The fuel system of the B-17F consists of 4 independent fuel supplies of approximately equal capacities, each feeding one engine. There are 3 tanks in each wing, with provisions for 2 additional groups of outer wing feeder tanks. These outer wing feeder tanks (Tokyo tanks) are composed of 9 individual, collapsible self-sealing cells per wing. The fuel supply can also be increased by auxiliary installations of re-leasable fuel tanks in the bomb bay.
The fuel in any tank is available to any engine supply tank in the airplane through a fuel transfer system consisting of 2 selector valves and an electrical transfer pump.
There is also a hand transfer pump in the bomb bay as an emergency transfer medium. Fuel booster pumps in the outlets of the 4 major wing tanks eliminate vapor lock between the tank and the engine fuel pump. They also provide fuel to the carburetor when the engine pump fails. An electrically controlled fuel shut-off valve is installed in the line beyond the fuel booster pump to prevent fuel flow through a severed fuel line.
|U.S. GALLONS * EACH
|TOTAL U.S. GALLONS
|No. 1 and No. 4 engines
|No. 2 and No. 3 engines
|Outboard Wing 1-5 (Total)s
|Inboard Wing 6-9 (Total)
|Total Fuel (Overload)
|Bomb Bay Extras (2)
|Total Fuel (Special)
|3600 (13626 l)
* 1 U.S. gallon=3.785 l
The booster pumps (at the outlet on the underside of each of the 4 main tanks) serve to: (1) assure fuel to the engine fuel pump on takeoff and landing, and when flying at less than 1000 feet or more than 10,000 feet above the ground; (2) prevent vapor lock in the fuel lines; (3) provide fuel to the carburetors when starting engines. No. 3 booster pump also supplies pressure to the primer pump at engine starting.
They are electrically operated and controlled by toggle switches on the central control stand. At high altitudes, bubbles form in the gasoline. As the gasoline is drawn through the funnel, the centrifugal action of the propeller throws these bubbles out through the sides of the screen, back into the tank. Only the liquid gasoline enters the pump and is sent to the fuel system.
Turn booster pumps on below 1000 feet; turn them on above 10,000 feet as a safeguard against vaporization.
Fuel Shut-off Valves
Shut-off valves provide an emergency means of shutting off fuel flow in case the fuel lines are severed. Valves for tanks No. 1 and No. 4 are forward of the tanks between the oil coolers. Valves for tanks No. 2 and No. 3 are between the tanks and the rear spar. Each valve is spring-loaded to stay open and is closed by means of a solenoid controlled by an individual toggle switch in the cockpit.
Engine-Driven Fuel Pump
The fuel pump forces sufficient fuel to the engines for operation at altitudes up to 10,000 feet. Above 10,000 feet, the fuel pump must be assisted by the fuel booster pump located on the right-hand engine accessory pad.
Fuel is drawn into the pump by the paddle-wheel action of the vanes within the liner. Fuel caught between the vanes at the inlet port is forced between the inner wall of the liner and the rotor and is carried to the outlet port. When the pumped fuel is in excess of the carburetor's demand, the excess fuel has sufficient pressure to lift the pressure-regulating valve from its seat. This permits the excess fuel to escape to the inlet side of the pump.
Fuel used in starting is pumped by the booster pumps through the engine-driven fuel pump. The fuel enters the inlet port (the engine driven fuel pump is now idle) and forces the bypass valve open, which permits the starting fuel to flow through the engine-driven pump to the carburetor.
Provides a means of priming the engines for starting. It is on the floor to the right of the copilot. Fuel is drawn into the primer from the nacelle No. 3 fuel strainer and is forced into the top 5 cylinders of the engine selected. Several strokes are usually necessary to draw the initial flow of fuel into the primer.
(See starting procedure, p. 57, for operating information.)
Fuel booster pump for No. 3 engine must be turned "ON" to operate the primer. Do not leave plunger of engine primer in the up position as this allows fuel to pass directly through the primer to the engine selected.
The oil system of the B-17F airplane has several functions: (1) it provides lubrication for wearing surfaces of the engine; (2) it aids as a coolant in transferring heat away from the engine; (3) it supplies hydraulic pressure to operate the supercharger regulation; (4) it supplies hydraulic pressure to operate the propeller pitch and propeller feathering mechanism.
