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In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficiency under given flight conditions. The L/D ratio for any given body will vary according to these flight conditions.
A glider's glide ratio varies with airspeed, but there is a maximum value which is frequently quoted. Glide ratio usually varies little with vehicle loading; a heavier vehicle glides faster, but nearly maintains its glide ratio. [21] Glide ratio (or "finesse") is the cotangent of the downward angle, the glide angle (γ). Alternatively it is ...
Glide slope is the distance traveled for each unit of height lost. In a steady wings-level glide with no wind, glide slope is the same as the lift/drag ratio (L/D) of the glider, called "L-over-D". Reducing lift from the wings and/or increasing drag will reduce the L/D allowing the glider to descend at a steeper angle with no increase in airspeed.
open class sailplanes – typically around 60:1, but in more common 15–18 meter span aircraft, glide ratios are between 38:1 and 52:1; [4] high glide performance enabling long distance flight, with 3,000 kilometres (1,900 mi) being current (as of November 2010) record [5]
Glide ratio is dependent on an aircraft's class, and can typically range from 44:1 (for modern designs in the Standard Class) up to 70:1 (for the largest aircraft). A good gliding performance combined with regular sources of rising air enables modern gliders to fly long distances at high speeds.
The tangent defines the minimum glide angle, for maximum range. The peak of the curve indicates the minimum sink rate, for maximum endurance (time in the air). Without power, a gliding aircraft has only gravity to propel it. At a glide angle of θ, the weight has two components, W.cos θ at right angles to the flight line and W.sin θ parallel ...
One measure of performance is the glide ratio. For example, a ratio of 12:1 means that in smooth air a glider can travel forward 12 metres while only losing 1 metre of altitude. Some performance figures as of 2006: Topless gliders (no kingpost): glide ratio ~17:1, speed range ~30–145 km/h (19–90 mph), best glide at 45–60 km/h (28–37 mph)
The wing's small size and unique design give it a much smaller glide ratio making it more suitable to fly close to the slope. [23] The smaller size also allows the wing to be flown in windier environments, and minimizes weight for hiking. [24] The speed glider flies at speeds of 20 to 95 mph versus a paraglider's 12 to 50 mph. [9]