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Aviation History
1957
1957 - 1389.PDF
FLIGHT, 20 September 1957 479 Flying the H.D. 34 Air Experience with the Latest Hurel- Dubois Product: a Notable Survey Aircraft By ARCTURUS WHEN I first saw the drawings of the early Hurel-DuboisH.D. 31 my immediate reaction was one of shock; butthose drawings played false, and so did the photographswhich accompanied them. The Hurel-Dubois plan-form is not photogenic, and it is only when one sees the aeroplane in theflesh, as it were, that one is suddenly aware of its extreme, func- tional beauty. Anyway, that is how it seemed to me, and whenI saw the H.D. 31 sitting outside her hangar at Villacoublay 1 knew that she was going to be "right." She didn't fail me, either.And like a lady, she was so very illogical. With both throttles against the stops she leaped from the ground as though eager toenter her natural element with the least possible delay. Yet nothing was easier than to return her to the ground, with alanding run that was almost a joke. In the air, of course, she was elegant and docile in her behaviour, and a pleasure to fly. With this background it can be imagined how I reacted to aninvitation to fly the latest product of Avions Hurel-Dubois. This is the H.D. 34 photographic survey version of the H.D. 321transport, which itself springs from the H.D. 31. Essentially the airframes of the production H.D. series are similar, the transportH.D. 321 being the basis of them all. In addition to the H.D. 34 there are the H.D. 331, which is available in troop-transport, am-bulance, police surveillance, ground attack, and vehicle transport roles, and projected the Dart-powered H.D. 324, which is virtu-ally a modified H.D. 321 transport. But I digress; let it suffice to say that the thought of flying a Hurel-Dubois again enthralledme. So much has been written about the theories of CommandantHurel that there is no need to go into the matter of high-aspect- ratio wings and their advantages. What is of greater interest is thatin the H.D. 34 there exists a photographic survey aircraft with an exceptionally high degree of crew comfort, a staggering payload,and a very long endurance, coupled with the fact that the aircraft can take off fully loaded with a run of well under 500 yd from arough grass field. With a take-off weight of 42,430 lb the H.D. 34 can fly 500 miles to its objective, undertake an eight-hour photo-graphic mission and return to base, carrying a photographic pay- load of 5,270 lb. It is thus an eminently suitable aircraft forcolonial survey work, which is doubtless the reason for its selec- tion by the French Institut Geographique Nationale. The first difference one notices between this aircraft and theH.D.321 transport is the Perspex nose, housing the navigator. Access to the navigator's position is by means of a passage-way atcabin floor level which passes between the two pilot's seats and beneath the central panel. This, of course, means that the enginecontrol pedestal has to be discarded; all engine and propeller con- trols are of the plunger type and are accommodated in this centralpanel. A sort of shelf below the throttles houses the trim controls. The two pilots sit on either side of the central passage, raised some2|ft, resulting in an exceptionally wide field of vision. The flight instruments are duplicated, and are well laid out and easily read;engine instruments are placed to the right of the central panel. I was particularly pleased with the trim indicators, which tookthe form of dials upon which the trimmer settings were clearly shown. Too often with strange aeroplanes one has to peer atobscure scales to ascertain the position of the trimmers. The whole cockpit was well-planned and functionally laid out. The navigator's position in the nose has provision for an addi-tional navigator seated to the left of, and slightly behind, the chief navigator. Behind the co-pilot's seat and against a bulkhead areAe radio rack and the radio operator's position, facing forward, while a hinged jump-seat between the pilots allows for the car-riage of a flight engineer as a member of the operational crew. In the main cabin are the two photographers, together with theirequipment. Essentially this equipment consists of two large sur- vey cameras and two oblique cameras aft, to port and starboard,and their associated film magazines. A monorail loading winch is incorporated, an arm of which can be extended outside the reardouble