Before any construction work was started on the early models of the PBM series, a small scale version was built and test flown. The model was complete in every detail insofar as external configuration is concerned. It had two engine nacelles but was powered by a single engine located in the hull. The two propellers were driven by belts. Many characteristics of the full scale airplane were learned from the flight tests conducted on the model.
The first prototype full scale airplane was designed in 1937 and was known as the PBM-1. This airplane had a gross weight of 37,500 lb. Only a few of these early models were built but they served the Navy for a considerable length of time. In 1941 the first of the current series of PBMs were built. These were known as the PBM-3 series and had a design gross weight of 48,000 lb. The early models had no self-sealing fuel tanks, no armor plate and only single-gun turrets. Radio and electrical equipment was also meager. As the war in Europe progressed, changes were made that militarized the airplane according to the present standards.
The hull lines of the current airplane are an outgrowth of the lines laid down for the flying model in 1937. Some changes have been made but these are minor in nature. The hull is divided into nine compartments; some of which are separated by watertight bulkheads, making five watertight sections. The airplane will remain afloat with any one of these sections completely flooded. The bow compartment, which is used for the bow turret and anchor handling gear, is separated from the rest of the plane by a watertight bulkhead and door. The galley compartment, which is directly aft of the bow compartment, has a watertight bulkhead and door at its aft end. In early models, this compartment was equipped with refrigerator, stove and sink as well as a table and benches. In later models, some of this equipment was removed so as to save weight and also to make room for more essential equipment.
The flight deck extends over the galley compartment. The pilot, co-pilot, radio operator, radar operator, navigator and flight engineer stations are located on the flight deck. Below the aft end of the flight deck and just aft of the galley compartment is located the fueling compartment. This compartment is separated from the forward bunk room by a bulkhead which is not watertight. Aft of the forward bunk room is located the aft bunk room, which is in turn separated from the waist compartment by a watertight bulkhead and door. Above the aft bunk room is located the auxiliary power plant compartment. The bulkhead at the aft end of the aft bunk room extends up only to the level of the floor of the auxiliary power plant compartment. This arrangement allows free access to the auxiliary power plant and to the life rafts which are stowed on the deck of this compartment. The waist compartment contains the deck turret and the side waist guns. There is a watertight bulkhead at the aft end of this compartment, which separates it from the tail section.
The pilot house is unique in construction. All structure is aluminum alloy extrusion, welded into a complete assembly. Showcase-type sliding windows are used on the sides and exceptional visibility is obtained. This type construction offers ease of fabrication as well as a watertight pilot house. The glass is installed in the pilot house in a subassembly operation before the assembly is attached to the hull. All windows of any size throughout the hull are the Hunter Sash type.
The hull bottom is a "two step" design and the fundamental structure starts with the keelson. The forward end of the keelson is at the bulkhead at the aft end of the galley compartment and it extends a short distance aft of the main step. The main step is located below the aft end of the forward bunk room. All floor frames and bulkheads are attached to the keelson which supplies the main support for the hull bottom structure.
Plating on the bottom of the hull from the bow to the main step is varied from .051 to .072 in thickness. Afterbody bottom plating varies from .040 to .051 in thickness. Hull side and crown skin varies from .020 to .045 in thickness.
Bulkheads throughout are constructed from extrusions and flat sheet. The main front spar bulkhead is of semi-truss type construction and uses corrugated sheet for the webbing. In general, floor frames throughout the hull are constructed from extrusions and corrugated or flat sheet webs. The bottom skin of the hull is attached to the floor frames, bulkheads and fore-and-aft stringers which form the main structural strength of the bottom. A heavy extruded section is used for the longerons which extend from the forward end of the flight deck, aft through the side waist compartment. Most of the fuel in the airplane is carried in self-sealing tanks in the hull under the floor. Bulkheads and floor frames supply the fore-and-aft support for the hull tanks while the side skin and the keelson provide the athwartship support. The use of below deck level fuel cells serves to keep the CG of the airplane low. The flooring throughout the airplane is made up of ½ and ¾" deep square corrugations and is attached with quickly removable fasteners. Small access doors are provided conveniently in the flooring for bilging the hull bottom.
