Introduction

1. The Tempest II is a single-seat, low wing cantilever land monoplane with retractable main wheels and tailwheel, designed for day and night fighting duties in temperate climates and, in the case of later aircraft, in tropical climates also. It is powered by a Centaurus V radial air-cooled engine which has 18 cylinders and drives a Rotol variable-pitch left-hand tractor propeller. The armament consists of four 20 mm. Mk. V Hispano guns installed two in each wing. Provision is made for carrying either a 250 lb., 500 lb., or 1,000 lb: bomb, four rockets or, on later aircraft, a drop fuel tank of 45 or 90 gallons capacity under each wing.

2. The cockpit is totally enclosed; entry and exit are normally obtained by sliding the hood backwards but, in case of emergency, the hood and a panel on the starboard side of the cockpit may be jettisoned. The pilot and the more vulnerable parts of the aircraft are protected by armour plating. The flying controls are of conventional stick and rudder bar type; the seat is adjustable for height and the rudder bar for leg reach.

3. The fuselage is of composite construction, the engine mounting and centre fuselage being formed of steel and light-alloy tubes covered with fixed and detachable metal panels while the rear fuselage, including the tail end, which has an integral fin, is of metal monocoque construction. The engine cooling shutters, which are situated aft of the main engine cowling, are controlled on early aircraft by a selector switch in the cockpit, but on later aircraft are controlled automatically by a thermostatic inching control unit.

4. The stressed-skin cantilever main plane consists of port and starboard wings which are attached directly to the fuselage; the undersurface is horizontal for approximately one-third of the span and the outboard portions rise to form a dihedral angle. The ailerons are of modified Frise type with mass-balance, and the hydraulically-operated split-flaps extend from the root to the inner ends of the ailerons. Two direct-entry carburettor air intakes are provided, one in the leading edge of each wing. On later aircraft, there is also a filtered intake under the top engine cowling, for use in the tropics. An oil cooler is situated in the leading edge of the starboard wing outboard of the air intake. The yolume of air passing through the cooler is regulated by a shutter, which, on early aircraft is controlled by a lever in the cockpit. On later aircraft, the shutter is auto-matically controlled by a thermostatic inching unit which operates two electro-hydraulic solenoid valves.

5. The non-adjustable cantilever tail plane comprises two separate inter-changeable half-planes bolted to the fuselage sides. The rudder and elevator are mass-balanced and are provided with trimming tabs which are controlled from the cockpit.

6. The alighting gear consists of two main wheel units which retract inwards and slightly backwards into wells between the wing spars, and a tail wheel unit which retracts forward into the fuselage, the operations being effected hydraulically. A pneumatic assister comes into operation when the under-carriage is retracted. Mechanical locking and electrical indicating devices are provided as well as a warning lamp, The wheel of each undercarriage unit is carried on a stub axle, the shock-absorber being of the oleo-pneumatic type. Each wheel is fitted with a pneumatically-operated brake actuated by a lever on the control column; the brakes operate differentially in conjunction with the rudder bar. The tail wheel is fitted tith a twin-contact self-earthing tyre and is carried on a fully castoring &o-pneumatic shock-absorber strut; the wheel is self-centring during retraction.

7. The main fuel tank is carried in the fuselage just aft of the forward firewall: two further tanks are housed, one in the inner portion of each wing, between the main spars; there is also a nose tank in the port wing. All fixed tanks are of the self-sealing type. Later aircraft have a transfer fuel system, which means that the fuel is always supplied to the engine from the main tank, into which it is transferred from the wing tanks by air pressure. On these aircraft, two 45 or two 90 gallon drop tanks may be carried, one under each wing. The oil tank, which is also self-sealing, is mounted above the top longerons between the aft firewall and the pilot’s instrument panel, and is protected by armoured cowling.

8. The four 20 mm. guns are electro-pneumatically controlled from a push-switch on the control column spade grip. All guns fire outboard of the propeller disc and the ammunition for them is carried in the wings. A camera gun, mounted in the starboard wing, can be operated separately or in conjunction with the guns.

9. The radio installation, carried behind the pilot, comprises standard transmitter-receiver, beam approach and I.F.F. installations. A retractable landing light, electrically controlled from the cockpit, is fitted to the undersurface of the port wing; a first-aid outfit is stowed on the inner face of the radio access panel. An engine-driven generator supplies electrical current for the navigation, identification, landing and cockpit lamps, the fuel content gauges, fuel-pressure warning lamp, cartridge engine starter, booster coil, pressure head heater, undercarriage position indicator and warning lamp, wheel door control, gyro gunsight, gun firing, camera gun, heated clothing, bomb fazing and control switches, R.P. selector and firing switches, magnesyn compass, radio supply, and in addition, on later aircraft, fuel pump switch, air intake control, engine cooling shutter and oil cooler shutter controls. One oxygen bottle is carried on the port side of the fuselage immediately aft of the pilot’s seat.

10. Aircraft equipped for operation in tropical climates carry desert equipment for use in the event of a forced landing in an isolated locality. This equipment consists of two large water bottles, one small water bottle and carrier, canvas signalling stripes, a signalling pistol and cartridges, a heliograph, a tool kit and emergency rations.

Sliding hood

Control column and Flying controls group

Tailplane

Each plane is tapered in plan and thickness and consists of two spars and a number of plate ribs covered with sheeting, the structure being almost entirely of light-alloy. The covering is reinforced with extruded angle-sections on the innerface, spaced approximately equally between the spars.

