Which formula is correct for the Specific Air Range (SAR)?
Specific Air Range (SAR) or Specific Range (SR) offers a measure of fuel efficiency which may be useful in deciding the altitude and speed for the cruise, ignoring the effect of the wind.
It tells us the nautical air mile distance a helicopter travels per unit of fuel used and is given by the formula:
- SAR or SR = TAS / Fuel Flow
The most typical units of measurement are: NAMs/Kg or NAMs/Lb.
The greater the SAR, the greater the efficiency, since the helicopter covers a greater air distance burning a smaller amount of fuel.
The best (optimum) SAR is obtained when the greatest number of NAMs are travelled for each kg/lb of fuel.
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