Design Analysis No 5
Bristol Beaufighter

Comprehensive engineering study —complete with detail photos, sectional sketches, and pertinent tables —of Britain's famed night fighter, with notes included on its strategic adaption for Army cooperation and Coastal Command torpedo-bomber work.

Britain's Beaufighter is an all-metal mid-wing monoplane used as a two-seat long-range fighter or fighter-bomber for day or night duties. Special equipment is installed when these aircraft are operated by the Coastal Command. A number also act as torpedo-carriers.

The main wing, of light-alloy stressed-skin construction, is made up of a center section and two outer wing panels with detachable wingtips. The center section forms the basic structure of the aircraft, for not only are the outer wing panels attached directly to it but also the front and rear fuselage sections, undercarriage units, and engine nacelles. Ailerons are light-alloy fabric- or metal-covered structures. They are inset and are of Frise type, with both aerodynamic and mass balance. There is an adjustable tab on the left aileron and a trim tab on the right one. Hydraulically operated all-metal split flaps extend between the inner ends of the ailerons and the sides of the fuselage.

Fuselage of this craft is a semi-monocoque structure with closely spaced Alclad formers of lipped channel or Z-section, extruded angle-section stringers, and an Alclad skin. There is a reinforced crash frame immediately behind the pilot's cockpit and others at the joint midway between the rear cockpit and the tail. Otherwise the formers are mainly of light construction. Keel members along the bottom of the fuselage carry the concentrated loads from the 20-mm guns.

Fixed surfaces of the tail unit are conventional stressed-skin structures. The rudder and elevators have light-alloy framework with fabric covering. A trim tab is fitted to the rudder, while there are both trim and balance tabs on the elevators.

The landing gear of consists of two retractable undercarriage units and a retractable tail wheel. Each undercarriage unit is composed of two oleo-pneumatic shock absorber legs, in the form of a frame, with two inclined drag struts, and a single central hydraulic retracting jack. Medium pressure tires with pneumatically-operated brakes are fitted.

Engines attach to the center wing by steel tube mountings and are enclosed in long-chord cowlings with controllable air flaps. The fuel supply is carried in four tanks, two in the center wing and one in each outer section. Long-range tanks may be fitted. The oil coolers are mounted in ducts in the leading edges of the outer wings.

The pilot's cockpit is in the extreme nose of the fuselage and is entered through a hatch in the floor (also used as the pilot's main parachute exit) mounted on trunnions at its mid-point so that when open it forms a wind-break for the pilot when leaving by parachute. Under hatches cannot be used when a torpedo is carried, entry then being made via the hinged roof or hood. A "spectacle"-type hand-wheel is used for aileron control. The front panel of the windshield is armored glass and there are armor plates forward of the instrument panel. As rearward protection for the pilot, a pair of armor-plate bulkhead doors are attached to the rear spar where the latter crosses the fuselage. The pilot is provided with all the usual instruments required for long-range fighter and fighter-bomber duties.

Entire armament of the plane is under control of the pilot. Carried are four 20-mm guns, mounted in the bottom of the fuselage, also four .303 machine guns in the right wing and two .303 machine guns in the left wing. However, the .303s may be replaced by extra fuel tanks. Bombs may be carried under the wings.

The rear cockpit, which is aft of the trailing edge of the wing, is occupied on Fighter Command aircraft by a radio operator, who also acts as lookout and as 20-mm gun loader for the earlier-type drum-fed guns. On Coastal Command aircraft, the occupant is a radio operator-avigator, but with the same additional duties. In fighter aircraft a seat-type parachute is used, but on the coastal type a lap pack gives the avigator greater freedom. Coastal aircraft are also equipped with DF radio, general avigational equipment, and a chart table forward of the rear seat. The rear cockpit is entered by a hatch in the floor similar to the pilot's. There is free movement from the rear cockpit to the pilot's seat. On early aircraft, the 20-mm guns had drum feed, with racks of spare drums, but on the later types a belt feed is fitted. All usual radio and operational equipment is installed and a crate of desert equipment can also be carried. The dinghy, in the rear left center wing, is manually released by pulling any one of three handles: 1. Above front spar on left side, 2. below observer's emergency door release handle on left side, 3. externally, atop fuselage forward of fin. The dinghy can be automatically released by an immersion switch below the cockpit floor. Marine distress signals are stowed with dinghy.

Fuselage

The fuselage, in three sections of all-metal monocoque construction, consists of Alclad formers, mainly of lipped Z-section, extruded light alloy beaded angle stringers, and Alclad skin plating. Countersunk aluminum-alloy rivets secure the formers and stringers to the skin but are not attached to each other, the formers being notched to clear the stringers.