Each engine has its own independent oil system. The self-sealing oil tanks are in the nacelles. The oil cooler and oil temperature regulators are in the leading edge of the wings. The hydraulic supercharger regulators are in the nacelles for the outboard engines and just aft of the superchargers for the inboard engines. The propeller feathering motors and pumps are on the forward side of each nacelle firewall.
Oil flows from the tank by gravity and by suction from the engine-driven oil pump, which forces the oil under pressure to the various moving parts of the engine. The oil then drops down to the sump, where it is picked up by the engine-driven scavenging pump and forced through the oil cooler. The oil then returns to the tank.
The oil lines to the supercharger regulators are tapped off the engine accessory cases on the pressure side of the pump. This oil circulates under pressure to the regulator and then returns to the engine, where it drains into the sump.
The propeller feathering oil line is tapped off the main oil line from the tank to the engine. The propeller feathering pump draws the oil from this line and forces it under pressure to the propeller feathering valve in the propeller dome.
All the oil lines are lagged (insulated) in order to prevent oil cooling and congealing at high altitude.
An oil dilution fuel line is tapped into the main oil line from the tank at the Y cock drain valve.
To cool engine oil returning from the crank case to the supply tank, there is an oil cooler for each engine. It consists of the core and muff and the oil temperature regulator.
The core passes the oil through a large cooling area; the muff is a bypass of the core in case the core becomes congealed.
The oil temperature regulator controls the amount of cooling air that passes through the core and is operated by the temperature and pressure of the engine oil.
Operation of the oil cooler shutters is fully automatic; therefore there are no oil cooler controls in the cockpit.
Each engine is equipped with a self-sealing oil tank having a capacity of 37 gallons plus approximately 10 per cent expansion space.
The total of 148 gallons for all four tanks is required for maximum fuel load with wing tanks and bomb bay tanks full.
Fill oil tanks with Specification No. AN VV-0-446, grade 1120 for normal operations, grade 1100A for cold weather.
Hydraulic System (B-17F)
The hydraulic system on the B-17F operates the cowl flaps and the wheel brakes. It consists of a main system and an emergency system for operation of the cowl flaps and the brakes.
Operating pressures of the system are from 600 to 800 lb. sq. in. These pressures are developed by an electrically driven hydraulic pump which serves both the main and emergency systems. However, in all flight operations, the emergency system is shut off from the main system and relies on the hydraulic fluid stored in the emergency accumulator for its source of power.
System Oil and Capacity
The hydraulic oil used in the hydraulic system of the B-17F is AN VV-O-366a, and the total hydraulic oil capacity in the system is approximately 6 gallons.
When the hydraulic pump switch on the pilot's control panel is in the "AUTO" position, pressure is automatically regulated by a pressure cut-out switch, starting the pump when the pressure drops to 600 lb., and stopping the pump when the pressure builds up to 800 lb. In case the automatic pressure switch fails, maintain pressure by holding the hydraulic pump switch in the "MANUAL" position. A relieve valve opens if the pressure in the system reaches 900 lb.
Should leakage occur in the hydraulic system, stop the pump to prevent loss of fluid. Remove the hydraulic pump switch fuse in the main fuse panel in the cockpit, or disconnect the electrical receptacle at the pressure switch.
In some airplanes the hydraulic pump is controlled by an on-off switch on the pilot's control panel. This switch must be "ON" to maintain pressure.
The brake assemblies are on the inboard side of the main landing wheels, except in B-17G and late F's, which have dual brakes.
Hydraulic pressure applied from the cockpit expands the expander tubes, forcing the brake lining against the brake.
Apply the brakes as little as possible and then only for short, hard intervals. Excessive and unnecessary use of the brakes will generate sufficient heat to cause failure of the expander tubes and cracking of the brake drums and wheels. Taxi the airplane with the inboard engines shut off and maintain directional control with the outboard engines when mission is completed.
Do not leave the parking brake on while the brakes are hot from previous use. This will cause the heat in the drums to pass through the lining and literally cook the expander tube, which then becomes brittle. Do not apply hydraulic pressure to the brake with the wheel removed, as this will burst the expander tubes.
Emergency Brake System
A spare accumulator and auxiliary metering valve provide emergency brake operation. A red warning lamp on the pilot's instrument panel lights when pressure in the emergency system falls to approximately 700 lb. sq. in. To charge the emergency accumulator, open the manual shut-off valve. If a selective check valve is installed, place it in the "SERVICING" position unless it is lock-wired in the "NORMAL" position. (These units are on the right side wall at the rear of the pilot's compartment.) Build up 800 lb. pressure in the system, then return the selective check valve to "NORMAL" and close the manual shut-off valve.
