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Commercial Aviation

Commercial aviation

Aviation or Air transport refers to the activities surrounding mechanical flight and the aircraft industry. Aircraft, include fixed wing (airplane) and rotary wing (helicopter/autogyro) types, as well as lighter-than-air craft such as balloons and airships (also known as dirigibles.) There are two major categories of aviation:
- Civil aviation
- Military aviation Civil aviation includes both scheduled air transport and general aviation.

Flight

Flight is the process of flying: either movement through the air by aerodynamically generating lift or aerostatically using buoyancy, or movement beyond earth's atmosphere by spacecraft.

Animal flight

spacecraft The most successful groups of living things that fly are insects, birds, and bats. Each of these groups' wings evolved separately from different structures. Pterosaurs were a group of flying vertebrates contemporaneous with the dinosaurs. Bats are the only mammals capable of true flight. However, there are several gliding mammals which are able to glide from tree to tree using fleshy membranes between their limbs; some can travel hundreds of metres in this way with very little loss of height. Flying tree frogs use greatly enlarged webbed feet for a similar purpose, and there are flying lizards which employ their unusually wide, flattened rib-cages to the same end. Certain snakes also use a flattened rib-cage to fly, with a back and forth motion much the same as they use on the ground. Flying fish can glide using enlarged wing-like fins, and have been observed soaring for hundreds of metres using the updraft on the leading edges of waves. It is thought that they evolved this ability to help them escape from underwater predators. Most birds fly (see bird flight), with some exceptions. The largest birds, the ostrich and the emu, are earthbound, as were the now-extinct dodos, while the non-flying penguins have adapted their wings for use under water. Most small flightless birds are native to small islands, and lead a lifestyle where flight would confer little advantage. The Peregrine Falcon is the fastest animal in the world; its terminal velocity exceeds 320 km/h (199 mph) while diving down on its prey. Among living animals that fly, the wandering albatross has the greatest wingspan, up to 3.5 metres (11.5 feet), and the trumpeter swan perhaps the greatest weight, at 17 kilograms (38 pounds). Among the many species of insects, some fly and others do not (See insect flight).

In fiction

- Dumbo, the Disney-created elephant, employs his comically oversized ears as wings for flight.
- Many dragons are depicted with wings capable of flight.
- Superman is a well known superhero in comic books, cartoons, and films; unaided flight is among the various super powers he is portrayed to obtain from the yellow rays of earth's sun. Most flight-capable fictional comic book superheroes are said to fly by sheer will rather than by telekinetically levitating themselves. Jean Grey of the X-men is an exception who uses telekinesis to levitate slightly above ground. telekinesis

Mechanical flight

Flying machines are aircraft, including aeroplanes, helicopters, airships and balloons, and spacecraft. In the case of an aeroplane flight involves
- Taxiing
- Take off
- Climb
- Cruise
- Descent
- Landing See aviation history for the history of mechanical flight.

Aircraft

An aircraft is any machine capable of atmospheric flight. flight. This is a wide-bodied long-haul aircraft]]

Categories and classification

Aircraft fall into two broad categories:

Heavier than air

- Heavier than air aerodynes, including autogyros, helicopters and variants, and conventional fixed-wing aircraft: aeroplanes in Commonwealth English (excluding Canada), airplanes in North American English. Fixed-wing aircraft generally use an internal-combustion engine in the form of a piston engine (with a propeller) or a turbine engine (jet or turboprop), to provide thrust that moves the craft forward through the air. The movement of air over the airfoil produces lift that causes the aircraft to fly. Exceptions are gliders which have no engines and gain their thrust, initially, from winches or tugs and then from gravity and thermal currents. For a glider to maintain its forward speed it must descend in relation to the air (but not necessarily in relation to the ground). Helicopters and autogyros use a spinning rotor (a rotary wing) to provide lift; helicopters also use the rotor to provide thrust. The abbreviation VTOL is applied to aircraft other than helicopters that can take off or land vertically. STOL stands for Short Take Off and Landing. Mainly used internationally.

Lighter than air

STOL
- Lighter than air aerostats: hot air balloons and airships. Aerostats use buoyancy to float in the air in much the same manner as ships float on the water. In particular, these aircraft use a relatively low density gas such as helium, hydrogen or heated air, to displace the air around the craft. The distinction between a balloon and an airship is that an airship has some means of controlling both its forward motion and steering itself, while balloons are carried along with the wind.

Types of aircraft

:See also: List of aircraft There are several ways to classify aircraft. Below, we describe classifications by design, propulsion and usage.

By design

A first division by design among aircraft is between lighter-than-air, aerostat, and heavier-than-air aircraft, aerodyne. Examples of lighter-than-air aircraft include non-steerable balloons, such as hot air balloons and gas balloons, and airships (sometimes called dirigible balloons) such as blimps (that have non-rigid construction) and rigid airships that have a rigid frame. The most successful type of rigid airship was the Zeppelin, although there were some accidents such as the Hindenburg Zeppelin which was destroyed in a fire at Lakehurst, NJ, in 1937. In heavier-than-air aircraft, there are two ways to produce lift: aerodynamic lift and engine lift. In the case of aerodynamic lift, the aircraft is kept in the air by wings or rotors (see aerodynamics). With engine lift, the aircraft defeats gravity by use of vertical thrust greater than its weight. Examples of engine lift aircraft are rockets, and VTOL aircraft such as the Hawker-Siddeley Harrier. Among aerodynamically lifted aircraft, most fall in the category of fixed-wing aircraft, where horizontal airfoils produce lift, by profiting from airflow patterns determined by Bernoulli's equation and, to some extent, the Coanda effect. The forerunner of these type of aircraft is the kite. Kites depend upon the tension between the cord which anchors it to the ground and the force of the wind currents. Much aerodynamic work was done with kites until test aircraft, wind tunnels and now computer modelling programs became available. In a "conventional" configuration, the lift surfaces are placed in front of a control surface or tailplane. The other configuration is the canard where small horizontal control surfaces are placed forward of the wings, near the nose of the aircraft. Canards are becoming more common as supersonic aerodynamics grows more mature and because the forward surface contributes lift during straight-and-level flight. The number of lift surfaces varied in the pre-1950 period, as biplanes (two wings) and triplanes (three wings) were numerous in the early days of aviation. Subsequently most aircraft are monoplanes. This is principally an improvement in structures and not aerodynamics. Other possibilities include the delta-wing, where lift and horizontal control surfaces are often combined, and the flying wing, where there is no separate vertical control surface (e.g. the B-2 Spirit). A variable geometry ('swing-wing') has also been employed in a few examples of combat aircraft (the F-111, Panavia Tornado, F-14 Tomcat and B-1 Lancer, among others). The lifting body configuration is where the body itself produce lift. So far the only significant practical application of the lifting body is in the Space Shuttle, but many aircraft generate lift from nothing other than wings alone. A second category of aerodynamically lifted aircraft are the rotary-wing aircraft. Here, the lift is provided by rotating aerofoils or rotors. The best-known examples are the helicopter, the autogyro and the tiltrotor aircraft (such as the V-22 Osprey). Some craft have reaction-powered rotors with gas jets at the tips but most have one or more lift rotors powered from engine-driven shafts. A further category might encompass the wing-in-ground-effect types, for example the Russian ekranoplan also nicknamed the "Caspian Sea Monster" and hovercraft; most of the latter employing a skirt and achieving limited ground or water clearance to reduce friction and achieve speeds above those achieved by boats of similar weight. A recent innovation is a completely new class of aircraft, the fan wing. This uses a fixed wing with a forced airflow produced by cylindrical fans mounted above. It is (2005) in development in the United Kingdom. And finally the flapping-wing ornithopter is a category of its own. These designs may have potential but are not yet practical.

