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Aviation History
1949
1949 - 1360.PDF
124 FLIGHT AUGUST 4TH, 1949 AMERICAN NOTEBOOK By "Favonius " MONEY-BOX SLOTTERYR ESEARCH studies now being conducted by Northrop indicate that an equatorial round-the-world non-stop ' range of 25,000 miles may eventually be possible with an all-wing aircraft equipped with boundary-layer control and powered by twin turbo-prop engines—presum- ably Northrop's own 10,000 h.p, Turbodynes. The present Northrop scheme employs air blowers installed within the wing envelope and drawing air from the boundary-layer .aft of the transition point through a series of spanwise suction slots in the top and bottom wing skins. An appreciable jet thrust is also expected from the rearward expulsion of the air in the region of the trailing edge. Both theory and wind-tunnel tests have demonstrated that boundary-layer control by suction should be an effect- tive means of obtaining high wing lifts. If flow separation on the upper surface could be sufficiently delayed, maxi- mum lift coefficients of the order of 5.0 to 6.0 appear feasible. In full-scale practice, however, the aerodynamic efficiency of such a scheme is dependent on many variables such as the number, location, width and shape of the slots; aerofoil section; types of flaps (and ailerons, if employed); and, of course, the power expenditure involved. It is not surprising, therefore, that earlier full-scale experiments have not yet approached the theoretical possibilities. Wright Field, for example, did some very interesting experiments with a suction-slotted wing fitted on a Stinson-Vultee L-i Vigilant in 1944. The blower was mounted in a hump over the wing centre-section and was driven by an 80 h.p. Franklin air-cooled auxiliary engine located in the fuselage, while spanwise ducts between the spars connected the three full-span suction slots to the blower. These slots were located at fio, 80 and 98 per cent of the wing chord. Despite the added incentive of full-span, 40-per-cent- chord double-section trailing-edge flaps, with the front section adjustable to 35 degrees and the rear section drooped down 82 degrees, this wing was unable to develop a maxi- mum lift coefficient greater than 3.6. Such a value, of course, is not much higher than can be expected with full- span front slats and double-slotted or Fowler-type rear flaps —albeit obtained without the mechanical complexity and power expenditure of suction blowers. The structural diffi- culties of obtaining adequate torsional stiffness with a large proportion of the wing skin mutilated must also be formidable. Current Northrop research is being directed more towards increasing the range of all-wing aircraft by reduction of the drag at cruising lift coefficients. Heading this scientific exploration is Dr. Werner Pfenninger, formerly of the Federal Institute of Technology at Zurich, Switzerland, who was brought to the U.S.A. by Northrop in January this year. Dr. Pfenninger's Swiss research on boundary-layer control, started in 1941, has shown promise of drag reduc- tions up to 50 per cent—which would mean in the case of an all-wing bomber such as the B-35 or B-49, an overall minimum drag coefficient of the order of 0.005. Although this figure is admittedly based on low-scale model data, there is general agreement that an ecaudate wing configuration does lend itself admirably to this type of aerodynamic research, since the obtrusion of the conven- tional fuselage and tail takes a lot of the gilt off the ginger- bread. Full-scale evidence of this can be seen in the Armstrong-Whitworth AW-52 twin-jetted all-wing with boundary-layer control. Based' on a suction of about 3,000 cu ft per second, the Northrop researchers expect to cut down the power required, due to reduction of the drag through boundary-layer control, to about one-quarter of that normally required on the present Flying Wing. This big reduction also includes the requisite pumping power expenditure! On these cheerful assumptions, then, our Northrop friends estimate that a turbo-propped B-35 could circum- navigate the earth at the equator—without refuelling. Just where such an equatorial equipage fits into the military rangefinder now that high-speed aerial refuelling has suc- cessfully reached the global stage is, perhaps, a contro- versial point. Looking over the civil transport side of the balance sheet, we fancy that any economy-minded operator would prefer to exploit the boundary-layer by sucking in more pay-load instead of fuel for unnecessary range. In this way, the all-wing slottery might become a very useful money-box. A FIGHTING WEATHERCOCK tpOLLOWING hard on the tail-pipe of Lockheed's XF-90 -*• penetration fighter, test flown at Muroc only a few weeks ago, comes announcement of another Lockheed nona- genarian, the F-94 two-seater all-weather jet fighter. The An early full-scale experiment in boundary-layer control. A Stinson-Vultee L-I Vigilant modified by the Dow Chemical Co. for Wright Field in 1943-44. The suction blower for the wing slots is installed in the hump over the centre-section. c ?
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