There are three entrance hatches in the hull and seven other hatches useable as escape hatches. One large hatch is located in the bow compartment on the port side and is used for mooring purposes and also for the anchor gear. Another large hatch is located on the starboard side at the forward end of the galley compartment. This hatch is used for mooring from the starboard side and as a forward entrance hatch. In the fueling compartment there are hatches on each side, which are used for attachment of the main beaching gear. The pilot and co-pilot each have escape hatches directly over the pilot's and copilot's seat. Side waist hatches, both sides, are large so as to provide free movement for the guns. These hatches, therefore, provide ready access to the airplane and for convenient escape hatches. Another escape hatch is located in the overhead in the auxiliary power plant compartment. This hatch is considered the aft ditching hatch and the life rafts are stowed adjacent to it. A tunnel hatch it located in the tail compartment and is used primarily for the attachment of the tail beaching gear. A number of port lights are located throughout the airplane. Some of these port lights are hinged and removable so that they may be opened for ventilation.
Wing airfoil tapers from an NACA 23020 to an NACA 23010 modified section at the tip. Total wing area is 1400 sq ft. Center wing is gull shaped, full cantilever and extends from the centerline of the hull to a point just outboard of the engines. Outer panels are detachable at the splice. Landing flaps extend from the side of the hull out to the inboard end of the aileron.
The wing is two-spar using corrugations and flat sheet for the top surface and stressed skin covering for the bottom surface. Spars are made from extruded chord sections and flat sheet web. Extruded sections are used for stiffeners on the spar web. Corrugations which form the top surface are spliced at the detachable point between the center and outer panels. All hand holes and access holes are cut in the bottom surface of the wing so as to prevent the necessity of cutting through the corrugated top surface. Access holes aft of the rear spar are provided in the top skin of the wing for access to the flap hinges and actuating screws. Wing tips are detachable and may be replaced without undue difficulty. The leading edge of the center section wing is attached with piano hinges for each access to the engine controls and piping which is routed through the area.
The bomb bays are located directly aft of the engine nacelles at the outer ends of the center wing. In order to accommodate the large bomb load, the full nacelle size is carried back to the rear spar and then tapered in a beaver tail. Access to the bomb bays in flight is provided by an access door through the bottom skin of the wing where it extends into the forward bunk room in the hull. No access to the engines in flight is provided, however.
On all models since the first PBM-3s, fixed wing tip floats are provided. The earlier model PBM-1 had retractable wing tip floats but these did not prove as practical as the fixed floats. A retractable float must necessarily be restricted in size and shape to fit into the wing when retracted. This restriction prevents the satisfactory hydrodynamic shape from being used. When retractable floats are used, it is also necessary to increase the weight of the wing structure to provide reinforcement around the openings cut in the wing to allow the float to retract. A further reason for using fixed floats lies in the fact that it is practically impossible to build as rigid and as strong a bracing for the retractable float as for the fixed float for comparable weight. A rugged float bracing is essential for satisfactory rough water operation of a sea plane.
Many ribs for the wing are made from sheet metal stampings. One main rib aft of the engine is built with extrusions and formed hat sections.
The tail is the twin fin and rudder type, fully cantilever. Stabilizer and elevators have a 15° dihedral angle. A distinguishing feature of the tail assembly results from the fins and rudders being mounted perpendicular to the stabilizer spars; thereby being tilted in at the top 15° from the vertical. This configuration was found to give excellent stability in a turn and precludes the necessity for complicating the attachment fitting construction. It also greatly simplifies the rudder and tab controls where they lead from the stabilizer to the fin. Small airfoils are mounted top and bottom of the stabilizer just inboard of the fins. These airfoils are used to maintain a smooth airflow over the rudder in the area immediately aft of the stabilizer at the outboard end of the elevator.
Stabilizer and fins are of two-spar construction, using extrusions for the top and bottom chords of the spars and a flat sheet for the webs. Most of the ribs are made from formed flat sheet, the same as those in the wing.