Front fuselage: Here the main structure is of Alclad Z-section and channel-section formers and skin plating, with extruded beaded-angle, fore-and-aft stringers. Substantial keel members extend forward and two longerons are fitted left and right. The top longeron and a longitudinal member one each side carry a shelf for the engine auxiliary controls and other equipment. The bottom longeron is near floor level. A tubular structure, mainly of mild steel, supports the pilot's seat. Below the windshield and reaching forward are non-magnetic bullet-proof armor plates, and forward of these the nose piece is detachable. Blast tubes for the four guns are under the floor outside the keel members. Front hatch is between main wing spars.

The roof and part of the sides of the pilot's cockpit are covered with transparent sheeting, and a bullet-proof windshield is fitted at the front. The frame work of light-alloy tubular members and magnesium-alloy castings is bolted to the main structure. Transparent sheeting, mounted on rubber, is secured to the framework by light alloy cover strips. Additional emergency exits are a knock-out window on the right side and a hinged roof window. Two screens compose the pilot's windshield, the outer of ¼-in Triplex and the inner one of six ¼-in glass plates, making a bullet-proof shield. The screens are separated by a 3/8-in air gap through which warm air is passed to prevent frosting.

Rear fuselage is generally similar to the main structure of the front fuselage. The observer's hood — about midway along its length — is made of transparent sheeting supported on a tubular frame, hinged on the right side for emergency exit. Keel members extend the whole length of the rear fuselage. Armor is fitted on the front of the rear spar and extends upwards 20 in, while two doors with a central handle are above the spar.

In the rear fuselage are several double formers of lipped channel placed back to back some distance apart with a plate riveted across their flanges on the inboard side. The formers at the center wing spars have Hiduminium forked blocks riveted and bolted to the web of the channels at the bottom for attachment to the box ribs on the center wing. The rear fuselage is strengthened by three longerons on each side. The top and middle longerons are of channel riveted to top and bottom angles attached to the skin; the bottom longeron is of lipped channel, built up of a plate and two Z-sections, the top and bottom flanges of which are attached to the skin.

Rear frame comprises lipped Z-section formers, bulb-angle stringers, and Alclad skin plating. The aft end of the frame is formed by a sternpost carrying the rudder bottom hinge and extended upward to carry the top hinge. A special section stringer is near the bottom on each side. An aperture in the underside of the frame, boxed in with aluminum-manganese alloy and plastic sheet, provides a housing for the tail wheel unit when it is retracted.

Attachment of Front and Rear Fuselage and Center Plane

Ends of the skin plating of the front and rear fuselage butt together and are secured by setscrews and Simmonds nuts to butt straps underneath. The other attachments are made at the Hiduminium blocks on the box ribs of the center wing. Two blocks, near the bottom of the front fuselage, are riveted to channels that are in turn riveted to angles on the skin and are secured by high-tensile steel bolts in steel bushings to the formed horizontal pair of blocks at the bottom of the center wing box ribs. Extruded and plate angles strengthen the curve of the fuselage over the top of the wing. The rear horizontal blocks on the box ribs are attached by bolts and steel bushings to a block riveted to each middle longeron of the rear fuselage.

Hatches and Seats

As for the front entry and exit hatch, the front hatch, under the fuselage between front and rear spars, is a door with a double skin of Alclad on Alclad formers. The door is pivoted midway along its length on a tubular shaft supported on two bearings attached to the keel members. Dash-pots are provided on either side of the hatch for retarding its movement when used as a parachute exit. The door has a short ladder at the bottom and a foot step with a spring-loaded flap for entry. Catches, holding the door in the open or closed position, are operated by three handles, one under the front fuselage and two inside the airplane. The rear hatch is generally similar.

The pilot's seat takes a seat parachute and is adjustable for height. It is attached to a steel and duralumin tube structure extending from the top boom of the front spar to a keel plate. On the lever on the left side of the seat is an adjusting handle by which the seat can be raised 4 in. As a twist grip on the front end of the handle is rotated, an external cam forces down a spring-loaded sleeve and disengages a locking bolt from a toothed quadrant attached to the tube. Elastic cords at the back of the seat relieve the levers of the weight of the occupant and facilitate raising the seat. On the right side is a lever for collapsing the seat — when pulled up it releases a catch that allows the seat pan and back to be straightened out by pressure from the pilot's shoulders.

The observer's seat takes a seat parachute, and rotates on rollers around a pivot on a duralumin tube mounting. A hand-operated catch on the seat engages with slots in the mounting and locks the seat in either the forward or aft position. Two foot rests are at front and rear.

Front and rear hatches are used as emergency parachute exits. Ground emergency exits are provided by the pilot's knock-out window and pilot's and observer's hoods.

