Saturday, 14 December 2013

Beechcraft Model 76 Duchess Four Place Light Twin Aircraft

Beechcraft Model 76 Duchess Four Place Light Twin Aircraft

Introduction :

The Beechcraft Model 76 Duchess is an American twin-engined monoplane built by Beechcraft. The Duchess is a cantilever low-wing monoplane with an all metal structure, four seats, retractable tricycle undercarriage and a T-tail. It is powered by one 180hp (134kW) Lycoming O-360-A1G6D on the left wing and one LO-360-A1G6D on the right wing, which drive counter-rotating, constant-speed two-bladed propellers. Piper was producing the Seneca  and their brand new Seminole, Cessna had their very successful twin engine 310, Grumman American had a similar twin engine Cougar and Beech had their high end, high performance Baron. Admittedly not in the same league as the others. Beechcraft marketing department wanted a modestly priced light twin to compete in the same price category so the Beech Aero Centers could also offer twin engine ratings at competing prices. Beech engineers started with the basic Musketeer, added a T tail, twin Lycoming counter rotating 180 hp engines with constant speed props and kept the interior of the Musketeer with four seats unlike the six seats offered by the Seneca. 

Piper’s new T tail Seminole also had four seats, twin 180 hp Lycoming engines and was doing very well in  market place. Flight schools scooped up most of Piper’s production runs. The new Beech along with the Piper Seneca and Seminole light twins would meet head on in the market place. Eventually, the flight schools would purchase both, but the Piper Seminole which became the light twin trainer of choice. I am very familiar with this subject as we were operating four flight schools at this time and we used Piper Senecas, far from ideal due to empty seats we had to pay insurance on and the 200 and 210 hp engines installed on the Seneca models. The first Senecas with the 200 Lycoming non turbo engines was our trainer of choice, and the airplane was an excellent trainer due to its slightly poor single engine performance and very poor cross wind and engine out performance. Easy flying twins do not make a good trainer.

History :  

The Model 76 Duchess was one of a new class of light four place twins developed in the mid 1970s. The prototype of the Duchess, designated the PD-289, made its first flight in September 1974. However a further 30 months of development work passed before the first production Model 76 took to the air on May 24 1977. Certification was granted in early 1978, with first deliveries commencing in that May. The Duchess was positioned between the Bonanza and the Baron in the Beechcraft model range. Beech developed it for its Beech Aero Centers, and pitched it at the personal use light twin, light charter and multi engine training markets. Design aims included good low speed and single engine handling.

Aside from the prototype PD-289, no variations of the Duchess 76 were built before production ended in 1982. All Duchesses therefore feature two Lycoming O-360 engines (with counter rotating propellers), a T-tail (incorporated to reduce control forces and improve elevator response), entry doors on either side of the cabin and electric trim and flap controls (the prototype PD-289 featured manually operated flaps). The fuselage was based loosely on the single engine Sierra's, and like the Sierra and its Musketeer predecessors featured a bonded honeycomb construction wing. The Sierra and Duchess also share common structural components. Beech offered three factory option packages on the Duchess - the Weekender, Holiday and Professional - and 11 factory installed avionics packages.

Beech developed the Duchess for low cost, high volume production, but the falling popularity of light twins, an economic recession and crippling product liability laws in the USA all contributed to a relatively short production run which wound up in 1982. Sales had peaked in 1979 when 213 were built.

Like its contemporaries the Grumman/Gulfstream American Cougar and Piper Seminole, the Duchess' success was hampered through unfortunate timing. Ever increasing advances in engine efficiency, safety and reliability led to a rise in popularity for big high performance singles such as Beech's own Bonanza series, which lacked the maintenance overheads of two engines, but had comparable performance. However, to a greater extent than the Seminole and Cougar, the Duchess enjoyed some success as a twin engine pilot trainer, a role in which it is widely used for today. 

Specifications Beechcraft Duchess Model 76 :

  -  Capacity: Pilot and 3 passengers
  -  Length: 29ft 0½ in. (8.86 m)
  -  Wingspan: 38 ft 0 in (11.58 m)
  -  Height: 9 ft 6 in (2.89 m)
  -  Wing area: 181 sq ft (16.81 m2)
  -  Airfoil: Root NACA 63A413.2 Tip NACA 63A415[6]
  -  Aspect ratio: 7.973:1
  -  Empty weight: 2,460 lb (1,116 kg)
  -  Max. takeoff weight: 3,916 lb. (1,769 kg)
  -  Engines: Lycoming O-360-A1G6D air-cooled flat-four, 180 hp (134 kW) each

Performance :

  -  Never exceed speed: 171 knots (197 mph, 317 km/h)
  -  Cruise speed: 158 knots (182 mph, 293 km/h) at 10,000 ft (3,050 m)
  -  Stall speed: 60 knots (69 mph, 111 km/h) flaps down, (IAS
  -  Range: 780 nmi (898 mi, 1,445 km) at 12,000 ft (3,660 m) (econ cruise) – 151 knots
  -  Service ceiling: 19,650 ft (5,990 m)
  -  Rate of climb: 1,248 ft/min (6.3 m/s)

Beechcraft Model 76 Duchess Four Place Light Twin.


Preeti Bagad [BE(CS)] 
SW Engineer Cum Blogger

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