Ailerons, elevators and rudders are all similar in construction. A single spar using extruded top and bottom chord members and a flat sheet web is provided. Extrusions and formed sections are used for stiffeners. Most of the ribs are sheet stampings with lightening holes and stiffening beads. The leading edge of all surfaces is metal covered for stiffness. The area from the spar aft, however, is fabric covered except for the area occupied by the tab. Each surface is equipped with a single tab for trim and balance. The tab ribs are sheet metal stampings and the surfaces are metal covered. All main control surfaces are statically and dynamically balanced. The rudders are built so as to be interchangeable left and right.
There are two flaps on each wing; one for the center section wing and one for the outer panel. The detail construction of the flap includes a single spar and metal stamped ribs. The flaps are completely covered with a metal covering. Skin on the wing just forward of the flap leading edge maintains the slot between the wing and the flap at the desired dimension.
The elevator control system is operated by control columns located directly in front of the pilot and copilot. The columns are attached to each other through a torque tube under the pilot's floor. On the left end of the torque tube is located an arm which operates a push-pull tube attached to the cable quadrant beside the pilot's seat. Cables are run from the quadrant to a corresponding quadrant in the tail. A push-pull tube from the tail section quadrant operates a jackshaft arrangement which in turn is attached to the elevator surfaces. Adjustable stops to limit travel are located immediately under the pilot's floor so that the pilot has a definite travel limitation without being able to feel the stretch in the control cable. Emergency stops are located at the tail to prevent the surrounding structure from being damaged if the controls are left unlocked in a high wind. The cable between the two quadrants is 3/ l6" diameter, extra flexible tinned carbon steel.
The aileron control wheel mounted on the control column operates through a bevel gear arrangement and drives a torque tube located inside the control column. A universal joint is located on the control column hinge point to absorb the movement of the control column. At the base of the column, sprockets are mounted and the two aileron control wheels are tied together by a continuous chain running between the sprockets. A third sprocket, located at the base of the pilot's column, is the take-off point for the controls running aft through the ship. The control cables are spliced to the chain a short distance aft of the column. The cables run aft to a triple-groove quadrant on the rear spar at the centerline ship. Independent cables are run from this quadrant to each aileron. At each aileron, another cable quadrant is provided and a push-pull tube from this quadrant operates the aileron. Fixed stops are provided at the control column head for the aileron wheel to limit its travel in each direction. Adjustable stops are provided at each cable quadrant at the aileron to prevent damage to surrounding structure due to cable stretch in the event the controls are left unattended. The aileron cables are 3/l6" diameter, extra flexible tinned carbon steel throughout except for a short section at the aileron. This section is 3/l6" diameter, corrosion resistant steel.
In the cockpit the rudder pedals are supported from torque tubes located under the pilot's floor. The pilot's and copilot's left pedal are mounted on a single tube and the pilot's and copilot's right pedals are mounted on a separate tube. The two tubes are geared together by gear segments; thus maintaining a fixed relative position. Pedals are equipped with an aligning tube so that the face of the pedals stay in the same plane regardless of their fore and aft position. No fore and aft adjustment is supplied for the rudder pedals.
One of the torque tubes under the floor is extended to the left side of the airplane at which point a lever arm attached to the torque tube operates a push-pull tube to the cable quadrant. The cables are run from this forward control quadrant aft to the stabilizer and out to the rudders themselves. A cable quadrant is built into the rudder structure for the operation of the rudders and a bus cable is run between the two rudders. The rudder cable is 3/l6" diameter, extra flexible tinned carbon steel except for the length installed along the rear spar of the stabilizer. This section is 3/l6" corrosion resistant steel cable. Adjustable stops are provided on the torque tubes under the pilot's floor for adjusting the fore and aft travel of the rudder pedals. Non- adjustable stops are provided in the fins to prevent damage to surrounding structure due to cable stretch in the event the cables are left unattended.