Center Wing

The main center wing is a cantilever two-spar metal-covered structure tapered in chord and thickness and constructed in three portions, the center and two outer panels. The center wing spars are continuous through the fuselage and are bolted to it. Hydraulically operated split-trailing-edge flaps are fitted inboard of the ailerons and extend to the fuselage sides. Near the outboard ends of the center wing are mounted structures of steel tube for the engine mounting, nacelles, and undercarriage units. Two fuel tanks are carried in the center section, one on each side of the center line, and single tanks are carried in each outer wing plane. Two landing lights are fitted under a transparent panel in the leading edge of the left outer wing.

The center wing has two spars with Alclad webs and extruded light-alloy booms, Alclad ribs and skin covering,and spanwise skin stiffeners of bulb-angle light alloy similar to the fuselage stringers. The main ribs extend between the spars only, the leading and trailing edge ribs being separate structures. Between the nacelles and the fuselage, the lower leading edge is hinged to permit access to the controls on the front spar. Four fittings are provided on each box rib near the fuselage for attachment of the center wing to the fuselage, and fairing fillets are fitted at the juncture of the two parts and secured by screws to a wood strip under the skin.

Spars have a shear web of Alclad sheet to which extruded light alloy booms are riveted. An angle for attaching the skin is also fitted at the booms. Extruded bulb-angles are riveted vertically to the inner faces of the web for attaching the ribs and for web stiffeners. The ends of the booms have steel bushings for the wing-joint bolts. End fittings are bolted toe each side of the booms and a web doubling plate is also fitted near the end of the spar.

Ribs: At each fuselage side Rib 1 is of built-up box form and has horizontal forked blocks of light alloy riveted tot he bottom corners and vertical forked blocks bolted to it at the top corners. These blocks have pressed-in steel bushings for the center wing-to-fuselage attachment bolts. Undercarriage attachment ribs have an Alclad web with top and bottom flanges of Alclad lipped angle and are reinforced by a bracing of square light-alloy tubes and vertical bulb-angles.

End ribs each consist of an Alclad plate web with flanged lightening holes and vertical light-alloy stiffeners of bulb-angle and top and bottom flanges of Alclad channel riveted on one side. Remaining interspar ribs, which are without web plate or bracing, consist of top and bottom booms. Top booms consist of channel and I-sections riveted to the skin; bottom ones form bearers for the tanks and are I-section.

Leading edge is of the plate ribs is stiffened diagonally by bulb-angle and supported by similar struts. Upper skin is riveted, while lower forms a hinged door. Ribs are bolted to the spar booms, and skin is riveted to the angle bracket on the front spar.

Trailing edge is in two portions, built of Alclad ribs and skin. Ribs are bolted to the spar booms and the skin is riveted to the angle bracket on the rear spar. The after portion, opening on the bottom for the flaps, is secured to a false spar by setscrews and bolts with Simmonds nuts at the aft end of the forward portion. There is also bulb-angle stringer, top and bottom, at about midchord.

Outer wings are generally of similar construction to the center section and are attached to it at the spars. Spar and trailing edge construction resembles that of the center wing. A sealing strip between the center and the outer wings is secured by setscrews. Top booms of the outer wing spars have forked, steel-bushed end fittings which interlock with, and are bolted directly to, the center wing spar end fittings. Similar bottom boom fittings are secured to the center wing spars by bolts and link plates on each side. In addition, the webs of the center and outer wing spars are connected by bolted channels and tie plates.

Main interspar ribs have an Alclad web plate stiffened by vertical light-alloy angles and flanges of Alclad bulb-angle. The remaining ribs have top and bottom booms of Alclad channel interconnected by light-alloy bulb-angle. At the fuel tank position, upper and lower booms are similar to those of the center wing.

Leading edge ribs have two overlapped plates stiffened diagonally by flanges and bulb angle with front portions competed by fitting a wood block. Skin of both upper and lower surfaces is riveted to the ribs, which are bolted to the spar booms, while the skin overlaps the angle bracket on the front spar and is riveted to it.

Outer wing tips are of flanged plate construction supported by plate ribs with intermediate ribs of light-alloy bulb-angle and riveted Alclad skin. They are secured by screws to the outermost wing rib and are detachable. The outer end is transparent sheet enclosing the avigation and formation-keeping lamps, which are mounted on the outer end rib. A recent modification introduces plastic lamps mounted in tubular brackets to to replace the formation-keeping lamps.

Flaps are constructed in four section —the left and right center and the outer wing flaps —and they extend from the fuselage sides out to the ailerons. They are operated by two hydraulic jacks, the left and right flaps being interconnected by balance cables for simultaneous action. Flaps are mainly of Alclad and have channel ribs, a Z-section spar at the forward face, channel transverse stiffeners near mid-chord, and a rectangular tube trailing edge. Brazier head rivets secure most of the bottom skin to the ribs, stiffeners, and spars. Chobert rivets are used on the top and in the last three rows on the bottom. The lower skin projects beyond the trailing edge and, when the flaps are raised, closes the rear gap beneath the wing. Piano hinges on the bottom of the flap spar connect the flaps to the false spar of the wing. A duralumin horn is bolted to the outboard end of each center flap and to the inboard end of each outer flap.

