Germany the Federal Republic of Germany, is a country in Central and Western Europe, lying between the Baltic and North Seas to the north, the Alps to the south. It borders Denmark to the north and the Czech Republic to the east and Switzerland to the south, France to the southwest, Luxembourg and the Netherlands to the west. Germany includes 16 constituent states, covers an area of 357,386 square kilometres, has a temperate seasonal climate. With 83 million inhabitants, it is the second most populous state of Europe after Russia, the most populous state lying in Europe, as well as the most populous member state of the European Union. Germany is a decentralized country, its capital and largest metropolis is Berlin, while Frankfurt serves as its financial capital and has the country's busiest airport. Germany's largest urban area is the Ruhr, with its main centres of Essen; the country's other major cities are Hamburg, Cologne, Stuttgart, Düsseldorf, Dresden, Bremen and Nuremberg. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity.
A region named Germania was documented before 100 AD. During the Migration Period, the Germanic tribes expanded southward. Beginning in the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation. After the collapse of the Holy Roman Empire, the German Confederation was formed in 1815; the German revolutions of 1848–49 resulted in the Frankfurt Parliament establishing major democratic rights. In 1871, Germany became a nation state when most of the German states unified into the Prussian-dominated German Empire. After World War I and the revolution of 1918–19, the Empire was replaced by the parliamentary Weimar Republic; the Nazi seizure of power in 1933 led to the establishment of a dictatorship, the annexation of Austria, World War II, the Holocaust. After the end of World War II in Europe and a period of Allied occupation, Austria was re-established as an independent country and two new German states were founded: West Germany, formed from the American and French occupation zones, East Germany, formed from the Soviet occupation zone.
Following the Revolutions of 1989 that ended communist rule in Central and Eastern Europe, the country was reunified on 3 October 1990. Today, the sovereign state of Germany is a federal parliamentary republic led by a chancellor, it is a great power with a strong economy. As a global leader in several industrial and technological sectors, it is both the world's third-largest exporter and importer of goods; as a developed country with a high standard of living, it upholds a social security and universal health care system, environmental protection, a tuition-free university education. The Federal Republic of Germany was a founding member of the European Economic Community in 1957 and the European Union in 1993, it is part of the Schengen Area and became a co-founder of the Eurozone in 1999. Germany is a member of the United Nations, NATO, the G7, the G20, the OECD. Known for its rich cultural history, Germany has been continuously the home of influential and successful artists, musicians, film people, entrepreneurs, scientists and inventors.
Germany has a large number of World Heritage sites and is among the top tourism destinations in the world. The English word Germany derives from the Latin Germania, which came into use after Julius Caesar adopted it for the peoples east of the Rhine; the German term Deutschland diutisciu land is derived from deutsch, descended from Old High German diutisc "popular" used to distinguish the language of the common people from Latin and its Romance descendants. This in turn descends from Proto-Germanic *þiudiskaz "popular", derived from *þeudō, descended from Proto-Indo-European *tewtéh₂- "people", from which the word Teutons originates; the discovery of the Mauer 1 mandible shows that ancient humans were present in Germany at least 600,000 years ago. The oldest complete hunting weapons found anywhere in the world were discovered in a coal mine in Schöningen between 1994 and 1998 where eight 380,000-year-old wooden javelins of 1.82 to 2.25 m length were unearthed. The Neander Valley was the location where the first non-modern human fossil was discovered.
The Neanderthal 1 fossils are known to be 40,000 years old. Evidence of modern humans dated, has been found in caves in the Swabian Jura near Ulm; the finds included 42,000-year-old bird bone and mammoth ivory flutes which are the oldest musical instruments found, the 40,000-year-old Ice Age Lion Man, the oldest uncontested figurative art discovered, the 35,000-year-old Venus of Hohle Fels, the oldest uncontested human figurative art discovered. The Nebra sky disk is a bronze artefact created during the European Bronze Age attributed to a site near Nebra, Saxony-Anhalt, it is part of UNESCO's Memory of the World Programme. The Germanic tribes are thought to date from the Pre-Roman Iron Age. From southern Scandinavia and north Germany, they expanded south and west from the 1st century BC, coming into contact with the Celtic tribes of Gaul as well
In control engineering a servomechanism, sometimes shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the action of a mechanism. It includes a built-in encoder or other position feedback mechanism to ensure the output is achieving the desired effect; the term applies only to systems where the feedback or error-correction signals help control mechanical position, speed or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position—the operator does this by observation. By contrast a car's cruise control uses closed-loop feedback, which classifies it as a servomechanism. A common type of servo provides position control. Servos are electrical, hydraulic or pneumatic, they operate on the principle of negative feedback, where the control input is compared to the actual position of the mechanical system as measured by some type of transducer at the output. Any difference between the actual and wanted values is amplified and used to drive the system in the direction necessary to reduce or eliminate the error.
