# Polar curve (aviation)

A

**polar curve**is agraph of the rate of sink of anaircraft , often aglider , versus its horizontal speed.**Measuring a glider's performance**Knowing the best

speed to fly is important in exploiting the performance of a glider. Two of the key measures of a glider’s performance are its minimum sink rate and its bestglide ratio , also known as the best 'glide angle'. These occur at different speeds. Knowing these speeds is important for efficient cross-country flying. In still air the polar curve shows that flying at the minimum sink speed enables the pilot to stay airborne for as long as possible and to climb as quickly as possible, but at this speed the glider will not travel as far as if it flew at the speed for the best glide. When in sinking air, the polar curve shows that best speed to fly depends on the rate that the air is descending. UsingPaul MacCready 's theory, the optimal speed to fly may often be considerably in excess of the speed for the best glide angle to get out of the sinking air as quickly as possible.**Glide ratio**The glide ratio is expressed as the ratio of the distance travelled to height lost in the same time. The ratio of the horizontal speed versus the vertical speed gives the same answer. (If the glider flies at 40 knots for an hour and experiences a convert|2|kn|km/h|0|sing=on sink rate, it will travel 40

nautical mile s and descend convert|2|nmi|km|0. The glide ratio is 20 using both methods.**Plotting the curve**By measuring the rate of sink at various air-speeds a set of data can be accumulated and plotted on a graph. The points can be connected by a line known as the ‘polar curve’. Each type of glider has a unique polar curve.

The "origin" for a polar curve is where the air-speed is zero and the sink rate is zero. In the first diagram a line has been drawn from the origin to the point with minimum sink. The slope of the line from the origin gives the glide angle, because it is the ratio of the distance along the airspeed axis to the distance along the sink rate axis. A whole series of lines could be drawn from the origin to each of the data points, each line showing the glide angle for that speed. However the best glide angle is the line with the least slope. In the second diagram, the line has been drawn from the origin to the point representing the best glide ratio. The air-speed and sink rate at the best glide ratio can be read off the graph. Note that the best glide ratio is shallower than the glide ratio for minimum sink. All the other lines from the origin to the various data points would be steeper than the line of the best glide angle. Consequently, the line for the best glide angle will only just graze the polar curve, ie it is a

tangent .**External links*** [

*http://home.att.net/~jdburch/polar.htm Speed to fly*]

*Wikimedia Foundation.
2010.*

### Look at other dictionaries:

**Polar curve**— For a plane curve given C by the equation f(x 0,x 1,x 2)and a point a = (a 0,a 1,a 2), the polar curveP a(C) is a curve given by the equation a 0 f 0 + a 1 f 1 + a 2 f 2 = 0, where f i are partial derivatives.The intersection of C and P a(C) is… … Wikipedia**international modified polyconic projection**— A modified polyconic map projection chosen by an international committee in 1909 for construction of maps of the whole world, except polar caps, on one projection and on a scale of 1:1,000,000. The size of the sheet is 4° change of latitude by 6° … Aviation dictionary**Speed to fly**— is a principle used by soaring pilots when flying between sources of lift, usually thermals, ridge lift and wave. The aim is to maximize the average cross country speed by optimizing the airspeed in both rising and sinking air. The optimal… … Wikipedia**Glide ratio**— Glide ratio, also called, Lift to drag ratio, glide number, or finesse, is an aviation term that refers to the distance an aircraft will move forward for any given amount of lost altitude (the cotangent of the downward angle). Alternatively it is … Wikipedia**OMRE OE-01**— OE 1 Role Glider National origin Hungary Manufacturer MRSz Központi Repülögépjavító Üzem, Dunakeszi (Central Aircraft Repair Plant of the MRSz, Dunakeszi) First flight 14 May 1951 Number built 1 The OMRE OE 1 (a.k.a. Rubik R 20) was an ex … Wikipedia**List of Russian people**— The Millennium of Russia monument in Veliky Novgorod, featuring the statues and reliefs of the most celebrated people in the first 1000 years of Russian history … Wikipedia**Drag (physics)**— Shape and flow Form drag Skin friction 0% 100% 10% 90% … Wikipedia**Mathematics and Physical Sciences**— ▪ 2003 Introduction Mathematics Mathematics in 2002 was marked by two discoveries in number theory. The first may have practical implications; the second satisfied a 150 year old curiosity. Computer scientist Manindra Agrawal of the… … Universalium**Centripetal force**— Not to be confused with Centrifugal force. Classical mechanics Newton s Second Law … Wikipedia**Timeline of Islamic science and engineering**— This timeline of Islamic science and engineering covers the general development of science and technology in the Islamic world during the Islamic Golden Age, usually dated from the 7th to 16th centuries.From the 17th century onwards, the advances … Wikipedia