Editing Speed to fly (section)

[[File:MacCready Ring and variometer.jpg|thumb|350px|[[Paul MacCready|MacCready]] speed to fly ring for a [[variometer]]. The outer ring show various [[airspeed]]s, while the variometer shows [[climb rate]].  The index arrow, white triangle, on the ring is placed against the expected rate of climb at the next thermal.  The variometer needle will then point to the optimum airspeed, listed on the ring, to be flown to that thermal.  The greater the expected rate of climb, the more clockwise the ring is rotated, and the faster is the optimum airspeed.<ref name=faa/>]]
'''Speed to fly''' is a principle used by [[Gliding|soaring]] pilots when flying between sources of lift, usually [[thermal]]s, [[ridge lift]] and [[Lee waves|wave]].  The aim is to maximize the average [[Cross-country flying|cross-country]] speed by optimizing the [[airspeed]] in both rising and sinking air.  The optimal airspeed is independent of the wind speed, because the fastest average speed achievable through the airmass corresponds to the fastest achievable average [[groundspeed]].<ref>''Modern Elementary Gliding'', British Gliding Association, n.d. Appendix D: "Making the Most of it".</ref>

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.<ref name=faa>{{cite book |title=Glider Flying Handbook, FAA-H-8083-13 |date=2003 |publisher=U.S. Department of Transportation, FAA |isbn=9780160514197 |pages=4–8, G-4}}</ref>

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 [[Knot (unit)|knots]] (kn) and climb rate in feet per minute (ft/min).