# Coefficient of lift and drag relationship

In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or . One method for estimating the zero-lift drag coefficient of an aircraft is the equivalent skin-friction method. For a well Dietrich Küchemann developed an empirical relationship for predicting L/D ratio for high Mach: L / D m a x = 4. For an aeroplane with velocity m/s, wing area 20 m2, a drag coefficient and a lift coefficient - the lifting force acting on the airfoil can be calculated. Is there a relationship between the force of drag and lift for an airfoil Is there any difference between the lift coefficient of airfoil and the lift.

In steady and level flight: If during steady and level flight, thrust is increased, then the aircraft will start to accelerate in the direction of thrust will start to gain speed. The increase in speed will lead to increase in drag.

### Lift-to-drag ratio - Wikipedia

In the reverse situation, when during steady and level flight thrust is reduced, the aircraft will start to accelerate in the direction of drag the speed will start to decrease. The decrease in speed will lead to a decrease in drag. The shape of an airfoil and other lift producing devices i. Since the glide ratio is based only on the relationship of the aerodynamics forces acting on the aircraft, aircraft weight will not affect it.

The only effect weight has is to vary the time that the aircraft will glide for.

The heavier the aircraft is, the higher the airspeed must be to obtain the same glide ratio. Both aircraft will cover the same distance but the lighter one will take a longer time to do so.

From the practical point of view one should remember that although it is well known that winglets reduce drag and save fuel, their effect on speed control may not have been highlighted before. Crews therefore need to be aware that reduced drag makes speed control on the approach more difficult. Drag will also increase if the landing gear or flaps are extended and the airspeed will then decrease unless the pitch attitude is reduced. When pitch is reduced, the glide angle increases and the distance traveled will reduce.

These two quantities are not measured with respect to the velocity, but with respect to the geometry of the airfoil itself. In the case of a 2D airfoil like that shown here, the key geometrical parameter is the chord line. The chord line is defined as a straight line from the leading edge to the trailing edge of the airfoil. Similar to lift and drag, normal force and axial force are defined as being perpendicular and parallel to the chord line, respectively.

### AP4ATCO - Lift/Drag Ratio, Forces Interaction and Use - SKYbrary Aviation Safety

We have already seen that lift and drag always keep the same orientation with respect to the velocity no matter what the angle of attack is. However, the orientation between these two forces and the chord line of the airfoil does change. The reverse is true for the normal and axial forces. As angle of attack changes, the normal and axial forces change orientation with respect to the velocity, but the two vectors always maintain the same orientation with respect to the body.

That brings us to the equations you mention.

The quantities lift, drag, normal force, and axial force are all related by simple trigonometry. If we know the values in one reference system, we can easily convert to the other system using the following equations.

If you know normal force N and axial force Acalculate lift L and drag D: If you know lift L and drag Dcalculate normal force N and axial force A: Up until now, we have only talked about the actual forces L, D, N, and A. These quantities would be measured in force units like pounds or newtons. However, we have seen in previous discussions that engineers often convert these forces into nondimensional coefficientslike CL for lift and CD for drag, to make comparisons more easily.

Similar coefficients also exist for the normal force CN and axial force CA.

## Lift-to-drag ratio

We will continue to use these coefficients for the remainder of this article for reasons that will become obvious shortly. As described above, the equations you discovered are indeed correct, yet the answers you calculated when applying them are not. The error in your simple analysis is that you assumed values for N and A that are constant with angle of attack.

You applied the mathematics of the equations properly but assumed faulty inputs for the variables.

We need a more realistic example to better demonstrate the relationships between these two sets of aerodynamic forces. Instead of making up numbers, we can use an example provided in a previous article about the aerodynamic behavior of airfoils at high angle of attack. Several of the values provided in these graphs have been extracted and are listed in the table below.

**Airfoil Design**

The table also shows the corresponding normal and axial force coefficients converted using the equations provided earlier. You can use these values yourself to convert back and forth and make sure you understand how all four variables are calculated.