SPARS:

The spars comprise extruded T-section booms to which are riveted plate webs, lightened with circular flanged holes. In the case of the rear spar the aft arm of the T-section boom is cut-away to form an L-section from one third of the section outboard. At their rot ends the webs are reinforced with plates and fitted with high-tensile steel fittings carrying studs for attaching the plane to the fuselage. The spars extend from the root end rib to the semi-circular tip or washout. In this washout portion the spars are continued by tapered tip portions which are similar in construction to the normal inter-spar ribs. Two similar tapered sub-spars are approximately equally spaced between the tip portions of the spars

INTER-SPAR RIBS:

Except for the root rib, the washout rib and the washout attachment rib, the normal inter-spar ribs are made from single sheets of light-alloy flanged along their upper and lower edges and cut away to accommodate the angle-section stringers riveted to the inner face of the skin. Extruded angles are riveted to the ends of the ribs to provide means of attachment to the spars. Each rib is li ht g ened with three circular flanged holes, and is stiffened by means of two rolled Z-section stiffeners.

The inner end rib has extruded T-section booms with a plate web: the washout attachment rib also has similar booms, and the web is lightened to a girder pattern, the verticals and diagonals being reinforced with rolled Z-section stiffeners.

The washout rib is made in five portions, which include a nose and a tail portion, the breaks occurring at the front and rrar spars and the two sub-spars.

NOSE RIBS:

With the exception of the root rib and the washout attachment rib, the nose ribs are constructed from flanged light-alloy sheet in a similar manner to the normal inter-spar ribs. The rook rib has booms of extruded T-section with a plate web and the washout attachment nose rib has channel-section light-alloy booms and channel-section girder-bracing. The nose ribs are fitted in line with, and midway between, each inter-spar rib.

ELEVATOR SHROUDING:

Attached to the rear face of the rear spar, and in continuation of the ribs, are light sheet-metal formers supporting the skin aft of the spar and providing a support for the nose shroud of the elevator. The shrouding is made in two portions, one past being from the elevator inner hinge to the outer hinge at the washout attachment rib, and the other part in the washout portion. Light-alloy bearing blocks for the elevator hinges are bolted between double formers at the root rib and the outermost rib.

INSPECTION DOOR:

A single inspection door, attached by six screws, is situated just inboard of the washout attachment rib approximately mid-way between the spars. As the two tail planes are interchangeable and identical, the inspection door is in the upper surface when on the port side and in the lower surface on the starboard side.

Elevators

Each elevator has a channel-section main spar incorporating nose ribs and nosing. Flanged sheet metal ribs are incorporated, the whole structure being of duralumin with the exception of the skin covering aft of the spar, on early aircraft, which is of Elektron sheet stiffened with stringers parallel to the main spar. On later aircraft the entire skin covering is of duralumin sheet. Additional stiffness is provided in the washout portion by two short sub-spars of the plate rib type. A trimming tab in the trailing edge is operated by a handwheel in the cockpit.

SPAR:

The spar assembly is, in section, an isosceles triangle the base of which is vertical and consists of a heavy-gauge channel spar with its flanges turned rearwards; the apex of the triangle is forward of the base and the two equal sides are formed by a single sheet of light-gauge metal, folded at the apex and riveted to the flanges of the base; these sides provide an aerodywmlc balance. The whole is stiffened by means of a number of internal ribs at the points of attachment M the main ribs, with one additional rib to provide a fairlead for the elevator tab control cables. The spar tapers from the root to the tip, a sub-spar being fitted at a position 3 in. aft of the main spar outboard of the outer hinge.

RIBS:

The ribs consist of flanged plate webs and are cut away to clear the stringers where the latter cross the ribs. The larger ribs, towards the root end, are lightened with circular flanged holes.

HINGES:

The hinge spools are high-tensile steel fittings. The outer spool is situated between two closely-spaced ribs, to the webs of which is bolted through flanges at each end. The inner spool is in the form of a spigot, bolted through its flange to the inboard rib of the elevator; the spigot is forked at its inner end and engages with the end of the elevator countershaft which projects through the monocoque skin and to which it is connected by a single bolt. Each hinge assembly consists of needle roller bearings housed m a base block and cap which contain the elevator spools. Retaining rings are utilised to locate the rollers laterally. The cap and block are held together by two distance tubes which are forced into them at the elevator attachment holes; these holes pick up with the attachment studs on the tail-plane. The needle bearings are packed with lubricant and a grease nipple is incorporated on each hinge for lubrication in service.

TRIMMING TAB:

A trimming tab is provided in the trailing edge of each elevator. The tab is formed from a single sheet of light-alloy bent to the required profile, and is reinforced by four internal wooden former5 attached with woodscrews. The tab is held in place at each end by a projecting spigot which engages with a bush mounted on the web of the adjacent rib.

Rudder

The rudder is fabric covered and is mass-balanced by a lead weight mounted forward of the spar approximately mid-way along its length. The structure consists of a spar conneded by ribs to a nosing and a trailing edge, the latter being interrupted towards the centre of the rudder to accommodate a trimming tab. Five diagonal flanged channel-section stiffeners and one diagonal tubular stiffener brace the spar to two points at the trailing edge and two points at the trimming tab cut-away. An additional diagonal stiffener, comprising a flanged plate web with flanged lightening holes, is fitted between the spar and the bottom rib, Immediately above and below the cutaway for the tab in the trailing edge, on later aircraft, small stay tubes have been added to stiffen the rudder locally. The bottom edge of the rudder consists of a detach-able fairing which, when removed, by withdrawing ten screws, provides access I to the lower hinge.

