Learjet 60 - FUEL FLOW Indicator

Learjet 60

Pilot's Manual
FUEL FLOW INDICATOR
A
FUEL
FLOW indicator for each engine is installed on the center in-
strument panel . Each indicator utilizes both a three-place digital dis-
play and a circular scale with pointer to indicate the fuel burn rate of
the respective engine . The circular scale reads from 0 to 3000 pounds
per hour in 100 pound-per-hour increments . The digital display uses
lighted segments to indicate fuel flow to the nearest 10 pounds per
hour . A fuel-flow transmitter (flowmeter) for each engine measures
fuel flow by means of a rotary vane installed in the engine fuel supply
line between the hydro-mechanical fuel control unit and the fuel dump
valve . As fuel flows through the flowmeter, an amplitude-modulated
constant-frequency sine wave signal is generated and applied to the
fuel flow indicator . The indicator converts this signal into an indication
of fuel burn rate (pounds per hour) . The indicator also provides a signal
to the flight management system for each pound of fuel burned . The
fuel flow indicating system operates on 28 VDC supplied through the
5-amp
L
and
R FUEL
FLOW circuit breakers on the pilot's and copilot's
circuit breaker panels .
N l INDICATORS
An N2 indicator for each engine is installed on the center instrument
panel . Each indicator utilizes both a four-place digital display and a cir-
cular scale with pointer to indicate N7 . The circular scale is marked
from 0% to 110% in 5%
RPM
increments . The digital display uses light-
ed segments to show the fan speed to the nearest tenth of a percent .
Each indicator also has a trapezoid-shaped N7 bug driven by a signal
from the associated
FADEC
. The N7 bug represents the speed the en-
gine should achieve given the ambient conditions, thrust lever setting,
flap setting, and squat switch position . N7 is an indication of engine
speed plus compensation . The
FADEC
takes into consideration its in-
puts to calculate and transmit the proper N7 bug settings for the ambi-
ent conditions . While airborne with the flaps up, the N7 bugs will show
the proper N7 for the selected throttle detent or, if the throttles are in be-
tween detents, the next higher setting . While on the ground, or inflight
with flaps 3° or lower, the N7 bugs will show takeoff power . On the
ground with the thrust reversers deployed, the N7 bugs will show the
maximum reverse N2 for the current conditions . Each engine
FADEC
has an externally mounted trim plug which provides trim compensa-
tion to the N7 signal . This trim plug will ensure consistent N7 indica-
tions for a specific paired throttle position . When ENG SYNC is On,
compensation is removed . Each engine is also equipped with two in-
duction-type speed sensors at the aft end of the low-pressure rotor . A
toothed wheel is attached to the low-pressure shaft rotating adjacent to
the stationary speed sensors . As the toothed wheel turns, its teeth cause
the frequency output of the speed sensors to change proportionally .
PM-123
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Change 5