doors when loading, for handling the magazines simply " . . . a photographic survey aircraft with . . . a staggering payload." A TYPICAL product of French ingenuity and originality, the Hurel-Dubois series of aircraft with high-aspect-ratio wings represent one of the earliest entries in the STOL field; and the layout is being activelydeveloped in Britain by the joint Anglo-French company, Hurel-Dubois Miles, Ltd. The photographic survey and anti-submarine versionsmentioned in this article are succeeding the first transport versions in France. This new first-hand account by a contributor confirms reportsof the type's excellent handling qualities. and with the minimum of effort. The cabin itself is well sound-proofed and trimmed, four comfortable airliner-type crew rest seats being provided at the rear, together with toilet facilities.Provision is made for oxygen, as the aircraft is unpressurized. The H.D. 34 has two Wright 982 C9 HE 2 engines. METOpower is 1,035 b.h.p. each, while at the cruising power setting of 691 b.h.p. a cruising speed (T.A.S.) of 149 kt is obtained at10,000ft. A somewhat unusual undercarriage arrangement is em- ployed, in that while the mainwheels are fixed, the nose gearretracts. In the transport aircraft, the nosewheel is fixed and faired; in the H.D. 34 not only does the unit retract but it is alsooffset to port. The reason for the use of twin retractable nosewheels is incidental only, as the H.D. 34 uses the same airframe as theanti-submarine version (about which little can yet be written) and provision of a ventral radar scanner necessitated the retraction ofthe nose gear during flight, to avoid interfering with the scanner. Having arranged details of what I wanted to do with the air-craft, M. Marchand, Hurel-Dubois test pilot, two engineers and myself climbed aboard. The plan was that M. Marchand woulddemonstrate the short-take-off procedure and climb, after which I should carry out general handling, and asymmetric flying, fol-lowed by take-offs and landings and a spiral climb. After starting up, the aircraft is taxied easily and precisely using the steerablenose gear. There is no runway at the Hurel-Dubois airfield at Villacoublay, the surface being grass and rough into the bar-gain. With the outside air temperature at 26 deg C and the aircraft at its genuine all-up weight, having just arrived from certificationtrials at Bretigny, M. Marchand lined-up on receiving the green from A.T.C. Let us not be in any doubts at all about this beinga "bush" aircraft—at Villacoublay, apart from the length of the field, almost bush conditions obtain. A.T.C., in fact, consisted ofa man with red and green flags. In addition to external conditions of I.S.A.+ 11 there was nosurface wind whatsoever, so considering our weight I scarcely expected anything startling in the take-off line. Neatly fitted toeach control column was a Breguet stop-watch so I decided to time the take-off run. Take-off is a simple affair indeed. Withbrakes hard on, the engines are opened up to full power, after which the brakes are released. At Hurel-Dubois the throttles areapparently sacred to the flight engineer; no one else touches them, so once you say the word you're committed. With the brakesreleased the H.D. 34 accelerated slowly, it seemed, to its take-off I.A.S. of 85 kt. From brakes off to unstick took 18 seconds; byassuming a constant acceleration as an integral and time as an- other, with the final speed being known, it is possible mathemati-cally to deduce distance. In this instance, assuming the fact that the undulations of the airfield surface would cancel each other out,thus allowing for a constant acceleration, I found that the take-off run was approximately 1,300ft. Remember the conditions obtain-ing at the time—all-up weight 42,500 lb, air temperature 26 deg C, no wind, rough grass surface. From unstick M. Marchand allowed the aircraft to accelerateto 105 kt, climbing at 500 ft/min. He then eased back the control column until the I.A.S. was a mere 85 kt, with the H.D. 34climbing at 1,500 ft/min. From brakes off to 3,000ft took exactly 4 min 45 sec. At 3,000ft I took over the controls, and climbedat an I.A.S. of 85 kt to 5,000ft. With a nose-up attitude, and not far off the stall, the aeroplane inspired immense confidence: thecontrols were pleasant and responsive and there was no tendency to wander. My French, although passable for the ordinary things of life, is
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