This procedure is one used application of control theory. Typical servos can give a linear output. Speed control via a governor is another type of servomechanism; the steam engine uses mechanical governors. Prior to World War II the constant speed propeller was developed to control engine speed for maneuvering aircraft. Fuel controls for gas turbine engines employ either electronic governing. Positioning servomechanisms were first used in military fire-control and marine navigation equipment. Today servomechanisms are used in automatic machine tools, satellite-tracking antennas, remote control airplanes, automatic navigation systems on boats and planes, antiaircraft-gun control systems. Other examples are fly-by-wire systems in aircraft which use servos to actuate the aircraft's control surfaces, radio-controlled models which use RC servos for the same purpose. Many autofocus cameras use a servomechanism to move the lens. A hard disk drive has a magnetic servo system with sub-micrometre positioning accuracy.
In industrial machines, servos are used to perform complex motion, in many applications. A servomotor is a specific type of motor, combined with a rotary encoder or a potentiometer to form a servomechanism; this assembly may in turn form part of another servomechanism. A potentiometer provides a simple analog signal to indicate position, while an encoder provides position and speed feedback, which by the use of a PID controller allow more precise control of position and thus faster achievement of a stable position. Potentiometers are subject to drift when the temperature changes whereas encoders are more stable and accurate. Servomotors are used for both low-end applications. On the high end are precision industrial components that use a rotary encoder. On the low end are inexpensive radio control servos used in radio-controlled models which use a free-running motor and a simple potentiometer position sensor with an embedded controller; the term servomotor refers to a high-end industrial component while the term servo is most used to describe the inexpensive devices that employ a potentiometer.
Stepper motors are not considered to be servomotors, although they too are used to construct larger servomechanisms. Stepper motors have inherent angular positioning, owing to their construction, this is used in an open-loop manner without feedback, they are used for medium-precision applications. RC servos are used to provide actuation for various mechanical systems such as the steering of a car, the control surfaces on a plane, or the rudder of a boat. Due to their affordability and simplicity of control by microprocessors, they are used in small-scale robotics applications. A standard RC receiver sends pulse-width modulation signals to the servo; the electronics inside the servo translate the width of the pulse into a position. When the servo is commanded to rotate, the motor is powered until the potentiometer reaches the value corresponding to the commanded position. James Watt's steam engine governor is considered the first powered feedback system; the windmill fantail is an earlier example of automatic control, but since it does not have an amplifier or gain, it is not considered a servomechanism.
The first feedback position control device was the ship steering engine, used to position the rudder of large ships based on the position of the ship's wheel. John McFarlane Gray was a pioneer, his patented design was used on the SS Great Eastern in 1866. Joseph Farcot may deserve equal credit for the feedback concept, with several patents between 1862 and 1868; the telemotor was invented around 1872 by Andrew Betts Brown, allowing elaborate mechanisms between the control room and the engine to be simplified. Steam steering engines had the characteristics of a modern servomechanism: an input, an output, an error signal, a means for amplifying the error signal used for negative feedback to drive the error towards zero; the Ragonnet power reverse mechanism was a general purpose air or steam-powered servo amplifier for linear motion patented in 1909. Electrical servomechanisms were used as early as 1888 in Elisha Gray's Telautograph. Electrical servomechanisms require a power amplifier. World War II saw the development of electrical fire-control servomechanisms, using an amplidyne as the power amplifier.
