Ihab Salloum[ad_1]
The increasing demand for Boeing 727 routes, consistently exceeding the capacity of the stretched -200 series version, along with advancements in technology, called for either a larger variant of the tri-jet or a completely new design.
The first attempt at a larger variant involved stretching the fuselage to accommodate 189 passengers and using three refanned, high-capacity Pratt and Whitney JT8D-217 engines with 20,000 pounds of thrust each. Known as the 727-300B, it made its debut at the 1975 Paris Air Show. United Airlines showed initial interest, but other carriers believed it needed quieter and more advanced powerplants.
A major redesign, referred to as “7N7,” retained the 727’s nose, forward fuselage, and t-tail while featuring a further fuselage stretch and a new technology wing. Like the smaller 737, it had two pylon-mounted engines, with options including the Pratt and Whitney JT10D-4, Rolls Royce RB.211-535, and General Electric CF6-32. The wing had sufficient fuel tank volume for long-range flights, unlike its predecessor.
To cater to passenger comfort on intercontinental routes, a concept with a wider fuselage cross section for twin-aisle accommodation was briefly explored. This would have provided increased comfort and made it more competitive with the upcoming Airbus A-300 on short domestic US routes. It would have also eliminated the need for excessively long fuselages to accommodate future capacity increases. However, the width was deemed impractical, as it resulted in weight and drag issues and was still too narrow to accept standard baggage and cargo containers.
Returning to narrow body studies, Boeing proposed an advanced, large-capacity 727 that featured a new wing, two turbofans, and a 170-passenger capacity. It shared many commonalities with the simultaneously-developed twin-aisle 7X7 design. This new aircraft, designated the 757, became Boeing’s fifth major commercial jetliner with the seven-dash-seven model sequencing numbers, following the 707, 727, 737, and 747. It offered a 15% lower fuel consumption compared to the 727 it aimed to replace, while also allowing for potential future enhancements in weight, range, and capacity.
In an effort to reduce development costs, Boeing aimed for maximum commonality between the 757 and its widebody twin-aisle counterpart, the 767. Both aircraft shared many components including the forward nose sections, windscreens, main undercarriage units, avionics, and flight deck systems. This offered airlines the ability to have a common type rating, allowing them to operate both aircraft efficiently. The 767-style t-tail was eventually replaced with the more conventional 767 low-wing configuration for increased commonality.
Eastern Airlines and British Airways placed launch orders for the 757, with Rolls Royce RB.211-535C engines, in August 1978. The aircraft featured a 196-passenger capacity and was optimized for 2,000-nautical mile flights, with the option to increase range to 2,500 miles with a higher gross weight. Advanced composite and aluminum alloy construction reduced the structural weight and lowered seat-mile costs.
The 757 had a 155.3-foot overall length and a two-spar wing with a 124.10-foot span and a 1,994 square foot area. It featured full-span leading edge slats, double-slotted trailing edge flaps, and ailerons for lift and roll control. Power was provided by two high bypass ratio turbofans mounted on the wing’s leading edge, offering bending movement relief.
The Rolls Royce RB.211-535C, a variant of the RB.211-22B engine used on the Lockheed L-1011 TriStar, was chosen by launch customers Eastern and British Airways. The more advanced RB.211-535E4 version offered improved fuel efficiency and performance.
Another powerplant option was the Pratt and Whitney PW2037, which had a bypass ratio of 5.8:1 and was specified by American Airlines and Delta. It featured a two-shaft turbofan design with improved high-pressure compressor efficiency.
The 757’s fuel was stored in two wing-integral tanks and one center section tank, with the outer tanks burned last to maintain wing bending movement relief. The aircraft had a conventional low-wing tailplane and a tricycle undercarriage with dual-wheeled nose gear and quad-wheeled main units.
Inside the aircraft, the cockpit featured two operating crew seats and one observer seat. The cabin was 118.5 feet long, 11.7 feet wide, and seven feet high, resembling a widebody aircraft with spacious overhead storage compartments, a sculpted ceiling, recessed lighting, molded sidewalls, and slimline seats. Various seating arrangements were available depending on the airline’s preferences.
All in all, the Boeing 757 was a technologically advanced, high-capacity aircraft that aimed to meet the increasing demands of airlines while offering improved fuel efficiency and passenger comfort.
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