Glass

This property can be seen in the University of Queensland's pitch drop experiment, where each drop has taken approximately 10 years to fall into the beaker. Navy usage) or "paraffin budgie" (the latter term being mostly used in the UK offshore oil industry). Note that pitch, another seemingly-solid material, is in fact a highly viscous liquid, 100 billion times as viscous as water. Some common nicknames for helicopters are "copter", "chopper", "whirlybird", "windmill", "helo" (common U.S. Occasionally such glass has been found thinner side down, as would be caused by carelessness at the time of installation. A helicopter should not be mistaken for an autogyro, which is a historical predecessor of the helicopter that gains lift from an unpowered rotor. When actually installed in a window frame, the glass would be placed thicker side down for the sake of stability and visual sparkle. Marine Corps and will be the first mass produced tilt-rotor aircraft to enter service.

The pieces were not, however, absolutely flat; the edges of the disk would be thicker because of centripetal forces. Hybrid types that combine features of helicopters and fixed wing designs include the experimental Fairey Rotodyne of the 1950s and the Bell Boeing Osprey, which is on order by the U.S. This plate was then cut to fit a window. Rotomotion is currently selling a line of small (less than 50 kg) rotorcraft UAVs, including an all electric helicopter. The likely source of this belief is that when panes of glass were commonly made by glassblowers, the technique that was used was to spin molten glass so as to create a round, mostly flat and even plate (the Crown glass process, described above). Some companies, notably Schweizer Aircraft Corporation in the USA, are developing remotely-controlled variants of light helicopters for use in future battlefields. It is then assumed that the glass was once uniform, but has flowed to its new shape. In identifying conventional helicopters during flight it is helpful to know that when viewed from below, the rotor of a French, Russian, or Soviet designed helicopter rotates counter-clockwise, whilst that of a helicopter built in Italy, the UK or the USA rotates clockwise.

Supporting evidence that is often offered is that old windows are often thicker at the bottom than at the top. For this reason, good pilotage demands operation within safe flight regimes and avoiding hazardous conditions. One common misconception is that glass is a super-cooled liquid of practically infinite viscosity when at room temperature. Each of these conditions is potentially fatal and recovery might not be possible. See also Window. The following is a list of some of the potential hazards:. These glass types can be further utilised by the following processes:. For helicopters the hazards are particularly acute since they are flying at relatively low altitude, with little time to react to a sudden event.

Several methods of producing glass for applications have been developed, including:. As with any moving vehicle, operation outside of safe regimes could result in loss of control, structural damage, or fatality. Foamed glass, made from waste glass, can be used as lightweight, closed-cell insulation. The whirling rotor blades of a helicopter can cause large charges to build up on the airframe, large enough to cause injury to shipboard personnel should they touch any part of the helicopter as it approaches the deck. Glass fibre insulation is common in roofs and walls. A secondary purpose of the haul-down device is to equalize electrostatic potential between the helicopter and ship. Glass in buildings can be of a safety type, including wired, toughened and laminated glasses. Navy implementation of this device, based on Beartrap, is called the "RAST" system (for Recovery Assist, Secure and Traverse) and is an integral part of the LAMPS MK III (SH-60B) weapons system.

Typical uses for glass in buildings include as a transparent material for windows in the building envelope, as internal glazed partitions and as architectural features. The U.S. Glass has been used in buildings since the 11th century. This device was pioneered by the Royal Canadian Navy and was called "Beartrap". Main articles: Architectural Glass and Glazing. Tension is maintained on the cable as the helicopter descends, assisting the pilot with accurate positioning of the aircraft on the deck; once on deck locking beams close on the probe, locking the aircraft to the flight deck. Stained glass is an art form with a long history; many churches have beautiful stained-glass windows. Shipboard landing for some helicopters is assisted though use of a haul-down device that involves attachment of a cable to a probe on the bottom of the aircraft prior to landing.

See the Harvard Museum of Natural History's page on the exhibit for further information. In the Royal Navy, landing on is usually achieved by lining up slightly astern and on the port quarter, as the ship steams into the wind and the aircraft captain slides across and over the deck. The Blaschka Glass Flowers are still an inspiration to glassblowers today. Navy it is commonly and properly referred to as the flight deck. These were lampworked by Leopold Blaschka and his son Rudolph, who never revealed the method he used to make them. In the U.S. The Harvard Museum of Natural History has a collection of extremely detailed models of flowers made of painted glass. A helicopter deck (or helo deck) is a helicopter pad on the deck of a ship, usually located on the stern and always clear of obstacles that would prove hazardous to a helicopter landing.

