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Aviation History
1982
1982 - 0369.PDF
twice the size of the -200 slat, it in creases the chord of the entire wing by an average of 4 per cent. Its un usual droop-snoot profile, creating a local reflex camber under the leading edge of the wing, was hammered out in 7,500hr of tunnel testing; Boeing says that the new slat is worth around 4,000ft of cruising altitude at long-range cruise speed, and knocks 5kt off the approach speed (both figures are compared to a baseline 737-300 with a -200 slat). The most recent tunnel testing, concluded last autumn, is claimed to have substanti ated a 4 per cent improvement in aerodynamic efficiency, but unques tionably its main contribution is in countering the tendency of added weight and pay-load to increase approach speeds and reduce the buffet-limited cruise altitude. The new boom A visually striking feature of the new wing is the anti-flutter boom under each extended tip. The booms are needed because the forward- slung nacelle "bobs" on its pylon and twists the wing, unlike the nacelle of the basic -200. Most aircraft with pylon engines are designed with suffi cient torsional stiffness to counter nacelle bobbing, but the basic 737 wing did not need it. Now, it is far cheaper (if not so tidy) to add inertial resistance with weighted booms than to start designing more stiffness into the wing box. This particular use of flutter booms came out of the pro digious Boeing corporate memory, having first been considered for the original 707. Apart from the wing modifications, the shape of the 737 is changed rela tively little. The fuselage is stretched by three standard frames aft of the wing and two extended frames for ward. The tail tip is extended, as is the elevator span, to improve fore-and-aft loading flexibility, and the dorsal fin is slightly enlarged to cope with greater asymmetric thrust potential. The nose landing gear pivot is moved a few inches lower, to yield a little extra ground clearance for the engines while using an identical re traction geometry. Beneath the skin the 737-300 will benefit from a general structural up grade to the standards of the 757 and 767. Boeing has now decided to build the rudder, dorsal fin extension, ele vators, ailerons, and spoilers of car- bonfibre: CF cowlings have always been a feature of the design. Addi tionally, the interior will be based on components developed for the 757, using crushed core honeycomb materials. It will feature longer bins and revised lighting. The new compo site components and new interior will be standardised on the 737-200 (with the exception of convertibles) from late 1983. Another internal change is a new and tidier air-conditioning sys tem, externally detectable because one cabin window has been removed to make way for a larger air duct. Longer life The 737-300 will also use some of the aluminium alloys introduced on the new Boeings, as well as some of the techniques adopted on the 757 and 767 to meet operator criticisms of Boeing's structural longevity. These include new adhesive bonding techniques developed over the past ten years, and a more liberal touch of enamel and wet sealant in the bilges. The structure will have to work harder than Boeing envisaged in the early 737-300 brochures, aimed at the short-haul US regional market, because both take-off and zero-fuel weights have been substantially in creased to make the aircraft more attractive in longer-range, high- density-seating markets like the Euro pean inclusive-tour business. Boeing comparative studies show the new aircraft with 140 seats against 120 in the standard 737. In terms of performance, it will carry its greater payload and still do nearly anything that the standard aircraft can do. Landing field length is 500-600ft greater, under comparable conditions. BOEING 737-300 Wing tip flutter boom Fin extension \ y W\ ^x& fiO in hnfh' ovtoriQirm ^•*^X\>-"''^ Modified slat aerofoil % Y\\ ^-^3?^i" ^10^^"^ \$i$i: / „ccC ^ Px i3SE^^— 44 'n body extension Lengthened & repositioned nose undercarriage strut 1 \o\ j 7 X Tip extension ^syS Revised flipper flaps ^<3^p<\ . ^\ Strengthened New engine installation CFM 56-3 or RJ-500 Revised flap track fairing wing-""'^ FLIGHT International. 13 February 1982 355
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