By propulsion

ornithopter adapted as a floatplane]] Some types of aircraft, such as the balloon or glider, do not have any propulsion. Balloons drift with the wind, though normally the pilot can control the altitude either by heating the air or by releasing ballast, giving some directional control (since the wind direction changes with altitude). For gliders, takeoff takes place from a high location, or the aircraft is pulled into the air by a ground-based winch or vehicle, or towed aloft by a powered "tug" aircraft. Airships combine a balloon's buoyancy with some kind of propulsion, usually propeller driven. Until World War II, the internal combustion piston engine was virtually the only type of propulsion used for powered aircraft. (See also: Aircraft engine.) The piston engine is still used in the majority of aircraft produced, since it is efficient at the lower altitudes used by small aircraft, but the radial engine (with the cylinders arranged in a circle around the crankshaft) has largely given way to the horizontally-opposed engine (with the cylinders lined up on two sides of the crankshaft). Water cooled V engines, as used in automobiles, were common in high speed aircraft, until they were replaced by jet and turbine power. Piston engines typically operate using avgas or regular gasoline, though some new ones are being designed to operate on diesel or jet fuel. Piston engines normally become less efficient above 7,000-8,000 ft (2100-2400 m) above sea level because there is less oxygen available for combustion; to solve that problem, some piston engines have mechanically powered compressors (blowers) or turbine-powered turbochargers or turbonormalizers that compress the air before feeding it into the engine; these piston engines can often operate efficiently at 20,000 ft (6100 m) above sea level or higher, altitudes that require the use of supplemental oxygen or cabin pressurisation. During the forties and especially following the 1973 energy crisis, development work was done on propellers with swept tips or even scimitar-shaped blades for use in high-speed commercial and military transports. Pressurised aircraft, however, are more likely to use the turbine engine, since it is naturally efficient at higher altitudes and can operate above 40,000 ft. Helicopters also typically use turbine engines. In addition to turbine engines like the turboprop and turbojet, other types of high-altitude, high-performance engines have included the ramjet and the pulse jet. Rocket aircrafts have occasionally been experimented with. They are restricted to rather specialised niches, such as spaceflight, where no oxygen is available for combustion (rockets carry their own oxygen).

By usage

The major distinction in aircraft usage is between military aviation, which includes all uses of aircraft for military purposes (such as combat, patrolling, search and rescue, reconnaissance, transport, and training), and civil aviation, which includes all uses of aircraft for non-military purposes.

Military aircraft

Combat aircraft like fighters or bombers represent only a minority of the category. Many civil aircraft have been produced in separate models for military use, such as the civil Douglas DC-3 airliner, which became the military C-47/C-53/R4D transport in the U.S. military and the Dakota in Britain and the Commonwealth. Even the little fabric-covered two-seater Piper J3 Cub had a military version, the L-4 liaison, observation and trainer aircraft. In the past, gliders and balloons have also been used as military aircraft; for example, balloons were used for observation during the American Civil War and World War I, and cargo gliders were used during World War II to land intruding German troops in many European countries in the 1940/42 period, while Allied troops used them in Europe after D-Day . Combat aircraft themselves, though used a handful of times for reconnaissance and surveillance during the Italo-Turkish War, did not come into widespread use until the Balkan War when first air-dropped bomb was invented and widely used by Bulgarian air force against Turkey. During World War I many types of aircraft were adapted for attacking the ground or enemy vehicles/ships/guns/aircraft, and the first aircraft designed as bombers were born. In order to prevent the enemy from bombing, fighter aircraft were developed to intercept and shoot down enemy aircraft. Tankers were developed after World War II to refuel other aircraft in mid-air, thus increasing their operational range. By the time of the Vietnam War, helicopters had come into widespread military use, especially for transporting and supporting ground troops.

Civil aviation

helicopter]] Civil aviation includes both scheduled airline flights and general aviation, a catch-all covering other kinds of private and commercial use. The vast majority of flights flown around the world each day belong to the general aviation category, ranging from recreational balloon flying to civilian flight training to business trips to firefighting to medevac flights to cargo transportation on freight aircraft. Within general aviation, the major distinction is between private flights (where the pilot is not paid for time or expenses) and commercial flights (where the pilot is paid by a customer or employer). Private pilots use aircraft primarily for personal travel, business travel, or recreation. Usually these private pilots own their own aircraft and take out loans from banks or specialized lenders to purchase them. Commercial general aviation pilots use aircraft for a wide range of tasks, such as flight training, pipeline surveying, passenger and freight transport, policing, crop dusting, and medical transport (medevac). Piston-powered propeller aircraft (single-engine or twin-engine) are especially common for both private and commercial general aviation, but even private pilots occasionally own and operate helicopters like the Bell JetRanger or turboprops like the Beechcraft King Air. Business jets are typically flown by commercial pilots, although there is a new generation of small jets arriving soon for private pilots.