A significant exception is the collection of pieces by the Blaschkas. The traditional low-tech system is to mount coloured chalk on the rotor tips, and see how they mark a linen sheet.
. Colored glass is often used, and sometimes the glass is painted, although many glassblowers consider this crude. The most common adjustment measurement system is to use a stroboscopic flash lamp, and observe painted markings or coloured reflectors on the underside of the rotor blades. Objects made out of glass include vessels (bowls, vases, and other containers), paperweights, marbles, beads, smoking pipes, bongs, and sculptures. Adjustment is difficult in part because measurement of the vibration is hard. Glass can also be cut with a diamond saw, and polished to give gleaming facets. Usually the feedback system uses a mass as a "stable reference" and a linkage from the mass operates a flap to adjust the rotor's angle of attack to counter the vibration.

Glass that is manipulated in a kiln is called warm glass, and traditional stained glass work is commonly called cold glass work. Some also use mechanical feedback systems to sense and counter vibration. Someone who works with hot glass is called a glassblower or lampworker, and these techniques are how most fine glassware is created. Most also have vibration dampers for height and pitch. There are many techniques for creating fine glass art; each is suitable for certain kinds of object and unsuitable for others. To reduce vibration, all helicopters have rotor adjustments for height and pitch. The term "crystal glass", derived from rock crystal, has come to denote high-grade colourless glass, often containing lead, and is sometimes applied to any fine hand-blown glass. An unadjusted helicopter can easily vibrate so much that it will shake itself apart.

Some artists in glass include Lino Tagliapietra, Sidney Waugh, Rene Lalique, Dale Chihuly, and Louis Comfort Tiffany, who were responsible for extraordinary glass objects. Helicopters vibrate. Even with the availability of common glassware, hand blown or lampworked glassware remains popular for its artistry. The redesigns followed the closure of some city heliports and government action to constrain flight paths in national parks and other places of natural beauty. Volcanic glasses, such as obsidian, have long been used to make stone tools, and flint knapping techniques can easily be adapted to mass-produced glass. Urban communities have often expressed great dislike of noisy aircraft, and police and passenger helicopters can be unpopular. Most such glass is mass-produced using various industrial processes, but most large laboratories need so much custom glassware that they keep a glassblower on staff. During the closing years of the 20th century designers began working on helicopter noise reduction.

For the most demanding applications, quartz glass is used, although it is very difficult to work. There are several reasons why a helicopter cannot fly as fast as a fixed wing aircraft. For these applications, borosilicate glass (such as Pyrex) is usually used for its strength and low coefficient of thermal expansion, which gives greater resistance to thermal shock and allows for greater accuracy in laboratory measurements when heating and cooling experiments. The current record is around 400 km/h set by the Westland Lynx. In laboratories doing research in chemistry, biology, physics and many other fields, flasks, test tubes, lenses and other laboratory equipment are often made of glass. The single most obvious limitation of the helicopter is its slow speed. Drinking glasses, bowls, and bottles are often made of glass, as are light bulbs, mirrors, the picture tubes of computer monitors and televisions, and windows. While fixed-wing aircraft are generally designed so pilots sit on the left side of the aircraft, freeing up their right hand for dealing with radios, engine controls, and the like, helicopters are generally designed so pilots sit on the right side of the aircraft so they can keep their right hand (usually the strong hand) on the cyclic at all times, leaving the radios and engine controls for their left hand (usually the weaker hand).

Many household objects are made of glass. Small helicopters can be so unstable that it may be impossible for the pilot to ever let go of the cyclic while in flight. Since glass is strong and unreactive, it is a very useful material. Changing collective will also cause a change in torque, which will require the pilot to adjust the foot pedals. See also: Broad sheet, Blown plate, Polished plate, Cylinder blown sheet, Machine drawn cylinder sheet. Increasing collective will reduce rotor RPM, requiring an increase in throttle to maintain constant rotor RPM. This reduced manufacturing costs and, combined with a wider use of coloured glass, led to cheap popular glassware in the 1930s, which later became known as Depression glass. Moving the cyclic forward causes the helicopter to move forward, but will also cause a reduction in lift, which will require extra collective for more lift.

In the 1920s a new mould-etch process was invented, in which art was etched directly into the mould, so that each cast piece emerged from the mold with the image already on the surface of the glass. Adjusting one flight control on a helicopter almost always has an effect that requires an adjustment of the other controls. Traditionally this was done by a trained artisan after the glass was blown or cast. Hovering a helicopter has been compared to balancing yourself while standing on a large beach ball. Art is sometimes etched into glass via acid or other caustic substance (causing the image to be eaten into the glass). When a hovering helicopter is nudged in one direction by a gust of wind, it will tend to continue in that direction, and the pilot must adjust the cyclic to correct the motion. Blenko in the 1920s. Simply hovering requires continuous, active corrections from the pilot.

