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Given the following information, calculate the required sector fuel in US gallons for a Twin-Engined Turbine Helicopter:

SAR: 7.55 SM/USG
Sector distance: 88 NGM
TAS: 135 kt
Wind: 240°(T)/25 kt
True Track: 160°

  • A
    13.8 USG
  • B
    15.7 USG
  • C
    13.4 USG
  • D
    12.3 USG

Specific Air Range (SAR) is a measure of fuel efficiency and indicates the Air distance covered per unit of fuel used. One thing that SAR does not account for is the wind.

The greater the SAR, the greater the efficiency and is given by the formula:

  • SAR = TAS / FUEL FLOW = NAMs / Unit of fuel.

SAR 7.55 SM/USG means that the helicopter covers 7.55 Statute air miles, burning 1 USG.

To calculate the required trip fuel proceed as follows:

  1. Convert SAR in SM/USG into SAR in NAM/USG (knowing that: 1 NM = 1.15 SM). So, 7.55 SM = 7.55/1.15 = 6.56 NAM. Thus, SAR = 6.56 NAM/USG.
  2. The horizontal wind component, which is a headwind is: Headwind component = Cos Angle difference between Track and Wind x Wind velocity = Cos (240° - 160°) x 25 kt = 4.34 kt.
  3. The Groundspeed is: TAS - Headwind component = 135 kt - 4.34 kt = 130.66 kt.
  4. The Sector Air distance covered is: NAM = NGM x (TAS/GS) = 88 NM x (135 kt/ 130.66 kt) = 90.92 NAM.
Therefore, since the helicopter covers 6.56 NAMs burning 1 USG, then the Required Sector Fuel is: Sector distance in NAM / SAR = 90.92 NAM / 6.56 = 13.8 USG.

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