FUEL SUPPLY SYSTEM
To improve aircraft performance at supersonic speeds, an automatic fuel transfer system is installed to shift the cg (center of gravity) forward and aft under specific flight conditions. To facilitate this cg change as desired, fuel is transferred between the ‘F’ tank and 2 transfer tanks located along the aft wing sections.
The aircraft may be fueled to 'full internal fuel' or 'full internal and external fuel' configuration.
The 3 main tanks in each wing function as an individual tank and the fuel systems in each wing operate independently of each other. The pilot cannot transfer fuel from one wing to the other. All internal fuel tanks are Integral type composed of airplane structure and are not self-sealing.
Fuel tank capacities are listed in the table below. These quantities are exact, however could have varied due to temperatures, fuel probe tolerances and fuel gage tolerances.
The F-106B has the same fuel system design and number of tanks, however different fuel capacities as shown in the table.
FUEL TRANSFER SYSTEM
The main fuel tanks in each wing are numbered in the order in which they are emptied. Tank No. 1 is located in the forward section of the wing, tank No. 2 is located in the aft-outboard section and tank No. 3 is located in the aft-inboard section of the wing.
Fuel is supplied under pressure from each No. 3 tank by two electrically driven boost pumps through fuel shutoff valves to the engine fuel control system. These pumps were located in the forward-outboard and aft-inboard sections of each No. 3 tank. Boost pump inlets were located in the top and bottom of the fuel tanks to ensure fuel supply during all aircraft attitudes.
A fuel flow equalizer provided symmetrical fuel usage from the left and right-hand fuel systems. If the boost pumps failed, the engine-driven fuel pumps would draw fuel through a dual check valve inlet located on the outside of the boost pumps.
Fuel tank pressurization was provided to facilitate fuel transfer, to provide adequate fuel pressure to the engine fuel control system, and to prevent excessive high-altitude fuel vaporization. The fuel tank pressurization air was engine bleed air, which was pressure regulated and passed through the air-conditioning primary heat exchanger. For tank pressurization and to provide fuel flow through each wing tank system, air pressure enters No. 1 tank in each wing fuel system. As fuel is drawn from No. 3 tank by the boost pumps, the pressure differential between tanks forced fuel from No. 1 tank into No. 2 tank, which in turn forces fuel into No. 3 tank.
EXTERNAL WING FUEL TANKS
Two jettisonable 360-gallon external wing tanks could be installed under each wing to augment the internal fuel supply. These external tanks could be jettisoned by a ballistic charge and were mounted on ‘ejection racks’ under each wing.
The fuel in the external tanks was transferred into No. 1 wing tanks by engine bleed air pressure, which was regulated at a higher pressure than the normal fuel system.
Normally, transfer of fuel from the external tanks to No. 1 wing tanks would not occur until the landing gear was up and locked. However, if needed, the pilot could transfer fuel with the landing gear down by placing the External Tank Emergency Switch to the ON position, which then had to remain in the ON position until the external tanks were empty, otherwise pressurization in the tanks would cause fuel to be vented overboard.
NOTE: Originally these external wing tanks were 230-gallon tanks, at least that's what they were always referred to although they were actually 227 gallons, which were limited to about Mach 1.25, although they were called sub-sonic tanks. Sometime around 1967 these were replaced/upgraded with the know well known 360-gallon supersonic tanks rated to Mach 2.0. These tanks became a 'fixture' on the F-106 as they almost always flew with them since these tanks did not limit the aircrafts performance under Mach 2. Some mission types that did not fly with the external tanks were Aerial Combat Tactics (ACT fighter vs.fighter) missions, previously called Aerial Combat Maneuvering (ACM), and Functional Check Flight's (FCF). Even the Alert birds carried external 360 tanks.
SINGLE POINT REFUELING
The internal and external fuel tanks were all serviced through an SPR, Single Point Refueling adapter, located on the lower right engine inlet duct fairing (right intake). The tanks were refueled in a reverse order from normal tank transfer sequence. Selective refueling of internal tanks was not possible. You could however, differentiate between all-tanks and internal only. If the refuel selector valve was in the OPEN position, all internal and external tanks would be fueled. However, if the valve was CLOSED only the internal tanks would be refueled.
The external tanks could also be refueled through a filler-cap on top of each tank.
External electrical power was not required for ground SPR refuel operations.
In 1967 in-flight refueling capability was added to the F-106 with an IFR (In-flight Fuel Receptical) on top of the fueslage just aft of the cockpit. The mod took a few years to complete across the entire fleet of aircraft. Some of the first aircraft to receive the IFR mod were 318th jets at McChord. Partly because of this, the 318th was selected to fly to Korea during the Pueblo incident in Jan 1968, which required used of in-flight refueling.