The cylinder method of creating flat glass was first used in the United States of America by William J. In contrast, helicopters are very unstable. The invention of the glass pressing machine in 1827 allowed the mass production of inexpensive glass articles. Many small, fixed wing aircraft are stable enough that a pilot can let go of the controls while looking at a map or dealing with a radio, and the plane will generally stay on course. Around 1688, a process for casting glass was developed, which led to its becoming a much more commonly used material. If a gust of wind or a nudge to one of the controls causes a fixed wing aircraft to pitch, roll, or yaw, the aerodynamic design of the aircraft will tend to correct the motion, and the aircraft will return to its original attitude. Venetian glass was highly prized between the 10th and 14th centuries as they managed to keep the process secret. Fixed wing aircraft are usually inherently stable.

The disk would then be cut into panes. It took inventors many years to recognize precession, and to learn how to arrange the cyclic's control system to overcome it. In this process, the glassblower would spin around 9 lb (4 kg) of molten glass at the end of a rod until it flattened into a disk approximately 5 ft (1.5 m) in diameter. The helicopter's control linkages rotate the pitching forces 90 degrees backwards against the rotor spin, to push on the sides of the rotor rather than its front and back. The Crown glass process was used up to the mid-1800s. For example, forward motion requires less lift at the front of the disk and more lift at the rear of the disk, so the pilot pushes the cyclic forward. Eventually some of the Venetian glass workers moved to other areas of northern Europe and glass making spread with them. So control forces on the rotor are rotated 90 degrees before the desired motion.

The centre for glass making from the 14th century was Venice, which developed many new techniques and became the centre of a lucrative export trade in dinner ware, mirrors, and other luxury items. This is called "gyroscopic precession". Until the 12th century, stained glass (i.e., glass with some colouring impurities, usually metals) was not widely used. This is because when one tries to tilt a spinning object (like a rotor), it moves at right angles to the direction of the force. This technique was perfected in 13th century Venice. A very peculiar feature of the cyclic is that the lift is made to occur 90 degrees of rotation before the direction of tilt. The 11th century saw the emergence, in Germany, of new ways of making sheet glass by blowing spheres, swinging these out to form cylinders, cutting these while still hot, and then flattening the sheets. (see Height-velocity diagram).

From this point on, northern glass differed significantly from that made in the Mediterranean area, where soda remained in common use. Autorotation can allow a pilot to make an emergency landing if the engine failure occurs while the helicopter is traveling high enough or fast enough. About 1000 AD, an important technical breakthrough was made in Northern Europe when soda glass was replaced by glass made from a much more readily available material: potash obtained from wood ashes. A transmission connects the main rotor to the tail rotor so that all flight controls are available after engine failure. These form an important link between Roman times and the later importance of that city in the production of the material. This technique is known as autorotation. Glass objects from the 7th and 8th centuries have been found on the island of Torcello near Venice. The main rotor acts like a "windmill" and turns.

When gem-cutters learned to cut glass, they found clear glass was an excellent refractor of light, the popularity of cut clear glass soared, that of coloured glass diminished. Helicopters are powered aircraft, but they can still fly without power by using the momentum in the rotors and using downward motion to force air through the rotors. Glassmakers learned to make coloured glass by adding metallic compounds and mineral oxides to produce brilliant hues of red, green, and blue - the colours of gemstones. On a helicopter, this can happen in any of three ways. Common glass today usually has a slight green or blue tint, arising from these same impurities. This condition is called aerodynamic stall. This colour is caused by the varying amounts of naturally occurring iron impurities in the sand. If the angle of attack of any wing, including rotor blades, is too high, the airflow above the wing separates causing instant loss of lift and increase in drag.

The colour of "natural glass" is green to bluish green. And the angle of attack is decreased on the advancing blade to produce less lift, compensating for the faster airspeed over the blade. This was the discovery of glassblowing, both free-blowing and mould-blowing. The angle of attack is increased on the retreating blade to produce more lift, compensating for the slower airspeed over the blade. In the first century BC, somewhere at the eastern end of the Mediterranean, a new invention caused a true revolution in the glass industry. To compensate for the added lift on the advancing blade and the decreased lift on the retreating blade, the angle of attack of the blades is regulated as the blade spins around the helicopter. As time passed, it was discovered (most likely by a potter) that if glass is heated until it becomes semi-liquid, it can be shaped and left to cool in a new, solid, independently standing shape. As the blade swings to the other side of the helicopter, it moves at rotor tip speed minus aircraft speed and is called the retreating blade.