SPAR:

The spar is constructed, in three pieces, from steel tube, the joints being effected at thb top and centre hinge spools which are bolted into the ends of the spar sections. The bottom hinge spool is similarly fitted to the bottom of the spar. Spools for the attachment of tail ribs are sweated on to the outside of the tube. At each attachment spool except the lower one a semi-circular nosing rib is riveted; at the lower spool, however, the nose rib is integral with the tail rib extension. At four points along the spar, eyebolts are fitted for the attachment of the diagonal stays, and two brackets for the mass-balance weight are fitted above the centre hinge. The trimming tab operating gear is situated just above the mass-balance weight brackets.

NOSING:

The nose fairing is constructed from light-alloy sheet in three portions. the cross-section being an arc about the spar centre-line. The upper portion extends from the top of the rudder to the top hinge, the middle portion between the top and centre hinges, and the lower portion from the centre hinge to the bottom hinge. The nosing is riveted to each of the nose ribs mounted on the rudder spar.

RIBS:

The ribs are constructed of light-alloy and, except the lower one, all have M-section booms: the majority are diagonally braced by tubular members riveted inside the booms. Ribs D, F, and J, however, have plate webs pierced with flanged lightening holes and are additionally stiffened with transverse channel-section members. Rib L is a flanged plate rib having three flanged lightening holes and is the only rib which includes the nosing rib in its construction. At all the other ribs, the corresponding nose rib is of semi-circular form, constructed separately from flanged-up plate and riveted to the spar spools and rib booms.

HINGES:

Three hinge assemblies are provided for the rudder. The top hinge is just below the third rib from the top of the rudder, the centre (locating) hinge is between the eighth and ninth ribs, and the bottom hinge is below the bottom rib. The hinges consist of needle roller bearings housed in a base block and cap, retaining rings being utilised to locate the rollers laterally. The cap and block are held together by two distance tubes which are forced into them at the rudder attachment holes; these holes pick up with attachment studs in the fin and with studs on brackets attached to the sternpost and rudder shrouding. The needle bearings are packed with lubricant and a grease nipple is incorporated in each hinge for lubrication in service.

TRIMMING TAB:

The rudder trimming tab is of steamline section and is constructed of light-alloy skin riveted to a channel-section spar which runs the entire length of the tab, being broken only at the operating lever. The tab is stiffened internally with light-alloy ribs which are riveted in position. A mild steel plug-end fits inside the skin at each end of the tab and is drilied vertically to receive the hinge pin, and slotted and drilled horizontally for the hinge pin fixing rivets. The hinge bearings are formed by oilite bushes in the upper and lower trimming-tab bay ribs; a hinge pin fits into each plug-end at the end of the tab and is initially positioned by a tubular rivet passing through locking plates and the slotted hole. The hinge pin is capable of sliding stiffly in the slot and, on assembly with the rudder, is pushed into the oilite bushes in the ribs until the remaining holes of the locking plate line up with the drilled hole in the plug-end; another tubular rivet at this point locks the hinge pin in position.

GENERAL:

The stressed-skin cantilever main plane consists of port and starboard wings which axe attached directly to the fuselage, are semi-elliptical in shape and taper in thickness towards the tip; the undersurface is horizontal for approxmately one-third of the span and the outboard portions rise to form a dihedral angle. Two 20 mm. Hlspano Mk. V guns are carried in each wing.

In the bottom surface of the inboard portion of each wing there is a well which houses the undercarriage wheel in the "up" position; a fairing attached to the shock-absorber strut, and a hydraulically-operated door hinged at the root end rib, cover the housing when the wheel is retracted. A fuel tank is situated in each wing between the spars, immediately outboard of the wheel well. A nose fuel tank, shaped to form the leading edge of the aerofoil section, is fitted on the front spar of the port wing only, in front of the inter-spar tank and the wheel well. The oil cooler is mounted in a similar position in the starboard wing and an air intake for the carburettor is situated at the root end of each wing, in the leading edge inboard of the nose fuel tank or the oil cooler. The guns, together with their ammunition boxes, case and link chutes and pneumatic firing gear are housed in the inboard portions of the outer planes. Navigation lamps are fitted in the wing tips and there is a remotely-controlled retractable landing lamp in the lower surface of the port wing. On early aircraft the electrically-heated pressure-head is mounted on the outer portion of the port wing, just aft of the rear spar. On subsequent aircraft it extends from the leading edge of the port wing tip.

STRUCTURE:

Basically, each wing consists of a structure of front and rear spars, inter-spar ribs, nose ribs and tail ribs, with a covering of light-alloy sheet strengthened by stiffeners. An unusual feature is that the rear spar is cranked sharply forward from the root to the dihedral point. There is a torsion box between ribs A and L, made up of the front and rear spars in that area together with the inter-spar ribs and the top and bottom skin coverings of heavy gauge light-alloy sheet. High-tensile steel plug-ends are bolted to the spars for attachment to the fuselage,’ the tapered joint pins being horizontal at the front spar and vertical at the rear.

