Harmon Technologies, Inc.

Manifold pressure and Fuel flow Indicator

(Note: The picture shows a similar indicator.  The actual indicator in N4907J shows manafold pressure on the top and fuel flow on the bottom.)

This indicator has two parts.  The upper part indicates the engine intake manifold pressure.  This is the primary indication of the engine power setting.  The meter reads absolute pressure in inches of mercury.  This is the instrument that the pilot looks at when changing power settings with the throttle.  Fill power (at sea level) is between 25 and 27 inches.  Normal climb power is around 25 inches and normal 75% cruise power is usually 24 inches.  At high altitudes, maximum power may be lower because of the thin air found at high altitude.

The lower half indicates how fast fuel is being used.  This confirms proper engine operation and that fuel consumption is as expected given the altitude and power settings being used.  A typical climb consumption rate for N4907J is 11 Gallons per hour.  Normal cruise is about 10 to 10.2 gallons per hour.  Fuel consumption is typically a little lower at high altitude since less fuel is needed to mix with the thinner air.  The thinner air also offers less resistance (drag) and so the airplane can move faster given the same power setting.  This is one consideration when choosing an alitiude for the flight.

Copyright © 2004 Harmon Technologies, Inc.