Dive brakes: Torpedo-carrying Beaufighters have a speed above 300 mph, and, while the precise technique of dropping torpedoes from high-speed aircraft is very secret, it is generally known that they may be released from heights up to about 150 ft and that the maximum aircraft speed at the drop should not exceed about 180 mph. To give a quick change from the high speed approach to the slow dropping speed, special bellows airbrakes are fitted. Immediately outboard of each engine is a venturi tube with a butterfly throttle at the rear end. This tube is connected to the air brakes, and when the throttle is open, the partial vacuum in the venturi sucks the brakes flat against the wing surfaces. When the throttle is closed the air pressure builds up and fills the bellows, extending the brakes.

Ailerons: Each aileron has a duralumin tube spar, with ribs, nosing and trailing edge of Alclad sheet and a fabric skin. Two mass-balance weights are fitted in the nose of each aileron, and the hinge points are inset to obtain aerodynamic balance. The spar is of duralumin tube on which flanged Alclad plate ribs are secured by collars and taper pins. Eyelets for attaching the fabric are in the rib flanges. The Alclad sheet nosing is bent round and riveted to the nose of the ribs, and the lead mass-balance weights are riveted inside along its entire length.

Outboard and inboard of the trimming tab, the trailing edge of Alclad sheet is riveted to the ribs. A duralumin tube, from the rear outboard corner to an eyebolt through the spar, reinforces the outboard end of the aileron. Three ball bearing hinges on each aileron are attached to special tail ribs on the outer wing.

Trimming tabs: The tab on the left aileron is made of light gage stainless steel sheet secured by countersunk screws on top and by round head screws in elongated holes on the underside, thous allowing a small amount of adjustment for lateral trimming to be made on the ground. The fabric of the aileron passes round the former to which the tab is secured but does not pass over the tab.

The trimming tab on the right aileron, operated from the cockpit, is of Alclad sheet, bent to shape and hinged to the trimming tab former. A horn is fitted to the underside of the tab.

Landing Gear

There are two independent undercarriage units and a tail wheel unit making up the landing gear, all simultaneously raised or lowered by hydraulic power, the undercarriage units swinging backward and upward into the nacelles and the tail wheel forward and upward into the underside of the stern frame.

Indicating and warning devices include three electrical position indicators, one for each unit, and an electrical buzzer. Oleo-pneumatic shock-absorber legs are fitted both the undercarriage (either Vickers or Lockheed) and to the tail wheel. Dunlop brakes are used on the undercarriage.

Undercarriage: Each unit has a single wheel on an axle between two shock-absorber units cross-braced to form a rigid frame. The frame is connected to the nacelle at pivot points at the top of the shock-absorber and is braced in the down position by a pair of knee-jointed radius rods, the supper portions of which are fixed to a transverse torque shaft supported in bearings on the rear tubes of the nacelle structure.

When the undercarriage is retracted, nacelle doors, shut by shock-absorber cords, fair the gap at the bottom of the nacelle, completely enclosing the undercarriage and wheel. A catch, operated by levers and Teleflex controls, is interconnected to the hydraulic selector lever. When the undercarriage is retracted and the hydraulic selector lever is returned to the "off" position, the catch locks the doors.

Empennage

The tail comprises a cantilever stabilizer and fin, elevators, and a rudder. On later models, the stabilizer has a pronounced dihedral of 12°. Early planes have no dihedral. All-metal construction is employed for stabilizer and fin, while elevators and rudder have metal framework and fabric covering. Rudder and elevators have inset trimming tabs, and each elevator has a balance tab. Stabilizer attachment fittings, extending to the upper surface, also serve as fin attachment points. Stabilizer and fin are faired, at the juncture with the rear frame, by fillets secured by woodscrews to wooden fairing strips on fin and frame.

Stabilizer: Early planes had a stabilizer built in one piece. I later models it is built in three pieces, a small center and two outer panels. The outer panels are riveted to the center section. Construction of both types is similar. Two Alclad channel spars, with extruded light-alloy booms riveted on as reinforcements for the flanges, flanged Alclad sheet ribs, and Alclad skin covering, form the tail plane structure. Between the spars, the skin is stiffened by transverse stringers, and aft of the rear spar, inboard of the cutaways for the elevator balance portions, a false spar is fitted. On either side of the stabilizer center-line, a steel inter-spar tube between the stabilizer-to-fuselage attachment fittings reinforces the structure.

An inspection door is in the upper surface. Elevator hinge bearings are on two brackets, one secured to the rear spar and false spar on the stabilizer center-line and one on each outer panel inboard of the elevator cutaway. The stabilizer tip edge is of wood, secured by woodscrews to the skin overlap.