Small pieces of coloured glass were considered valuable and often rivalled precious gems as jewellery items. As a helicopter moves forward, the rotor blades on one side move at rotor tip speed plus the aircraft speed and is called the advancing blade. The earliest use of glass was as a coloured, opaque, or transparent glaze applied to ceramics before they were fired. If the pilot pushes the cyclic forward, then the helicopter tilts forward, and the rotor produces a thrust in the forward direction. Glass was made from sand, plant ash and lime. This causes the helicopter to tilt in the same direction as the cyclic. During the Roman Empire many forms of glass were created, usually for vases and bottles. When it is tilted, the links give a pitch-up at some azimuthal angle and a pitch-down at the opposite angle, hence creating a sinusoidal variation in blade angle of attack.

In the first century BC the technique of blowing glass was developed and what had once been an extremely rare and valuable item became much more common. When the swashplate is not tilted, the blades are all at the collective angle. Glass making instructions were first documented in Egypt around 1500 BC, when glass was used as a glaze for pottery and other items. The rotating section rotates with the rotor and is connected to blade pitch horns through pitch links, one link for each blade. Naturally occurring glass, such as obsidian, has been used since the stone age. The cyclic controls the angle of the stationary section of the swashplate, which in turn controls the angle of the rotating section of the swashplate. New coloured glasses are frequently discovered. The cyclic is similar to a joystick and is usually positioned in front of the pilot.

The chemistry involved is complex and not well understood. This variation in lift causes the rotor disk to tilt, and the helicopter to move during hover flight or change attitude in forward flight. The way the glass is heated and cooled can significantly affect the colors produced by these compounds. The cyclic changes the pitch of the blades cyclically, causing the lift to vary across the plane of the rotor disk. Silver compounds (notably silver nitrate) can produce a range of colors from orange-red to yellow. Turbine engined helicopters, and some piston helicopters, use servo-feedback loop in their engine controls to maintain rotor RPM and relieves the pilot of routine responsibility for that task. Uranium glass is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic. The pilot manipulates the throttle to maintain rotor RPM and therefore regulates the effect of drag on the rotor system.

Uranium (0.1 to 2%) can be added to give glass a fluorescent yellow or green colour. In many piston-powered helicopters, the pilot must manage the engine and rotor RPM. Metallic gold, in very small concentrations (around 0.001%), produces a rich ruby-coloured glass, while lower concentrations produces a less intense red, often marketed as "cranberry". In general, RPM must be maintained within a tight tolerance, usually a few percent. Adding titanium produces yellowish-brown glass. If the RPM is too high, damage to the main rotor hub from excessive forces could result. Nickel, depending on the concentration, produces blue, or violet, or even black glass. If the RPM is too low, rapid descent with power, known as settling with power could result.

Pure metallic copper produces a very dark red, opaque glass, which is sometimes used as a substitute for gold in the production of ruby-coloured glass. Helicopter rotors are designed to operate at a specific RPM. 2 to 3% of copper oxide produces a turquoise colour. RPM control is critical to proper operation for several reasons. Tin oxide with antimony and arsenic oxides produce an opaque white glass, first used in Venice to produce an imitation porcelain. The throttle control is a twist grip on the collective control. Small concentrations of cobalt (0.025 to 0.1%) yield blue glass. The throttle controls the absolute power produced by the engine that is connected to the rotor by a transmission.

Like manganese, selenium can be used in small concentrations to decolorize glass, or in higher concentrations to impart a reddish colour. Simultaneously increasing the collective and adding power with the throttle causes a helicopter to rise. Manganese can be added in small amounts to remove the green tint lent by iron, or in higher concentrations to give glass an amethyst colour. The collective control is usually a lever at the pilot's left side, near his leg. Metals and metal oxides are added to glass during its manufacture to change its colour. When the angle of attack is increased, the blade produces more lift. sol gel is a good example of glass prepared in this way. The collective pitch control lever controls the collective pitch, or angle of attack, of the helicopter blades altogether, that is, equally throughout the 360 degree plane-of-rotation of the main rotor system.

By polymerizing glass it is possible to embed active molecules, such as enzymes, to add a new level of functionality to the glass vessels. Helicopters maneuver with three flight controls besides the pedals. Putting in additives that modify the properties of glass is problematic, because the high temperature of preparation destroys most of them. More lift at the rear of the rotary wing will cause the aircraft to pitch forward, an increase on the left will cause a roll to the right and so on. An innovative way for making glass involves preparation by polymerization. For pitch (tilting forward and back) or roll (tilting sideways) the angle of attack of the main rotor blades is altered or cycled during the rotation creating a differential of lift at different points of the rotary wing. Large amounts of iron are used in glass that absorbs infrared energy, such as heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths (biologically damaging ionizing radiation). Yaw controls are usually operated with anti-torque pedals, on the floor in the same place as a fixed-wing aircraft's rudder pedals.

