The fuel system on a B-29 is similar to that on the B-17. Fuel is supplied from two inboard and two outboard self-sealing wing tanks and seven auxiliary tanks. Each inboard wing tank has a capacity of 1436.5 gallons. The outboard wing tanks each hold 1367.5 gallons. Two to four bomb bay tanks, holding 640 gallons, may be incorporated to increase the fuel supply, and the wing center section tank holds 1315 gallons (1100 in B-29A).
Each engine receives its fuel supply from a system separate from the other three engines, thereby eliminating the possibility of failure of all four engines in case of fuel-line trouble.
Fuel pressure maintained through conventional engine-driven fuel pumps. If one of these fails, there is an electrically driven fuel-boost pump at the outlet of each gasoline tank. These supply pressure up to 18 psi.
You must use fuel boost on take off and landing as an added safety precaution against engine failure resulting from mechanical trouble developing in the normal engine-driven fuel pumps.
Under normal operations, if an engine-driven fuel pump fails and you use fuel boost to supply pressure, turn the turbo-supercharger control to 0 position, since fuel boost does not increase with carburetor duct pressure, and a lean mixture results, causing detonation.
Besides engine lubrication, the oil system on the B-29 also serves to operate the propeller governor and propeller feathering.
Each engine receives its oil supply from an 80-gallon self-sealing tank located in the nacelle. On some airplanes a 100-gallon reserve oil tank is located on the port side of the center wing section near the oil transfer pump and the oil transfer selector valve. An oil cooler, incorporated in the oil "out" line between the oil tank and the engine, is operated automatically, or manually by the flight engineer, if so desired. Oil dilution, when low ground temperatures are anticipated, is accomplished by operating four switches on the flight engineer's switch panel. These switches control four solenoid valves which, in turn, control the dilution of the oil.
The B-29 hydraulic system has one exclusive function; it transmits force to actuate the brake mechanism. The system is divided into two units—one for normal use and one for emergency use. The emergency system receives pressure from the normal system, but is isolated by a check valve and shut-off valve to prevent reverse flow. A hand pump is provided on the floor at the left of the copilot's seat permits building up the pressure when the electrically driven pump does not operate. The emergency system must be recharged after 5 to 7 applications of the brakes.
The electric hydraulic pump cuts in when the main hydraulic pressure falls below 800 psi, and cuts out when the main hydraulic pressure reaches 1000 psi. If the main pressure drops below 800 psi, an amber warning light on the copilot's panel goes on. The hydraulic pump runs continuously at pressures below 800 psi, unless the pressure falls below 200 psi, when it cuts out to prevent overheating if the hydraulic fluid is lost.
When the emergency pressure falls below 900 psi, the amber warning light on the flight engineer's panel goes on. To service: switch the emergency system filler valve (on flight engineer's panel) to OPEN, press the momentary contact toggle switch (on engine stand) until the pressure builds up to 1075 psi. The momentary contact switch operates the pump, regardless of pressure in either system. The pressure relief valve opens at 1075 psi and reaches its full-open position at 1200 psi.
The capacity of the hydraulic tank is 3 gallons, plus a 1/2 gallon expansion space. Note: Tank gage should read approximately 2 gallons when parking brakes are set.
The hydraulic panel, at the rear of the tor-ward pressurized compartment under the floor, contains an electric pump, a floating piston-type accumulator, a filter, a pressure switch, a relief valve, and a shut-off valve.
Don't set your parking brakes if the brakes are hot, as the brakes cannot cool properly with parking brakes on.
Air pressure preload in both normal and emergency accumulators is 400 psi.
When using the emergency brakes, a steady application of pressure is mandatory. Do not pump your brakes.
Six 28.5-volt engine-driven generators on the B-29 furnish 300 amperes each for a total of 1800 amperes. These generators are mounted two on each outboard engine and one on each inboard engine. The engines must be turning at least 1375 rpm for the generators to put out rated current.
The putt-putt drives a 28-volt 200-ampere generator. However, it cannot be used at altitudes greater than 10,000 feet. This, plus the battery, provides an additional source of power for ground operations and emergencies and as a safety precaution during landings and take-offs, but should not be considered a normal source of power during flight.
All engine-driven generators must be ON from takeoff to landing unless a unit fails. A defective generator should be switched OFF.
Try not to overload the system. If you operate the flaps and gear simultaneously, snap the switches ON at least a fraction of a second apart to separate the peak loads and prevent any possibility of momentarily overloading the system. Avoid sudden reversals in direction in the operation of either gear or Raps. A sudden reversal can cause an overload of several thousand amperes more than the capacity of the system. Allow about 10 seconds for the motor to slow down before flipping a switch in the opposite direction.
If one or more of the engine-driven generators fail, reduce the over-all load on the system, if possible, to a value within the capacity of the system. This is particularly important when attempting to operate flaps and gear on a go-around. The following table shows the electrical loads imposed by the operation of the various pieces of equipment:
|Upper forward turret
Upper aft turret
Lower forward turret
Lower aft turret
Tail ammunition booster motors (2)
Bombs doors (Forward and aft)
Landing gear (2)
Wheel doors (2)
Landing lights (2)
ATC radio set
|132.5 (Battle load 275)
132.5 (Battle load 275)
242 (Battle load 420)
200 (350 in flight)
Emergency Electrical System
Two electrical buses, or wiring systems, are available—a normal bus and an emergency bus. Through the use of the landing gear transfer switch and the bus selector switch on the battery solenoid shield, you can use either power source—the engine-driven generators or putt-putt and/or battery—with either the normal bus or the emergency bus. Or you can use them in combination.
Both normal and emergency motors are provided for the nose gear and the main gear. A portable electric motor can be used for the emergency operation of flaps or bomb bay doors (see Emergency Procedures).
The tailskid, however, can be operated only by the normal electrical system. It has no emergency motor.
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