At which airspeed is maximum range achieved for a turboprop or jet?

Maximum range for a turboprop or jet is achieved at an airspeed just above L/Dmax, where L/Dmax is the point of maximum lift-to-drag ratio. At this airspeed, the aircraft is able to balance the amount of lift generated with the drag experienced, optimizing aerodynamic efficiency.

Operating just above this point allows the aircraft to take advantage of a greater speed while still maintaining a favorable lift-to-drag ratio, thus maximizing the distance flown per unit of fuel consumed. This slight increase in speed above L/Dmax enables efficient cruising, which is essential for long-distance travel, as it helps in utilizing altitude and fuel characteristics effectively.

While the point of L/Dmax is where the lift-to-drag ratio is at its highest, flying too slowly—a scenario represented by speeds below L/Dmax—would increase drag considerably without significant benefit to lift, ultimately not achieving maximum range. High stall speeds are also not conducive to efficient range performance because they do not allow for optimal aerodynamic efficiency or fuel economy. Hence, the best performance for range occurs just above L/Dmax.