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Refer to figure or CAP 758 figure 2.20.
Given the following information for a SEPH, determine the fuel consumption during flight:

Groundspeed: 60 kt
Ground distance: 120 NM
Cruise altitude: 2 000 ft
Manifold pressure: 24 in Hg

  • A

    29.8 gal

  • B

    14.9 gal

  • C

    89 lb

  • D

    89 gal

Refer to figure.

The flight time is: Time = Ground Distance / Groundspeed = 120 NM / 60 kt = 2 hours.

Determine the fuel flow at 2 000 ft, proceeding with one of the following manners:

  • Enter with Manifold Pressure 24 in Hg and move horizontally to the right until crossing the middle point between the SL and 4 000 ft pressure altitude curves.
  • Continue vertically down and read the Fuel Flow at 2 000 ft: 14.9 gal/hr or 89 lb/hr.
  • Thus, the fuel required is: Fuel flow x Flight time = 14.9 gal/hr x 2 hr = 29.8 gal or 89 lb/hr x 2 hr = 178 lb.

OR

  • Enter the graph from the left with Manifold Pressure 24 in Hg and move to the right intersecting both Sea Level and 4 000 ft lines.
  • From the two intersections move vertically down to read Fuel flow at SL: 14.3 gal/hr (85.5 lb/hr) and Fuel flow at 4 000 ft: 15.5 gal/hr (93.2 lb/hr).
  • Find the average fuel flow interpolating for Fuel Flow at 2 000 ft: (14.3 gal/hr + 15.5 gal/hr)/2 = 14.9 gal/hr or (85.5 lb/hr + 93.2 lb/hr)/2 = 89 lb/hr.
  • Thus, the fuel required is: Fuel flow x Flight time = 14.9 gal/hr x 2 hr = 29.8 gal or 89 lb/hr x 2 hr = 178 lb.

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