and flaps are deployed. The accompanying diagram shows against for a typical light aircraft. The minimum point is at the left-most point on the plot. One component of drag is induced drag (an inevitable side-effect of producing lift, which can be reduced by increasing the indicated airspeed). This is proportional to . The other drag mechanisms, parasitic and wave drag, have both constant components, totalling , and lift-dependent contributions that increase in proportion to . In total, then The effect of is to shift the curve up the graph; physically this is caused by some vertical asymmetry, such as a cambered wing or a finite angle of incidence, which ensures the minimum drag attitude produces lift and increases the maximum lift-to-drag ratio. Power required curves One example of the way the curve is used in the design process is the calculation of the power required () curve, which plots the power needed for steady, level flight over the operating speed range. The forces involved are obtained from the coefficients by multiplication with , where ρ is the density of the atmosphere at the flight altitude, is the wing area and is the speed. In level flight, lift equals weight and thrust equals drag, so and . The extra factor of /η, with η the propeller efficiency, in the second equation enters because = (required thrust)×/η. Power rather than thrust is appropriate for a propeller driven aircraft, since it is roughly independent of speed; jet engines produce constant thrust. Since the weight is constant, the first of these equations determines how falls with increasing speed. Putting these values into the second equation with from the drag curve produces the power curve. The low speed region shows a fall in lift induced drag, through a minimum followed by an increase in profile drag at higher speeds. The minimum power required, at a speed of 195 km/h (121 mph) is about 86 kW (115 hp); 135 kW (181 hp) is required for a maximum speed of 300 km/h (186 mph). Flight at the power minimum will provide maximum endurance; the speed for greatest range is where the tangent to the power curve passes through the origin, about 240 km/h (150 mph).) If an analytical expression for the curve is available, useful relationships can be developed by differentiation. For example the form above, simplified slightly by putting = 0, has a maximum at =