External links

History
- [http://www.nasm.si.edu/ Smithsonian Air and Space Museum] - Excellent online collection with a particular focus on history of aircraft and spacecraft
- [http://invention.psychology.msstate.edu/Tale_of_Airplane/taleplane.html Virtual Museum]
- [http://www.centennialofflight.gov/essay/Prehistory/PH-OV.htm Prehistory of Powered Flight]
- [http://www.hq.nasa.gov/office/pao/History/SP-468/contents.htm The Evolution of Modern Aircraft (NASA)]
- [http://www.check-six.com Check-Six] - Information on historic aircraft crashes including the X-15 and Flying Wing
- [http://www.anythingplanes.net Aircraft community ] Information
- [http://www.aircraft-info.net Aircraft-Info.net]
- [http://www.airliners.net/info/ Airliners.net]
- [http://www.HomebuiltAircraft.com HomebuiltAircraft.com]- Information Portal about Homebuilt Aircraft
- [http://www.DefenceTalk.com Airforces ]
- [http://www.challoner.com/aviation/index.html Series of Photo Essays on British Aviation]
- [http://www.usenet-replayer.com/webrings/aviation.html Pictures of Aircraft] published on Usenet
- [http://www.sulman4paf.tk PAF Procedures and Information, Wallpapers, Picture Gallery, Updated News] Patents
- US[http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=821393.WKU.&OS=PN/821393&RS=PN/821393 821393] -- Flying machine -- O. & W. Wright Category:Aircraft Category:Aviation zh-min-nan:Hui-hêng-ki ko:항공기 ms:Pesawat udara ja:航空機 simple:Aircraft

Aircraft

An aircraft is any machine capable of atmospheric flight. flight. This is a wide-bodied long-haul aircraft]]

Categories and classification

Aircraft fall into two broad categories:

Heavier than air

Lighter than air

Types of aircraft

:See also: List of aircraft There are several ways to classify aircraft. Below, we describe classifications by design, propulsion and usage.

By design

By propulsion

By usage

Military aircraft

Civil aviation

External links

Helicopter

]] , a four seat development of the R22]] A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors (propellers). Helicopters are classified as rotary-wing aircraft to distinguish them from conventional fixed-wing aircraft. The word helicopter is derived from the Greek words helix (spiral) and pteron (wing). The engine-driven helicopter was invented by the Slovak inventor Jan Bahyl. The first stable, fully-controllable helicopter placed in production was invented by Igor Sikorsky. 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 compensating advantage is maneuverability: helicopters can hover in place, reverse, and above all take off and land vertically. 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).

Applications

Helicopters have many uses, both military and civil, including troop transportation, infantry support, firefighting, [http://www.tropicaled.com/helicopter2.htm 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. Helicopters suffer from significantly higher operating and maintenance costs compared with fixed wing aircraft. The costs are due to inherent mechanical complexity and greater power requirements for a given gross weight. For these reasons, helicopters are not economically viable for commercial transportation. Speed and range limitations also constrain commercial applications.

History

police] Since around 400 BC the Chinese had a flying top that was used as a children's toy. This toy eventually made its way to Europe via trade and has been depicted in a 1463 European painting. Incidentally, the Wright brothers as children were given a rubber-band-powered version of this toy invented by Alphonse Penaud and were very much fascinated by it and built their own copies. "Pao Phu Tau" was a 4th century book in China that described some of the ideas in a rotary wing aircraft. 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. 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. A flight of the first fully controllable helicopter was demonstrated by Raúl Pateras de Pescara 1916 in Buenos Aires, Argentina. The German Focke-Wulf Fw 61 was the first practical helicopter. It first flew in 1934. The Bell 47 designed by Arthur Young was the first helicopter to be licensed (in March 1946) for use in the United States. Reliable helicopters capable of stable hover flight were developed decades after fixed wing aircraft. This is largely due to higher engine power density requirements when compared with fixed wing aircraft. Igor Sikorsky is reported to have delayed his own helicopter research until suitable engines were commercially available. Improvements in fuels and engines during the first half of the 20th century were a critical factor in helicopter development. 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. Turboshaft engines are the preferred powerplant for all but the smallest and least expensive helicopters today.

Generating lift

A conventional aircraft is able to fly because the forward motion of its angled wings forces air downwards, creating an opposite reaction called lift that forces the wings upwards. A helicopter uses exactly the same method, except that instead of moving the entire aircraft, only the wings themselves are moved, in a circular motion. The helicopter's rotor can simply be regarded as rotating wings (hence the military appellation of "rotary wing aircraft"). lift

Conventional layout

There are several possible design layouts for arranging a helicopter's rotors. The most common design is the Sikorsky-layout, which is used by approximately 95% of all helicopters manufactured to date. 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. 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. This rotor creates thrust which is in the opposite direction from the torque generated by the main rotor. 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. The world's largest and smallest series-produced helicopters follow this principle. 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). Almost all civilian helicopters have the main rotor and tail rotor system. The world's fastest helicopter, the Westland Lynx can perform aerobatic loops and rolls with this conventional rotor system. aerobatic (Poland)]] 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. AH-64 Apache). If the tail rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. The fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox to turn the fan. 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. 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. Notars adjust thrust by opening and closing a sliding circular cover near the end of the tail boom. The amount of power required to prevent a helicopter from spinning is significant. A tail rotor can use up to 30% of the engine's power, and this power does not help the helicopter produce lift or forward motion. To reduce this waste during cruise, the vertical stabilizer is often angled to produce a force which helps counter the main rotor torque. At high speeds, it is possible for the vertical stabilizer to counteract the entire torque, leaving more power available for forward flight. This is commonly known as slip-streaming and can make hovering turns difficult on windy days. 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. Many military helicopters, especially attack types, have short wings called stub wings to add lift during forward motion. They are also used as external mounts for weapons. 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.