Ailerons, rudders and elevators are equipped with combination trim and balance tabs. One tab has been used for a dual purpose in each case. As previously explained, the balance feature is adjustable only on the ground. The pilot, however, may control the trim of the tabs in flight. In the cockpit a dual unit for elevator and aileron tab is provided beside the pilot's seat on the right hand side. A single unit, which controls the rudder tab, is located on the left side of the co-pilot's seat. This location permits either the pilot or copilot to handle all tabs. The cockpit units are gear boxes on which are mounted control wheels. The entire tab systems from these control boxes to the tab surfaces are torque tube. No cables or chains are used in the tab systems. The torque tubes are provided with universal joints to allow for manufacturing misalignment and slip joints to prevent endwise binding. The torque tubes are divided into short lengths of approximately 36". Length is determined by the critical vibrating frequency of the tube. Each tube length is selected so that no impulses from the engine or other sources will cause the tube to vibrate excessively. Gear boxes are provided for right angle turns in the tube systems wherever necessary. "Tee"-type gear boxes are provided in all three tab systems to route the torque tubes to the tabs on each side of the airplane. The "tee" type boxes are installed in the hull in all cases. Torque tubes terminate at irreversible screws at each tab which are mounted on the hinge line of the control surface. Screws are mounted on solid structure and movement of the control surface does not actuate the tab since its attaching point is on the surface hinge line. An "L"-shaped fitting is affixed to the tab screw so that the push-pull rod to the tab may be set off center if desired. If it is set off center, relative motion between the tab and the surface results when the surface is moved. This provides the balance tab feature. If the push-pull tube to the tab is attached to the actuator at the surface hinge line location, no relative motion between the two surfaces exists and the zero balance condition is obtained. By moving the actuating screw in or out, the tab surface is deflected and the trim of the surface thus varied.
Use of torque tubes for the tabs in lieu of cable provides a free turning, friction free system. By this means the manually controlled tabs can be used in large airplanes without the high friction forces usually associated with the cable system.
The main surface control locks consist of a locking bar for the cockpit controls and locking pins for the tail surfaces. Two small pins of different lengths are permanently fixed to the forward face of the control column. The locking bar must be fitted on these pins when installing the control locks. The opposite end of the locking bar fits into a ring fitting on the copi1ot's column. After placing the locking bar across the two columns, a "Y"-shaped yoke must be fitted over the center spoke of the pilot's control wheel. A half turn on the tail surfaces' locking pins, which are stowed in sockets in the locking bar, locks the yoke to the bar and allows the locking pins to be removed. The locking pins must then be carried aft in the hull and inserted in fittings in the elevator and rudder cable quadrants located adjacent to the surfaces in the tail of the hull. The yoke on the pilot's wheel locks the ailerons and the locking pins in the quadrants lock the tail surfaces.
In order to prevent the possibility of beginning a takeoff with controls locked, the locking bar is designed so that the "Y" yoke cannot be removed from the pilot's wheel until both locking pins have been inserted in the bar and turned to the stowed position. This action releases the yoke and the bar from the columns. The two small pins permanently secured to the forward face of the pilot's column act as keys and unless they are pressed into the locking bar, the tail surfaces' locking pins cannot be removed from the locking bar. This prevents the use of the locking pins without first installing the bar in the cockpit.
The flap linkage design is a Martin development. Motion of the flap is somewhat similar to that obtained from a Fowler type flap but the weight and complication of the tracks which must be used with the Fowler type have been eliminated. The flaps are hung on double links arranged so that they first move aft and then down and aft. This type of flap is quite powerful and its travel had to be limited to 30° down. The links on which the flaps are hung are called the "hanger" links to distinguish them from the actuating links. Each outboard flap has two actuating links, but one is sufficient for the inboard flap. Flaps are operated electrically through a motor and gear box located at the centerline ship in the hull. A chain drive is run from the gear box to irreversible screws which operate the flaps. The mounting points of the screw jacks are equipped with universal joints which are sealed and lubricated to prevent maintenance difficulties. The screw jacks are covered to reduce the damaging effect of salt water spray.
Operation of the flaps is controlled by an electric switch in the pilot's cockpit. The pilot can set the flaps at any desired angle up to 30°. An automatic switch arrangement is built into the gear box which controls the operation of the electric motor so that the flap motion is automatically stopped at the full-up position and at the 30° position. The switch mechanism is adjustable for manufacturing variations. An electric indicator is also supplied in the cockpit for the pilot. An emergency hand crank for lowering or raising the flaps in the event of power failure is located in the overhead of the aft bunk room. In the event power fails, the hand crank may be used to operate the gear box to lower or raise the flaps.