Elevators are fabric covered, built in separate halves, having a tubular spar, Alclad ribs and nosing, and a trailing edge of oval tube. A trimming tab, controlled by the pilot, is in the inboard trailing edge of each elevator. A balance tab in the trailing edge is operated by a rod, one end of which is attached to the balance lever and the other to a fixed lever on the elevator outboard end bearing bracket.

The steel tube spar has a sleeve and liner at the outboard hinge and a flanged extension bolted at the tip. The ribs, of flanged Alclad with flanged lightening holes, are secured to the spar by collars fastened by Chobert rivets. Eyelets for fabric are in the flanges. An oval steel tube forms the trailing edge outboard of the trimming tab. From the inboard end to the balance portion, the nosing is of Alclad sheet riveted to the ribs. The balance portion is covered with Alclad, with a wooden nose fillet held by woodscrews. Mass-balance weights are secured to the nose. A fairing of aluminum-manganese sheet is fitted at the inboard end of each elevator, aft of the Alclad nosing. Fabric covering extends round both the balance portion and the nosing.

The elevator horn is bolted to a socket on the inboard end of the spar. The pin for the final connecting tube from the elevator control passes through both the left and right levers and (with a bolt and distance piece and two packing blocks between the levers) interconnects both elevators. A spigot at the inboard end of each spar centers in a ball bearing on the stabilizer bracket and forms the center hinge. Outboard hinge has two split bearings in which the spar rotates.

Elevator trimming tabs: A tubular light-alloy spar, Alclad ribs and skin, and an oval tube trailing edge form the construction of both trimming tabs, which may quickly be detached and which are fitted with mild steel hinge pins in slots at the spindle ends.

The fin has front and rear posts and a rear member of channel-section. Alclad is used for the above, also for ribs and skin, but the nosing is aluminum-manganese sheet. Front and rear posts are reinforced at their lower ends to form box-sections to which the steel-bushed fin attachment lugs are bolted. The front lugs are bolted directly to the stabilizer front spar, while the rear lugs are connected through links to the rear stabilizer fittings. A rearward extension of the second rib from the fin base is bolted to the rear post.

Secured by setscrews, a removable panel covers the gap between the bottom rear channel and sternpost. This is a mahogany filling piece inside the top rear channel member and there is a spruce strip for attachment of the fairing fillets on each side of the bottom rib. The steel aerial attachment bracket is riveted to the apex of the fin.

Rudder: In construction, the rudder is similar to the above. An inset trimmer tab is controlled by the pilot. The spar is a light-alloy tube with a flattened extension near the tip. Ribs and their attachments are similar to those of the elevator. Above the trimming tab and up to the top of foremost point of the balance portion, the trailing edge is mild steel tube, but below the trimming tab it is light-alloy. The nosing and balance portion are similar to those on the elevator; mass-balance weights are bolted under the nose fillets. A fairing of aluminum-manganese is secured to the rudder bottom by Chobert rivets. In the trailing edge are two tail lamps, with the cables running in conduits along a rib and through a door in the nosing. The fabric covering extends right round the nosing and balance portion. Inspection doors are on the left side at mass-balance weights and trimming tab actuator, also on right side, at rudder horn.

The rudder is hinged at two points by double split bearings bolted to the sternpost. The horn is in halves bolted to a socket on the spar above the bottom hinge.

Rudder trimming tab: This is of the same construction as the elevator trimming tab and is mounted in the same manner. The horn is fitted on the right side at the bottom and is linked to the actuator in the rudder.

Flying Controls

Pendulum rudder pedals and the spectacle control column are connected to their control surfaces by chains and cables. A trimmer tab, adjustable on the ground, is fitted to the left aileron and, for directional control, there are longitudinal and lateral trimmer tabs controllable by the pilot in the rudder, elevators and right aileron. The flaps are hydraulically operated.

The control column, pivoted on a box bracket on the control frame, consists of a light-alloy tube on which is bolted the control column head, which is in two halves with a ball bearing for the spectacle aileron control handwheel. At the center of the handwheel are the undercarriage brake lever and parking lock, and at the top right is the gun firing button. A sprocket is on the handwheel spindle and from it a chain extends down the control column and over two ball bearing pulleys on the mounting bracket behind the column pivot. A socket on the bottom of the control column is secured to spigots pivoted on ball bearings in the mounting bracket. The elevator control lever, riveted to the socket and spigots, extends below the mounting bracket. Adjustable stops are at the forward and after ends of the bracket.

Rudder pedals pivot on a transverse support tube between the sides of the fuselage and are of stirrup form with leather toe-straps. Each pedal lever, near mid-length, is connected by a link to a lever turning a vertical countershaft, at the bottom of which is an outboard-pointing lever. For leg-reach adjustment the two levers at the top of the countershaft are fixed to a sliding trunnion which can be moved backwards by a crank below the instrument panel to give 3 in adjustment to the pedals, either side of normal.

