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Aviation History
1975
1975 - 0005.PDF
FLIGHT International, 2 January 1975 -1- **5Sssss^g& POT DC-9-50 FLIGHT REVEALS AERODYNAMIC FEATURES THE FIRST DC-9-50 made its maiden flight on December 17 from Long Beach. The stretched DC-9 has a fuselage length of 133-6ft, some 8ft longer than the DC-9-40, and is unique among subsonic airliners in having small strakes on the forward fuselage (see photograph). McDonnell Douglas says simply that the strakes help stability at low speeds. The first flight lasted 5hr lOmin, took the aircraft to 350ki and 35,000ft, and was used to check on the per formance and control characteristics of the engines, auto pilot and major systems. The flight was described as "flawless" and was monitored in real time by the Long Beach flight-test department. The first DC-9-50 is equipped with an anti-spin tail parachute for the test programme; two aircraft have been assigned to certifi cation flying. McDonnell Douglas will begin flight-testing a shorter- bodied DC-9 powered by refanned JT8Ds at the end of this month or early in February. Although Pratt & Whitney is to go ahead with development of a 19,0001b- thrust refanned version of the JT8D with the new Boeing 727-300B in mind (see Flight for December 26, page 898), McDonnell Douglas says that it has no plans at present to offer the refanned engine as an option. In the middle of last year McDonnell Douglas made a number of presen tations of a further-stretched model of the DC-9 family, the Series 60, powered by two 22,0001b-thrust CFM56 engines. McDonnell Douglas says the airlines have expressed "con siderable interest" in stretched versions of the DC-10 shown in model form at Farnborough. The company declines, however, to name any potential customers. The stretched DC-10 is seen as the next likely development of the trijet and wind-tunnel testing is well under way. Civil applications of the military McDonnell Douglas H. H. "Knick" Knickerbocker was at the controls for the maiden flight of the DC-9-50. A. P. "Flip" Johnson was co-pilot and David Houle flight-test engineer. The latest version of the McDonnell Douglas twinjet has a number of improvements to systems and avionics. Certification and first deliveries, to Swissair, are planned for July. The DC-9-50 has to its credit 34 orders plus 29 conditional firm orders and options from eight airlines and potentially worth $650 million. The American Air Line Pilots' Association has decided that it will operate the DC-9-50 with two crew if so certificated by the Federal Aviation Administration AIR TRANSPORT YC-15 AMST (Advanced Medium Stol Transport), which will fly in the third quarter of 1975, are under study. The first of two prototypes is now structurally almost complete with one engine in place and the horizontal stabiliser is about to be added. • The shedding of vortices from the forward portion of long and slender fuselages at incidence can cause lateral instability which is aggravated if the aircraft is flying at small angles of yaw. This condition only occurs at low speed and few aircraft have a sufficiently high overhang ratios (the ratio of length of fuselage ahead of the centre of gravity to fuselage diameter) to give a problem. The rear-engined DC-9-50 has an overhang ratio of about 6:1, very similar to that of the long-bodied, wing-engined DC-8-61/63, which was not fitted with strakes. Small, very- low-aspect-ratioi forward fuselage strakes act to prevent any lateral instability by fixing the vortex pattern. Con corde is the only other airliner to make use of such strakes and the DC-9-50 is the first subsonic airliner to follow suit. The DC-9 strakes are probably insufficient in area to provide anything but a minimal nose-up pitching moment or contribution to lift during low-speed flight and there fore serve a completely different purpose from that of the retractable foreplanes on the Tu-144. The primary role of the latter is to provide a trimming force which also contributes to lift. The strakes were not shown on earlier general-arrangement drawings of the DC-9-50 (although they have been apparent on drawings of the longer DC-9-60 project shown to airlines) and were probably added after wind-tunnel testing. LOCKHEED OFFERS LONG-RANGE -250 TRISTAR LOCKHEED has made presentations to Aeroflot, and to airlines in the West, of a new uprated version of the TriStar. Designated the L-1011-250, the latest TriStar variant would have a gross weight of 484,0001b, some 18,0001b greater than the L-1011-200. Lockheed is already selling the L-1011-100 and L-1011-200 with gross weight options of 440,0001b, 450,0001b or 466,0001b. The weight increase over the L-1011-200 is accounted for by additional fuel and tankage to provide extra range; there are only minor changes to the basic airframe and no fuselage stretch or undercarriage modifications. Powerplant could be the 48,0001b-thrust RB.211-524. With a range with full
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