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40-473: The Discus was the first production sailplane to have a distinctive swept-back leading edge. This is now common in contemporary sailplanes. Studies had long shown that the ideal wing for minimizing induced drag should be an elliptic planform. To keep production costs down, a triple-trapezoidal approximation of this shape was adopted for the Discus. The wing section was also new. Winglets were only available towards

80-422: A constant amount of lift, induced drag can be reduced by increasing airspeed. A counter-intuitive effect of this is that, up to the speed-for-minimum-drag, aircraft need less power to fly faster. Induced drag is also reduced when the wingspan is higher, or for wings with wingtip devices . The total aerodynamic force acting on a body is usually thought of as having two components, lift and drag. By definition,

120-413: A function of angle of attack, induced drag increases as the angle of attack increases. The above equation can be derived using Prandtl's lifting-line theory . Similar methods can also be used to compute the minimum induced drag for non-planar wings or for arbitrary lift distributions. According to the equations above, for wings generating the same lift, the induced drag is inversely proportional to

160-441: A horizontal line on the fuselage as the reference line (and also as the longitudinal axis). Some authors do not use an arbitrary chord line but use the zero lift axis where, by definition, zero angle of attack corresponds to zero coefficient of lift . Some British authors have used the term angle of incidence instead of angle of attack. However, this can lead to confusion with the term riggers' angle of incidence meaning

200-430: A lower, flatter curve with a higher critical angle. The critical angle of attack is the angle of attack which produces the maximum lift coefficient. This is also called the " stall angle of attack". Below the critical angle of attack, as the angle of attack decreases, the lift coefficient decreases. Conversely, above the critical angle of attack, as the angle of attack increases, the air begins to flow less smoothly over

240-470: A maximum angle of attack is reached, regardless of pilot input. This is called the 'angle of attack limiter' or 'alpha limiter'. Modern airliners that have fly-by-wire technology avoid the critical angle of attack by means of software in the computer systems that govern the flight control surfaces. In takeoff and landing operations from short runways ( STOL ), such as Naval Aircraft Carrier operations and STOL backcountry flying, aircraft may be equipped with

280-517: A planform approaching the elliptical — the most famous examples being the World War II Spitfire and Thunderbolt . For modern wings with winglets, the ideal lift distribution is not elliptical. For a given wing area, a high aspect ratio wing will produce less induced drag than a wing of low aspect ratio. While induced drag is inversely proportional to the square of the wingspan, not necessarily inversely proportional to aspect ratio, if

320-403: A row from 1985 to 1995. The best measured glide ratio is 42.5:1. Though it is considered a high performance sailplane, its handling is well within the capabilities of inexperienced pilots. With no bad manners, powerful airbrakes and a low landing speed, the Discus is popular with clubs. Discuses are easy gliders to assemble, having light wings, automatic control hookups and a single pin securing

360-491: Is achieved. This is also the speed for greatest range (although V MD will decrease as the plane consumes fuel and becomes lighter). The speed for greatest range (i.e. distance travelled) is the speed at which a straight line from the origin is tangent to the fuel flow rate curve. The curve of range versus airspeed is normally very shallow and it is customary to operate at the speed for 99% best range since this gives 3-5% greater speed for only 1% less range. Flying higher where

400-500: Is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars with airfoil wings that redirect air to cause a downforce . It is symbolized as D i {\textstyle D_{\text{i}}} , and the lift-induced drag coefficient as C D , i {\textstyle C_{D,i}} . For

440-409: Is made of carbon fiber . There is a 6.5 L (1.7 US gal; 1.4 imp gal) water ballast tank in the fin for trimming purposes when the main wing mounted ballast tanks are in use (184 L combined) for a maximum wing-loading of 50 kg/m (10 lb/sq ft) The Discus dominated standard class sailplane racing throughout the 1980s, winning six World Gliding Championships in

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480-456: Is only indirectly related to stall behavior. Some military aircraft are able to achieve controlled flight at very high angles of attack, but at the cost of massive induced drag . This provides the aircraft with great agility. A famous example is Pugachev's Cobra . Although the aircraft experiences high angles of attack throughout the maneuver, the aircraft is not capable of either aerodynamic directional control or maintaining level flight until

520-443: Is proportional to the square of the airspeed, the combined overall drag curve shows a minimum at some airspeed - the minimum drag speed (V MD ). An aircraft flying at this speed is operating at its optimal aerodynamic efficiency. According to the above equations, the speed for minimum drag occurs at the speed where the induced drag is equal to the parasitic drag. This is the speed at which for unpowered aircraft, optimum glide angle

