Introduction to Glider Flying > Aerodynamics of Flight > Forces of Flight > Lift

Lift opposes the downward force of weight and is pro-duced by the dynamic effects of the surrounding airstream acting on the wing. Lift acts perpendicular to the flight path through the wing’s center of lift. There is a mathematical relationship between lift, angle of attack, airspeed, altitude, and the size of the wing. In the lift equation, these factors correspond to the terms coef-ficient of lift, velocity, air density, and wing surface area. The relationship is expressed in Figure 3-3.

Figure 3-3. The lift equation is mathematically expressed by the above formula.

This shows that for lift to increase, one or more of the factors on the other side of the equation must increase. Lift is proportional to the square of the velocity, or air-speed, therefore, doubling airspeed quadruples the amount of lift if everything else remains the same. Likewise, if other factors remain the same while the coefficient of lift increases, lift also will increase. The coefficient of lift goes up as the angle of attack is increased. As air density increases, lift increases. However, you will usually be more concerned with how lift is diminished by reductions in air density on a hot day, or as you climb higher.