FUEL TANKS AND TANK
VENTING SYSTEM
GENERAL
Approximately 23 gallons of fuel in the 20 se-
ries fuel system is trapped. The weight of this
fuel is included in the airplane basic weight.
The approximate total usable fuel is 4,800
pounds in the 24E model, 5,600 pounds in the
24D and F models, 6,050 pounds in the 25B and
D models, and 7,350 pounds in the 25C model.
More detailed information is provided in the
“Weight and Balance” section of the AFM.
TIP TANKS
Each tip tank capacity is 1,235 pounds of us-
able fuel; capacity is reduced to 1,195 pounds
with installation of a recognition light. The
tanks are permanently attached to the wings
and are positioned at 2° nose down relative to
the airplane centerline. Baffles are installed
to minimize slosh and prevent adverse effects
on the airplane center of gravity during ex-
treme pitch attitudes.
A jet pump installed in each tip tank transfers
fuel into the wing tank. Approximately one half
of the fuel will gravity-flow through two flap-
per valves into the wing tank; however, any fuel
at a level lower than one-half full must be
transferred using the jet pump. A standpipe is
installed in each jet pump transfer line to pre-
vent fuel from being siphoned from the wing
tank to the tip tank when the applicable engine
is shut down.
The tip tank is vented through two vent float
valves located in the forward and aft ends of
the tank.
A fuel probe in each tip tank provides infor-
mation to the fuel quantity indicating system.
All tip tank fuel can be jettisoned through a
valve in the tank tailcone, if the optional jet-
tison system is installed.
A filler cap on each tip tank is used to service
the entire airplane fuel system.
WING TANKS
Each wing tank extends from the airplane cen-
terline to the tip tank and holds 1,160 pounds
of usable fuel. Areas which are not part of the
wing fuel cell are the main landing gear wheel
well, the leading edge forward of spar 1 (wing
heat area), and the trailing edge between spars
7 and 8 (flap, spoiler, and aileron areas).
The 2.5° wing dihedral makes the inboard por-
tions of the wing tanks the lowest areas. In each
wing tank, a jet pump and an electric standby
pump are located within these areas and will
remain submerged in fuel until the tanks are
nearly empty.
Wing ribs and spars act as baffles to minimize
fuel shifting. Flapper valves located in the
wing ribs allow unrestricted inboard flow of
fuel and limit outboard flow. Two pressure-re-
lief valves at the centerline rib equalize inter-
nal pressures between the two wing tanks. The
wing tanks begin to fill through the two tip tank
flapper valves as tip tank fuel increases beyond
one-half full.
Two fuel probes in each wing tank provide
information to the fuel quantity indicating
system.
FUSELAGE TANK
The fuselage tank consists of rubber bladder
fuel cells located between the aft pressure
bulkhead and tailcone section. The 24D and F
and 25B and D models are equipped with two
fuel cells with a capacity of 840 and 1,305
pounds, respectively, of usable fuel. The model
25C is equipped with four fuel cells with a ca-
p a c i t y o f 2 , 6 0 3 p o u n d s o f u s a b l e f u e l .
Depending on the airplane, either one or two
fuel lines connect the fuselage tank to the wing
tanks for filling and transfer. This is explained
in sections entitled “Transfer Valve/XFER-
FILL Switch.” Model 24E has no fuselage tank.
One fuel probe provides information to the
fuel quantity indicating system.
5-3
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
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