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Fuel Quantities Print E-mail
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Written by Sabc   
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FUEL LOW Caution
Fuel Capacities
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fuel_quantity_imageThe fuel quantity indicating system provides readouts in pounds of all usable internal, external and CFT fuel quantities. Fuel quantities are measured by floating type fuel level sensors hence erroneous fuel indications are possible during and immediately after hard maneuvering resulting from fuel slosh in the tanks.

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Fuel quantities are indicated by the fuel quantity indicator located in the lower right corner of the pilot's cockpit (at the pilot's right knee). Beside the fuel quantity indicator, the system components include a built-in test ( BIT), a BINGO caution display and an independent FUEL LOW caution light. The fuel quantity indicator display is pictured below.

fuel_quantity_indicator

1
2
3
- Power off indicator
- Fuel indicator dial and counter
- Bingo fuel bug
4
5
6
- Bingo fuel knob
- Indicated fuel counters (left, right)
- Indicated fuel selector knob

The main indicator is a pointer-counter combination (2) display. The pointer indicates total internal fuel (in thousands of pounds) and the counter marked as "TOTAL LBS" indicates total internal, external plus CFT fuel. During flying the external tanks are drained first, which means that the pointer remains fixed at its max position as long as there is fuel in the external tanks.

The two lower counters marked "LEFT" and "RIGHT" (5) provide individual tank monitoring possibility. The tank to be monitored must be selected by a selector knob (6) and the current fuel levels of the selected tank are indicated by the two counters. When the knob is turned to select a tank which is a single one (and has no left and right parts), then the fuel quantity is displayed by the left counter and the right counter displays zero.

Selector knob positions are "FEED" for engine feed tanks, "INTL WNG" for internal wing tanks, "TANK 1" for tank 1 (main fuel tank), "EXT WNG" for external wing mounted tanks, "EXT CTR" for external centerline pylon mounted tank and "CONF TANK" for conformal tanks.

A " BIT" position is available on the selector knob for bult-in test. This position is spring loaded and drives the internal (pointer) and total (counter) indicators to 6000 pounds and the left and right counter indicators to 600 pounds to check if the fuel quantity indicator is working properly.

A separate "OFF" flag (1) displays if there is no electrical power available to drive the fuel quantity indicating system.

During flight there is a certain fuel level which is a minimal quantity of fuel required to return the aircraft to the base. This fuel level is called "bingo fuel" and the fuel quantity indicating system provides means of setting and monitoring bingo fuel level. Setting bingo fuel is done by a knob in the upper right corner of the display (4). This knob sets the bingo fuel bug (3) to the desired bingo fuel level. Once this level is reached by the fuel quantity pointer, a BINGO FUEL caution on the MPD/ MPCD display comes on, plus a voice warning is played in the headsets of the aircrew by Bitching Betty saying "bingo fuel" twice. Note, that when the bingo fuel bug is set above 6000 pounds and built-in test is activated by turning the selector knob to the BIT position, then the bingo fuel warning is automatically displayed.

FUEL LOW Caution

There is an extra warning feature which works independently of the fuel quantity indicator system. This is called the FUEL LOW caution, which automatically displays on MPD/ MPCD (and the appropriate caution light illuminates) if fuel level in one of the engine feed tanks decrease below a minimal limit. This caution is triggered by individual fuel level sensors in the engine feed tanks. Minimal limit is 960 pounds for the right tank and 540 pounds for the left tank. These sensors are independent of the indicated total fuel quantity, but the caution usually comes up when total internal fuel is around 1500 pounds (give or take 200 pounds).

Since the FUEL LOW caution is based purely on the engine feed tank sensors, it may occur in situations when there is plenty of fuel onboard of the aircraft. If fuel transfer rate to engine feed tanks falls behind engine fuel consumption, then fuel level in engine feed tanks may become critically low. If a LOW FUEL condition occurs, fuel automatically starts to transfer from CFT's and external tanks towards the transfer tanks, regardless of cockpit switch settings (see article Internal Fuel System). This "emergency" transfer stops when fuel level in engine feed tanks raise above the critical value. Note, that tank 1 and CFT transfer pumps do not activate when the aerial refueling door is open (the slipway switch is in OPEN or in ORIDE position, see article Air Refueling System) even under FUEL LOW condition.

Fuel Capacities

The following table contains the maximum amounts of usable fuel each tank can contain. Amounts are given in gallons and its tank is placed into its respective (left, center, right) column according to its location.

Tank Name Capacity
Left
Capacity
Center
Capacity
Right
Tank 1
Engine Feed Tanks
Internal Wing Tanks
-
189 gal
496 gal
604 gal
-
-
-
234 gal
496 gal
TOTAL Internal Tanks 2,019 gal
Conformal Fuel Tanks
External Drop Tanks
728 gal
610 gal
-
610 gal
728 gal
610 gal
TOTAL External Tanks 3,286 gal

Fuel weights depend on temperature and type of fuel used. For conversion purposes use the following numbers at 65 degrees fahrenheit: 6.3 or 6.5 lb/gal for JP-4 (depending on manufacturer), 6.7 lb/gal for JP-8, and 6.8 lb/gal for JP-5.

Based on the data above we give fuel amounts for typical loadouts in the following table (both in gallons and in pounds for JP-4 of 6.5 lb/gal).

Loadout Volume Weight
Fuel capacity with CFT's
Fuel capacity with CFT's and 2 external drop tanks
Maximum possible fuel capacity
3,475 gal
4,695 gal
5,305 gal
22,588 lbs
30,518 lbs
34,483 lbs

It should be noted that although 3 external drop tanks can be fitted to an F-15E, they practically never fly in this configuration. For long missions CFT's and two external drop tanks (under the wings) are used.

Sources

  • F-15E Flight Manual (TO 1F-15E-1) C 15 August 1990, courtesy of eFlightManuals

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Last Updated on Wednesday, 08 September 2010
 


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