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Aviation History
1956
1956 - 0916.PDF
62 FLIGHT, 6 July 1956 Airliners of the World .D. 321 SOCI£TE DE CONSTRUCTION DES HUREL-DUBOIS, MEUDON IN the H.D.321, the Wright-engined higher-powered develop-ment of the H.D.32, the Hurel-Dubois company of Francehave moved a step further in the evolution of perhaps the most aerodynamically original transport aeroplane yet built. Itsdesigners have conclusively shown the world the startling advan- tages offered by correctly applied high aspect-ratio. Their philo-sophy is that payload can be doubled for a given power and speed by the use of a suitably designed high aspect-ratio wing andassociated bracing struts. In addition, as the performance figures show, take-off and climb are remarkable for an aircraft of theH.D.321's power and weight. The words "suitably designed" are significant. The Hurel-Duboisformula has been the subject of immense research and a brief discussion of it is appropriate. The objections to high aspect-ratio are that aerodynamic efficiencyfalls off as it is increased, and that weight goes up to the power of about 1.5. The latter can be avoided by struts, but drag tends tocancel out any advantages. Other generally accepted objections are that the aircraft is more difficult to fly; that a high aspect-ratio wing suffersfrom torsion troubles; that e.g. travel is limited; and that leading edge de-icing presents problems. Hurel-Dubois claim to have overcome all these objections. Theirstruts are specially designed to overcome induced drag due to inter- action of wing and strut (which virtually form a biplane), and theincreased profile drag due to interference. By twisting the strut appre- ciable lift is generated in conditions where minimum induced drag isrequired; by making it as thin as possible and making its incidence follow the line of the flow, parasite and interference drag are reducedto a very low order. Thus, without excessive increase in weight, a lift- drag ratio of about 40 is achieved, this figure being exceeded by theuse of high-lift Fowler flaps during take-off and landing. Thus the first of the objections raised above is answered. So faras handling and manoeuvrability are concerned flight-tests have shown rate of roll to be satisfactory in every configuration (it exceeds 12 deg/secat low speeds). The centre of gravity margin exceeds 25 per cent of the reference chord, i.e. 2ft, a limit acceptable on a conventional aircraftof similar weight. Torsional rigidity and flutter have been shown to present no problems; there is no danger of aileron reversal at anyspeed, and flight test diving speeds of 222 kt have been reached (215 kt is required by regulations). Calculated flutter speed at cruising heightis 350 kt I.A.S. The de-icing system, supplied by combustion heaters, bleeds hot air into the leading edges of the wings and struts andhas been shown to work completely satisfactorily. Curves for H.D.321 with Wright 982 (R-1820) engines. Payload/range assumes 230 st. miles alternate + 75 min +/ive per cent; costs assume 8-yr depreciation at 1,500 hr utilization, S.B.A.C. method on I.F.R. / PAYLOAD (cargo) £ L 1_ The structure and systems of the H.D.321 conform closely to thoseof the H.D.32 (described in Flight, June 18, 1954) and are straight- forward and conventional. The basic difference between the two air-craft is the powerplant, two Wright 982 C9 HE-1 engines of 1,525 h.p. replacing the 1,200 h.p. Pratt and Whitney R-1830-92 engines. Air-screws of the H.D.321, like those of its predecessor, are by Hamilton Standard. The increase in power necessitated an increase in tailvolume, achieved by more fin and the addition of auxiliary fins on the tailplane. In addition, capacity of the leading edge de-icing combustionheaters has been increased. Payload Accommodation. Three versions are offered: a 44-passengerlayout; a mixed cargo-passenger version with seating for 34 and 346 cu ft of cargo space in place of five double chairs at the rear of thecabin; and an all-cargo version of 1,441 cu ft (including gangway provision). In each version flight crew accommodation for three isunaffected. A good point in the two passenger versions is that the portion of cabin in line with the airscrews is devoted to baggage space(106 cu ft). Hurel-Dubois offer the aircraft in other commercial roles also, andhave prepared schemes for a photographic survey version and an ambulance version. Commercial History. The Hurel-Dubois high-aspect-ratio theorieswere first tested in 1949 when the H.D.10, a small single-seat research monoplane of 39ft 4in span, was built and flown. As a result of itssuccess, the French Government ordered two H.D.31S, a twin-engined transport, the first of which flew in January 1953, powered by two800 h.p. Wright engines. The higher-powered H.D.32 followed later in the year. This aircraft was not produced in numbers, although it wasrumoured that Air France had ordered 24; production of the H.D.321 is, however, progressing well and first deliveries will be to the InstitutGeographique Internationale beginning next February. The Institut has ordered an undisclosed number of the type 34, which is thephotographic version of the 321 having a slightly longer front fuselage to accommodate a photographer in the extreme nose. H.D.321 Two Wright 982 C? HE-1 of 1,525 h.p. Dimensions: Span, 148ft 7.5in; length, 76ft 4.3in excluding nosewheel spat; height, 27ft 6.7in; gross wing area, 1,076.43 sq ft (aspect ratio 20.2); track, 23ft. Weights: Empty, 22,758 Ib; operating weight as freighter, 25,463 Ib; maximum take-off, zero-fuel and landing weights, all 41,225 Ib. Performance: Take-off to 50ft, 2,460ft; second-segment climb, one feathered, 254ft/min; climb at 5,000ft, 855/ft min; cruise at 39,600 Ib at 9,850ft on 690 b.h.p. per engine, 166 m.p.h.; landing from 50ft, 1,900ft (3,170ft required field length). 200 300 400 5O0 600 700 800 STAGE LENGTH (st.mite) 900 1,0001100
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