Vacuum tube amplifiers were used in the UNISERVO tape drive for the UNIVAC I computer
Brushless DC electric motor
A brushless DC electric motor known as electronically commutated motor and synchronous DC motors, are synchronous motors powered by DC electricity via an inverter or switching power supply which produces an AC electric current to drive each phase of the motor via a closed loop controller. The controller provides pulses of current to the motor windings that control the speed and torque of the motor; the construction of a brushless motor system is similar to a permanent magnet synchronous motor, but can be a switched reluctance motor, or an induction motor. The advantages of a brushless motor over brushed motors are high power to weight ratio, high speed, electronic control. Brushless motors find applications in such places as computer peripherals, hand-held power tools, vehicles ranging from model aircraft to automobiles. Brushed DC motors are common. Brushless DC motors were made possible by the development of solid state electronics in the 1960s. An electric motor develops torque by alternating the polarity of rotating magnets attached to the rotor, the rotating part of the machine, stationary magnets on the stator which surrounds the rotor.
One or both sets of magnets are electromagnets, made of a coil of wire wound around an iron core. DC running through the wire winding creates the magnetic field, providing the power which runs the motor. However, each time the rotor rotates by 180°, the position of the north and south poles on the rotor are reversed. If the magnetic field of the poles remained the same, this would cause a reversal of the torque on the rotor each half-turn, so the average torque would be zero and the rotor would not turn. Therefore, in a DC motor, in order to create torque in one direction, the direction of electric current through the windings must be reversed with every 180° turn of the rotor; this reverses the direction of the magnetic field as the rotor turns, so the torque on the rotor is always in the same direction. In brushed motors, invented in the 19th century, this is done with a rotary switch on the motor's shaft called a commutator, it consists of a rotating cylinder divided into multiple metal contact segments on the rotor.
The segments are connected to wire electromagnet windings on the rotor. Two or more stationary contacts called "brushes", made of a soft conductor like graphite press against the commutator, making sliding electrical contact with successive segments as the rotor turns, providing electric current to the windings; each time the rotor rotates by 180° the commutator reverses the direction of the electric current applied to a given winding, so the magnetic field creates a torque in one direction. The commutator has many engineering disadvantages that has led to the decline in use of brushed motors; these disadvantages are: The friction of the brushes sliding along the rotating commutator segments causes power losses that can be significant in a low power motor. The soft brush material wears down due to friction, creating dust, the brushes must be replaced; this makes commutated motors unsuitable for low particulate or sealed applications like hard disk motors. The resistance of the sliding brush contact causes a voltage drop in the motor circuit called brush drop which consumes energy.
The repeated abrupt switching of the current through the inductance of the windings causes sparks at the commutator contacts. These are a fire hazard in explosive atmospheres and a source of degrading UV radiation, create electronic noise, which can cause electromagnetic interference in nearby microelectronic circuits. During the last hundred years high power DC brushed motors, once the mainstay of industry, were replaced by alternating current synchronous motors. Today brushed motors are only used in low power applications or where only DC is available, but the above drawbacks limit their use in these applications. Brushless motors were invented to solve these problems; the development of semiconductor electronics in the 1970s allowed the commutator and brushes to be eliminated in DC motors. In brushless DC motors, an electronic servo system replaces the mechanical commutator contacts. An electronic sensor detects the angle of the rotor, controls semiconductor switches such as transistors which switch current through the windings, either reversing the direction of the current, or in some motors turning it off, at the correct time each 180° shaft rotation so the electromagnets create a torque in one direction.
The elimination of the sliding contact allows brushless motors to have less friction and longer life. Brushed DC motors develop a maximum torque when stationary, linearly decreasing as velocity increases; some limitations of brushed motors can be overcome by brushless motors. These benefits come at the cost of less rugged, more complex, more expensive control electronics. A typical brushless motor has permanent magnets which rotate around a fixed armature, eliminating problems associated with connecting current to the moving armature. An electronic controller replaces the brush/commutator assembly of the brushed DC motor, which continually switches the phase to the windings to keep the motor turning; the controller performs similar timed power distribution by using a solid-state circuit rather than the brush/commutator system. Brushless motors offer several advantages over brushed DC motors, including high torque to weight ratio, more torque per watt, increased reliability, reduced no
An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are considered aviators, because they are involved in operating the aircraft's navigation and engine systems. Other aircrew members, such as flight attendants and ground crew, are not classified as aviators. In recognition of the pilots' qualifications and responsibilities, most militaries and many airlines worldwide award aviator badges to their pilots; the first recorded use of the term aviator was in 1887, as a variation of "aviation", from the Latin avis, coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne. The term aviatrix, now archaic, was used for a female aviator; these terms were used more in the early days of aviation, when airplanes were rare, connoted bravery and adventure. For example, a 1905 reference work described the Wright brothers' first airplane: "The weight, including the body of the aviator, is a little more than 700 pounds".
