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The Tank 1 and 4 transfer pumps are also used to dump fuel through the dump valve and to transfer
fuel to the ARS through the ARS replenishment valve.
2.2.2.1.1 Fuel Transfer Schedule/CG Control. The SDC implements a fuel transfer schedule (figure
2-4) designed to keep aircraft CG at an optimum location. The system periodically shuts off the Tank
1 transfer pump to keep Tank 1 and Tank 4 properly balanced. Fuel transfer scheduling operates until
Tank 4 drops below 300 lb or the FUEL LO caution comes on. When Tank 4 reaches 300 lb, Tank 1
should indicate 250 lb or below.
The FUEL XFER caution is set when Tank 1 and 4 fuel is not scheduling properly or wing tank
imbalance exceeds 350 lb. The caution is inhibited when the inflight refueling probe is extended.
2.2.2.2 Fuel Transfer - Internal Wing Tanks. Fuel is transferred from the wing tanks to Tank 4 by
two motive flow powered ejector pumps, one in each tank. When Tank 4 is less than full, the SDC opens
both wing motive flow control valves, which direct motive flow to the ejector pumps and transfer fuel
from the wing tanks to Tank 4. When Tank 4 is full, the motive flow control valves are closed and
normal wing transfer is inhibited.
If motive flow is lost on one side (single engine shutdown), the cross-motive shutoff valve opens so
that one motive flow system can power the ejector pumps in both wing tanks. If both motive flow
systems are lost, the wing tanks gravity transfer to Tank 4. Bank angle changes or a steady sideslip may
be required to gravity transfer all available wing fuel.
2.2.2.2.1 Wing Tank Balancing. The SDC incorporates wing tank balancing logic designed to keep
wing tank asymmetry below 200 lb. If wing tank asymmetry exceeds 200 lb, the SDC shuts off fuel
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I-2-14 ORIGINAL
transfer from the lower tank by closing its wing motive flow control valve. If wing tank asymmetry
exceeds 350 lb for 15 seconds, the FUEL XFER caution appears.
Wing tank balancing also occurs during refueling, where the SDC alternately opens/closes the wing
refuel valves attempting to keep the wing tanks within 200 lb. The FUEL XFER caution is not set
during refueling. If SDC balancing logic cannot keep the wings from refueling asymmetrically (greater
than 350 lb), the FUEL XFER caution is set when the inflight refueling probe is retracted.
2.2.2.2.2 INTR WING Control Switch. The INTR WING control switch, located on the EXT LT
panel on the left console, is used to isolate the wing tanks (e.g., following battle damage).
INHIBIT Prevents normal transfer and refueling of the wing tanks (closes both wing motive
control valves, both wing refuel valves, and switches both diverter valves, located
in Tank 3, from the wing tanks to the feed tanks).
NORM Permits normal transfer and refueling of the internal wing tanks.
2.2.2.3 External Fuel Transfer. External fuel is transferred by regulated engine bleed air pressure
applied to all installed external tanks with WoffW. External tank pressurization is terminated for
inflight refueling (PROBE switch in EXTEND) and for arrested landing (both HOOK and LDG
GEAR handles down). With pressurization applied, external fuel transfer is controlled by the three
EXT TANKS transfer switches.
During external transfer, fuel is routed through the aircraft's refuel/defuel line. Refuel valves in each
tank open only if commanded by the SDC and space is available. At MIL power and below, the SDC
only allows external fuel to transfer to Tank 1 and the wing tanks. In afterburner, the SDC allows
external fuel to transfer to any internal tank that can accept it.
Figure 2-4. Tank 1 and 4 Fuel CG Control and FUEL XFER Caution Schedule
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2.2.2.3.1 EXT TANKS Transfer Switches. The three EXT TANKS transfer switches are located on
the FUEL panel on the left console and are labeled LM/RM, LI/RI, and CTR (left and right midboard,
left and right inboard, and centerline tanks, respectively). With the external tanks pressurized, fuel
transfers when the FUEL LO caution is displayed regardless of the position of the EXT TANKS
transfer switches.
ORIDE Applies pressurization and transfers fuel from all external tanks whose switches are not
in STOP. May be used to transfer external fuel during extended ground operations
(EXT TANK caution). Overrides any SDC stop transfer command.
NORM Permits normal transfer and refueling of controlled external tank(s).
STOP Prevents transfer and refueling of controlled external tank(s) except with a FUEL LO
caution.
2.2.3 Fuel Tank Pressurization and Vent. The internal fuel tank pressurization system provides
regulated engine bleed air pressure to all internal tanks to prevent fuel boil-off at altitude. Bleed air
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NATOPS Flight Manual 飞行手册 1(37)
