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Aviation History
1942
1942 - 0336.PDF
i34 FLIGHT FEBRUARY 12TH, 1942 ________ fc BOULTON PAUL DEFIANT Both the centre section and outer wings are built on two spars. These spars comprise top and bottom booms oi extruded light alloy, joined by vertically corrugated webs. The centre section spar booms are of " T " section ; those for the outers are angle sections, The lower booms of the centre section spars are bent at the centre to pro vide for the appreciable taper in wing thickness; all other booms are straight. The centre section v/ing houses at its outboard ends the two petrol tanks, and inboard of these carries and pro vides housing for the undercarriage, which retracts side ways. As a result the number of full-depth ribs which can be provided between spars in the wing centre section is limited to one at each outer end, one inboard of the tank compartment (serving to carry the undercarriage) and one on the centre line of the aircraft. The under carriage "rib" is a very stiff beam which is skewed rela tive, to the line of flight, the remaining ribs being of the usual girder type. Centre-section Structure As the bottom skin of the centre section is necessarily incomplete to allow for retracting the undercarriage, to permit of the removal and replacing of tanks, and for access to equipment in the wing, the combination of two spars and of such skin as is present does not produce a complete box structure. The centre section unit is completed by a leading edge— whose skin is continuous from spar boom to spar boom— which forms, with the spar, a •" D " section tube, and by a trailing-edge portion, which includes an auxiliary spar with a stiff corrugated web about half-way between the rear spar and the trailing edge. This auxiliary spar, plus the top and bottom covering skin, and the main rear spar, effectively produce a box rear spar, and the result ing centre section in the complete form is an extremely strong and rigid structure in consequence. In the outer sections, top and bottom skins are continuous between front and rear spars, so that here there is an effective box beam. In addition, the leading edge and the front spar form together a continuous "D" section tube as in the case of the centre section, thus still further strengthen ing the structure. The leading edge for both centre and outer wings is detachable. It consists of a sheet of light alloy bent to the correct profile, riveted to a series of nose rib formers. The joints of the spars between outer and centre section spars are provided by machined steel fittings attached to the spar booms which accommodate ground taper bolts. There is a definite gap between the outer and the centre sections when assembled. This gap is closed by screws at the trailing edge. Tail Construction The tailplane and the fin are unbraced metal-covered structures, each built on a series of tapered longerons,, covered with flush riveted covering. Ailerons, elevators and rudders are metal-framed structures, fabric covered^ The elevators and rudders are provided with trimnPfc^v'' tabs, adjustable, from the cockpit, those of the rudder having in addition some automatic servo action. It is of interest to note that the two elevators are identical, i.e., are not right and left hand. To secure this, elevator' and tab control connections are on the top of one elevator and on the bottom of the other. The undercarriage comprises two Lockheed " Airdrau- lic'' shock-absorber legs hinged to the diagonal beams already mentioned as among the few complete '' ribs •' on the wing centre section. Each leg is retracted or extended by a "break-back" strut which extends diagonally in wards towards the fuselage and rearwards towards the rear spar. When completely retracted, the undercarriage lies completely within the contour of the centre section, with the tyres of the two wheels nearly meeting on the centre line of the aircraft. The opening in the centre section into which the undercarriage retracts is completely closed, in flying condition, by two flaps carried from each undercarriage leg (which two flaps, between them, cover the openings up to the wheel centre) and by two semi circular flaps hinged to the central rib of the centre sec tion. The latter project vertically downwards whilst the undercarriage is extended, but are closed, when the under- (Coniinued on page 135.)
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