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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. [22] 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.
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 ...
Good trackers can cover nearly as much ground as the distance they fall, approaching a glide ratio of 1:1. The fall rate of a skydiver in an efficient track is significantly lower than that of one falling in a traditional face-to-earth position; the former reaching speeds as low as 40 metres per second (90 mph), the latter averaging around the 54 m/s (120 mph) mark.
Wing loading is a useful measure of the stalling speed of an aircraft. Wings generate lift owing to the motion of air around the wing. Larger wings move more air, so an aircraft with a large wing area relative to its mass (i.e., low wing loading) will have a lower stalling speed.
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]