Bomb controls are basically electrically operated. The bomber's switch panel, located in the bow compartment, controls the various dropping arrangements of which there are many. Bombs may be dropped singly, in train, alternately or all together. A cable system for emergency use is supplied and can be operated by the pilot to jettison bombs. The manner in which the bomb system is operated is at present restricted and cannot be discussed here.
Engine control systems are similar to the main flight control system in that cable quadrants are used throughout. A set of throttles and rpm controls are provided for the pilot and co-pilot and a separate set for the flight engineer. The remainder of the engine controls are located at the flight engineer's station. The cable systems terminate at the front spar just behind the engine. From this point forward flexible Simmonds-Corsey controls are used for all controls except the propeller governor. The propeller governor is a Teleflex type control. Use of these controls eliminates the necessity for complicated bellcrank or pulley combinations to prevent control setting change due to engine movement.
Early PBMs used the Wright 2600 series engines. The latest model, however, is equipped with Pratt & Whitney 2800 series engines. Several versions of both engines have been used in an effort to increase the power so that the airplane might fly at increased gross weights. For the Wright 2600-22 engine, a propeller driven fan was installed to provide sufficient cooling for high power operation. The fans were quite effective in reducing the operating temperatures of the cylinder heads. When the Pratt & Whitney 2800 engine was installed, the cooling fans were no longer necessary.
Engine mount is made of welded steel tubes for all models. The mount is attached to the wing at three points. The firewall is made from stainless steel and separates the engine accessory section from the wing. The oil tank for the engine is located directly aft of the firewall. A 75-gal capacity oil tank is supplied for each engine.
Cowling on the earlier models is made of stainless steel. Later, a development program provided aluminum alloy cowling which saved considerable weight. The cowling on the present models is aluminum alloy except for a short section of stainless steel immediately aft of the engines. Exhaust gases from the exhaust stacks have a tendency to impinge slightly on the forward edge of the cowling and the stainless steel prevents burning. The hood cowling is made in four pieces. Each piece is quickly removable and is secured with Dzus fasteners. The accessory section cowling is made in six sections. The upper section follows the contour of the carburetor air scoop and the bottom section fits around the oil cooler. The four side panels provide ready access to the engine accessories. Cowling is constructed from formed sheet reinforced with formed modified hat section stiffeners. Cowl flaps are attached to the hood cowl support ring and are operated by an electric motor. The flight engineer operates the cowl flaps and sets the angle according to cylinder head temperatures. The degree of opening is indicated on the side of the carburetor air scoop which the flight engineer can see from his station and no remote indicator is required. The oil cooler is a Harrison type cooler, using .2l0" diameter tubes. A shutter is provided aft of the air cooler to control the flow of air through the cooler. The shutter is controlled from the flight engineer's station by an electric motor driven actuator.
The carburetor air scoop is made from an aluminum alloy casting. To prevent the casting from being subjected to the engine movement, it is mounted rigidly to the engine mount. An adapter is installed between the air scoop and the carburetor which allows for the engine movement and maintains a seal between the carburetor and the air scoop.
The exhaust stacks used on the PBM series airplanes are short, individual cylinder ejector type stacks. Considerable experimentation was carried on in the development of these stacks. Various types of material and design of stack were tried before a final design was developed consisting of 1025 steel tubing, welded into a 1025 steel flange. Reinforcing gussets are welded to the tubing at the base to provide the necessary strength and the gussets are ventilated to allow for cooling. The stacks are coated with an extremely thin coat of a specially developed enamel to prevent rusting and to provide more adequate cooling. This design of stack has given many hours of satisfactory performance in service. Where it is impossible to put an individual stack on two adjacent cylinders, a twin stack is made, but no more than two cylinders exhaust into any one exhaust stack. The twin cylinder exhaust stacks are made from 1025 steel sheet stampings welded together, and coated with the thin coating of enamel.
The majority of PBM airplanes have been equipped with four-bladed Curtiss electric propellers. A few of the later models have been equipped with three-bladed Hamilton Standard propellers. The hollow steel Curtiss electric propellers have proven quite satisfactory for the rough water operations to which these airplanes are subjected.