To ensure the safety of people in the air and on the ground, early aviation soon required that aircraft be under the operational control of a properly trained, certified pilot at all times, responsible for the safe and legal completion of the flight. The Aéro-Club de France delivered the first certificate to Louis Blériot in 1908—followed by Glenn Curtiss, Léon Delagrange, Robert Esnault-Pelterie; the British Royal Aero Club followed in 1910 and the Aero Club of America in 1911. Civilian pilots fly aircraft of all types for pleasure, charity, or in pursuance of a business, or commercially for non-scheduled and scheduled passenger and cargo air carriers, corporate aviation, forest fire control, law enforcement, etc; when flying for an airline, pilots are referred to as airline pilots, with the pilot in command referred to as the captain. There are 290,000 airline pilots in the world in 2017 and aircraft simulator manufacturer CAE Inc. forecasts a need for 255,000 new ones for a population of 440,000 by 2027, 150,000 for growth and 105,000 to offset retirement and attrition: 90,000 in Asia-Pacific, 85,000 in Americas, 50,000 in Europe and 30,000 in Middle East & Africa.
Boeing expects 790,000 new pilots in 20 years from 2018, 635,000 for commercial aviation, 96,000 for business aviation and 59,000 for helicopters: 33% in Asia Pacific, 26% in North America, 18% in Europe, 8% in the Middle East, 7% in Latin America, 4% in Africa and 3% in Russia/ Central Asia. By November 2017, due a shortage of qualified pilots, some pilots are leaving corporate aviation to return to airlines. In one example a Global 6000 pilot, making $250,000 a year for 10 to 15 flight hours a month, returned to American Airlines with full seniority. A Gulfstream G650 or Global 6000 pilot might earn between $245,000 and $265,000, recruiting one may require up to $300,000. At the other end of the spectrum, constrained by the available pilots, some small carriers hire new pilots who need 300 hours to jump to airlines in a year, they may recruit non-career pilots who have other jobs or airline retirees who want to continue to fly. The number of airline pilots could decrease as automation replaces copilots and pilots as well.
In January 2017 Rhett Ross, CEO of Continental Motors said "my concern is that in the next two decades—if not sooner—automated and autonomous flight will have developed sufficiently to put downward pressure on both wages and the number and kind of flying jobs available. So if a kid asks the question now and he or she is 18, 20 years from now will be 2037 and our would-be careerist will be 38—not mid-career. Who among us thinks aviation and for-hire flying will look like it does now?" Christian Dries, owner of Diamond Aircraft Austria said "Behind the curtain, aircraft manufacturers are working on a single-pilot cockpit where the airplane can be controlled from the ground and only in case of malfunction does the pilot of the plane interfere. The flight will be autonomous and I expect this to happen in the next five to six years for freighters."In August 2017 financial company UBS predicted pilotless airliners are technically feasible and could appear around 2025, offering around $35bn of savings in pilot costs: $26bn for airlines, $3bn for business jets and $2.1bn for civil helicopters.
Regulations have to adapt with air cargo at the forefront, but pilotless flights could be limited by consumer behaviour: 54% of 8,000 people surveyed are defiant while 17% are supportive, with acceptation progressively forecast. AVweb reporter Geoff Rapoport stated, "pilotless aircraft are an appealing prospect for airlines bracing for the need to hire several hundred thousand new pilots in the next decade. Wages and training costs have been rising at regional U. S. airlines over the last several years as the major airlines have hired pilots from the regionals at unprecedented rates to cover increased air travel demand from economic expansion and a wave of retirements". Going to pilotless airliners could be done in one bold step or in gradual improvements like by reducing the cockpit crew for long haul missions or allowing single pilot cargo aircraft; the industry has not decided
A radio-controlled aircraft is a small flying machine, controlled remotely by an operator on the ground using a hand-held radio transmitter. The transmitter communicates with a receiver within the craft that sends signals to servomechanisms which move the control surfaces based on the position of joysticks on the transmitter; the control surfaces, in turn, affect the orientation of the plane. Flying RC aircraft as a hobby grew from the 2000s with improvements in the cost, weight and capabilities of motors and electronics. A wide variety of models and styles is available. Scientific and military organizations are using RC aircraft for experiments, gathering weather readings, aerodynamic modeling and testing. Unmanned aerial vehicle or spy planes add video or autonomous capabilities, may be armed; the earliest examples of electronically guided model aircraft were hydrogen-filled model airships of the late 19th century. They were flown as a music hall act around theater auditoriums using a basic form of spark-emitted radio signal.
