For the same aircraft speed and an horizontal trajectory:
- When the aircraft is lighter, less lift is required.
- To decrease the lift, the angle of attack needs to be reduced (said otherwise: the aircraft flies more horizontal).
- A smaller AoA creates less induced drag.
Lift and drag coefficients as a function of the angle of attack are represented in the following diagram.
The ratio L/D is also represented, with its maximum L/D max. L/D max is an economical angle of attack. After L/D max, a gain in lift is at the expense of a larger increase in induced drag.
Side-effect of reduced drag:
- The thrust can be reduced to achieve the previous speed.
- The range is increased thanks to the thrust reduction.
For a more accurate representation of lift and drag coefficients against the angle of attack, and additional information: Lift and drag curves for the wing.