Each airplane is equipped with an auxiliary power plant for the purpose of generating the electric power when the main engines are not operating. Several different types of auxiliary power plants have been used; the latest being the Andover two-cylinder auxiliary power plant. This unit is equipped for electrical or manual starting. The space requirements for this power plant are small and it has proven to be a generally satisfactory installation.
A recent addition to the power available for take-off is the installation of jet assist takeoff units (JATO). After trying tests on several arrangements, the final installation developed mounts the units on the side waist hatches. These hatches were strengthened to take the thrust load of the units and fittings bolted to the outer face on which the bottles hang. This arrangement allows for the JATO bottles to be installed on the doors from the inside of the airplane while on the water. The doors may then be closed and an assisted takeoff made. After take-off the empty bottles may be jettisoned without opening the doors. Additional bottles may be stowed in the hull for later takeoffs if desired.
Two JATO bottles are mounted on each side waist door and a total thrust of 4000 lb obtained. The bottles are fired by switches located on the switch pedestal between the pilots. A master switch must first be turned on and then the upper and lower pairs of bottles are fired by separate switches. By properly timing the firing of the pairs of bottles, fast takeoffs may be made at high gross weights.
Each airplane is provided with an anchor and anchor handling gear. The handling gear consists of a davit which may be retracted or swung out through the bow compartment hatch. The davit permits the raising of the anchor without danger of striking the side or bottom of the hull. A manually operated anchor winch is also provided. A mooring pendant is attached permanently to the bow so that the anchor line may be held by the pendant and all hatches closed. Mooring bits are also provided at the two bow and two waist hatches for temporary mooring at a buoy and/or handling.
The pilot's and co-pilot's instrument panels are equipped with dual sets of flight instruments. The tachometer and manifold pressure gauges are conveniently located between the pilots so that they may be seen by either. The majority of the electrical switches, propeller feathering controls and items of a similar nature are mounted on a small pedestal located between the two pilots. The center of the instrument panel is occupied by a Sperry type A-3 autopilot. The hydraulic power for the autopilot is obtained from an electric motor driven pump.
A heater is supplied for cold weather operation. The heater is located in the bow compartment and heating ducts are led to the flight deck, galley compartment and bomber's window. The heater is supplied with ram air so that a fresh air supply is available as well as recirculated air. Adjustable ventilators are also supplied at various convenient locations throughout the hull. These ventilators may be adjusted so as to scoop air from the outside and used as exhaust air exits.
The flight deck of the airplane is equipped with soundproofing and an interior trim cloth. A door is provided at the exit from the flight deck so that engine noise may be reduced by closing the opening. The flight deck floor was originally equipped with carpeting to further soundproof the area, but this was removed on later models in the interest of weight saving. No other compartments are equipped with soundproofing because of the weight involved. The pilot's and co-pilot's seats are adjustable fore and aft and up and down. The back of the pilot's seat may also be tilted and is equipped with a padded head rest. The radio operator's and flight engineer's seats are full-swiveling and can be adjusted fore and aft. The radar operator's seat is stationary and cannot be adjusted. The navigator is supplied with a stool which can be secured to the floor when desired. All of the seats with the exception of the navigator's stool are Warren McArthur seats and are equipped with safety belts.
The navigator is supplied with a large chart table with a drawer for folded charts. The airspeed indicator, drift sight, clock and other navigational aids are located conveniently nearby. Gooseneck extension lights are supplied so that the navigator may have ample light for night operation.
The galley compartment under the flight deck is equipped with a Tappan stove with food drawers. The food drawers are electrically heated so as to keep cooked food warm for a considerable time. Two hot plates are supplied on the top of the stove. A bench is also provided in this compartment for the use of the crew while eating. No provisions are made for cooking elaborate meals in the later models because of the weight of equipment involved. The stove installed, however, will accommodate provisions for the crew sufficient for the duration of their flight. Water breakers are located in the galley compartment, on the flight deck and in the waist compartment for the convenience of the crew during flight.