Thorium oxide gives glass a high refractive index and low dispersion, and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern glasses. Dual-rotor helicopters have a differential between the two rotor transmissions that can be adjusted by an electric or hydraulic motor to transmit differential torque and thus turn the helicopter. Adding barium also increases the refractive index. Varying the pitch of the tail rotor alters the sideways thrust produced. Lead glass, such as lead crystal or flint glass, is more 'brilliant' because the increased refractive index causes noticeably more "sparkles", while boron may be added to change the thermal and electrical properties, as in Pyrex. For rotation about the vertical axis (yaw) the anti-torque system is used. As well as soda and lime, most common glass has other ingredients added to change its properties. In a helicopter, however, there often isn't enough airspeed for this method to be practical.

Soda-lime glasses account for about 90% of manufactured glass. In a fixed-wing aircraft, this is easy: small movable surfaces are adjusted to change the aircraft's shape so that the air rushing past pushes it in the desired direction. The resulting glass contains about 70% silica and is called a soda-lime glass. Useful flight requires that an aircraft be controlled in all three dimensions (see flight dynamics). However, the soda makes the glass water-soluble, which is obviously undesirable, so lime (calcium oxide, CaO) is the third component, added to restore insolubility. Although this method is simple and eliminates precession, development of such helicopters ceased soon, because their extreme noise levels preclude both military and civilian use. One is soda (sodium carbonate Na₂CO₃), or potash, the equivalent potassium compound, which lowers the melting point to about 1000 °C (1800 °F). The most unusual design is the roto-rocket principle, where the single main rotor draws power not from the shaft, but from its own wingtip jet nozzles, which are either pressurized from a fuselage-mounted gas turbine or have their own pulsejet combustion chambers.

Pure silica (SiO₂) has a melting point of about 2000 °C (3600 °F), and while it can be made into glass for special applications (see fused quartz), two other substances are always added to common glass to simplify processing. The NOTAR system was developed in the United States and is used exclusively by McDonnel Douglas Helicopters, or MD Helicopters. Collecting obsidian from national parks and some places may be prohibited by law, but the same toolmaking techniques can be applied to industrially-made glass. The NOTAR eliminates the tail rotor by conducting high-velocity air through the tail boom. Obsidian is a raw material for flint knappers, who have used it to make extremely sharp knives since the stone age. A recent development in helicopter technology is the NOTAR system, which stands for NO TAil Rotor. This glass is called obsidian, and is usually black with impurities. V-22 Osprey tilting rotorcraft is similar, although its nacelles can be rotated, and shares some of the inherent technical problems of a cross system.

Glass is sometimes created naturally from volcanic magma. The U.S. The glasses are arranged by composition, refractive index, and Abbe number. The world's largest ever helicopter, the Soviet Mil-V-12 prototype, was a cross of two Mil Mi-6 turbine-rotor units built onto a modified Antonov cargo plane. For example, BK7 is a low-dispersion borosilicate crown glass, and SF10 is a high-dispersion dense flint glass. The 1930s German FW-61 helicopter was built to such design. Glasses used for making optical devices are commonly categorized using a six-digit glass code, or alternatively a letter-number code from the Schott Glass catalogue. Such helicopters are rare, because structural integrity of the wings is difficult to maintain against the amplified resonance of far off-board rotor-turbine units.

Amorphous SiO₂ is also used as a dielectric material in integrated circuits, due to the smooth and electrically neutral interface it forms with silicon. In the cross system, the rotary wing aircraft resembles a traditional fixed-wing airplane, with the two main rotors mounted at the extremities of its wings. Undersea cables have sections doped with erbium, which amplify transmitted signals by laser emission from within the glass itself. These were placed at the corners of an equilateral triangle and all turned the same direction. Individual fibres are given an equally transparent core of SiO₂/GeO₂ glass, which has only slightly different optical properties (the germanium contributing to a higher index of refraction). A helicopter built by Juan de la Cierva had three main rotors. This type of glass can be made so pure that hundreds of kilometres of glass are transparent at infrared wavelengths in fibre optic cables. The main drawback of a waggon is limited agility in air and the need for a highly trained crew, as the large main rotors have long outreach beyond the fuselage and may easily hit nearby obstacles (in 2001, a South Korean army CH-47 Chinook crashed onto a bridge for that reason while being shown live on TV).

Pure SiO₂ glass (also called fused quartz) does not absorb UV light and is used for applications that require transparency in this region, although it is more expensive. The rotors and turbines are located very high on top of the fuselage, making them less sensitive to damage and dirt. This is due to the addition of compounds such as soda ash (sodium carbonate). Waggon helicopters are practical for military logistical purposes, because entry and unloading is easily facilitated via the unobstructed front and rear ramps. Ordinary glass does not allow light at a wavelength of lower than 400 nm, also known as ultraviolet light or UV, to pass. A prime example is the Boeing CH-47 Chinook, that can carry 14 tons of payload. The transparency is due to an absence of electronic transition states in the range of visible light, and to the fact that such glass is homogeneous on all length scales greater than about a wavelength of visible light (inhomogeneities cause light to be scattered, breaking up any coherent image transmission). examples), the two main rotors are located at the front and rear extremity of a long, boxy fuselage that resembles a railway wagon.