560-401: Is small and has little effect on the lift. However, there is an increase in the drag equal to the product of the lift force and the angle through which it is deflected. Since the deflection is itself a function of the lift, the additional drag is proportional to the square of the lift. The vortices created are unstable, and they quickly combine to produce wingtip vortices which trail behind

600-449: Is the angle between a reference line on a body (often the chord line of an airfoil ) and the vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the body's reference line and the oncoming flow. This article focuses on the most common application, the angle of attack of a wing or airfoil moving through air. In aerodynamics , angle of attack specifies

640-490: Is the largest component of total drag, at almost 48%. Reducing induced drag can therefore significantly reduce cost and environmental impact. In 1891, Samuel Langley published the results of his experiments on various flat plates. At the same airspeed and the same angle of attack, plates with higher aspect ratio produced greater lift and experienced lower drag than those with lower aspect ratio. His experiments were carried out at relatively low airspeeds, slower than

680-465: The air is thinner will raise the speed at which minimum drag occurs, and so permits a faster voyage for the same amount of fuel. If the plane is flying at the maximum permissible speed, then there is an altitude at which the air density will be sufficient to keep it aloft while flying at the angle of attack that minimizes the drag. The optimum altitude will increase during the flight as the plane becomes lighter. The speed for maximum endurance (i.e. time in

720-453: The air) is the speed for minimum fuel flow rate, and is always less than the speed for greatest range. The fuel flow rate is calculated as the product of the power required and the engine specific fuel consumption (fuel flow rate per unit of power ). The power required is equal to the drag times the speed. Angle of attack In fluid dynamics , angle of attack ( AOA , α , or α {\displaystyle \alpha } )

760-403: The aircraft of speed very quickly due to induced drag, and, in extreme cases, increased frontal area and parasitic drag. Not only do such maneuvers slow the aircraft down, but they cause significant structural stress at high speed. Modern flight control systems tend to limit a fighter's angle of attack to well below its maximum aerodynamic limit. In sailing , the physical principles involved are

800-399: The angle between the chord line of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. Since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is simply defined. Often, the chord line of the root of the wing is chosen as the reference line. Another choice is to use

840-407: The angle between the chord of an airfoil and some fixed datum in the airplane. The lift coefficient of a fixed-wing aircraft varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases. As the angle of attack of a fixed-wing aircraft increases, separation of the airflow from

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880-574: The angle of attack or Lift Reserve Indicators . These indicators measure the angle of attack (AOA) or the Potential of Wing Lift (POWL, or Lift Reserve) directly and help the pilot fly close to the stalling point with greater precision. STOL operations require the aircraft to be able to operate close to the critical angle of attack during landings and at the best angle of climb during takeoffs. Angle of attack indicators are used by pilots for maximum performance during these maneuvers, since airspeed information

920-412: The center of gravity of the aircraft and other factors. However, the aircraft normally stalls at the same critical angle of attack, unless icing conditions prevail. The critical or stalling angle of attack is typically around 15° - 18° for many airfoils. Some aircraft are equipped with a built-in flight computer that automatically prevents the aircraft from increasing the angle of attack any further when

960-412: The component of force parallel to the oncoming flow is called drag ; and the component perpendicular to the oncoming flow is called lift . At practical angles of attack the lift greatly exceeds the drag. Lift is produced by the changing direction of the flow around a wing. The change of direction results in a change of velocity (even if there is no speed change), which is an acceleration. To change

1000-407: The direction of the flow therefore requires that a force be applied to the fluid; the total aerodynamic force is simply the reaction force of the fluid acting on the wing. An aircraft in slow flight at a high angle of attack will generate an aerodynamic reaction force with a high drag component. By increasing the speed and reducing the angle of attack, the lift generated can be held constant while

1040-412: The drag component is reduced. At the optimum angle of attack, total drag is minimised. If speed is increased beyond this, total drag will increase again due to increased profile drag . When producing lift, air below the wing is at a higher pressure than the air pressure above the wing. On a wing of finite span, this pressure difference causes air to flow from the lower surface, around the wingtip, towards

1080-480: The end of the production run, though many have been retro-fitted. The fuselage and tail were adapted from the Schempp-Hirth Ventus . A version with a narrow fuselage is called the Discus 'a' and the wider fuselage version is called the 'b'. The fuselage is made of glass-reinforced plastic around a steel tube frame. The wings and tail surfaces are also fiberglass with the exception of the main wing spar, which

1120-409: The induced drag by the span efficiency factor e {\displaystyle e} . To compare with other sources of drag, it can be convenient to express this equation in terms of lift and drag coefficients: and This indicates how, for a given wing area, high aspect ratio wings are beneficial to flight efficiency. With C L {\displaystyle C_{L}} being