FRONT SPAR:

From the root end to the dihedral point, the front spar has top and bottom T-section booms made up from two thick L-section extrusions riveted together; outboard of this point the booms are of normal extruded T-section. Both the inner and the outer booms are fixed to a heavy-gauge light-alloy sheet webi outboard of the break and as far as inter-spar rib K, access hoies are prowded in the web, and are covered with light-alloy plates riveted in position.

REAR SPAR:

The rear spar is similar in most respects to the front spar. except that it is cranked sharply forward from the root end to the dihedral point and has access holes covered with plates, from the break to the tip.

SUB SPARS:

The sub-spars are all aft of the rear spar and consist of light-alloy flanged webs.

INTER-SPAR RIBS:

These ribs, of which there are sixteen in each wing, extend between the front and rear spars. The main ones are known as the inner end rib, the undercarriage girder and inter-spar rib A. The inner end rib consists of a light-alloy web with top and bottom booms of light-alloy angle and double-angle sections. The undercarriage girder has a light-alloy sheet web with extruded T-section booms. Inter-spar rib A consists of a light-alloy web with an extruded L-section top boom and an extruded T-section lower boom, the undercarriage pivot casting being mounted on the inboard face of the web at the forward end. The remaining inter-spar ribs consist of light-alloy webs, flanged aiong the top and pottom edges.

NOSE RIBS:

The nose ribs, of which there are eighteen in each wing, consist of plate webs flanged along the top and bottom edges, with flanged lightening holes. Nose ribs A, C and 0 are additionally stiffened round their top and bottom contours by light-alloy angles rireted in place. The inner air-intake’rib on the port side is fireproofed with asbestos sheet to protect the nose tank, should the engine catch fire.

TAIL RIBS:

The tail ribs are of several types. Ribs 1 to 6 consist of light-alloy plate webs with their top and bottom edges flanged to a channel section above the gap for the flap; tail ribs 1 to 5 have, in addition, tubular bracing members between the rear spar and the flap gap, all the ribs being recessed to accommodate the flap, Between the rear spar and the sub-spar, fomard of the cut-away for the aileron, are tail ribs H to NO. These are not full ribs but consist of light-alloy plate flanged webs, each containing lightening holes. The inner and outer aileron hinge ribs comprise light-alloy flanged webs and are fitted with hinge brackets to support the ailerons.

AILERON OPERATING GEAR:

The aileron operating gear is situated approximately half-way between tail rib G and the wing tip, between the rear spar and the main sub-spar. It consists of a light-alloy plate structure to which the control lever is pivoted.

GUN AND MAGAZINE BAYS:

The gun-bay is of unusual construction as there is no internal structure aft of the rear spar, in spite of the fact that the latter is much further forward than is usually the case. Forward of the rear spar, the construction of the gun bay is similar to that of the rest of the wing outboard of the break joint, having normal inter-spar and nose ribs with a covering of light-alloy skin. Aft of the rear spar the top surface of the wing above the gun bay consists of two access doors, the trailing edge of the rear top access door forming the trailing edge of the wing. Another gun access door is provided in t’ne undersurface of the wing, and all three doors are held in place on metal landings by turnbutton fasteners. The magazine bays are covered in the upper surface of the wing by detachable access doors held in place by turnbutton fasteners.

DROP TANK SUPPORTS (later aircraft only):

Additional structure has been 1 introduced in the wings just outboard of rib D to provide attachment points for the drop fuel tanks. In each wing there are two support hooks. The front hook is part of a special spring-loaded release unit which is bolted in a mounting bracket. This bracket is, in turn, bolted to the forward face of the front spar. The rear hook is attached to a bracket which bolts on to the forward face of the rear spar and is supported by a tie channel picking up with bolts at the top spar boom.

BOMB RACK SUPPORTS:

Additional structure has been introduced into the wings ta provide attachment points for the bomb carriers and, aft of these, the bottom wing skin is reinforced by angle-section stringers to prevent cracking due to buffeting caused by certain types of bomb. The front points consist of two support channels, on each of which there is a special anchor nut, attached to the rear face of the front spar on each side of rib D. At the rear, the anchor nuts are mounted on two channels attached to inter-spar ribs C, D and E by angle brackets. On the rear face of the rear spar there is a pulley for the Bowden cable of the mechanical release control, and also a bracket which supports the mechanical release operating lever.

R.P. MOUNTINGS:

To cater for the installation of rocket projectiles additional structure is provided in the wings to support the R.P. mountings. Bearer channels are mounted in the outboard ammunition tank bays forward of the tanks, between tail ribs C, E and G. Suspension sockets are mounted between the bearers at an angle of 7 deg. to compensate for the taper and dihedral of the wing. At the lower ends of the sockets sealing caps are fitted to provide attachment to the wing skin. At the top of the rear sockets sealing caps containing electrical sockets are mounted and held in place by elastic cords. The front mountings for the R.P. rails are attached to the brackets mounted on the forward face of the front spar.