One of the most obvious characteristics of ordinary glass is that it is transparent to visible light (not all glassy materials are). In the flying-waggon or tandem rotor system (sometimes called "flying banana" for the peculiar shape of early U.S. Common glass contains about 70% amorphous silicon dioxide (SiO₂), which is the same chemical compound found in quartz, and its polycrystalline form, sand. Kamans have high stability and powerful lifting capability, thus the latest Kaman V-Max model is a dedicated sky crane design, used for construction works. These properties can be modified, or even changed entirely, with the addition of other compounds or heat treatment. During the Cold War the American Kaman company started to produce similar helicopters for USAF firefighting purposes. Glass is, however, brittle and will break into sharp shards. The contra-rotating rotors are located on top of the fuselage, close to each other.

These desirable properties lead to a great many uses of glass. The Kaman system of intermeshing rotors, which was developed in Nazi Germany for a small anti-submarine warfare helicopter, features two main rotors on separate, obliquely mounted axles. In its pure form, glass is a transparent, relatively strong, hard-wearing, essentially inert, and biologically inactive material which can be formed with very smooth and impervious surfaces. Another example is the Kamov Ka-26, a successful crop duster aircraft. The remainder of this article will be concerned with a specific type of glass—the silica-based glasses in common use as a building, container or decorative material. Co-axial helicopters in flight are highly resistant to side-winds, which makes them suitable for shipboard use, even without a rope-pulley landing system. The term enamel is used to describe glass fused as a decorative or functional coating on metal. The co-axial design, where rotors are mounted on top of each other at the top of the fuselage and share a common main axle complex, was first built by Theodore von Karman and Asbóth Oszkár in 1918 and later became the hallmark of soviet Kamov design bureau (see for example the Kamov Ka-50 "Hokum").

Germanic tribes used the word glaes to describe amber, recorded by Roman historians as glaesum. Anglo-Saxons used the word glaer for amber. These methods introduce even more mechanical complexity to the design and are usually relegated to specialized helicopter types. glaes. All of these systems are designed for the same purpose: the torques from each rotor have opposite signs, so the net effect on the vehicle is negligable. glas, A.S. Such designs use two rotors which turn in opposite directions, or contra-rotate. The word glass comes from Latin glacies (ice) and corresponds to German Glas, M.E. There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor.

The resulting solid is amorphous, not crystalline like the sugar was originally, which can be seen in its conchoidal fracture. In extreme cases, such as that of the Mil Mi-24, the wings are large enough to obstruct airflow down from the rotors, making the helicopter all but unable to hover. A simple example is when table sugar is melted and cooled rapidly by dumping the liquid sugar onto a cold surface. They are also used as external mounts for weapons. The materials definition of a glass is a uniform amorphous solid material, usually produced when a suitably viscous molten material cools very rapidly to below its glass transition temperature, thereby not giving enough time for a regular crystal lattice to form. Many military helicopters, especially attack types, have short wings called stub wings to add lift during forward motion. . Another reason for the angled vertical stabilizer is to make it possible to stage a successful high-speed, run-on landing, in case of the tail rotor failure or damage.

This (along with chromatic aberration and other effects) limits the size of refracting telescopes, with the largest refractor in the World being the Yerkes Observatory telescope with a diameter of 102cm. This is commonly known as slip-streaming and can make hovering turns difficult on windy days. The result is a loss of focus and is sometimes argued to occur not because of the liquid properties of glass but rather sagging of the telescope itself, but this is not correct. At high speeds, it is possible for the vertical stabilizer to counteract the entire torque, leaving more power available for forward flight. This sag happens because the lens is only supported around its edge. To reduce this waste during cruise, the vertical stabilizer is often angled to produce a force which helps counter the main rotor torque. Glass in Refracting Telescopes, with objective lenses greater than 105cm in diameter, is observed to sag under its own under weight over time. A tail rotor typically uses about 5 to 6% of the engine's power, and this power does not help the helicopter produce lift or forward motion.

Similarly, it should not be possible to see Newton's rings between decade-old fragments of window glass—but this can in fact be quite easily done. The amount of power required to prevent a helicopter from spinning is significant. If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then changes in optical telescope mirrors should be observable (by interferometry) in a matter of days—but this also is not observed. Notars adjust thrust by opening and closing a sliding circular cover near the end of the tail boom. If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more—but this is not observed. Other helicopters use a NOTAR (an acronym meaning no tail rotor) design: they blow air through a long slot along the tail boom, utilizing the Coanda effect to produce forces to counter the torque. In layperson's terms, he wrote that glass at room temperature is very strongly on the solid side of the spectrum from solids to liquids. It is less efficient but the advantages are that less noise is generated, it's safer for people that may walk near it and there is less chance of the blades being damaged by objects because it's shrouded, unlike the traditional tail rotor.

