In physics and geometry , isotropy (from Ancient Greek ἴσος ( ísos ) 'equal' and τρόπος ( trópos ) 'turn, way') is uniformity in all orientations . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix a- or an- , hence anisotropy . Anisotropy is also used to describe situations where properties vary systematically, dependent on direction. Isotropic radiation has the same intensity regardless of the direction of measurement , and an isotropic field exerts the same action regardless of how the test particle is oriented.
22-682: The Grumman X-29 is an American experimental aircraft that tested a forward-swept wing , canard control surfaces, and other novel aircraft technologies. Funded by NASA , the United States Air Force and DARPA , the X-29 was developed by Grumman , and the two built were flown by NASA and the United States Air Force. The aerodynamic instability of the X-29's airframe required the use of computerized fly-by-wire control. Composite materials were used to control
44-423: A center of gravity well aft of the aerodynamic center , made the craft inherently unstable . Stability was provided by the computerized flight control system making 40 corrections per second. The flight control system was made up of three redundant digital computers backed up by three redundant analog computers ; any of the three could fly it on its own, but the redundancy allowed them to check for errors. Each of
66-644: A research vessel . The term "experimental aircraft" also has specific legal meaning in Australia, the United States and some other countries; usually used to refer to aircraft flown with an experimental certificate . In the United States , this also includes most homebuilt aircraft , many of which are based on conventional designs and hence are experimental only in name because of certain restrictions in operation. This aircraft-related article
88-558: A total of 242 times from 1984 to 1991. The NASA Dryden Flight Research Center reported that the X-29 demonstrated a number of new technologies and techniques, and new uses of existing technologies, including the use of " aeroelastic tailoring to control structural divergence", aircraft control and handling during extreme instability, three-surface longitudinal control, a "double-hinged trailing-edge flaperon at supersonic speeds", effective high angle of attack control, vortex control, and demonstration of military utility. The first X-29, 82-003,
110-509: Is a stub . You can help Misplaced Pages by expanding it . Isotropic Within mathematics , isotropy has a few different meanings: In the study of mechanical properties of materials , "isotropic" means having identical values of a property in all directions. This definition is also used in geology and mineralogy . Glass and metals are examples of isotropic materials. Common anisotropic materials include wood (because its material properties are different parallel to and perpendicular to
132-473: Is an idealized "radiating element" used as a reference ; an antenna that broadcasts power equally (calculated by the Poynting vector ) in all directions. The gain of an arbitrary antenna is usually reported in decibels relative to an isotropic antenna, and is expressed as dBi or dB(i). In cells (a.k.a. muscle fibers ), the term "isotropic" refers to the light bands ( I bands ) that contribute to
154-419: Is described as a three surface aircraft , with canards , forward-swept wings , and aft strake control surfaces, using three-surface longitudinal control. The canards and wings result in reduced trim drag and reduced wave drag, while using the strakes for trim in situations where the center of gravity is off provides less trim drag than relying on the canard to compensate. The configuration, combined with
176-756: Is now on display in the Research and Development Gallery at the National Museum of the United States Air Force on Wright-Patterson Air Force Base near Dayton, Ohio . The other craft is on display at the Armstrong Flight Research Center on Edwards Air Force Base . A full-scale model was on display from 1989 to 2011 at the National Air and Space Museum 's National Mall building in Washington, DC. The full-scale replica
198-470: The National Aeronautics and Space Administration . Experimental aircraft An experimental aircraft is an aircraft intended for testing new aerospace technologies and design concepts. The term research aircraft or testbed aircraft , by contrast, generally denotes aircraft modified to perform scientific studies, such as weather research or geophysical surveying, similar to
220-558: The aeroelastic divergent twisting experienced by forward-swept wings, and to reduce weight. The aircraft first flew in 1984, and two X-29s were flight tested through 1991. Two X-29As were built by Grumman after the proposal had been chosen over a competing one involving a General Dynamics F-16 Fighting Falcon . The X-29 design made use of the forward fuselage and nose landing gear from two existing F-5A Freedom Fighter airframes (63-8372 became 82-0003 and 65-10573 became 82-0049). The control surface actuators and main landing gear were from
242-479: The F-16. The technological advancement that made the X-29 a plausible design was the use of carbon-fiber composites. The wings of the X-29, made partially of graphite epoxy , were swept forward at more than 33 degrees; forward-swept wings were first trialed 40 years earlier on the experimental Junkers Ju 287 and OKB-1 EF 131 . The Grumman internal designation for the X-29 was "Grumman Model 712" or "G-712". The X-29