WHEEL WELL AND FUEL TANK BAY:

In the wheel well, between the inner end rib and the undercarriage girder, the upper skin incorporates two heavy longitudinal girders and a number of lateral stiffeners, which eliminates the necessity for internal structure. Similarly, the girder over the inter-spar fuel. tank is incorporated in the top skin of the wing, and attached to a number of lateral stringers. When the wheel is retracted the undersurf?ce of the well is closed by a fairing on the shock-absorber strut and by two wheel doors, one of which is hinged on the inner end rib and a smaller one at the top of the leg, hinged at the undercarriage girder. The lower skin under the inter-spar tank is attached to the latter and is detachable with the tank. It is normally unfastened from the fuel tank only when it is necessary to obtain access to the tank sump.

TANK COMPARTMENT FRONT WALL:

The tank compartment front wall consists of a single sheet of light-alloy with a flanged upper edge and an angle section boom riveted to its lower edge.

COVERING:

The covering of the wing is entirely of light-alloy sheets, varying in thickness according to the load distribution on the structure. The area between inter-spar ribs A and L, bounded by the front and rear spars, has a top and bottom covering of heavy gauge plate to form a torsion box.

A detachable gun door is provided in the nosing between nose ribs A and C, to accommodate the muzzles of the guns.

WING TIP:

The wing tip is riveted to inter-spar rib 0 and consists of two light spar extensions with light-alloy flanged web type ribs. Four pegs fixed to the spar extensions locate the wing tip for assembly. A navigation lamp is situated in the angle between inter-spar rib 0 and the front spar extension, and is covered by a detachable transparent acetate sheet window which thus forms the front portion of the tip. The remainder of the wing tip is covered with a light-alloy skin. On all but a few early aircraft the pressure-head is mounted on nose rib 0 inside the port wing tip, and it extends forward of the leading edge of the tip.

A retractable landing lamp is provided in the lower surface of the port wing, outboard of tail rib G and aft of the rear spar.

ACCESS DOORS:

Doors and detachable panels in the wings provide access to control connections and components within the wing structure; they are secured either by screws around their edges or by turnbutton fasteners.

AILERONS:

Each of the ailerons is of sheet metal construction and consists of a light-alloy channel section spar built up to form a D-shaped nosing. Aft of this spar, the structure comprises a number of light sheet metal ribs, and is covered with pre-tensioned duralumin skin riveted to the spar and ribs. At each end of the aileron spar is a self-aligning ballrace which is contained in a bearing housing in each of the aileron hinge ribs. The aileron operating gear is situated in the wing between the rear spar and the sub-spa at approximately the middle of the aileron, which it operates by means of an arm and rod which are bolted to a hinge bracket attached to the aileron spar. An adjustable trimming tab is provided in the trailing edge at the inboard end.

TRIMMING TABS:

Each aileron trimming tab consists of a streamline section light-alloy tube riveted on to a light-alloy former at each end. A hinge pin in the nose of the tab pivots it on the aileron inner end rib and rib No. 5. The tab may be adjusted on the ground, to the required angle of incidence.

The flaps are in four portions, two being provided under each wing, and they extend outboard from the wing root to tail rib G. The two portions in each wing are joined together at the inner end of the gun bay (where the dihedral commences), the spars being connected by a universal joint. Each flap consists of a single sheet of light-alloy stiffened with ribs of the same material, with a tubular steel spar. Each portion is supported by three journal bearings which are bolted to the trailing rib structure.

FLAP-OPERATING GEAR:

Each pair of flaps is operated by a hydraulic jack, anchored by means of a shackle to an eyebolt passing through the lower boom of the rear spar. The flaps are interconnected by a spar extension which passes across the fuselage to ensure that both port and starboard flaps are at the same setting.

The radio installations are carried on two trays mounted behind the pilot's seat in the monocoque forward of frame A. They comprise T.R.1143, beam approach and I.F.F.

T.R.1143

The transmitter-receiver and its power unit are carried on the upper tray, on a level with the radio access panel in the port side of the monocoque. A whip aerial is mounted above on the monocoque skin.

I.F.F. installation

A receiver, R.3003, R.3078 or R.3090 is mounted at the forward end of the lower tray. A blade aerial is on the underside of the monocoque near the beam approach aerial. When R.3003 or R.3078 are used there is also a wire aerial slung between the fuselage and the tips of the tailplane. The control panel is mounted on the port side of the cockpit.

Beam approach

The amplifier A.1271 is mounted at the rear of the lower tray, a "boat"-type aerial being fitted on the underside of the monocoque.

GENERAL: The upper end of the undercarriage leg embodies a spindle which is held in bearings on a steel casting bolted to the front spar of the wing and the inboard face of rib A. The leg is braced laterally by a side-stay, the lower end of which is connected by a universal joint to lugs at a point about mid-way down the strut of the leg. The upper end of the side stay pivots about a horizontal spindle projecting rearwards from a bearing in the front spar web, the rear end being supported by a bearing on the undercarriage girder of the main plane. The side stay is knuckle-jointed and a triangulated tubular lever is attached to its upper portion. For raising and lowering the main wheel units, a hydraulic jack, anchored to a bracket on the rear face of the front spar web, acts on the triangulated lever as described in para. 6. There is no radius rod and the main undercarriage leg is a cantilever unit as far as fore-and-aft loads are concerned. The upper portion of the side-stay, above the knuckle-joint, can rotate about the spindle attached to the front spar and the undercarriage girder and can swing about the pillar of the triangulated lever, carrying the stay of the latter with it.   RAISING: The piston of the hydraulic jack is connected to a jack lever Divoted inside the fulcrum bracket. During its initial travel the piston pulls over this lever until movement is checked by spigots on the jack lever reaching the end of slots in the fulcrum bracket. As the lever moves over in this stage of the operation its upper face bears against a spring-loaded locking-latch, raising the latter clear of a bolt in the fulcrum bracket. The fulcrum bracket is no longer locked and further movement of the piston inboard pivots it about the bearing spindle. This brings into play the triangulated lever formed by the upper portion of the side stay which moves upwards "breaking" the side stay at the knuckle joint, and consequently drawing the undercarriage leg inboard. The axis of the spindle at the top of the shock-absorber strut has its rear end slightly below and outboard of the front end ; this inclination of the spindle ensures that the leg, carrying the wheel, travels slightly backwards as it swings inwards and upwards, thus enabling the wheel to be housed between the main plane spars. When retraction is complete, a stirrup, mounted tangentially approximately half-way down the leg, engages with the catch gear which then supports the leg.