During World War II, the U. S. Army and Navy used. There are many types of radio-controlled aircraft. For beginning hobbyists, there are park trainers. For more experienced pilots there are glow plug engine, electric sailplane aircraft. For expert flyers, pylon racers, autogyros, 3D aircraft, other high-end competition aircraft provide adequate challenge; some models are made to operate like a bird instead. Replicating historic and little known types and makes of full-size aircraft as "flying scale" models, which are possible with control line and free flight types of model aircraft reach their maximum realism and behavior when built for radio-control flying; the most realistic form of aeromodeling, in its main purpose to replicate full-scale aircraft designs from aviation history, for testing of future aviation designs, or to realize never-built "proposed" aircraft, is that of radio-control scale aeromodeling, as the most practical way to re-create "vintage" full-scale aircraft designs for flight once more, from long ago.
RC Scale model aircraft can be of any type of steerable airship lighter-than-air aviation craft, or more of the heavier-than-air fixed wing glider/sailplane, fixed-wing single or multi-engine aircraft, or rotary-wing aircraft such as autogyros or helicopters. Full-scale aircraft designs from every era of aviation, from the "Pioneer Era" and World War I's start, through to the 21st century, have been modeled as radio-control scale model aircraft. Builders of RC Scale aircraft can enjoy the challenge of creating a controllable, miniature aircraft that "looks" like the full scale original in the air with no "fine details", such as a detailed cockpit, or replicate many operable features of a selected full scale aircraft design down to having operable cable-connected flight control surfaces, illuminated navigation lighting on the aircraft's exterior, realistically retracting landing gear, etc. if the full-sized aircraft possessed such features as part of its design. Various scale sizes of RC scale aircraft have been built in the decades since modern digital-proportional, miniaturized RC gear came on the market in the 1960s, everything from indoor-flyable electric powered RC Scale models, to "giant scale" RC Scale models, in scale size ranges that run from 20% to 25%, upwards to 30 to 50% size of some smaller full scale aircraft designs, that can replicate some of the actual flight characteristics of the full scale aircraft they are based on, have been enjoyed, continue to be built and flown, in sanctioned competition and for personal pleasure, as part of the RC scale aeromodeling hobby.
Gliders are planes that do not have any type of propulsion. Unpowered glider flight must be sustained through exploitation of the natural lift produced from thermals or wind hitting a slope. Dynamic soaring is another popular way of providing energy to gliders, becoming more and more common; however conventional slope soaring gliders are capable of achieving speeds comparable with similar sized powered craft. Gliders are partial to slow flying and have high aspect ratio, as well as low wing loading. Two and three-channel gliders which use only rudder control for steering and dihedral or polyhedral wing shape to automatically counteract rolling are popular as training craft, due to their ability to fly slowly and high tolerance to error. Powered gliders have seen an increase in popularity. By combining the efficient wing size and wide speed envelope of a glider airframe with an electric motor, it is possible to achieve long flight times and high carrying capacity, as well as glide in any suitable location regardless of thermals or lift.