Elevator control: From the lever at the bottom of the control column one cable passes forward and around a pulley on the rudder and elevator torque tube and another passes aft to a pulley assembly (mounted on the control frame) and then to a pulley assembly on the front keel member forward of the front spar. From there the cables, with turnbuckles at the rear hatch, extend inboard along the left keel member over pulleys aft of the crate in the rear fuselage to a central vertical double countershaft in the stern frame carrying the ball bearing elevator levers for rudder control. Form this countershaft, movement is transmitted by an adjustable connecting tube to a horizontal countershaft and to the elevators by an adjustable connecting tube to which the horns for the elevators are secured by a special bolt.

Rudder control: From the lever at the bottom of the rudder pedal vertical countershaft, movement is transmitted by a connecting tube to the rudder and elevator torque tube, thence by a cable to the stern frame countershaft from the top of which cables, with turnbuckles at the levers, lead over pulleys to the rudder horn.

Aileron control: Here, control chains at the foot of the control column are connected by another chain to a sprocket on the aileron relay post aft of the control frame just forward of the front spar. Chains and cables extend outboard from the four quadrants over sprockets and pulleys (on the front face of the front spar) to a point between ribs 11 and 12, where their directions turns toward the ailerons. Turnbuckles for adjustments are fitted between the control column and the relay post, also just outboard of the outer and center wing joints. A telescoping conduit encloses the chains and cables between the spars. The final chain passes over the sprocket behind the rear spar and around a sprocket on the differential gear.

Two special tail ribs behind the rear spar support the aileron differential gear. This consists of a sprocket on the inboard tail rib which has an integral differential lever that is connected by a link to the aileron horn. A lever on the outboard tail rib also supports the connecting link. The top pivot point of the connecting link in the neutral position of the aileron is mounted above the horizontal line through the sprocket center so that, for the same rotation on either side of neutral, the vertical movement of the pivot point and angularity of the aileron is greater when the aileron is being raised than when lowered in flight.

Trimming tab controls: Tabs in trailing elevators and rudder are controlled from the right side of pilot's cockpit by cables and chains connected to actuating units at the stern frame. Aileron trimming tab on left aileron can be adjusted only when on the ground, but right aileron tab is controllable by the pilot.

Elevator tabs: The tab control which is atop the column on the right side of pilot's cockpit, and it operates (by a chain) a drum at the bottom of the column from which cables extend along the right keel member to just forward of tail wheel. Here the cables are connected by turnbuckles to chains (on later models Teleflex cables) that operate a drive unit behind the stabilizer rear spar, whence flexible drives go to a screw jack or actuator at the inboard end of each elevator and coupled directly to the tab horn by an adjustable rod. An indicator is mounted partly on the starboard shelf and partly on the aft side of the column supporting the handwheel.

Rudder tab: Here, the tab control handle and indicator is mounted on the right shelf in the pilot's cockpit and is connected by bevel wheel and torque shaft to a drum from which cables and chains (on later models Teleflex cables) connect to a drive unit from which a flexible drive operates an actuator coupled to the tab horn by an adjustable rod.

Aileron tab (right): The aileron tab control handle and indicator is mounted on the right shelf in the pilot's cockpit in line with the seat back and is connected by cable to a pulley and sprocket (on the rear face of the rear spar, right side) whence cables and chains drive an actuator mounted behind the aileron spar and coupled to the tab horn by an adjustable rod.

Flap operating gear: The two flaps on each side of the main plane are operated by a hydraulic jack pivoted on the rear face of the rear spar inboard of the center and outer wing joint. The piston rod of the hack is coupled to the bottom of a quadrant pulley on a support frame behind the rear spar, with two links at the top of the pulley connected to the operating levers of the flaps. A cable round the quadrant pulley is connected by chain to a small sprocket on a relay shaft further inboard. From the large sprocket on the relay shaft, chains and cables extend across the center plane and interconnect the flaps on each side so that they are raised and lowered simultaneously.

The lever for flap control is on the left side below the pilot's instrument panel. An indicator, showing the position of the flaps, is connected by Teleflex controls to a lever on the flap hinge at the left side of the fuselage.

Engine Installation

Two Bristol Hercules engines are fitted in nacelles near outboard ends of the center plane. The nose of each cowling is formed by an exhaust collector ring, while the flow of air is controlled by flaps at the trailing edge. Fuel is carried in four main tanks, two in the center wing (one on each side) and one in each outer wing. The fuel is fed to the carburetor by engine-driven pumps.