LOVERING:
As in the case of raising the main undercarriage leg, the first stage of the outward travel of the hydraulic jack piston moves only the jack lever pivoted in the fulcrum bracket, this action releasing the catch gear. The undercarriage leg then falls under its own weight but its rate of descent is checked by the oil pressure in the return pipe of the hydraulic system. As the jack piston continues its outward travel, the spigot on the jack lever bears against the fulcrum bracket of the triangulated lever and rotates the upper portion of the side stay downwards. This straightening of the side stay is assisted by a spring carried on the telescopic strut of the pneumatic assister gear which acts on the lower portion of the side stay near the knuckle joint. At the moment when the two portions of the side stay become co-axial the slot in the locking latch rides home over the bolt on the fulcrum bracket, thus locking the side stay and, consequently, the undercarriage leg, in a position for landing.

LATCH AND CATCH GEAR: 
The latch and catch gear is mounted on the front spar and the undercarriage girder. The latch gear is the mechanism nearest to the front spar and its function is to lock the undercarriage side stay rigidly in the "down" position. The catch gear supports the undercarriage in the "up" position. Both gears are operated by a jack lever which is common to both, the operation being automatically carried out by the movement of the hydraulic jack.
The catch gear consists of a torque tube carried in two bearings on the undercarriage girder and the front spar, on which are bolted two levers which operate the stirrup catch and a shackle connected to the fulcrum bracket of the side stay assembly. The main stirrup catch is also mounted on this torque tube but is free to revolve on it, and is spring-loaded to prevent accidental opening. A small lever connected by a Bowden cable to the fairing door catch is pivoted on the main stirrup catch.

EMERGENCY RELEASE GEAR:
An emergency release gear is provided which can operate the catch gear should the undercarriage fail to disengage from the catch gear when the undercarriage control lever is set to DOWN. Depression of the two pedals opens the catch gear thus allowing the undercarriage to fall under its own weight. The operation is assisted by pneumatic pressure in the pneumatic assister strut.
Cables attached to the undercarriage emergency release pedals at each side of the rudder bar run forward over pulleys bolted to the fuselage structure and then out to a lever mounted on each catch gear torque tube. This lever is free to rotate on the tube, and depression of the pedals causes it to bear against the main stirrup catch in the same manner as the normal operating lever, and the stirrup is consequently released.
An undercarriage pneumatic assister strut forms part of each under-carriage assembly to ensure that the legs lock fully down when the emergency release gear is operated. This pneumatic assister installation consists simply of a cocking valve on the port side of the cockpit connected by a pipe to the pneumatic assister strut. Air released by the cock causes the strut to extend and so force the side-stay mechanism into the fully locked position for landing. The pneumatic pressure is supplemented by a spring on the outside of the strut.

SAFETY DEVICES: 
A composite undercarriage and tail wheel indicator is situated on the pilot's instrument panel on the port side. It is provided with three lamps which are controlled by three micro-switches, mounted at the locking latch, the stirrup catch and the wheel door landing respectively. When the wheels are down, the plunger of the micro-switch incorporated in the locking latch is depressed by the bolt on the fulcrum bracket. This micro-switch overrides the main stirrup catch forcing it open against the springs. At the limit of the upward movement of the leg the stirrup rounds the apex of the stirrup catch and the latter shuts home by means of the springs, thus locking the under-carriage up. As it rounds the apex of the stirrup catch the stirrup bears against the small lever, thus pulling over the catch that locks the leg fairing, allowing the landing on the latter to pass the catch. As the stirrup finally rides home and is locked by the catch gear the small lever closes once more and allows the catch to lock under the leg fairing. In addition, a small spring-loaded catch on the wheel fairing door locks the latter up by engaging with a landing on the leg fairing.

SHOCK-ABSORBER STRUT:
Three types of shock-absorber units can be fitted to this aircraft, types C.8625, C.9759 and A.9835. Types C.8625 and C.9759 are completely interchangeable in the undercarriage leg assemblies, but type A.9335 can only be fitted to leg assemblies of issue 29 or later unless Mod. No. 126 has been incorporated.

WHEELS AND BRAKES:
The cast Elektron wheels are fitted with high-pressure balloon tyres. Each wheel is carried on two bearings on the stub axle at the bottom of each shock-absorber strut. A steel brake drum liner for the Dunlop pneumatic brake unit is fitted into the outboard side of each wheel.