Phys, 66(5):392-5, May 1998). The fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox to turn the fan. J. If the tail rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer" (Am. AH-64 Apache). Zanotto states "...the predicted relaxation time for GeO₂ at room temperature is 10³² years.
Sometimes the blades of a tail rotor are not separated by the same angle, but laid out in an X-shape, which is supposed to reduce the noise levels for military use (e.g.

Writing in the American Journal of Physics, physicist Edgar D. The world's fastest helicopter, the Westland Lynx can perform aerobatic loops and rolls with this conventional rotor system. double-glazing. Almost all civilian helicopters have the main rotor and tail rotor system. application of a self-cleaning catylist. The Mil Mi-26 can lift 27 metric tons, the Robinson R22 has a crew of two and a gross weight of 1300 lbs (590 kg). chemical strengthening. The world's largest and smallest series-produced helicopters follow this principle.

toughening. When the thrust from the tail rotor is sufficient to cancel out the torque from the main rotor, the helicopter will not rotate around the main rotor shaft. laminating. This rotor creates thrust which is in the opposite direction from the torque generated by the main rotor. figure rolled glass. At low speeds, the most common way to counteract this torque is to have a smaller vertical propeller mounted at the rear of the aircraft called a tail rotor. float (annealed) glass. It is as follows: turning the rotor generates lift but it also applies a reverse torque to the vehicle, which would spin the helicopter fuselage in the opposite direction to the rotor.

polished plate glass. The most common design is the Sikorsky-layout, which is used by approximately 95% of all helicopters manufactured to date. rolled plate glass. There are several possible design layouts for arranging a helicopter's rotors. sheet glass. The helicopter's rotor can simply be regarded as rotating wings, from where the military appellation of "rotary wing aircraft" originates. cylinder glass. A helicopter makes use of the same principle, except that instead of moving the entire aircraft, only the wings themselves are moved in a circular motion.

However, the more the lift of the airfoil, the more drag that is caused. This pressure difference integrated over the airfoil area causes a net lift. Thus, by causing the air to flow faster over the top surface than the bottom, the airfoil causes a pressure difference directed upward. The higher the speed of a fluid, the lower the dynamic pressure (as opposed to static pressure) on the surface.

The longer path that the fluid (in this case air) must travel across the top surface equates to a higher speed. In conventional aircraft, the wing profile (called airfoil) is designed to have a shape where the bottom surface has a shorter path than the top surface. Turboshaft engines are the preferred powerplant for all but the smallest and least expensive helicopters today. The availability of lightweight turboshaft engines in the second half of the 20th century led to the development of larger, faster, and higher performance helicopters.

Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. Igor Sikorsky is reported to have delayed his own helicopter research until suitable engines were commercially available. This is largely due to higher engine power density requirements when compared with fixed wing aircraft.
Reliable helicopters capable of stable hover flight were developed decades after fixed wing aircraft.

The Bell 47 designed by Arthur Young became the first helicopter to be licensed (in March 1946) for certified civilian use in the United States and two decades later the Bell 206 became the most succesful commercial helicopter ever built with more hours and set (and broken) more industry records than any other aircraft in the world. Mass production of the military version of the Sikorsky XR-4 began in May 1942 for the United States Army. Models such the Flettner FL 282 Kolibri were use in the Mediterranean Sea. Nazi Germany used the helicopter in combat during WWII in little numbers.

The German Focke-Wulf Fw 61 first flew with limited control achieving vertical and forward flight in 1934. A flight of the first fully controllable helicopter was demonstrated by Raúl Pateras de Pescara 1916 in Buenos Aires, Argentina. Developers such as Jan Bahyl, Oszkár Asbóth, Louis Breguet, Paul Cornu, Emile Berliner, Ogneslav Kostovic Stepanovic and Igor Sikorsky pioneered this type of aircraft, with Juan de la Cierva introducing the first practical autogiro in 1923 that was to be the basis for the modern helicopter. The first somewhat practical idea of a human carrying helicopter was first conceived by Leonardo da Vinci around 1490, but it was not until after the invention of the powered aeroplane in the 20th century that actual models were produced.

"Pao Phu Tau" was a 4th century book in China that described some of the ideas in a rotary wing aircraft. This toy eventually made its way to Europe via trade and has been depicted in a 1463 European painting. Since around 400 BC the Chinese had a flying top that was used as a children's toy. Speed and range limitations also constrain commercial applications.