An oil tank is fitted for each engine on the top of the wing at each nacelle, and separate oil coolers are mounted in the outer wings. To assure an adequate supply of oil when starting, a high initial oil pressure device is incorporated in each engine. The engines are fitted with electric starters, and for maintenance work, hand-turning gear is provided. Constant-speed feathering Hydromatic propellers are fitted.

Engine Mounting: Each power plant mounting is of welded steel tube attached to the main structure,near the outboard ends of the center wing, at five points, three on the front spar and two on the nacelle structure. The tubes at the rear attachment joints are split, wrapped around, welded to a steel bushing, and a steel gusset plate is welded over the joint. The engine ring is bolted to four points on the engine mounting, joints being formed by a steel barrel to which the tubes are secured by welding, and steel gussets. The engine ring is a steel tube of square section with welded steel side plates and bushings for the ring attachment and for the seven engine attachment points.

Fuel System

Fuel supply to the carburetors is maintained by engine-driven pumps. The system is similar on each side but is not symmetrical since the engine rear cover assemblies are identical and not handed. The tube systems are connected by a suction balance pipe, fitted with a pilot-controlled cock, enabling fuel to be drawn from any tank to either engine. Pipe-lines are of copper Superflexit or light-alloy tubing.

Fuel is drawn from each tank in turn through a cock on the tank, wired open, to a pilot-controlled 3-way cock in the nacelle. From here, fuel passes to a filter forward of the firewall. The suction balance pipe connection is made at the engine side of the pilot-controlled cock located in the leading edge of the center wing between the fuselage and the left engine. The engine pump draws fuel from the filter and delivers it through a pressure regulator to the carburetor. A connection for the fuel pressure gage is made at the carburetor and for the priming system at the filter.

Two main fuel tanks are carried between the wing spars on each side. Fuel gages for each tank are in pairs, one pair on the left sill tube and the other on the right. Fuel pressure gages are on the instrument panel below the right of the instrument-flying panel. The carburetor and induction-system priming pumps, on the bottom cross member of the nacelle, are accessible when the undercarriage is lowered.

Fuel tanks: Welded aluminum construction is used for fuel tanks. Transverse and fore-and-aft bulkheads with flanged holes are inside each tank. Transverse bulkheads, also an intermediate fore-and-aft bulkhead on the outer wing tank, have T-section flanges with the edges of the main shell panels butt-welded to the edges of the horizontal part of the T-sections. The fore-and-aft bulkheads have angle flanges on both sides of the plates, which are riveted to the transverse bulkheads, but no attachment of these bulkheads is made to the shell. Edges of the tank ends are welded to the shell and to a strip on the middle transverse bulkhead. Filler caps, vent adaptors, inspection doors, fuel contents gage attachments, and sumps are fitted on the tanks, which are protected by a self-sealing covering.

Outer and center wing tanks are strapped to bearers riveted to detachable panels on the undersurface of the wings and bolted to brackets at the spars.

Jettison equipment: A jettison valve is under the outer tanks, and is operated pneumatically from the instrument panel. Fuel is jettisoned through piping under the outer wing. On later models, provision is made for jettisoning the fuel from all tanks.

Oil System

The feed pipeline to the engine leads from the tank sump direct to the pressure pump on the engine. Return oil passes through an oil cooler on struts at the inboard end of the outer wing leading edge. From the forward end of the cooler, the oil returns to the top of the hopper in the tank. After starting up, when the oil in the tank is cold and thick, the warmer oil from the engine is recirculated, supplemented by a small quantity only of the cold oil that enters the sump through the holes at the bottom of the hopper. When the oil in the tank has become warm, a greater proportion of it enters the sump. Centrifugal oil clearers are incorporated in the engines.

A thermometer connection is on the feed pipe, and a pressure gage connection is made on the engine rear cover. Excess length of the tubing is wound round a spool mounted inboard of the nacelle behind the firewall. A cock for draining the oil system is fitted in the main feed pipe behind the firewall.

The oil cooler is of the two-element drum type. Each element of the cooler has a separate relief valve which bypasses the oil around a jacket outside the cooling tubes if the pressure exceeds a certain figure. Each relief valve has a different setting which is clearly marked on it. Air is collected by an opening forward of the cooler and is exhausted through the top surface of the center wing just forward of the front spar. The air outlet opening is adjustable on the ground.

Oil tanks: Each oil tank is constructed of welded aluminum and is strapped to the top of the center wing under the engine nacelle top panel. Inside the tank are two transverse bulkheads in line with the straps; they are not attached to the shell but are tightly fitted. Vertical fore-and-aft bulkheads are fitted between the transverse bulkheads. A hopper, having large diameter holes in its lower end, extends from the top of the tank to the sump at the base. The oil return enters the tank at the bottom near the front and is connected to the top of the hopper. The filter in the sump of the tank may be withdrawn through the cover of the hopper. In this tank the filler cap is situated in such a position that the tank cannot be over-filled, and it also assures the correct air space. A dipstick is provided adjacent to the filler cap for gaging depth of fuel.

