SECTION 7 CESSNA
AIRPLANE AND SYSTEM DESCRIPTION MODEL T182T NAV III
GFC 700 AFCS
U.S.
ENGINE (Continued)
TURBOCHARGING SYSTEM (Continued)
MANIFOLD PRESSURE VARIATION WITH AIRSPEED
When the waste gate is closed, manifold pressure will vary with
variations in airspeed. This is because the compressor side of the
turbocharger operates at pressure ratios of up to 3 to 1 and any change
in pressure at the compressor inlet is magnified at the compressor
outlet with a resulting effect on the exhaust flow and turbine side of the
turbocharger.
FUEL FLOW VARIATIONS WITH CHANGES IN MANIFOLD
PRESSURE
The engine driven fuel pump output is regulated by engine speed and
compressor discharge pressure. Engine fuel flow is regulated by fuel
pump output and the metering effects of the throttle and mixture
control. When the waste gate is open, fuel flow will vary directly with
manifold pressure, engine speed, mixture, or throttle control position. In
this case, manifold pressure is controlled by throttle position and the
waste gate controller, while fuel flow varies with throttle movement and
manifold pressure.
When the waste gate is closed and manifold pressure changes are due
to turbocharger output, as discussed previously, fuel flow will follow
manifold pressure even though the throttle position is unchanged. This
means that fuel flow adjustments required of the pilot are minimized to
(1) small initial adjustments on takeoff or climb-out for the proper rich
climb setting, (2) lean-out in cruise, and (3) return to full rich position for
approach and landing.
(Continued Next Page)
T182TPHBUS-00
7-44
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