retraction and nosewheel steering, with sufficient redundancy to cover the loss of one system without endangering the aircraft. While the original design of the undercarriage downlock system has proved to have been troublesome in service, de Havilland representatives assure us that the problem is now completely cured with a new positive double-acting hydraulic downlock.

The standard avionics fit offers dual conventional electromechanical instrumentation for the flight crew, although most operators have opted for the more advanced Sperry Electronic Flight Instrumentation System. Whilst initially, the EFIS had reliability problems which caused quite a bit of adverse comment from early operators, the equipment is now settling down in service and doubtless will become the industry standard. This writer had the opportunity for a couple of jump seat rides in an early demonstration aircraft (No. 4) which was fitted with EFIS on the left hand instrument panel and the conventional instruments on the right. The 747 aircraft I normally fly have only conventional instruments, but after a short time to become familiar with the symbology, the advantages of the EFIS display in providing a large amount of information in condensed form became very clear.

The standard aircraft provides accommodation for 36 passengers in considerable comfort with a 31″ seat pitch arranged four abreast. The seat design allows exceptional legroom, my companion on the demonstration flight was well-known aviation writer John Stackhouse, who is almost tall enough to need oxygen with his feet on the ground. As hard as he tried he could not bang his knees on the seat back in front! The 36 seat configuration leaves room for a toilet, coat closet, cabin attendants seat and a small buffet area. Access is via an integral airstair door at the front left of the cabin while three additional cabin emergency exits are provided. Fourteen overhead lockers each accommodate the equivalent of two Samsonite briefcases. The rear baggage hold of 300 cubic feet volume carries a maximum load of 2000Ibs with access through an external baggage door on the left hand side. The bulkhead separating the baggage compartment from the passenger cabin may be moved forward to reduce the passenger capacity to 28 or 20 passengers allowing additional freight to be carried. With removal of the seats and the bulkhead, the aircraft can be used purely for freight. For any of these extended freight configurations optional heavy duty flooring and tie-down points are available.

For passenger comfort engine bleed air is conditioned through an air cycle machine and heat exchanger then used to pressurise the cabin, allowing a cabin altitude of 8000 feet at a cruise altitude of 25,000ft. An optional auxiliary power unit can provide bleed air for air-conditioning and electrical power on the ground or alternatively, ground power and ground-conditioned air can be supplied to the aircraft. As with earlier de Havilland Canada designs, military and corporate versions of the Dash 8 are available and have already been ordered in small numbers.

Over the last year DHC have been offering a stretched version known as the Dash 8-300 seating 50 passengers. As sufficient orders have been received a decision has been made to stretch the No. 1 prototype by 11½ feet with plugs fore and aft of the wing to produce an aerodynamic prototype for the 300 series. It should fly in the first half of 1987 leading to certification and initial customer deliveries in the middle of 1988. Engines have been upgraded to PW124s of 2400 shaft horsepower to retain similar performance capabilities to those of the standard aircraft. Empty weight has increased by 2610lbs but maximum takeoff and landing weights have increased by 6000lbs giving a useful increase in payload. An improvement of 16% in seat mile costs has been achieved at a cost of only 12% in aircraft mile costs. Recent orders show that operators can certainly see the advantages of a mixed 100/300 series fleet with the commonality of spares and crewing.

My impressions on a couple of flights in the early demonstrator aircraft (No. 4) which was the first furnished example, were of a very solidly built, quiet and comfortable aircraft. Low propeller speed obviously contributed to the overall low noise and the passenger comfort items were outstanding. Runway closure at Camden combined with a very tight tour schedule, prevented a more detailed flight evaluation but DHC test pilots Mick Saunders and Dick Hutton showed obvious enthusiasm for their charge which has subsequently proved justified in the marketplace. Perhaps another day?

The Dash 8 has experienced a few problems early in its in service life. The most serious has been a couple of undercarriage collapses probably caused by surges in the hydraulic system. DHC states that the problem is completely cured with the new positive downlock and as of September 1986, only a handful of early aircraft remained to be modified. Problems with the Attitude and Heading Reference System have required modification to the logic circuits and the system seems to be settling down with maturity. As these and a couple of other problems subside operator confidence is increasing and several have placed additional orders. Passenger acceptance is reported to be very high as in many cases the aircraft replaces smaller, often unpressurised, types.

The future for the Dash 8 programme looks rosy. The Boeing takeover has given the programme long-term stability which is already showing up in the order books. DHC people at Farn-Borough last year commented to me on the positive effects of working as part of the world’s largest commercial aircraft manufacturer. There is no doubt that the Boeing and DHC lines of aircraft are complementary.

That the Dash 8 order book at the moment is extremely healthy is perhaps a gross understatement.