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refueling store (ARS). All tanks, internal and external, may be refueled on the ground through a
single-point refueling receptacle or inflight through the inflight refueling probe.
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The aircraft's fuel system is composed of the following subsystems: engine feed, motive flow, fuel
transfer, tank pressurization and vent, fuel recirculation, thermal management, refueling, fuel dump,
fuel quantity indicating, and fuel low level indicating. Refer to Fuel System, Foldout Section, for
simplified schematics.
2.2.1 Engine Feed System. Each engine feed system contains an airframe mounted accessory drive
(AMAD) driven motive flow/boost pump, a feed tank with an internal motive flow powered turbo
pump, and an engine feed shutoff valve. For survivability, the left and right feed systems are normally
separated but can be interconnected by a normally closed crossfeed valve and a normally closed feed
tank interconnect valve.
2.2.1.1 Motive Flow/Boost Pumps. Each AMAD drives a two-stage motive flow/boost pump. The
first stage supplies low pressure fuel to its respective engine mounted fuel pump, while the second stage
supplies high pressure fuel to the motive flow system. Fuel from the motive flow system is used to cool
accessories, power the feed tank turbo pumps and certain transfer/scavenge pumps, and control certain
transfer valves.
2.2.1.2 Feed Tanks. During normal operation, each engine receives fuel from separate fuel feed lines.
Tank 2 supplies fuel to the left engine; Tank 3 to the right. A motive flow powered turbo pump in each
feed tank supplies fuel to its respective motive flow/boost pump.
Each feed tank has a horizontal baffle which traps fuel, providing a minimum of 10 seconds of
negative g flight at MAX power. No sustained zero g capability is provided, and prolonged transitions
through zero g (greater than 2 seconds) may produce a L and/or R BOOST LO caution.
If a feed tank turbo pump fails, fuel is suction fed to the motive flow/boost pump. In this case, flight
at high altitude with high feed tank fuel temperatures may not supply enough fuel for high power
settings.
2.2.1.3 Feed Shutoff Valves. In the event of a fire or fuselage fuel leak, engine feed shutoff valves
provide the capability to isolate a fuel feed system immediately downstream of the feed tank. Pressing
the L or R FIRE warning light electrically closes the corresponding engine feed shutoff valve, isolating
that fuel feed system.
2.2.1.4 Crossfeed Valve. The crossfeed valve, normally closed, allows a single motive flow/boost
pump to feed both engines when boost pressure is lost on one side (e.g., single engine shutdown, a leak,
motive flow/boost pump failure, or feed tank depletion). A loss of boost pressure downstream of the
motive flow/boost pump sets the L or R BOOST LO caution and opens the crossfeed valve. An open
crossfeed valve allows the output from the good motive flow/boost pump to supply fuel to the opposite
engine at rates sufficient for at least MIL power.
Pressing the L or R FIRE warning light electrically closes (inhibits opening) the crossfeed valve,
isolating the two fuel feed systems.
2.2.1.5 Interconnect Valve. A feed tank interconnect valve, installed between Tanks 2 and 3, is used
to control gravity transfer/balancing between the two feed tanks. During normal operation, the dual
flapper-type valve is held closed by motive flow pressure on either side (left motive flow on the Tank
2 side and right motive flow on the Tank 3 side), and no fuel gravity transfers.
If motive flow is lost on one side (e.g., single engine shutdown), the valve opens to make sure that
feed tank fuel is available to the opposite engine. For instance, if motive flow is lost on the right side,
the Tank 3 side of the valve opens, allowing fuel to gravity transfer to Tank 2 anytime the Tank 3 fuel
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level is higher. If Tank 3 has a fuel leak (e.g., battle damage), motive flow pressure on the Tank 2 side
of the valve prevents Tank 2 fuel from gravity transferring into the leak.
2.2.1.6 Feed Tank Balancing. The SDC incorporates feed tank balancing logic, designed to keep
Tanks 2 and 3 within 100 lb of each other. With a normally operating fuel system, balancing begins
after Tank 4 is effectively empty (less than about 300 lb) and the feed tanks begin to deplete below full.
If a feed tank imbalance reaches 100 lb, the SDC shuts off the corresponding Tank 4 scavenge pump
until the imbalance is 50 lb in the opposite direction. With WoffW, feed tank balancing continues until
either feed tank reaches FUEL LO level (approximately 1,125 lb). Feed tank balancing stops at FUEL
LO to make sure tank 4 fuel is transferred to both feed tanks in case one feed tank is damaged and is
　
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本文鏈接地址：NATOPS Flight Manual 飛行手冊 1(35)