The aft bunk room has provisions for the installation of four bunks. The upper bunks on each side of the airplane may be lowered to form back rests so that the lower bunks may be used as seats. Bedding stowage racks are supplied under the bunks so that the bedding will not become soiled when the bunks are used for seats.
Life rafts are provided for the crew members and are stowed on the auxiliary power plant deck. There is an opening in the crown of the airplane adjacent to the stowage for quick exit in the event the airplane has to be abandoned on the water. Emergency food rations and a water breaker are stowed in the same vicinity so that these may be put aboard the life rafts. If more time is available, the life rafts may be put overboard through the side waist hatches, but these hatches are too low for an emergency ditching exit in the event the hull bottom was damaged on landing.
Flares are supplied and two flare release tubes are installed in the aft end of the side waist compartment. The flares can be released electrically by the pilot and the tubes reloaded by a crew member stationed in the side waist compartment. Additional flares are stowed conveniently so that more than one drop may be made.
Many other items of equipment are supplied with the airplane. These items include provisions for aircraft type camera at the tunnel hatch in the tail compartment, deicer system for the leading edge of the wing and tail surfaces, first aid kits, chart boards, binoculars, signal lights, Very pistol, etc. The airplane is equipped for long range patrol with all the necessities but with most of the luxury items omitted so as to save weight.
Fuel is carried in self sealing tanks. Most of the fuel is divided between seven cells in the hull which are interconnected to form three separate sources. Additional fuel is carried in service tanks located in each wing. A large metal auxiliary tank may be installed in each bomb bay for use in ferrying or in extremely long flights where self sealing is not essential.
The fuel system is so arranged that any tank may be used to supply either engine. The only exception to this occurs when the bomb bay tanks are used. These tanks may only be used to supply fuel for the engine immediately in front of the tank. Two valves are located at the flight engineer's station for controlling the flow of fuel to the engines. These selector valves automatically operate the transfer pumps which transfer the fuel from the hull tanks to the wing service tanks when the level of the fuel in the service tank reaches a predetermined low point. The transfer pumps automatically shut off when the wing service tanks are filled. The selector valves can also be used to drain fuel from the wing service tanks back to the hull tanks. Booster pumps are installed in the wing service tanks to supply fuel under pressure to the engine so that the engine may continue to operate should the engine fuel pump fail.
The hull fuel tanks are filled through separate filler connections located on the side of the hull adjacent to the beaching gear hatch. Strainers are installed in the outlet lines of each tank to prevent foreign matter from entering the fuel system. A fuel jettisoning system is installed in the hull and is capable of jettisoning fuel from the tanks at about 160 gal per min. There are two separate jettisoning pumps and one or both may be used as desired. Electrical switches are located at the flight engineer's panel for the jettisoning pumps.
An oil tank is mounted behind the firewall at each engine. The tank has a capacity of 75 gal plus an expansion space of approximately 10 gal additional. The center of the tank is equipped with a small warmup hopper. When the engine is cold, all oil from the engine and oil cooler is circulated in the hopper; thus supplying warm oil to the engine in a short time. At a given temperature of the oil, an automatic valve changes the flow of oil from the hopper to the main body of the tank. Oil is drawn from the hopper to the engine but returning oil is dumped into the main body of the tank instead of the hopper. This arrangement provides for a more rapid warmup of the engine oil in extremely cold weather.
Earlier model airplanes were equipped with both an oil quantity stick at the tank and a remote oil quantity gauge on the flight engineer's panel. On later models the remote reading gauge was eliminated.
An oil dilution system is provided so as to dilute the oil left in the engine with gasoline when shutting down in cold weather. The diluted oil prevents the engine from being stiff when starting in extremely low temperatures. The dilution system is used when starting in cold weather as well as when closing down.
As previously mentioned, a 16" diameter oil cooler is installed for oil cooling.
This article was originally published in the September, 1945, issue of Industrial Aviation magazine, vol 3, no 3, pp 7-8, 10, 12-14, 16, 18-20, 97.
The original article includes small portrait of the author and three photos of the plane, a three-view and 14 detail drawings, and a cutaway rendering.
Two photos are credited to Industrial Aviation.