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Aviation History
1957
1957 - 1454.PDF
544 CANADAIR ARGUS... the bogie beams of the main undercarriage units do not have to lie completely horizontal when the units are in the retracted posi- tion. Instead, the relative angular movement between the beam and the leg during the retraction cycle is no more than 60 deg, and Canadair were thereby able to dispense with the hydraulic pivoting of the British Messier undercarriage of the Britannia, substituting mechanical actuation. At one stroke this eliminated a number of jacks, pipes and sequence valves, replacing them with a simple linkage attached to the upper scissors-link, with a resultant weight-reduction of 12 1b on each main-gear unit. In other respects, however, the main undercarriage is substan- tially similar to that of the Britannia. The total of eight mainwheel tyres, each 36xllin, allow the Argus to operate from I.C.A.O. Class 4 runways. Subcontractors to Canadair for the complete main undercarriage unit are Jarry Hydraulics, who last month opened a new 18,000 sq ft shop equipped with heavy machine tools specially suited to the big Argus gear. A major change, dictated by the possibility of combat damage, is the addition of a completely distinct system for emergency brake operation. In the Britannia, dual-piston braking is con- trolled by a four-way valve operated by conventional linkages from the pilots' pedals. For the Argus, Canadair have separated the main and emergency feed-lines and control valves, the emergency system being energized by a special switch on the cockpit pedestal. Eight braking operations can be obtained from the emergency accumulator, and the system is also energized by an electrically driven stand-by hydraulic pump described later. It is intended to fit an anti-skid system (the Britannia has Dunlop Maxaret), but such a feature was not called for in the original R.C.A.F. specification. Also made by Jarry to Canadair design, the nose undercarriage differs from that of the Britannia in that it retracts in a rearwards direction. This change was necessary in order to permit an opti- mum installation under the nose for the search radar, the fairing for which is provided with a large recess to accommodate the nose leg in the extended position. As the gear retracts to the rear, under the pull of a hydraulic jack by the Fairey Aviation Com- pany of Canada, two sets of doors are simultaneously operated to seal off the compartment into which the unit retracts. The lower doors, which remain open when the gear is down, are mechanically linked to an upper pair which are stressed to resist the maximum calculated water impact loads which could occur during ditching. The nose tyres are 29x7.7in and the wheels are steered by a system operating at 3,000 lb/sq in. The latter is 1,000 lb/sq in greater than that employed in the Britannia (in which a reducing- valve is fitted to halve the main supply pressure), and the reduced diameter of the steering cylinder has permitted a weight-saving of 9.6 lb. Superficial inspection of the Argus and Britannia shows at once that the two aircraft differ considerably in their fuselage design. Throughout the entire airframe, however, engineering changes have resulted from the conversion from British to American material standards, the dictates of military requirements and the suitability of the British airframe to Canadair's manufacturing ability. From the outset a stringent programme of weight control was applied and in certain items efforts were even made to save fractions of an ounce. At the same time a ruling dictum on the Argus structure was "strength equal to, or greater than, that of the Bristol airframe." As a commercial transport the Britannia is designed to a limiting load-factor of 2.5; the Argus, however, is designed to a factor of 3, and it is conceivable that relaxation of this factor will permit a substantial increase in gross weight, thus conferring upon the Canadian aircraft an unusual growth potential. This one-4Hth-scole model, of wood covered with copper mesh, was built in order to assess radio performance, particularly in relation to the isolated fin aerial. The Argus has no fewer than 41 aerials. Except for the ruling diameter of 144in, little of the Britannia fuselage has been carried across to the Argus. Much of the basic structure has been changed, and interior arrangements and fur- nishing bear no resemblance whatever to those of the Britannia. Canadair have assessed the fuselage redesign as representing 95 per cent of that required for a wholly new project. As far as possible the Britannia fuselage is a perfect monocoque, bearing a peak pressure differential of 8.3 lb/sq in. In contrast' the unpressurized Argus hull is broken open by two large weapons bays, each 18ft 6in in length, which are disposed ahead of and behind the wing. The main wing-box passes through