Alternative layouts

Mil Mi-24]] There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor. Such designs use two rotors which turn in opposite directions, or contra-rotate. All of these systems are designed for the same purpose: to produce a net rotational speed of zero. These methods introduce even more mechanical complexity to the design and are usually relegated to specialized helicopter types. 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"). 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. Another example is the Kamov Ka-26, a successful crop duster aircraft. 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. The contra-rotating rotors are located on top of the fuselage, close to each other. During the Cold War the American Kaman company started to produce similar helicopters for USAF firefighting purposes. 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. In the flying-waggon or tandem rotor system (sometimes called "flying banana" for the peculiar shape of early U.S. examples), the two main rotors are located at the front and rear extremity of a long, boxy fuselage that resembles a railway wagon. A prime example is the Boeing CH-47 Chinook, that can carry 14 tons of payload. Waggon helicopters are practical for military logistical purposes, because entry and unloading is easily facilitated via the unobstructed front and rear ramps. The rotors and turbines are located very high on top of the fuselage, making them less sensitive to damage and dirt. 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). A helicopter built by Juan de la Cierva had three main rotors. These were placed at the corners of an equilateral triangle and all turned the same direction. equilateral triangle 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. 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. The 1930s German FW-61 helicopter was built to such design. 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. The U.S. 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. nacelleA recent development in helicopter technology is the NOTAR system, which stands for NO TAil Rotor. The NOTAR eliminates the tail rotor by conducting high-velocity air through the tail boom. The NOTAR system was developed in the United States and is used exclusively by McDonnel Douglas Helicopters, or MD Helicopters. 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. 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.

Controlling flight

Useful flight requires that an aircraft be controlled in all three dimensions (see flight dynamics). 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. In a helicopter, however, there often isn't enough airspeed for this method to be practical. flight dynamics, an aerodynamically restyled F28 for the corporate market.]] For rotation about the vertical axis (yaw) the anti-torque system is used. Varying the pitch of the tail rotor alters the sideways thrust produced. 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. Yaw controls are usually operated with anti-torque pedals, on the floor in the same place as a fixed-wing aircraft's rudder pedals. 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. More lift at the rear of the rotary wing will cause the aircraft to pitch forward, a increase on the left will cause a roll to the right and so on. Helicopters maneuver with three flight controls besides the pedals. 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. When the angle of attack is increased, the blade produces more lift. The collective control is usually a lever at the pilot's left side, near his leg. Simultanously increasing the collective and adding power with the throttle causes a helicopter to rise. angle of attack] The throttle controls the absolute power produced by the engine that is connected to the rotor by a transmission. The throttle control is a twist grip on the collective control. RPM control is critical to proper operation for several reasons. Helicopter rotors are designed to operate at a specific RPM. If the RPM is too low, rapid descent with power, known as settling with power could result. If the RPM is too high, damage to the main rotor hub from excessive forces could result. In general, RPM must be maintained within a tight tolerance, usually a few percent. In many piston-powered helicopters, the pilot must manage the engine and rotor RPM. The pilot manipulates the throttle to maintain rotor RPM and therefore regulates the effect of drag on the rotor system. 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. The cyclic changes the pitch of the blades cyclically, causing the lift to vary across the plane of the rotor disk. 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 cyclic is similar to a joystick and is usually positioned in front of the pilot. 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. The rotating section rotates with the rotor and is connected to blade pitch horns through pitch links, one link for each blade. When the swashplate is not tilted, the blades are all at the collective angle. 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. This causes the helicopter to tilt in the same direction as the cyclic. If the pilot pushes the cyclic forward, then the helicopter tilts forward, and the rotor produces a thrust in the forward direction. angle of attack] 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. 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. 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. The angle of attack is increased on the retreating blade to produce more lift, compensating for the slower airspeed over the blade. And the angle of attack is decreased on the advancing blade to produce less lift, compensating for the faster airspeed over the blade. 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. This condition is called aerodynamic stall. On a helicopter, this can happen in any of three ways. #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. #As helicopter speeds increase, the retreating blade experiences lower relative airspeeds and the controls compensate with higher angle of attack. With a low enough relative airspeed and a high enough angle of attack, aerodynamic stall is inevitable. This is called retreating blade stall. #Any low rotor RPM flight condition accompanied by increasing collective pitch application will cause aerodynamic stall. stall AH.1 (XV134), now on the UK Civil Register.]] 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. The main rotor acts like a "windmill" and turns. This technique is known as autorotation. A transmission connects the main rotor to the tail rotor so that all flight controls are available after engine failure. 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. (see Height-velocity diagram). A very peculiar feature of the cyclic is that the lift is made to occur 90 degrees of rotation before the direction of tilt. 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 is called "gyroscopic precession". So control forces on the rotor are rotated 90 degrees before the desired motion. 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. 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. It took inventors many years to recognize precession, and to learn how to arrange the cyclic's control system to overcome it.

Stability

Fixed wing aircraft are designed to be inherently stable. 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. A small, fixed wing aircraft can be 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. precession In contrast, helicopters are very unstable. Simply hovering requires continuous, active corrections from the pilot. 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. Hovering a helicopter has been compared to balancing yourself while standing on a large beach ball. Adjusting one flight control on a helicopter almost always has an effect that requires an adjustment of the other controls. 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. Increasing collective will reduce rotor RPM, requiring an increase in throttle to maintain constant rotor RPM. Changing collective will also cause a change in torque, which will require the pilot to adjust the foot pedals. Small helicopters can be so unstable that it may be impossible for the pilot to ever let go of the cyclic while in flight. 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).