FAIRINGS:
When the undercarriage is retracted, the well that houses the complete unit in the undersurface of each wing is covered by three Lairings. The main leg fairing is attached directly to the leg and the small top leg fairing is hinged on to the undercarriage pivot casting and connected to the leg with an adjustable rod. The third fairing is hinged on the main plane root rib and is elcctro-hydraulically operated through a solenoid.
The main leg fairing is bolted to the leg at three points. Each fixing consists of two eye-bolts which pick up lugs incorporated in the leg. The position of the fairing can be adjusted laterally by means of shims under the eye-bolts and, at the lower attachment, fore-and-aft adjustment is possible as the bolts lixing the eye-bolts to the fairing pick up in slots on the fairing lower rib. The light-alloy skin of this main fairing is shaped to close the gap in the wing skin left for the shock-absorber leg and approximately half of the wheel. This skin is stiffened by three top-hat section ribs and a number of top-hat and Z-section stiffeners. The forward and rear edges are strengthened by square-section tube and angle section stiffeners. A small access door is incorporated in the fairing skin opposite the bottom link attachment bolt, to enable the shock-absorber to be removed and replaced without removing the fairing.
The small top leg fairing door completes the sealing of the wing under the shock-absorber strut in the retracted position. It comprises light-alloy inner and outer skins stiffened with Z-, top-hat and square-section stiffeners and is hinged onto the undercarriage pivot casting. An adjustable connecting rod picks up a swivel eye-bolt on the fairing door and a bracket on the shock-absorber strut, so that retraction of the leg closes the door.
The undercarriage wheel door is designed to cover the gap in the lower wing skin not covered by the two leg fairing doors. It comprises inner and outer light-alloy skins spaced apart by Z-section light-alloy plate ribs. The inside edge is strengthened by a channel-section stiffener and a reinforcing skin faking. Two hinges are provided at this inboard edge, which pick up with the root rib of the main plane, and a large bracket is attached to the same rib to support the upper end of the hydraulic jack that operates the door. The lower end of the jack piston is connected to a boss at the top rear corner of the door.

GENERAL: The tail wheel unit consists of a main tube E (on which is mounted the retracting and locking mechanism), a pivot bracket assembly P, a pivot bracket assembly P, which houses the shack-absorber unit M and the self-centrinp mechanism, which houses the shack-absorber unit M and the self-centrinp mechanism. and a wheel fork assembly W which is hinged to the bracket by means of a pivot pin V. The unit is retracted hydraulically. The wheel runs on ball bearings on an axle located in the ends of the fork, and is fitted with a self-earthing twin-contact tyre. A ferrule bolted between two lugs on each side of the wheel fork enables a special tail wheel steering am to be used when manceuvring the aircraft on the ground without the aid of the engine. The tail wheel is retracted and lowered by a hydraulic jack attached at the front end of the retracting mechanism on the strut, and, at the rear end to the stempost. CONSTRUCTION: The main outer tube E is pivot-mounted in bearings at the junction of the front and rear diagonal diaphragms of the tail end of the fuselage by means of a pin passing through two lugs Jl to which are attached a pair of levers L; a spigot sleeve A is fitted over the end of the tube E and is loaded away from the tube by a spring B. A pair of lugs at the bottom of the spigot sleeve A are coupled by a T-piece G and tie-rod assembly Hl to two bell-cranks K pivoted between the outer ends of levers L. The hydraulic jack eye-bolt is bolted between the other arms of the cranks K, and the pin Fl securing the tie rod assembly to the lugs on the spigot sleeve extends beyond the lugs to engage a slot in each guide bracket J. The lower end of the tube E carries a bearing to support the pivot bracket P, and in the top of the tube a collar C and cam support tube F are secured by pins D. The top and lower self-centring cams (Rand S) and the thrust race T are mounted over the inner tube F. The lower cam S is secured by pins H to the pivot bracket and can rotate about tube F on the thrust race T. The upper cam R is prevented from rotating relative to tube F by a pin Q but can slide axially on F as pin Q passes through an elongated hole in the tube. The two cams are held in contact by a spring 0. The pivot bracket P carries a top shock-absorber pin U, and the shock-absorber is retained in position by two pins Ml, mounted in eccentric bushes Nl.

RETRACTION:
When the tail wheel is in the DOWN position the hydraulic jack is fully compressed and the pin Fl is at the top of the slots in the guide brackets J. This allows the spigot sleeve A to be extended away from the main tube E by spring B so that the spigot engages in a fitting in the top diaphragm of the tail end structure and locks the tail wheel down. As the jack piston rod extends, the bell cranks K are pivoted about the bolt supporting them between the levers L, and the tie-rod assembly HI draws pin Fl down the slots in the guide brackets J, at the same time withdrawing spigot A from the locking fitting in the top diaphragm. As the guide plates are bolted to the rear diaphragm further extension of the jack acts on levers L causing the tail wheel unit to rotate forward and upward about the main attachment pin. Simultaneously the pin F1 follows round the inside arc of the guide plates, holding spigot A in the unlocked position.

LOWERING: 
As the hydraulic jack is compressed it acts on levers L, causing them to rotate the tail wheel unit downward and rearward about the main attachment pin. This operation continues until pin Fl reaches the bottom of the locking slots in the guide brackets J, when the tail wheel is in the correct DOWN position. Final compression then pivots the bell cranks K, allowing pin F1 to move up the locking slots and so permit spring B to force spigot A into the locking lug in the top diaphragm.