For these reasons, helicopters are not economically viable for commercial transportation. The costs are due to inherent mechanical complexity and greater power requirements for a given gross weight. Helicopters suffer from significantly higher operating and maintenance costs compared with fixed wing aircraft. Unmanned helicopters are used in industrial and military applications in areas deemed dangerous for manned flight.

Helicopters have many uses, both military and civil, including troop transportation, infantry support, firefighting, shipboard operations, business transportation, casualty evacuation (including MEDEVAC, and air/sea/mountain rescue), police and civilian surveillance, carrying goods (some helicopters can carry slung loads, accommodating awkwardly shaped items), or as a mount for still, film or television cameras. . However these other configurations have considerably more cruise speed than a helicopter (270 km/h for a helicopter, 460 km/h for a tiltrotor, 900+ km/h for a vectored thrust airplane), giving each their place in the operational spectrum. Compared to other vertical lift aircraft like Tiltrotors (V-22 Osprey for example) and Vectored Thrust airplanes (AV-8 Harrier for example), helicopters are very efficient, carrying more than twice the payload, consuming less fuel in hover and costing considerably less to buy and operate.

Subject only to refuelling facilities and load/altitude limitations, a helicopter can travel to any location, and land anywhere with enough space (a diameter of length 1.5 times the rotor disk). The compensating advantage is maneuverability: helicopters can hover in place, reverse, and above all take off and land vertically. Compared to conventional fixed-wing aircraft, helicopters are much more complex, more expensive to buy and operate, relatively slow, have shorter range and restricted payload. The first stable, single-rotor, fully-controllable helicopter to enter large full-scale production was made by Igor Sikorsky in 1942.

The engine-driven helicopter was invented by the Slovak inventor Jan Bahyl. The word helicopter is derived from the Greek words helix (spiral) and pteron (wing). Helicopters are classified as rotary-wing aircraft to distinguish them from conventional fixed-wing aircraft. A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors (propellers).

Vortex ring state, a problem the V-22 Osprey was associated with. Operating within the shaded area of the height-velocity diagram. Low-G condition. Ground resonance.

Settling with power. Retreating blade stall. If this ring is augmented by terrain, wind, rain, or sea spray, the helicopter can lose enough lift to experience settling with power and hit the ground. In these, the downward wind from the rotor causes a circular vortex to form around the rotor.

Helicopters are susceptible to potentially disastrous vortex ring effects. Low or negative-G situations encountered in a semi-rigid system will result in blade flapping down until it hits the tail boom or other airframe structure, followed by rotor separation, causing a crash. Rotorhead design is a limiting factor on many helicopters. The adjustment is either by adjusting the angle of attack of the blades, or by engine-powered vacuum devices that suck air into the blades, adjusting the lift.

In most such designs, the lift is varied cyclically and according to the speed of the helicopter. Fully rigid rotors exist and create very responsive helicopters. The blades are made from composites which can bend without breaking. In some designs the hub is rigid.

At high speeds, the force on the rotors is such that they "flap" excessively and the retreating blade can reach too high an angle and stall. Conversely, the retreating blade flaps down, develops a higher angle of attack, and generates more lift. In consequence, rotor blades are designed to "flap" - lift and twist in such a way that the advancing blade flaps up and develops a smaller angle of attack, thus producing less lift than a rigid blade would. Because the advancing blade has higher airspeed than the retreating blade, a perfectly rigid blade would generate more lift on that side and tip the aircraft over.

Most rotors are not rigid. It is theoretically possible to have spiralling rotors, similar in principle to variable-pitch swept wings, which could exceed the speed of sound, but no presently known materials are light enough, strong enough, and flexible enough to construct them. It is possible for this blade to exceed the speed of sound, and thus produce vastly increased drag and vibration. The airspeed of the forward-going rotor blade is much higher than that of the helicopter itself.

In a moving helicopter, however, the speed of the blades relative to the air depends on the speed of the helicopter as well as on their rotational velocity. When the helicopter is at rest, the outer tips of the rotor travel at a speed determined by the length of the blade and the RPM. Unique to helicopters is vertical ring vortex which is when a helicopter in a hover or decent comes into contact with its own down wash causing imense turbulence and complete loss of lift. Any low rotor RPM flight condition accompanied by increasing collective pitch application will cause aerodynamic stall.

This is called retreating blade stall. With a low enough relative airspeed and a high enough angle of attack, aerodynamic stall is inevitable. As helicopter speeds increase, the retreating blade experiences lower relative airspeeds and the controls compensate with higher angle of attack. As helicopter speed increases, the advancing blades approach the speed of sound and generate shock waves that disrupt the airflow over the blade causing loss of lift.