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The speed to fly is the optimum speed through sinking or rising air mass to achieve either the furthest glide, or fastest average cross-country speed. [1] Most speed to fly setups use units of either airspeed in kilometers per hour (km/h) and climb rate in meters per second (m/s), or airspeed in knots (kn) and climb rate in feet per minute (ft ...
Drag vs Speed. L/DMAX occurs at minimum Total Drag (e.g. Parasite plus Induced) Coefficients of drag C D and lift C L vs angle of attack. Polar curve showing glide angle for the best glide speed (best L/D). It is the flattest possible glide angle through calm air, which will maximize the distance flown.
Polar curve showing glide angle for the best glide speed (best L/D). It is the flattest possible glide angle through calm air, which will maximize the distance flown. This airspeed (vertical line) corresponds to the tangent point of a line starting from the origin of the graph.
A straight line from the origin to some point on the curve has a gradient equal to the glide angle at that speed, so the corresponding tangent shows the best glide angle tan −1 (C D /C L) min ≃ 3.3°. This is not the lowest rate of sink but provides the greatest range, requiring a speed of 240 km/h (149 mph); the minimum sink rate of about ...
Thrust power is the speed multiplied by the drag, is obtained from the lift-to-drag ratio: =; here Wg is the weight (force in newtons, if W is the mass in kilograms); g is standard gravity (its exact value varies, but it averages 9.81 m/s 2).
The Netto variometer will always read zero in still air. This provides the pilot with the accurate measurement of air mass vertical movement critical for final glides (the last glide to the ultimate destination location). In 1954, Paul MacCready wrote about a sinking speed correction for a total energy venturi. MacCready stated, "In still air ...
The 360° Power-off approach requires the plane to glide in a circular pattern, starting 2,000 ft or more, above the intended landing point. [5] When the aircraft is positioned over the landing point, the throttle is closed and again, the proper glide speed must be attained.
For any given lift conditions, there is an optimal final glide speed to minimize the overall time required – the stronger the lift, the faster (and steeper) the final glide should be. Pilots use sophisticated glide computers to calculate the altitude required and to track progress along the way.