FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1958
1958 - 0760.PDF
776 FLIGHT Foretaste of the Caravan HDM.105 HANDLING AND HDM.106 PROSPECTS COLLABORATION between F. G. Miles, Ltd., and theFrench company Hurel-Dubois has already resulted in theremarkable HDM.105, basically a standard Miles Aerovan fitted with an Hurel-Dubois high-aspect-ratio wing. In Flight for June 18, 1954, we discussed in detail the raison d'etre and the structure of the HD.32 transport, an aircraft which seemed to have an outstanding potential as a DC-3 replacement. But initial interest by Air France did not result for some reason in confirmation of a tentative order for a score of HD.32s for their services in North Africa. Six HD.34s are, however, being delivered to the Institut Geographique National for use in high-altitude photographic mapping. Perhaps the indigenous Hurel-Dubois designs failed to establish themselves in airline and military service because the authorities were a little chary of committing themselves to a then radical wing. But the first Miles sortie into high-aspect-ratio aerodyna- mics does, one feels, stand a very much better chance of becoming accepted. What Miles are offering is, in fact, the HDM.106 Caravan, powered by two Lycoming supercharged GSO.480-Bs giving 340 h.p. each, and a maximum loaded weight of 8,000 1b. Miles' calculations of the performance of this machine have been examined in detail by independent designers; and the special capabilities of the aircraft for light transport, especially in tropical and high-altitude conditions, are shown in an accompanying table. Though the HDM.106 Caravan promises to be an excellent light transport (NATO have expressed strong interest in it as a close- support transport for the Fiat G.91 light attack squadrons), a relatively small company like F. G. Miles, Ltd., are not able to undertake series production. Nevertheless, larger concerns, either in Britain or abroad, might well consider it a highly profitable venture in view of the large market which undoubtedly exists. Briefly, the characteristics of the HDM-105 wing are as follows: span, 75ft 4in; area, 277 sq ft; aerofoil section, NACA 66-420, changing to 66-412 at the tips; aspect ratio, 20.5; t/c ratio, 20 per cent at the roots; dihedral, 3 deg; and wash-out, 5 deg. Retracted, the flaps occupy some 25 per cent of the wing area. The wing structure is based on a D-section torsion box formed by the single web spar and leading edge, with the skin (which is largely 20 s.w.g.) taking its share of the loads. A large proportion of the bending loads are taken by spanwise stringers. The high-aspect- ratio would produce an excessive structure-weight if the wing were not braced by struts; these, which impart a considerable stiffness to the whole lift system, are specially designed according to principles laid down by Hurel-Dubois to produce minimum of interference. The main undercarriage is supported on wide-chord vertical struts from the engine nacelles (incidentally, considerably increasing the track of the original Aerovan gear) and the strut bracing is completed by stub wings joining the undercarriage The double-slotted flaps, here seen extended for landing at Shoreham, lower the stalling speed from 65 m.p.h. to 30 m.p.h. I.A.S. At far right, the HDM.105 is turning over the coast near Beachy Head. "Flight" photographs A span of 75ft 4in and an aspect ratio of 20.5:1 characterize the HDM.105 wing. t "Flight" photograph By C. M. LAMBERT pylon to the lower fuselage. The strut and stub-wing assembly in fact assists aero- dynamically by providing some 15 per cent of the total lift in the climbing condition. In the HDM.105 two standard Aerovan flap actuators have been paired to operate the double-slotted, rearward-extending flaps; and lateral control is provided by a combination of ailerons and saw-toothed spoilers which extend above the wing as the neighbouring aileron moves up. Though the wing is stressed for a maximum gross weight of 6,000 lb, the gross weight of the aircraft as a whole has been kept at 5,800 lb. The standard Blackburn Cirrus Major powerplant of the Aerovan has been re-s- tained, with Fairey Reed fixed-pitch, metal propellers, and the maximum combined power available is 310 h.p. I flew the HDM.105 at a weight of about 4,500 lb—that is, with myself and one pas- senger, about 20 gal of fuel and a standard Aerovan 9-seat passenger interior. Visibility from the balcony-like cockpit was, of course, superb; and the layout of instru- ments and controls was virtually that of a standard Aerovan. Flaps and elevator trim were both controlled by electric switches placed close together on the port console next to their dial indi- cators. Limiting speeds for various flap settings were rather low and elevator trim was extremely effective, so I took good care not to confuse the switches while airborne. Full blind-flying instru- ments and a certain amount of test instrumentation was fitted.*5 Nosewheel steering from the rudder pedals could be engaged byr- pulling a lever or, conversely, wheel brakes could be applied wither a hand lever and controlled differentially with the rudder pedals. 5 Landings and take-offs could both be made with nosewheel steer-" ing engaged; with it free, differential brake could be applied to make tight turns on the ground. I took off normally, using 20 deg of flap, and climbed straight^; up to 3,000ft to explore handling characteristics before coming-? back for some "circuits and bumps." I was primarily interested?, in the wing, flap and aileron characteristics, because these form r the nucleus of the Caravan's design. I proceeded in three stages, namely from normal speed to the stall with the wing in turn clean, with 20 deg of flap and with the full 50 deg. At 3,000ft and 2,100 r.p.m. the speed stabilized at something over 90 m.p.h. The HDM.105 was pleasantly stable and, if it had not been that the left wing tended to drop, the aircraft would have flown hands-off indefinitely. Trim changes under large alterations in power were very small and both deceleration and acceleration were fairly slow. A good deal of rudder was needed to enter or leave turns and particularly when reversing from one direction to another. Because of the arrangement of the aileron cable runs in this particular aircraft the ailerons were rather heavy, but the rate of roll was remarkably good for such a long span. After throttling right back, speed dropped progressively and a gentle, completely straight stall came after ample buffet warning at about 65 m.p.h. I.A.S. Ailerons and elevator remained fully
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