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#1732765740364264-408: The aerodynamic lift produces a twisting force which rotates the wing leading edge upward. This results in a higher angle of attack, which increases lift, twisting the wing further. This aeroelastic divergence can quickly lead to structural failure. With conventional metallic construction, a torsionally very stiff wing would be required to resist twisting; stiffening the wing adds weight, which may make
286-404: The airframe led to wide predictions of extreme maneuverability. This perception has held up in the years following the end of flight tests. Air Force tests did not support this expectation. For the flight control system to keep the whole system stable, the ability to initiate a maneuver easily needed to be moderated. This was programmed into the flight control system to preserve the ability to stop
308-429: The design unfeasible. The X-29 design made use of the anisotropic elastic coupling between bending and twisting of the carbon fiber composite material to address this aeroelastic effect. Rather than using a very stiff wing, which would carry a weight penalty even with the relatively light-weight composite, the X-29 used a laminate which produced coupling between bending and torsion. As lift increases, bending loads force
330-440: The grain) and layered rocks such as slate . Isotropic materials are useful since they are easier to shape, and their behavior is easier to predict. Anisotropic materials can be tailored to the forces an object is expected to experience. For example, the fibers in carbon fiber materials and rebars in reinforced concrete are oriented to withstand tension. In industrial processes, such as etching steps, "isotropic" means that
352-416: The pitching rotation and keep the aircraft from departing out of control. As a result, the whole system as flown (with the flight control system in the loop as well) could not be characterized as having any special increased agility. It was concluded that the X-29 could have had increased agility if it had faster control surface actuators and/or larger control surfaces. In a forward swept wing configuration,
374-506: The process proceeds at the same rate, regardless of direction. Simple chemical reaction and removal of a substrate by an acid, a solvent or a reactive gas is often very close to isotropic. Conversely, "anisotropic" means that the attack rate of the substrate is higher in a certain direction. Anisotropic etch processes, where vertical etch-rate is high but lateral etch-rate is very small, are essential processes in microfabrication of integrated circuits and MEMS devices. An isotropic antenna
396-444: The three would "vote" on their measurements, so that if any one was malfunctioning it could be detected. It was estimated that a total failure of the system was as unlikely as a mechanical failure in an airplane with a conventional arrangement. If all of the flight computers failed mid-flight, the aircraft would have disintegrated due to aeroelastic forces before the pilot could keep it stable or even eject. The high pitch instability of
418-416: The wing tips to bend upward. Torsion loads attempt to twist the wing to higher angles of attack, but the coupling resists the loads, twisting the leading edge downward reducing wing angle of attack and lift. With lift reduced, the loads are reduced and divergence is avoided. The first X-29 took its maiden flight on 14 December 1984 from Edwards AFB piloted by Grumman's Chief Test Pilot Chuck Sewell. The X-29
440-779: Was moved to the Cradle of Aviation Museum in Garden City, New York in 2011. Data from Jane's All the World's Aircraft 1988-89 NASA X-Planes, Donald, Winchester General characteristics Performance Avionics The 1989 flight simulator game F29 Retaliator was based around the X-29 and imagined a future where it had been developed into a production fighter jet and fitted with various advanced weaponry. Aircraft of comparable role, configuration, and era Related lists [REDACTED] This article incorporates public domain material from websites or documents of
462-442: Was not equipped with a spin recovery parachute, as flight tests were planned to avoid maneuvers that could result in departure from controlled flight , such as a spin. The second X-29 was given such a parachute and was involved in high angle-of-attack testing. X-29 number two was maneuverable up to an angle of attack of about 25 degrees with a maximum angle of 67° reached in a momentary pitch-up maneuver. The two X-29 aircraft flew
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#1732765740364484-624: Was the third forward-swept wing jet-powered aircraft design to fly; the other two were the German Junkers Ju 287 (1944) and the HFB-320 Hansa Jet (1964). On 13 December 1985, an X-29 became the first forward-swept wing aircraft to fly at supersonic speed in level flight. The X-29 began a NASA test program four months after its first flight. The X-29 proved reliable, and by August 1986 was flying research missions of over three hours involving multiple flights. The first X-29
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