Engine Controls

Throttle, mixture, propeller speed, supercharger, and air-intake controls are mounted on a shelf on the left side of the pilot's cockpit. The carburetor cut-out controls are mounted on the top of the front spar, on the left side of the cockpit under a spring-loaded cover. Cowling flap switches are mounted on a sloping panel between the engine control shelf and the carburetor cut-out box.

Throttle and mixture levers are connected to rods in the engine nacelles by push-pull rods and torque tubes in Oilite and ball bearings along the nose of the wing. Carburetor cut-out knobs and the air-intake, propeller, and supercharger control levers are connected to their respective engine levers by Teleflex controls. The cowling flap switches operate electric motors mounted on the right-hand side, (looking aft), of the engine nacelle.

Auxiliary gear boxes: An auxiliary gear box is mounted on the firewall in each engine nacelle and is driven from the engine by a flexible jointed shaft so constructed that the generator drive face is positioned vertically. The accessories driven by gear boxes are:

  1. Generator (top face), Pesco B.3 vacuum pump (inboard face), and hydraulic system pump Mark IV (outboard face).
  2. Generator, air compressor (rear face), Pesco b.3 vacuum pump (outboard face) and hydraulic system pump Mark IV (inboard face).

Ignition

The two magnetos on each engine are controlled by separate switches combined in one unit below the instrument-flying panel in the pilot's cockpit. Switch knobs are prevented from being moved to the "on" position by an extension bar on the switch for the undercarriage and tail wheel electrical position indicators (mounted alongside on the left side) when that switch is off.

A booster magneto on a bracket forward of the firewall supplies starting current to the main magnetos. In the HT cables connecting the booster to the main magnetos are spark gaps which relieve the booster windings when the engines are running normally. A tumbler switch, mounted in each engine nacelle above the undercarriage pivot and accessible only when the undercarriage is "down", controls the starting magneto. The hand turning gear is also connected to a chain drive to the starter magneto.

Two temperature gages are mounted on the pilot's instrument panel alongside the magneto switches showing the temperatures of No 8 cylinders.

Extra Tankage

For long-range flying, such as coastal patrol and convoy work, provision has been made for additional fuel tanks in the wings. They are arranged as follows: One 50-gal tank in the right wing gun bay; one 24-gal tank in the left wing gun bay, and one 20-gal tank on each side at the outboard ends of the center wing. The center wing tank in each wing is connected to the outer series through the 3-way cock in the engine nacelle. The supplementary wing tanks are also connected with the fuel balance pipe in the engine nacelles —through Superflexit hose. They are vented through a common pipe which is carried along the wing to the fuselage and terminates near the fuselage roof on the right side.

Power Unit

The Bristol Hercules engine is a 14-cyl double-row sleeve-valve type with a total capacity of 2,360 cu in (38.7 liters). Bore is 5¾ in and stroke 6½ in. The latest production series of the Hercules fitted in the Beaufighter develops over 1,650 bhp and is fitted with a two-speed supercharger. Other figures are not yet available for publication. Provision is made for constant speed multi-blade propellers for the Hydromatic or electrically controlled type. The engine is mounted as a complete self-contained, cowled, and cooled installation power unit, with flame-damped exhaust system and the engine mounting designed for quick four-point connection to the airframe.

For some time Beaufighter has been in quantity production in a number of factories in Great Britain and also in Australia. Only performance information available for publication as yet are that it has a top speed of over 335 mph. Fitted with four cannon and six machine guns, it is still regarded as the most powerfully armed fighter in the world.

Originally designed as a night fighter, this powerfully armed craft brought down more night raiders than the enemy could replace, thus defeated blitzes by night. Once the unlucky raider was caught in the Beaufighter's guns sights, a brief burst from cannon and guns, and the enemy disintegrated. But the Beaufighter proved such a useful, fast, and reliable aircraft that it was further developed for many other services, including army cooperation work and ground strafing in North Africa and Italy, where its aircooled engines had the advantage of being able to cope with extreme conditions.

It was also developed for Coastal Command, which involved many modifications for long-range patrol work, convoy escort duty, and finally as a torpedo carrier, for which it is particularly adaptable, being fitted with automatic air brakes for the final run up to the target. Once the torpedo is released, the double flap air brakes close and it once again performs as a normal high-speed long-range fighter.

This design analysis article was originally published in the March, 1944, issue of Aviation magazine, vol 43, no 3, pp 117-137.
The original article includes 10 photos and 21 detail drawings and diagrams, plus a ledger-sized foldout with cross-section drawings (from each side), four more detail drawings, and 4 data tables.
Photos are not credited.
A draft PDF of the article, recovered from microfilms, is available.