Limitations

precession The single most obvious limitation of the helicopter is its slow speed. The current record is around 400 km/h set by the Westland Lynx. There are several reasons why a helicopter cannot fly as fast as a fixed wing aircraft.
- 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. 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. The airspeed of the forward-going rotor blade is much higher than that of the helicopter itself. It is possible for this blade to exceed the speed of sound, and thus produce vastly increased drag and vibration. 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.
- Most rotors are not rigid. 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. 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. Conversely, the retreating blade flaps down, develops a higher angle of attack, and generates more lift. 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. In some designs the hub is rigid. The blades are made from composites which can bend without breaking. Fully rigid rotors exist and create very responsive helicopters. In most such designs, the lift is varied cyclically and according to the speed of the helicopter. 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. speed of sound) twin rotor helicopter had a large cargo door and external hoist, and was used as personnel/paratroop transport, casualty evacuation, and for lifting large loads. The Belvedere had a production run of only 26 and went into RAF service in 1961.]]
- Rotorhead design is a limiting factor on many helicopters. 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.
- Helicopters are susceptible to potentially disastrous vortex ring effects. In these, the downward wind from the rotor causes a circular vortex to form around the rotor. 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. During the closing years of the 20th century designers began working on helicopter noise reduction. Urban communities have often expressed great dislike of noisy aircraft, and police and passenger helicopters can be unpopular. 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. Helicopters vibrate. An unadjusted helicopter can easily vibrate so much that it will shake itself apart. To reduce vibration, all helicopters have rotor adjustments for height and pitch. Most also have vibration dampers for height and pitch. Some also use mechanical feedback systems to sense and counter vibration. 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. Adjustment is difficult in part because measurement of the vibration is hard. 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. The traditional low-tech system is to mount coloured chalk on the rotor tips, and see how they mark a linen sheet.

Landing

On a ship

angle of attack] A 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. In the U.S. Navy it is commonly and properly referred to as the flight deck. 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. 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. Tension is maintained on the cable as the helicopter descends which assists 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. This device was pioneered by the Royal Canadian Navy and was called "Beartrap". The U.S. 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.

Hazards of helicopter flight

As with any moving vehicle, operation outside of safe regimes could result in loss of control, structural damage, or fatality. For helicopters the hazards are particularly acute since they are flying at relatively low altitude, with little time to react to a sudden event. The following is a list of some of the potential hazards:
- Retreating blade stall
- Settling with power
- Ground resonance
- Low-G condition
- Operating within the shaded area of the height-velocity diagram
- Vortex ring state, a problem the V-22 Osprey was associated with Each of these conditions is potentially fatal and recovery might not be possible. For this reason, good pilotage demands operation within safe flight regimes and avoiding hazardous conditions at all costs.

Helicopter models and identification

V-22 Osprey In identifying conventional helicopters during flight it is helpful to know that when viewed from below, the rotor of a French, Russian, Soviet or Ukrainian designed helicopter rotates counter-clockwise, whilst that of a helicopter built in Italy, the UK or the USA rotates clockwise (see list of helicopter models). Some companies, notably Schweizer in the USA, are developing remotely-controlled variants of light helicopters for use in future battlefields. [http://rotomotion.com/ Rotomotion] is currently selling a line of small (less than 50 kg) rotorcraft UAVs, including an all electric helicopter. 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. Marine Corps and will be the first mass produced tilt-rotor aircraft to enter service. A helicopter should not be mistaken for an autogyro, which is a historical predecessor of the helicopter that gains lift from an unpowered rotor. Some common nicknames for helicopters are "copter", "chopper", "whirlybird", "windmill", "helo" (common U.S. Navy usage) or "paraffin budgie" (the latter term being mostly used in the UK offshore oil industry).

External links

- : "Aircraft, especially aircraft of the direct lift amphibian type and means of construction and operating the same"
- [http://www.helis.com/ Helicopter history]
- [http://centennialofflight.com/history/helicopter.html Helicopter history]
- [http://www.aerospaceweb.org/design/helicopter/history.shtml Image of a Chinese flying top]
- [http://www.centennialofflight.gov/essay/Rotary/early_20th_century/HE2.htm Helicopter development in the early 20th century]
- [http://www.centennialofflight.gov/essay/Dictionary/helicopter/DI27.htm Description of a helicopter]
- [http://www.heli-szene.de/ Helicopter pictures and videos (in German)]
- [http://www.mh-53pavelow.com/ Sikorsky MH-53J/M PAVE LOW helicopter]

References

- Thicknesse P, Jones A et al, Military Rotorcraft, 2nd edition, 2000, Brassey's World Military Technology series, Shirvenham UK, xvi + 160pp, ISBN 1857533259
- Wragg D, Helicopters at War: A pictorial history, 1983, Robert Hale Ltd, London UK, 283pp, ISBN 0709008589
- ko:헬리콥터 ja:ヘリコプター nb:Helikopter

Autogyro

An autogyro (only an autogiro™ when produced by the Cierva Autogiro Company or one of its licensees (see below), sometimes called a gyroplane, gyrocopter™, or rotaplane) is an aircraft supported in flight by an unpowered rotor. Though the autogyro resembles a helicopter, it is driven in flight by an engine-powered propeller similar to that of an airplane. Often mistakenly characterized as a hybrid between an airplane and helicopter, the autogyro is a distinct type of aircraft that made its first successful flight on 17 January 1923 at Cuatro Vientos Airfield in Madrid, Spain, predating the first successful helicopter by 13 years. All helicopters utilize rotor technology first developed for the autogiro: the helicopter owes its existence to the brilliant work conducted by Juan de la Cierva and his associates. helicopter