A common method of maximising flight duration is to fly a powered glider upwards to a chosen altitude and descending in an unpowered glide. Folding propellers which reduce drag are standard. Powered gliders built with stability in mind and capable of aerobatics, high speed flight and sustained vertical flight are classified as'Hot-liners'.'Warm-liners' are powered craft with similar abilities but less extreme thrust capability. Jets can be expensive and use a micro turbine or ducted fan to power them. Most airframes are constructed from carbon fiber. For electric powered flight which are powered by electric ducted fans, may be made of styrofoam. Inside the aircraft, wooden spars reinforce the body to make a rigid airframe, they ha
Nitromethane is an organic compound with the chemical formula CH3NO2. It is the simplest organic nitro compound, it is a polar liquid used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, as a cleaning solvent. As an intermediate in organic synthesis, it is used in the manufacture of pharmaceuticals, explosives and coatings. Nitromethane is used as a fuel additive in e.g.. Top Fuel drag racing and miniature internal combustion engines in radio control, control line and free flight model aircraft. Nitromethane is produced industrially by combining propane and nitric acid in the gas phase at 350–450 °C; this exothermic reaction produces the four industrially significant nitroalkanes: nitromethane, nitroethane, 1-nitropropane, 2-nitropropane. The reaction involves free radicals, including the alkoxyl radicals of the type CH3CH2CH2O, which arise via homolysis of the corresponding nitrite ester; these alkoxy radicals are susceptible to C—C fragmentation reactions, which explains the formation of a mixture of products.
It can be prepared in other methods. The reaction of sodium chloroacetate with sodium nitrite in aqueous solution produces this compound: ClCH2COONa + NaNO2 + H2O → CH3NO2 + NaCl + NaHCO3 The principal use of nitromethane is as a stabilizer for chlorinated solvents, which are used in dry cleaning, semiconductor processing, degreasing, it is used most as a solvent or dissolving agent for acrylate monomers, such as cyanoacrylates. It is used as a fuel in some forms of racing, it can be used as an explosive. This type of mixture is called PLX. Another used mixtures are ANNM and ANNMAl – explosive mixtures of ammonium nitrate and aluminium powder. Nitromethane is a acidic carbon acid, it has a pKa of 17.2 in DMSO solution. This value indicates an aqueous pKa of about 11; the reason of that being so acidic is due to the resonance structure below: It is slow to deprotonate. Protonation of the conjugate base O2NCH2-, nearly isosteric with nitrate, occurs at oxygen. In organic synthesis nitromethane is employed as a one carbon building block.
Its acidity allows it to undergo deprotonation, enabling condensation reactions analogous to those of carbonyl compounds. Thus, under base catalysis, nitromethane adds to aldehydes in 1,2-addition in the nitroaldol reaction; some important derivatives include the pesticides chloropicrin, beta-nitrostyrene, trisnitromethane. Reduction of the latter gives trisaminomethane, 3CNH2, better known as tris, a used buffer. In more specialized organic synthesis, nitromethane serves as a Michael donor, adding to α,β-unsaturated carbonyl compounds via 1,4-addition in the Michael reaction. Nitromethane is used as a fuel in motor racing drag racing, as well as for radio-controlled models. In this context, nitromethane is referred to as "nitro", is the principal ingredient for fuel used in the "Top Fuel" category of drag racing; the oxygen content of nitromethane enables it to burn with much less atmospheric oxygen. 4 CH3NO2 + 3 O2 → 4 CO2 + 6 H2O + 2 N2The amount of air required to burn 1 kg of gasoline is 14.7 kg, but only 1.7 kg of air is required for 1 kg of nitromethane.
Since an engine's cylinder can only contain a limited amount of air on each stroke, 8.6 times more nitromethane than gasoline can be burned in one stroke. Nitromethane, has a lower specific energy: gasoline provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen. Nitromethane can be used as a monopropellant, i.e. a fuel that burns without added oxygen. The following equation describes this process: 2 CH3NO2 → 2 CO + 2 H2O + H2 + N2Nitromethane has a laminar combustion velocity of 0.5 m/s, somewhat higher than gasoline, thus making it suitable for high-speed engines. It has a somewhat higher flame temperature of about 2,400 °C; the high heat of vaporization of 0.56 MJ/kg together with the high fuel flow provides significant cooling of the incoming charge, resulting in reasonably low temperatures Nitromethane is used with rich air–fuel mixtures because it provides power in the absence of atmospheric oxygen.