1160-407: The low density of air in the upper atmosphere as well as at low speed at low altitude where the margin between level flight AoA and stall AoA is reduced. The high AoA capability of the aircraft provides a buffer for the pilot that makes stalling the airplane (which occurs when critical AoA is exceeded) more difficult. However, military aircraft usually do not obtain such high alpha in combat, as it robs

1200-513: The maneuver ends. The Cobra is an example of supermaneuvering as the aircraft's wings are well beyond the critical angle of attack for most of the maneuver. Additional aerodynamic surfaces known as "high-lift devices" including leading edge wing root extensions allow fighter aircraft much greater flyable 'true' alpha, up to over 45°, compared to about 20° for aircraft without these devices. This can be helpful at high altitudes where even slight maneuvering may require high angles of attack due to

1240-427: The speed for minimum drag. He observed that, at these low airspeeds, increasing speed required reducing power. (At higher airspeeds, parasitic drag came to dominate, causing the power required to increase with increasing airspeed.) Induced drag must be added to the parasitic drag to find the total drag. Since induced drag is inversely proportional to the square of the airspeed (at a given lift) whereas parasitic drag

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1280-477: The square of the wingspan . A wing of infinite span and uniform airfoil segment (or a 2D wing) would experience no induced drag. The drag characteristics of a wing with infinite span can be simulated using an airfoil segment the width of a wind tunnel . An increase in wingspan or a solution with a similar effect is one way to reduce induced drag. The Wright brothers used curved trailing edges on their rectangular wings. Some early aircraft had fins mounted on

1320-424: The tips. More recent aircraft have wingtip-mounted winglets to reduce the induced drag. Winglets also provide some benefit by increasing the vertical height of the wing system. Wingtip mounted fuel tanks and wing washout may also provide some benefit. Typically, the elliptical spanwise distribution of lift produces the minimum induced drag for a planar wing of a given span. A small number of aircraft have

1360-411: The upper surface flow becomes more fully separated and the lift coefficient reduces further. Above this critical angle of attack, the aircraft is said to be in a stall. A fixed-wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below a particular airspeed . The airspeed at which the aircraft stalls varies with the weight of the aircraft, the load factor ,

1400-422: The upper surface of the airfoil and begins to separate from the upper surface. On most airfoil shapes, as the angle of attack increases, the upper surface separation point of the flow moves from the trailing edge towards the leading edge. At the critical angle of attack, upper surface flow is more separated and the airfoil or wing is producing its maximum lift coefficient. As the angle of attack increases further,

1440-480: The upper surface of the wing becomes more pronounced, leading to a reduction in the rate of increase of the lift coefficient. The figure shows a typical curve for a cambered straight wing. Cambered airfoils are curved such that they generate some lift at small negative angles of attack. A symmetrical wing has zero lift at 0 degrees angle of attack. The lift curve is also influenced by the wing shape, including its airfoil section and wing planform . A swept wing has

1480-410: The upper surface. This spanwise flow of air combines with chordwise flowing air, which twists the airflow and produces vortices along the wing trailing edge. The vortices reduce the wing's ability to generate lift, so that it requires a higher angle of attack for the same lift, which tilts the total aerodynamic force rearwards and increases the drag component of that force. The angular deflection

1520-469: The wing area is held constant, then induced drag will be inversely proportional to aspect ratio. However, since wingspan can be increased while decreasing aspect ratio, or vice versa, the apparent relationship between aspect ratio and induced drag does not always hold. For a typical twin-engine wide-body aircraft at cruise speed, induced drag is the second-largest component of total drag, accounting for approximately 37% of total drag. Skin friction drag

1560-891: The wings. Over 850 Discuses had been built by 2004 and it remains in production today despite the introduction of its successor, the Schempp-Hirth Discus-2 . About 12 per year are built under license by Schempp-Hirth Vyroba in the Czech Republic as the Discus CS. Some models are fitted with small sustaining engines (turbos) and are designated Discus T. Data from Jane's All the World's Aircraft 1988-89 General characteristics Performance Aircraft of comparable role, configuration, and era Related lists Induced drag Lift-induced drag , induced drag , vortex drag , or sometimes drag due to lift, in aerodynamics ,

1600-432: The wingtip. For a planar wing with an elliptical lift distribution, induced drag D i can be calculated as follows: where From this equation it is clear that the induced drag varies with the square of the lift; and inversely with the square of the equivalent airspeed; and inversely with the square of the wingspan. Deviation from the non-planar wing with elliptical lift distribution are taken into account by dividing

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