General characteristics

Autogyros can take off and land in significantly smaller areas compared to airplanes, and depending on the model, can operate from helipads. When fitted with a jump start feature, an autogyro can takeoff from a standing start into forward flight, accelerate in ground effect, then commence a climb; hovering capability is not available however since the rotor is always declutched before the autogyro leaves the ground. If rotor collective pitch control is provided, an autogyro can execute a collective flare; otherwise landings are always made with a cyclic flare. Certificated autogyros flown by trained and qualified pilots are notably safe. As intended by la Cierva, the rotor always turns regardless of the airspeed of the aircraft, though as airspeed decreases rotor rpm reduces to a minimum value at zero airspeed. Reduction of engine power increases the descent rate, though the autogyro remains fully stable and controllable. Directional control, provided by a rudder, can become nonexistent at low airspeed and low propeller thrust. For example, the Air and Space 18A gyroplane rudder rapidly loses effectiveness below 50mph airspeed when the engine is throttled. Most autogyros are neither efficient nor very fast (for one exception see Wing Commander Ken Wallis, below - around 120mph on 60bhp). Fixed-wing aircraft are faster and use less fuel over the same distance, helicopters generally require more power (and hence fuel) than a fixed wing aircraft (or autogyro) for the same top speed/load etc. It must be noted, however, that large scale autogyro development ceased prior to WW2 and with few exceptions has not benefitted from rotary wing developments applied to helicopters. Gyroplanes are typically more maneuverable than fixed-wing aircraft, but do not hover as does a helicopter. When helicopters became practical, autogyros were neglected for nearly 30 years. They were however at one time used extensively by major newspapers and by the US Postal Service for mail service between the Camden, NJ airport and the top of the post office building in downtown Philadelphia, PA. As the infrastructure for service, repair, training and building increases the number of autogyro users may increase. Autogyros can be of tractor configuration with the engine(s) and propeller(s) at the front of the fuselage, or pusher configuration with the engine(s) and propeller(s) at the rear of the fuselage. Early autogyros were fitted with fixed rotor hubs, small fixed-wings and airplane-type control surfaces. At the low airspeed at which autogyros can easily operate, the airplane-type control surfaces became ineffective and could readily lead to loss of control, particularly during landing. The direct control rotor hub, which could be tilted in any direction by the pilot, was first developed on the Cierva C.19 Mk.V and saw production on the Cierva C.30 series of 1934. Rotor drives initially took the form of a rope wrapped around the rotor axle and then pulled by a team of men to accelerate the rotor prior to a long taxi to bring the rotor up to speed sufficient for takeoff. The next innovation was a fully deflectable horizontal stabilizer that directed propeller slipstream into the rotor. Cierva license, Pitcairn-Cierva Autogiro Company of Willow Grove, PA, finally solved the problem with a light mechanical transmission driven by the engine. The Groen Brothers Hawk 4 of the late 1992 is advertised as possessing Ultra-Short Take-Off and Landing (USTOL) capabilty, enabling the aircraft to take off and land within a very short distance (25 feet). This is merely a new name for performance autogyros have always possessed.

History

Juan de la Cierva, a Spanish engineer and aeronautical enthusiast, invented the first successful rotorcraft, which he named autogiro in 1923. His craft used a tractor-mounted forward propeller and engine, a rotor mounted on a mast, and a horizontal and vertical stabilizer. His first three designs, C.1, C.2, and C.3, were unstable due to aerodynamic and structural deficiencies in their rotors. His fourth design, the C.4, fitted with flapping hinges to attach each rotor blade to the hub, made the first successful flight of a rotary-wing aircraft, piloted by Alejandro Gomez Spencer, on 17 January 1923. The C.4 was fitted with conventional airplane ailerons, elevators and rudder for control. During a later test flight, the engine failed shortly after takeoff and the aircraft descended slowly and steeply to a safe landing, validating la Cierva's efforts to produce an aircraft that could be flown safely at low airspeeds. Juan de la Cierva This success eventually became well known and after further limited Autogiro development in Spain, la Cierva accepted an offer from Scottish industrialist James G. Weir to establish the Cierva Autogiro Company in England following a 20 October 1925 demonstration to the British Air Ministry at Farnborough. Test pilot for these flights was Frank T. Courtney. From this point on, Britain became the world center of rotary-wing aircraft development. A crash due to blade root failure in February 1927 led to an improvement in rotor hub design. Adjacent the flapping hinge a drag hinge was incorporated to allow each blade to slightly oscillate horizontally and relieve inplane stresses generated as a byproduct of flapping motion. Development work on means to accelerate the rotor prior to takeoff was also undertaken. Efforts with the C.11 in Spain showed that development of a light and efficient mechanical rotor transmission was not a trivial undertaking and led to the adoption of the intermediate expedient of inclining the horizontal stabilizer to redirect the propeller slipstream into the rotor while on the ground. This feature was later introduced on the production C.19 series of 1929. Further Autogiro development led to the Cierva C.8 L.IV which on 18 September 1928 made the first rotary-wing aircraft crossing of the English Channel followed by an extensive tour of Europe. US industrialist Harold F. Pitcairn had in 1925 visited la Cierva in Spain upon learning of the successful flights of the Autogiro; in 1928 he visited la Cierva in England after taking a C.8 L.IV test flight piloted by Arthur H.C.A. Rawson and being particularly impressed with the Autogiro's safe vertical descent capability, purchased a C.8 L.IV with a Wright Whirlwind engine. Arriving in the United States on 11 December 1928 accompanied by Rawson, this Autogiro was redesignated C.8W. (Further editing of the following to continue) The Cierva "Autodynamic" rotor used drag hinges with offset axes to perform this to good effect with great simplicity, but the Pitcairn collective pitch control advanced the "jump" ability. The C-19 technology was licensed to a number of manufacturers, including Harold Pitcairn in the U.S. (in 1928) and Focke-Achgelis of Germany. In 1931 Amelia Earhart flew a Pitcairn PCA-2 to a then world altitude record of 18,415 feet (5613 m). In World War II, Germany pioneered a very small gyroglider "rotor-kite", the Focke-Achgelis Fa 330 "Bachstelze" (Water-wagtail), towed by submarines to provide aerial surveillance. It's reported that German gyro pilots were often forgotten in the heat of battle when the submarine dived suddenly. The Japanese also developed the Kayaba Ka-1 Autogyro for reconnaissance, artillery-spotting, and anti-submarine uses. The autogyro was resurrected post WW2 when Dr. Igor Bensen (a doctor of Divinity) saw a captured German U-Boat's gyroglider, and was fascinated by its characteristics. At work he was tasked with the analysis of the British "Rotachute" gyro glider designed by expatriate Austrian Raoul Hafner. This led him to adapt the design for his own purposes and eventually market the B-7. Post WW2 autogyros, such as the Bensen B-8M gyrocopter, generally use a pusher configuration for simplicity and to increase visibility for the pilot. For greater simplicity, they generally lack both variable-pitch rotors and powered rotors. It must be noted that Bensen autogyros and its derivatives have established an abysmal safety record due to their deficient stability and control characteristics greatly worsened by use of a teetering rotor, and their marketing as a build it yourself and teach yourself how to fly it aircraft. Three FAA-certified designs, Umbaugh U-18/Air and Space 18A of 1965, Avian 2-180 of 1967, and McCulloch J-2 or 1972 have for various reasons been commercial failures.