The emergency brake system has been eliminated from later-model airplanes.
Pressure in the service and emergency brake systems is indicated by 2 gages on the pilot's instrument panel.
A hand pump on the side wall at the right of the copilot is used to supply pressure for ground operations and to recharge the accumulators if the electric pump fails.
Electrical System (B-17F)
Electrical power operates much of the auxiliary equipment in the airplane, such as the turrets, landing gear, wing flaps, instruments, bomb bay doors, and other miscellaneous equipment. Various units of the electrical system are distributed throughout the entire airplane. (See diagram.)
A 24-volt direct-current system is used in the B-17F. Type Mg-149 inverters are installed to furnish alternating current for all equipment requiring alternating current for its operation.
Control of the electrical system is accomplished mainly at the pilot's and copilot's stations. The bombardier and the navigator control the units necessary to their job's.
Fuse shields, accessible in flight, are on the bulkhead to the rear of pilot's seat and the bulkhead in the radio compartment. There are also fuse shields in each nacelle. An alternating current fuse shield, accessible in flight, is on the floor below the pilot.
The generators on the accessory panel on the rear of each engine are the primary source of electrical power. They keep the batteries charged and provide power for electrical equipment while in flight. The generators are driven by the engines at \Уг times engine speed. They will deliver power at engine speeds above 1350 or 1400 rpm.
Auxiliary Power Equipment
A gasoline engine-driven generator unit, in the rear of the fuselage and for use only on the ground and in the air for emergencies, supplies auxiliary electric power for battery recharging or limited radio operation.
Alternating current for the autosyn instruments, drift meter, radio compass, and warning signals transformer is furnished by either of 2 inverters, one of which is a standby for the other. One inverter is under the pilot's seat and the other under the copilot's seat. A single-pole, double-throw switch on the pilot's control panel controls the DC power to the inverters and selects the inverter to be used. In the "NORMAL" position the left-hand inverter is on and in the "ALTERNATE" position the right-hand inverter is on.
Use of Auxiliary Power
Don't use engine generators in ground operation. Since it is inadvisable to deplete the batteries unnecessarily, another source of energy should be used in starting the engines.
Use the auxiliary power unit wherever practicable for ground operation. This not only ¦ saves the batteries but charges them, and use of this unit assures that it is in serviceable condition if it should be needed in emergency.
If you cannot use the auxiliary unit, start engines with battery carts or with a field energizer. Saving the batteries is especially important in preflight and cold weather.
Function of the Voltage Regulator
The engine generator, mounted in back of each engine, is geared to turn three times while the engine turns twice. The variable rpm of the engine would tend to vary the generator output were it not for the voltage regulator in the accessory section of the airplane.
The regulator operates by a variable resistance which changes the strength of the field magnets of the generator. The variable resistance is affected by an electromagnet which operates against spring tension. Voltage setting of the generator is set by varying the spring . tension of the regulator or by varying the amount of current allowed to flow into the electromagnet, depending on the particular type of regulator used. Voltage regulators are in a shield under the pilot's floor in catwalk leading to bombardier's compartment.
(7) The purpose of the equalizing coil is to help equalize generator loads only when slight voltage variation causes unequal ammeter readings. If one generator is left off and the others are on and producing much current, too much load may be placed on the equalizer coil and the regulator may be damaged. Either have all properly functioning generators on or all off (except when checking).
(8) A bad generator is never completely disconnected from the electrical system until the regulator is removed. If a generator will not operate properly, remove its regulator. If you are flying, keep that switch off. If on the ground, remove the generator cannon plug also, to prevent wiring damage, and tape off the cockpit switch. In the B-17 the loss of a generator is not serious. More than twice as much power is available than will be needed. If a bad generator is properly disconnected the rest of the system will not suffer.
(9) Do not ask engineer to parallel generators when engines are operating at less than 1800 rpm. Don't try to parallel them on takeoff; wait until you have leveled off. Set voltage with all generator switches off. Do all your minor amperage paralleling with all switches on and little load on the system.
(10) The pilot must know location and disposition of fuses in fuse panels. Replacement of burned-out fuses often makes emergency action unnecessary.
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