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Aviation History
1951
1951 - 0841.PDF
The Leonides power installation is particularly neat and offers an unusual degree of accessibility. The bare engine is easily removable as a unit. PERCIVAL P. 56 . . . mounting terminate forward in ball ends which marry with sockets on the engine ring and are locked by cup-nuts enclosing the balls and screwing over the sockets. Carried direct on the back of the Leonides crankcase in the top-centre position is a Newton 1,500-watt generator, beneath and behind which is a direct-mounted direct-driven Rotol gearbox carrying a Hymatic 1,000 lb/sq in compressor, a Plessey vacuum pump and a Rotax starter; the tachometer generator is provided with a direct drive off the engine. Induction through the medium of a Hobson fuel-metering injector unit has proved to be remarkably efficient, and it is noteworthy in this connection that, vis-d-vis the Mk 1, the Mk 2 has an economical-cruising specific-consumption of 1.5 gall/hr less, so giving 30 minutes greater duration and 93 nautical miles greater range; moreover, it provides these advantages in conjunction with an increase in (economical cruising) speed of eight knots. Reference has already been made to the ducted cowling which, in addition to possessing the advantage of simplicity and lightness, also inherently provides unbroken cowling lines. A ram intake beneath the cowling gives into an up-draught duct to the fuel injector via & Vokes Mille Vee filter. From the air-intake duct is a branch pipe to the oil cooler (by Morris Radiators, Ltd.), the flow from which is exhausted to atmosphere through a pilot-operated flap. The oil tank is mounted to port on the forward face of the firewall, and embodies negative-g compartments, a hot-well, and a de-aeration system. A Purolator filter is introduced into the scavenge circuit, with a Teddington surge valve to protect the cooler from excess pressures. Fuel and oil lines forward of the firewall are Palmer fireproof flexible hose, with the exception of that between the surge valve and the oil tank, which is of Tungum; abaft the firewall, the fuel lines are of light alloy and, from each of the wing tanks, fuel is gravity-fed to a central collector tank. This is a metal, crash-proof- covered unit, located at the base of the firewall on the after- face, and embodies a B.P. Mk 5 submerged booster pump; a micronic-type filter is employed. From the firewall to the tail fairing, the fuselage structure of the P. 56 presents an excellent example of straightforward, no-nonsense aircraft engineering practice. It is a conventional semi-monocoque, incorporating four quandrantally-disposed longerons and, in common with the remainder of the airframe structure, exhibits traits of strict weight-control, the effective- ness of which can be seen in the value of 31 for the per- centage structure-weight. Both pairs of longerons are 14-gauge rolled sections, the upper pair being at canopy-rail height, and the lower pair at cockpit-floor level; the forward terminals of all four longerons are the main pick-up points of the engine mounting. In general, the fuselage skin panelling is carried on Z-section stringers and channel- section frames, many of the latter being doubled, reinforced 528 ^ or increased in gauge at stations where some degree of load concentration occurs. Beneath the floors, diaphragm webs are commonly used in conjunction with the frames to provide transverse bulkheads. In way of the instrument panel are doubled channel- frames spanned by a tube to which, in common with the longerons, the instrument panel supporting frame is a.v.- mounted. The instruments are grouped on two panels which are centrally hinged to the supporting, frame so that ready access is provided to the backs of the instruments. The P. 56 does not make use of a centre-section in the conventional sense; the wing-spar roots are attached to reinforced bridging members which span the fuselage. In way of the main spar, the bridging structure comprises two machined channel-section forged booms joined by a pair of plate-webs internally stabilized, and so forming a box- beam. In conjunction with this spanning structure is a box frame which runs like an unbroken U from one top longeron to the other, and encloses the ends of the spar bridge beam. The rear spar bridging structure is a simple diaphragm bulk- head, stabilized on its front face with rolled channel verticals, and spanned by horizontal members, the upper of which is a rolled lipped-channel section, whilst the lower is made up by two lipped channels placed back-to-back. The periphery of the diaphragm is bounded by a double-channel frame, and pick-up to the wing rear spars is effected through double plate fittings. Between the spar bridges and riveted to the outside skin of the fuselage belly flank is a 2iin-long top-hat- section drag member which, at its forward end, is attached through a channel fish-plate fitting bolted to the rear face of the lower spar-bridge boom. j Fabricated as a sub-assembly complete with longerons, tile pilots' floor is made up with light alloy sheeting, supported on fore/aft seat bearers of channel section with angle reinforcement, and laterally between these bearers run channel-section intercostals. The floor extends as a deck between the firewall and the rear bulkhead of the cockpit, and is interrupted only by the top booms of the main spar bridge, which rises ijin above floor level. About 55 per cent of the spar inter-distance rearward of the main spar bridge structure is an under-floor double-channel frame, the upper horns of which (immediately beneath the floor) provide pick-up points for the feet of the two forward tubes of the crash-pylon. Above the floor, at the rear spar station, is the cockpit rear bulkhead which, sloped rearward a few degrees, is an integrally swage-stabilized diaphragm, reinforced by diagonal top-hat-section and horizontal angle-section mem- bers. At the apex of the top-hat diagonals, on the crown of the bulkhead, is a pick-up fitting for attachment of the foot of the rearward central tube of the crash-pylon. One frame bay abaft the cockpit bulkhead is a structural break in the fuselage which, however, is not a transport joint; the skin panels are lap-jointed, and the longerons are butt-jointed with nesting sections. From the structural break aft, the fuselage is a continuous structure, skinned on rolled-channel frames, notched for the rolled Z-stringers. The top longerons—although they are cranked—run continuously back to the tailwheel bulkhead, Easy access to the radio equipment (and batteries) is provided through large hinged panels on the port and starboard sides of the fuselage.
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