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If the CG of an aircraft is close to its forward limit, what will be achieved if fuel is transferred from the wing tanks to the aeroplane’s fin or horizontal stabiliser tanks?

  • A
    Efficient stability control, by repositioning the CG aft.
  • B
    Best fuel economy, by repositioning the CG forward.
  • C
    Efficient fuel consumption, by repositioning the CG aft.
  • D
    Best range, by repositioning the CG forward.

With forward CG position the extra downforce produced on the elevator effectively adds to the aircraft weight and requires the lift produced by the wings to be increased to counter it. More lift means more drag, more drag means higher fuel consumption, range and endurance decrease, but longitudinal static stability increases.

For an aft CG position, the opposite effects are true. Better fuel consumption is achieved, range and endurance increases, but longitudinal static stability decreases.

The aft limit is usually just in front of the wing’s Centre of Pressure and the optimum centre of gravity position is near the aft limit.

Most modern aircraft use automatic fuel management to ensure that the CG remains at the optimum aft position in flight for range flying and best fuel economy. Tanks are generally located in the wings (outer and inner) and in a central position in the fuselage, but may also be found in the fin and the horizontal stabiliser. Fuel is fed from the tanks in the correct sequence to maintain wing bending relief and aft CG position.

Over the years, fuel tanks in the tail fin and stabiliser (trim tanks) have been employed by different manufacturers for two main reasons. Firstly, to provide extra fuel capacity and range and secondly, to help maintain the aircraft CG position at the optimum aft position.

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