the fuselage with a longitudinal separation of 20in between the rear bulkhead of the forward weapons bay and the front face of the front spar and the front bulkhead of the rear weapons bay and the rear face of the rear spar. Heavy channel sections, extruded in high-strength light alloy, form the boundary members for the weapons bays and carry structural loads through the cut-out portions. These keel- like members carry the mounting points for the wing and the hinges for the weapons-bay doors, the balance of fuselage loads being diffused through four torsion cells (one for each side of the two weapons bays) each roughly of triangular form. A constant fuselage section is maintained for a length of 48ft, and, compared with the Britannia, the windows are fewer in number. There are, however, numerous scanning windows— some of them bulged—to supplement the visual-search capability of the flight deck. The flight deck itself has a window and roof structure quite unlike that of the Britannia, the transparent area having been extended to meet an R.C.A.F. requirement for increased visibility ahead, upward and downward. The resulting structure has greater drag than the finely streamlined cabin of the Britannia and a slight increase in drag has also resulted from the blunt nose-cap, which is completely transparent and includes an observation and bombardier's station. Further changes to the fuselage structure have resulted from the installation of special electronic equipment beneath the nose and in the extreme tail, to which reference is made later. The main entrance door, which is situated on the port side aft of the wing, is 71 in square and is divided into forward and after portions. A second large door, in a single portion, is opposite, to starboard. In the design of the wing, Canadair adhered as far as possible to the structure of the Britannia, which is both efficient and fully proven in static and fatigue testing. Much of the Britannia wing, particularly the secondary structure aft of the rear spar, incor- porates Redux bonding. Although Canadair had no previous experience of bonding techniques, the weight-penalty imposed by a switch to all-riveted construction was sufficient to make them learn. Canadair engineers visited all the principal British and American plants experienced in metal bonding, in order to determine the exact processes and equipment which would best suit their require- ments. Eventually it was decided to use neither Redux nor the various bonding processes employed by their sister-company Con- vair, but to use Bloomingdale FM-47 as the adhesive, with tech- niques worked out largely by the company's own shop-engineers. A complete department was organized to make the bonded assemblies, and therein were installed a giant autoclave, hot- platen presses, tanks for cleaning and preparing the surfaces to be joined and spray booths for the application of the adhesive. Almost the only major changes made to the Britannia wing comprise three which are confined to localized areas: the inboard main (tank-end) ribs are moved outwards so that they can serve as anchorages for the main wing pick-ups on the heavy fuselage longerons; spoilers are provided above the outer wings, as described later; and the wing is stressed to carry operational loads from pylons mounted outboard of the outer nacelles. The flap system is almost identical to that of the Britannia, large double-slotted flaps being mounted in steel guide-rails and posi- tioned by screw-jacks driven by a central actuator via spanwise torque-tubes. There are eight operating jacks and, unlike the Britannia, they are of the ball-screw variety, the reduced friction of which substantially lowers the torque required for flap opera- tion and permits an overall weight-saving of 25 lb. The flap actuator is by the Western Gear Corporation, and comprises dual electric motors coupled to a common gearbox. In the design of the empennage Canadair have again, wherever possible, followed Bristol practice exactly. Almost the only major change is the insertion of a chordwise structural section of moulded glass laminate with a honeycomb filler, which electrically isolates the upper part of the fin and rudder and permits these portions to be used as aerials. Static testing of the new vertical tail has established that the dielectric insert is slightly more flexible than the surrounding metal structure, although it has in no way reduced the overall strength of the fin. Like the Britannia, all the main flying controls are manually operated by Flettner-type servo-tabs driven through high-speed rotary torque tubes. The Britannia's interconnection between the innermost tabs on the ailerons and the rudder is retained in the Argus. The spoilers are in separate circuits which are energized whenever an extreme rate of roll is desired, particularly at low J
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