SELF-CENTRING: Rotation of the pivot bracket in tube E caused by landing and taxying loads causes the lower cam S to rotate relative to the upper cam R. and the action of this cam forces cam R up the support tube F, so compressing spring 0. When the side load on the wheel is relieved spring 0 acts on cam R, returning cam S and consequently the pivot bracket to the neutral position, thus aligning the wheel and fork with the fore-and-aft datum of the aircraft.   SHOCK-ABSORBER:  The pneumatic shock-absorber consists of an outer oil cylinder C in which slides an air cylinder assembly M. The outer cylinder incorporates a bearing at the top which engages the top attachment pin U. On one side of the bearing is a bleeder screw R and on the other a filler screw A. The air cylinder assembly M is closed at one end by a fitting K, which houses the inflation valve J and is bushed for the lower attach-ment pin in the wheel fork, while the upper end is enclosed by diaphragm D on which a recoil valve P is mounted by means of a bolt and nut B. A floating piston E, sealed by a ring 0 at one end and carrying a piston ring N at the other end, is free to slide inside the air cylinder M. The inner cylinder assembly M is retained in the outer cylinder by a bearing nut G, oil leakage being prevented by rings F and H.

OPERATION:
Landing and taxying loads cause the wheel fork to rotate about the main pivot pin, thus compressing the shock-absorber. Since the outer cylinder C is filled with oil and the inner cylinder M inflated with air, this compression causes the oil to lift the recoil valve P and flow through holes in diaphragm D into the inner cylinder, thus driving the floating piston E down the cylinder and further compressing the air until the load has been completely absorbed. When the compression is arrested, the high air pressure forces the oil out of the air cylinder thus re-extending the shock-absorber. This return oil flow immediately closes the recoil valve P, however, so that the oil is confined to passing through the small hole in valve P. This retards the recoil of the shock-absorber unit and prevents sharp rebound of the fork and wheel.

TAIL WHEEL FAIRINGS DOORS:
Two tail wheel fairing doors are hinged to the lower edge of the skin of the rear monocoque. The doors are shaped to conform with the contours of the rear manocaque and, when in the closed position, completely seal the tail wheel cutaway in the latter, small bulges being incorporated to clear the tyre. A mounting bracket and cap are bolted to the tail wheel oleo-leg and adjustable connecting rods attach the doors to this bracket. The operation of opening or closing the doors is thus governed by the tail wheel; when the iatter is retracted the connecting rods first of all open the doors wider apart to clear the tyre and then close them as the oleo strut moves round its pivot, until, with the wheel fully retracted, the doors are just closed.

To assist in entering the cockpit, two footsteps and two handholes are provided on the starboard side. The first footstep used when entering the aircraft is retractable and employed in conjunction with a handhole in the monocoque to gain a foothold on the wing walkway. From there, access to the cockpit is obtained by means of a footstep at the lower forward corner of the emergency exit panel and a handhole in the upper part of the monocoque. When the retractable footstep is pulled downwards it loads an elastic cord and, at the bottom of its stroke, operates a trigger which trips the catch holding the spring-loaded cover over the handhole above. When the handhole cover is pressed back over the hole, the action releases the catch which has retained the footstep in the "down" position and it is returned into the fuselage under the action of the elastic cord. The remaining handbole and footstep are covered by spring-loaded doors which are flush with the skin when closed.

Drop tanks (later aircraft only): The 45 gallon drop tanks are made of tinned steel and have a filler cap at the forward end. They are of streamlined shape and contain two baffles. The drop tank attachment brackets and stabilising brackets are bolted to the tank in the locality of the baffles, and the assembly is stiffened internally by top-hat section channels which extend for the full depth of the tank and are bolted to the baffles.   The bolts fixing the drop tank attachment brackets to the tank pick up with flanges at the top of the internal stiffener channels. A roller on each attachment bracket engages with the hooks in the wing and, when the tank is in position, the open side of the front hook is closed by a paw1 in the release unit. The paw1 is locked when in the closed position by a spring-loaded latch, and the latch, in turn, is operated by a spring-loaded trip lever which is connected by a bowden cable to the jettison control in the cockpit. When the jettison lever is operated the trip lever is pivoted upwards against the action of its spring. This causes an arm on it to bear against the latch, pushing the latch upwards and so releasing the pawl. The tank then slides out of the hooks under gravity, pushing over the paw1 which is free to rotate about its pivot. An indicator arm carried on the latch protrudes below the wing skin, when the tank is locked in position. As the tank falls away it breaks the glass tubes of the fuel delivery and air pressure pipes. The tank fairings are made of light alloy, though some may still be of transparent acetate sheet.   They are made in four sections and are attached to the stabilising brackets on the tank, 20 s.w.g., light-alloy joint plates being provided at the attachment.points. Along the top of the fairings is a doubled-over strip of felt which seals the gap between the fairings and the undersurface of the wing when the tank is in position.

Drop tanks jettison lever and air pressure control:
The jettison lever and air pressure cock control lever are mounted together in a control box on the starboard leg panel. A lug on the jettison lever engages with and pushes back the air pressure cock control lever whenever the former is pulled back to the JETTISON position, thus cutting off the pressure supply to the drop tanks immediately they are jettisoned. The jettison lever must be retained in the JETTISON position whenever the drop tanks are not fitted, or a breakdown in the air pressure system will result.