Bensen's design

The Bensen Gyrocopter™, the protoype of many post WW2 gyroplanes, actually consists of three versions, the B-6, B-7 and B-8. All three were designed in both unpowered and powered forms. The basic design is a simple frame of square aluminum or galvanized steel tubing, reinforced with triangles of lighter tubing. It is arranged so that the stress falls on the tubes, or special fittings, not the bolts. All welds or soldered structural joints should be inspected. The rotor is on the top of the vertical mast. The outlying fixed wheels are mounted on an axle (of tubing). The front-to-back keel (more tubing) mounts the forward wheel (which casters), seat, other tubes, engine and a vertical stabilizer. Some versions mount seaplane-style floats and successfully land and take off from water. It is common for the vertical stabilizer to drag on the ground unless it is cut away. This is also why many frames have a small wheel mounted on the back end of the keel. Many light gyroplane rotors are made from aluminum, though GRP-based composite blades (Sport Copter, Averso, Revolution, RAF eg) and GRP-skinned blades are increasing in number. Even aircraft-quality birch was specified in early Bensen designs, and a wood/steel composite is still used in the world speed record holding Wallis.

Flight Controls

There are only three flight controls: a control stick, rudder pedals and a throttle. Modern designs typically use a between-legs control stick instead, and the precession is handled by a mechanical linkage so that left and right stick motions are more intuitive than Bensen's simple design. Another control is a simple set of rudder pedals that move the hinged back half of the vertical stabilizer, similar to a rudder on a fixed wing aircraft. This lets the pilot keep the craft lined up in the desired direction of motion. The stabilizer is mounted behind the pusher propeller, so one can steer the craft on the ground and during takeoff. Some builders use a pushrod between the rudder bar and stabilizer. Others use cables. Some simple autogyros, including Bensen's G-6, do not use controllable-vertical stabilizers at all. They are fixed - this works for towed gyro gliders, but not for powered gyros. The throttle and choke are usually levers mounted where convenient- often under the seat. The rotor generates more lift on the leading side and less on the lagging side, and this causes the rotor to tilt backwards with forward airspeed (helicopters tilt their rotor in the opposite way as they use their rotor to drag the vehicle through the air, whereas an autogyros's blades are unpowered). This increases drag and has a lot to do with the relatively low top speed that Autogyros can reach.

Flight characteristics

Autogyros are often regarded by fixed-wing aircraft pilots as "dangerously unstable", which is certainly true when its pilot is, as is so often the case, self-taught with no professional flight instruction received whatsoever. Piloted properly, a certificated autogyro is significantly safer than any other type of aircraft because it cannot stall, since the rotor of a autogyro is always spinning. If translational airspeed becomes zero, the autogyro will descend vertically to the ground, rotor still spinning. Though safe for the pilot and passengers, landing from a vertical descent usually results in damage to the autogyro. One weakness in certain types of autogyro is pitch instability (pitch is the tilting up or down of the craft as viewed from the front or the back). Pitch instability can be a problem because autogyros lose rotor control authority in negative-G forces (positive-G forces push people into their seats; negative-G forces make people float out of them, such as driving over a hump back bridge at high speed in an automobile). Negative-G forces "unload the rotor" and rotor control authority is lost. A flying autogyro hangs from the rotor much like an object hung from a string. As long as the plane is hanging from the rotor, stability is maintained. The instant zero or negative-Gs are introduced, rotor speed begins to decay and the forces stabilizing the plane are lost. Negative-Gs can be caused by Pilot-Induced Oscillation, or PIO. PIO happens when a pilot adjusts his pitch too much too quickly, then makes a countering control input to bring the pitch back. The countering input often overcompensates, and the autogyro begins to buck like a bronco. You can see a similar effect when some learner-drivers are doing kangaroo-hops in a car with a stick shift and clutch. This is most likely at higher engine throttle settings. If the pilot continues to fight the plane, the rotor (which is flexible) can slow down due to the lack of positive G force, and can flop down and strike the spinning propeller, which destroys both and sends the autogyro into an uncontrolled fall. The way to avoid this during an incipient PIO is to apply gentle back pressure on the stick (to raise the nose in pitch) and cut engine power. Note that this is the exact opposite of what fixed-wing pilots are trained to do when in trouble, which has led to some unfortunate accidents and the autogyro's undeserved reputation for being "dangerous." Another danger is "bunting over" or a Power Push-Over (PPO). An autogyro's vertical airspeed (climb or sink rate) is directly coupled to airspeed. Increase forward airspeed, increase rate of climb. In order to maintain level flight at high engine throttle settings, the pilot must tilt the rotor forward to prevent climbing and maintain level flight. The rotor thus becomes more nearly horizontal, and the control stick becomes more sensitive. Too much forward stick, and the autogyro's rotor can aim down towards the ground. When this happens, negative-Gs occur, rotor speed drops too low to provide lift, and a high-thrustline autogyro is then pitched forward by the propeller thrust and tumbles end-over-end in a somersault. It is virtually impossible to regain control after a full PPO. Two factors can lead to pitch instability: no or too small horizontal stabilizers (h-stabs) on too short a tail and high thrustline propeller placement which destabilises the force diagram. A large h-stab, ideally in the prop wash (where the propeller blows on it) will reduce the tendency of an autogyro to bunt over as a result of improper control input by damping the control response. If the propeller thrustline in an autogyro is high -- meaning the axis of propeller power is above the center of gravity for the aircraft -- the autogyro tends to pitch forward under sudden power application (see PPOs above, as for why this is Bad). (Unfortunately, Bensen-type autogyros have a notably high thrustline.) If the thrustline is low, the autogyro tends to pitch up under sudden power application, which is harmless. It's difficult to have a low thrustline without a really tall autogyro (such as a "Dominator" style) however, so most autogyro designs simply try to get the thrustline as low as possible though still being slightly above the center of gravity. In spite of these dangers, most autogyros are designed to reduce them. Also, the majority of autogyro pilot training involves avoidance of PIO and PPOs. Autogyro rotors usually feature a teeter-hinge in the middle. Picture a autogyro or helicopter from above, rotor spinning clockwise. If the aircraft is flying forward, the rotor tips on the left are traveling faster than the aircraft, while those on the right are actually going backwards relative to the craft. If the rotor blades were fixed, this would produce uneven lift -- more lift on the left side, since those blades are traveling faster. The teeter hinge on each blade lets it "flap" up and down. As the blade swings on the left, the increased speed makes it flap up with a greater angle of attack to the relative wind. This increases drag and reduces lift. As it swings to the right, it's now going slower, relative to forward speed. This reduced drag lets it flap down and get a better bite into the air, increasing lift. Pitch is controlled by a conventional joystick coupled to the rotor. Pulling back on the stick tilts the rotor back, increasing lift and decreasing forward airspeed. Pushing forward on the stick decreases lift and increases airspeed, as long as it is not pushed much beyond horizontal (see PPO above). The plane's direction is controlled by rudder pedals.