When rich air–fuel mixtures are used and carbon monoxide are two of the combustion products. These gases ignite, sometimes spectacularly, as the very rich mixtures of the still burning fuel exits the exhaust ports. Rich mixtures are necessary to reduce the temperature of combustion chamber hot parts in order to control pre-ignition and subsequent detonation. Operational details depend on engine characteristics. A small amount of hydrazine blended in nitromethane can increase the power output further. With nitromethane, hydrazine forms an explosive salt, again a monopropellant; this unstable mixture poses a severe safety hazard and the Academy of Model Aeronautics does not permit its use in competitions. In model aircraft and car glow fuel, the primary ingredient is methanol with some nitromethane (0% to 65%, but over 30%, 10–20% lubricants. Moderate amounts of nitromethane tend to increase the power created by the engine, making the engine easier t
Coaxial rotors or "coax rotors" are a pair of helicopter rotors mounted one above the other on concentric shafts, with the same axis of rotation, but turning in opposite directions. This configuration is a feature of helicopters produced by the Russian Kamov helicopter design bureau; the idea of coaxial rotors originates with Mikhail Lomonosov. He had developed a small helicopter model with coaxial rotors in July 1754 and demonstrated it to the Russian Academy of Sciences. In 1859, the British Patent Office awarded the first helicopter patent to Henry Bright for his coaxial design. From this point, coaxial helicopters developed into operational machines as we know them today. Two pioneering helicopters, the Corradino D'Ascanio-built "D'AT3" of 1930, the more successful French mid-1930s Gyroplane Laboratoire, both used coaxial rotor systems for flight. Having two coaxial sets of rotors provides symmetry of forces around the central axis for lifting the vehicle and laterally when flying in any direction.
Because of the mechanical complexity, many helicopter designs use alternate configurations to avoid problems that arise when only one rotor is used. Common alternatives are tandem rotor arrangements. One of the problems with any single set of rotor blades is the torque exerted on the helicopter fuselage in the direction opposite to the rotor blades; this torque causes the fuselage to rotate in the direction opposite to the rotor blades. In single rotor helicopters, the antitorque rotor or tail rotor counteracts the main rotor torque and controls the fuselage rotation. Coaxial rotors solve the problem of main rotor torque by turning each set of rotors in opposite directions; the opposite torques from the rotors cancel each other out. Rotational maneuvering, yaw control, is accomplished by increasing the collective pitch of one rotor and decreasing the collective pitch on the other; this causes a controlled dissymmetry of torque. Dissymmetry of lift is an aerodynamic phenomenon caused by the rotation of a helicopter's rotors in forward flight.
Rotor blades provide lift proportional to the amount of air flowing over them. When viewed from above, the rotor blades move in the direction of flight for half of the rotation, move in the opposite direction for the remainder of the rotation. A rotor blade produces more lift in the advancing half; as a blade moves toward the direction of flight, the forward motion of the aircraft increases the speed of the air flowing around the blade until it reaches a maximum when the blade is perpendicular to the relative wind. At the same time, a rotor blade in the retreating half produces less lift; as a blade moves away from the direction of flight, the speed of the airflow over the rotor blade is reduced by an amount equal to the forward speed of the aircraft, reaching its maximum effect when the rotor blade is again perpendicular to the relative wind. Coaxial rotors avoid the effects of dissymmetry of lift through the use of two rotors turning in opposite directions, causing blades to advance on either side at the same time.
Another benefit arising from a coaxial design includes increased payload for the same engine power. Reduced noise is a second advantage of the configuration. Helicopters using coaxial rotors tend to be more compact, though at the price of increased height, have uses in areas where space is at a premium. Another benefit is increased safety on the ground. A principal disadvantage of the coaxial rotor design is the increased mechanical complexity of the rotor hub; the linkages and swashplates for two rotor systems need to be assembled atop the mast, more complex because of the need to drive two rotors in opposite directions. Because of the greater number of moving parts and complexity, the coaxial rotor system is more prone to mechanical faults and possible failure. Coaxial helicopters are more prone to the "whipping" of blades and blade self-collision according to critics; the system's inherent stability and quick control response make it suitable for use in small radio controlled helicopters. These benefits come at the cost of a limited forward speed, higher sensitivity to wind.
These two factors are limiting in outdoor use. Such models are fixed-pitch, simplifying the model but eliminating the ability to compensate with collective input. Compensating for the slightest breeze causes the model to climb rather than to fly forward with full application of cyclic. Multirotor type Unmanned Aerial Vehicles exist in numerous configurations including duocopter, quadcopter and octocopter. All of them can be upgraded to coaxial configuration in order to bring more stability and flight time while allowing carrying much more payload without gaining too much weight. Indeed, coaxial multirotors are made by having each arm carrying two motors facing in opposite directions (one up and