. For a propeller aircraft this is the maximum endurance condition and gives a speed of 185 km/h (115 mph). The corresponding maximum range condition is the maximum of , at = , and so the optimum speed is 244 km/h (152 mph). The effects of the approximation = 0 are less than 5%; of course, with a finite = 0.1, the analytic and graphical methods give the same results. The low speed region of flight is known as the "back of the power curve" (sometimes "back of the drag curve") where more power is required in order to fly slower. It is an inefficient region of flight because speed can be increased and power decreased; there is no trade-off between increased speed and increased power consumption. It is regarded as a "speed unstable" region of flight, because a decrease in speed will lead to a further increase in speed if power if not adjusted, unlike in normal circumstances. Rate of climb For an aircraft to climb at an angle θ and at speed its engine must be developing more power in excess of power required to balance the drag experienced at that speed in level flight and shown on the power required plot. In level flight = but in the climb there is the additional weight component to include, that is = + .sin θ = + . Hence the climb rate .sin θ = . Supposing the 135 kW engine required for a maximum speed at 300 km/h is fitted, the maximum excess power is 135 - 87 = 48 Kw at the minimum of and the rate of climb 2.4 m/s. Fuel efficiency For propeller aircraft (including turboprops), maximum range and therefore maximum fuel efficiency is achieved by flying at the speed for maximum lift-to-drag ratio. This is the speed which covers the greatest distance for a given amount of fuel. Maximum endurance (time in the air) is achieved at a lower speed, when drag is minimised. For jet aircraft, maximum endurance occurs when the lift-to-drag ratio is maximised. Maximum range occurs at a higher speed. This is because jet engines are thrust-producing, not power-producing. Turboprop aircraft do produce some thrust through the turbine exhaust gases, however most of their output is as power through the propeller. "Long-range cruise" speed (LRC) is typically chosen to give 1% less fuel efficiency than maximum range speed, because this results