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Aviation History
1982
1982 - 0017.PDF
that for the 757 in Renton, and the 767 group up the road at Everett. A short-haul airliner like 757 spends a lot of each flight climbing and descending, and the cruise is comparatively short. Boeing calcu lates that climb consumes 60 per cent of the fuel that a 757 would use on a 500 n.m. trip—an important influence on design. The 757 wing uses more or less the same aerofoil section as the 767, ex cept that it is smaller in size and is thinner where it joins the narrowbody fuselage. The Boeing section is aft- loaded, with a comparatively flat top, and a small undersurface cusp to wards the trailing edge (an aft-loaded wing is essentially the same as a supercritical one). Benefits include delayed Mach drag-rise, less wing sweep, and an efficient wing structure. Both new Boeings are designed for a Mach 0-8 cruise, but the 757 has significantly less wing sweep (25° com pared with 31-5°). The lower sweep can be tolerated without much drag penalty because of the 757's lower average speed. It also allows Boeing to dispense with the complexity of in board ailerons (the wing is stiffer, raising aileron-reversal speed). Like its sister, the 757 has a generous wing, the root of which is particularly wide. This arrangement eases accommodation of the under carriage, and a side benefit is margin for stretched versions. The 757 wing- span is also larger than that of the 727, which reduces induced drag. Shorter sectors allow the 757 to make use of sophisticated high-lift devices, without cruise-drag penalty. The result is double-slotted flaps operated by a track and carriage, plus full-span slats. The 767 also has full-span slats, but employs a simpler flap linkage, and only the inboard surfaces are double-slotted. Two engines are natural in the drive for fuel efficiency, and it makes sense to relieve bending moment by hanging them on the wing. The adop tion of a low tail also follows 767 practice. It allows the aircraft to be kept shorter for a given passenger load, and eliminates the chance of in effective pitch control at nose-up attitudes. As with the 767, the airframe de sign goal is 50,000 flights, equivalent to about 20' years of service. Struc tural philosophy is also similar for the two types, with Boeing preferring the built-up approach to Europe's emphasis on integrally machined parts. About 35-40 per cent of the 757 was created by computer aided design (CAD), used mainly as a draughting aid. Boeing's first major use of CAD was in the 767, which used a similar amount although less was originally intended. Systems commonality between the 757 and 767 includes air conditioners, auxiliary power unit, the electrical power system, and hydraulic parts. 60 50 2 40 o o a = 30 •a ra o >. 20 10 c 178 Passengers ^V^vfxt; iSfc. **N ^SNS"^\ \\ RB211-535C ^'^AX "W PW2037 >\ \ V \\ \ \ i i i i i i i \\ i W i ) 1j000 2,000 3,000 4,000 Still air range (n.m.) 9,000 5 8000- O) •^ 7,000 1 •g 6,000 0) ™ 5,000 240,000 lb MTOW- 220,0001b MTOW < —- Improved climb performance l _L J_ JL 1,000 2,000 Still air range (n.m.) 3,000 6,0001— 3000 140 150 160 170 180 Landing weight(1,000 lb) 190 200 Top Payload-range, assuming a long range step-cruise and standard day. Centre Take-off performance at sea /eve/ and 29°C, assuming a load of I78 passengers and long range step-cruise. Above Landing requirement at sea level. All performance data is for the 757 four-door version (see cutaway), and is based on US domestic rules. The alternative version has three doors and two overwing exits on each side of the fuselage FLIGHT International, 2 January 1982 15
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