Records and Application

As of 2002, Wing Commander Ken Wallis, an enthusiast who has built several gyroplanes, holds or has held most of the type's record performances. These include the speed record of 111.7mph (186km/h), and the straight-line distance record of 543.27 miles (905km). The record picture is continually changing, and on 16 November 2002, Ken Wallis increased the speed record to 207.7 km/h - and simultaneously set another world record as the oldest pilot to set a world record! See: [http://records.fai.org/pilot.asp?from=rotorcraft&id=335] Ken Wallis also built and flew one of the most famous autogyros - "Little Nellie" - in the James Bond movie "You Only Live Twice".
- Hours flown :Autogyros are often used to herd range animals. An autogyro 'cowboy' holds the world record for total hours in the air each week. The Bensen design has also been used by hobbyists, sight-seers and scientists (for game counting).
- Speed :The CarterCopter fixed wing/autogyro hybrid has been unofficially flown in tests at speeds above 170 mph. The claimed theoretical top speed for this general design is in excess of 450 mph. :In the late 1950s, the Fairey Rotodyne, another hybrid was capable of 213 mph. Andy Keech made a TransContinental flight from Kitty Hawk, N.C. to San Diego, Ca. in October 2003 and set 3 World Records. The 3 records are for 'speed over a recognised course', and are verified by tower personnel or by Official Observers of the U.S. National Aeronautic Association:
- Sub-class : E-3a (Autogyros : take-off weight less than 500 kg) :Category : General :Group 1 : piston engine
- Speed over a recognised course : 16.45 km/h, :::Date of flight: 12 October 2003 :::Pilot: Andrew C. KEECH (USA) :::Course/place: Kitty Hawk, NC (USA) - San Diego, CA (USA)
- Speed over a recognised course : 31.89 km/h :::Date of flight: 22 October 2003 :::Pilot: Andrew C. KEECH (USA) :::Course/place: San Diego, CA (USA) - Kitty Hawk, NC (USA)
- Speed over a recognised course, round trip : 16.42 km/h :::Date of flight: 22 October 2003 :::Pilot: Andrew C. KEECH (USA) :::Course/place: Kitty Hawk, NC (USA) - San Diego, CA (USA) and return

Kits

Many autogyros are assembled from kits. Kits with all parts, ready to assemble, are listed for US$19,550 as of 18th July 2002. This is extremely inexpensive for an aircraft. This includes an engine, the major expense. It can be reduced. Some people are clever at scrounging materials. However, scrounging increases one's construction time and program risk. Buying both the engine and rotor hub is recommended by most vendors. Some people who actually completed an autogyro have said that it took them about a year, working in their spare time. Careful estimates place most build times at 100 to 200 hours. Kit vendors often say that since it has relatively few parts, hobbyists can assemble it more rapidly and correctly than most fixed-wing kit aircraft. Kit vendors recommend working on it every day for an hour or two.

Warnings

Most vendors recommend that a new pilot have at least ten hours of instruction by a rated instructor in small fixed-wing aircraft, followed by at least two hours of instruction in a dual-place autogyro with an experienced instructor. An autogyro is more similar to a fixed-wing aircraft than to a helicopter. One must be able to land safely and reliably before attempting to fly any aircraft alone. Autogyros are relatively safe, but not foolproof. There were 19 fatal autogyro accidents reported to the FAA between 1996 and 2001. Autogyros are aircraft. Do not neglect safety precautions: training, instrumentation, flight rules, preflight checklists and periodic inspections and maintenance. In the United States private, recreational, and commercial pilot licenses with rotorcraft category and gyroplane class rating are issued, or the rating is added to an existing license for other aircraft; holders of sport pilot licenses can also qualify to fly autogyros. Requirements include completing required training times, passing written exams, and successfully doing oral and practical tests. Sport pilot license in-flight tests can be conducted in single-seat aircraft, but a "single place only" limitation is placed on the certificate in such cases. "Learning to fly the rotor" is a vital ingredient for safe flight in an autogyro - models and rotary kites can help the learning process, and towed gyro-gliders and boom-trainers are ideal tools for this as well as being cheap to build and fly.

Airship

1931]] An airship is a buoyant aircraft that can be steered and propelled through the air. Unlike aerodynamic aircraft which stay aloft by moving an airfoil through the air in order to produce lift, airships stay aloft primarily by means of a cavity (usually quite large) filled with a gas of lesser density than the surrounding atmosphere. Airships are also known as dirigibles from the French dirigeable, meaning "steerable". The term airship is sometimes informally used to mean a machine capable of atmospheric flight. The term zeppelin is a genericized trademark that originally referred to airships manufactured by the Zeppelin Company. In modern common usage, the terms zeppelin, dirigible and airship are used interchangeably for any type of rigid airship, with the terms blimp or airship alone used to describe non-rigid airships. In modern technical usage however, airship is the term used for all aircraft of this type with zeppelin referring only to aircraft of that manufacture and blimp referring only to non-rigid airships. In the early days of airships, the primary lifting gas was hydrogen. Until the 1950s, all airships, except for those in the United States continued to use hydrogen because it offered greater lift and was cheaper than helium. The United States (until then the sole producer) was also unwilling to export helium because of its rarity a

Commercial aviation

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Flight

Animal flight

In fiction

Mechanical flight

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Aircraft

Categories and classification

Heavier than air

Lighter than air

Types of aircraft

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Military aircraft

Civil aviation

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Aircraft

Categories and classification

Heavier than air

Lighter than air

Types of aircraft

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By usage

Military aircraft

Civil aviation

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Helicopter

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Generating lift

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On a ship

Hazards of helicopter flight

Helicopter models and identification

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Autogyro

General characteristics

History

Bensen's design

Flight Controls

Flight characteristics

Records and Application

Kits

Warnings

See also

Airship