Inertia is the resistance, of any physical object, to any change in its velocity. This includes changes to direction of motion. An aspect of this property is the tendency of objects to keep moving in a straight line at a constant speed, when no forces are upon them—and this aspect in particular is called inertia; the principle of inertia is one of the fundamental principles in classical physics that are still used today to describe the motion of objects and how they are affected by the applied forces on them. Inertia comes from the Latin word, meaning idle, sluggish. Inertia is one of the primary manifestations of mass, a quantitative property of physical systems. Isaac Newton defined inertia as his first law in his Philosophiæ Naturalis Principia Mathematica, which states: The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavours to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line.
In common usage, the term "inertia" may refer to an object's "amount of resistance to change in velocity", or sometimes to its momentum, depending on the context. The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his First Law of Motion: an object not subject to any net external force moves at a constant velocity. Thus, an object will continue moving at its current velocity until some force causes its speed or direction to change. On the surface of the Earth, inertia is masked by the effects of friction and air resistance, both of which tend to decrease the speed of moving objects, gravity; this misled the philosopher Aristotle to believe that objects would move only as long as force was applied to them:...it stops when the force, pushing the travelling object has no longer power to push it along... Prior to the Renaissance, the most accepted theory of motion in Western philosophy was based on Aristotle who around about 335 BC to 322 BC said that, in the absence of an external motive power, all objects would come to rest and that moving objects only continue to move so long as there is a power inducing them to do so.
Aristotle explained the continued motion of projectiles, which are separated from their projector, by the action of the surrounding medium, which continues to move the projectile in some way. Aristotle concluded. Despite its general acceptance, Aristotle's concept of motion was disputed on several occasions by notable philosophers over nearly two millennia. For example, Lucretius stated. In the 6th century, John Philoponus criticized the inconsistency between Aristotle's discussion of projectiles, where the medium keeps projectiles going, his discussion of the void, where the medium would hinder a body's motion. Philoponus proposed that motion was not maintained by the action of a surrounding medium, but by some property imparted to the object when it was set in motion. Although this was not the modern concept of inertia, for there was still the need for a power to keep a body in motion, it proved a fundamental step in that direction; this view was opposed by Averroes and by many scholastic philosophers who supported Aristotle.
However, this view did not go unchallenged in the Islamic world, where Philoponus did have several supporters who further developed his ideas. In the 11th century, Ibn Sina argued that a moving object has force, dissipated by external agents like air resistance. Ibn Sina made distinction between'force' and'inclination', he claimed that an object gained mayl when the object is in opposition to its natural motion. So he concluded that continuation of motion is attributed to the inclination, transferred to the object, that object will be in motion until the mayl is spent, he claimed that projectile in a vacuum would not stop unless it is acted upon. This conception of motion is consistent with Newton's first law of inertia. Which states that an object in motion will stay in motion unless it is acted on by an external force; this idea which dissented from the Aristotelian view was abandoned until it was described as "impetus" by John Buridan, influenced by Ibn Sina's Book of Healing. In the 14th century, Jean Buridan rejected the notion that a motion-generating property, which he named impetus, dissipated spontaneously.
Buridan's position was that a moving object would be arrested by the resistance of the air and the weight of the body which would oppose its impetus. Buridan maintained that impetus increased with speed. Despite the obvious similarities to more modern ideas of inertia, Buridan saw his theory as only a modification to Aristotle's basic philosophy, maintaining many other peripatetic views, including the belief that there was still a fundamental difference between an object in motion and an object at rest. Buridan believed that impetus could be not only linear, but circular in nature, causing objects to move in a circle. Buridan's thought was followed up by his pupil Albert of Saxony and the Oxford Calculators, who performed various experiments that further undermined the classical, Aristotelian view, their work in turn was elaborated by Nicole Oresme who pioneered the practice of demonstrating laws of motion in the form of graphs. Shortly before Galileo's theory of inertia, Giambattista Benedetti modified the growing theory of impetus to involve linear motion a
The Boeing Company is an American multinational corporation that designs and sells airplanes, rockets and missiles worldwide. The company provides leasing and product support services. Boeing is among the largest global aircraft manufacturers. Boeing stock is included in the Dow Jones Industrial Average. Boeing was founded by William Boeing on July 15, 1916, in Washington; the present corporation is the result of the merger of Boeing with McDonnell Douglas on August 1, 1997. Former Boeing's chair and CEO Philip M. Condit continued as the chair and CEO of the new Boeing, while Harry Stonecipher, former CEO of McDonnell Douglas, became the president and chief operating officer of the newly merged company; the Boeing Company has its corporate headquarters in Illinois. The company is led by CEO Dennis Muilenburg. Boeing is organized into five primary divisions: Boeing Commercial Airplanes. In 2017, Boeing recorded $93.3 billion in sales, ranked 24th on the Fortune magazine "Fortune 500" list, ranked 64th on the "Fortune Global 500" list, ranked 19th on the "World's Most Admired Companies" list.
In March 1910, William E. Boeing bought Heath's shipyard in Seattle on the Duwamish River, which became his first airplane factory. Boeing was incorporated in Seattle by William Boeing, on July 15, 1916, as "Pacific Aero Products Co". Boeing was incorporated in Delaware. Boeing, who studied at Yale University, worked in the timber industry, where he became wealthy and learned about wooden structures; this knowledge proved invaluable in his subsequent assembly of airplanes. The company stayed in Seattle to take advantage of the local supply of spruce wood. One of the two "B&W" seaplanes built with the assistance of George Conrad Westervelt, a U. S. Navy engineer, took its maiden flight on June 15, 1916. Boeing and Westervelt decided to build the B&W seaplane after having flown in a Curtiss aircraft. Boeing bought a Glenn Martin "Flying Birdcage" seaplane and was taught to fly by Glenn Martin himself. Boeing soon crashed the Birdcage and when Martin informed Boeing that replacement parts would not become available for months, Boeing realized he could build his own plane in that amount of time.
He and his friend Cdr. G. C. Westervelt soon produced the B&W Seaplane; this first Boeing airplane was assembled in a lakeside hangar located on the northeast shore of Seattle's Lake Union. Many of Boeing's early planes were seaplanes. On April 6, 1917, the U. S. declared war on Germany and entered World War I. On May 9, 1917, the company became the "Boeing Airplane Company". With the U. S. entering the war, Boeing knew that the U. S. Navy needed seaplanes for training. So Boeing shipped two new Model Cs to Pensacola, where the planes were flown for the Navy; the Navy ordered 50 more. The company moved its operations to a larger former shipbuilding facility known as Boeing Plant 1, located on the lower Duwamish River, Washington state; when World War I ended in 1918, a large surplus of cheap, used military planes flooded the commercial airplane market, preventing aircraft companies from selling any new airplanes, driving many out of business. Others, including Boeing, started selling other products. Boeing built dressers and furniture, along with flat-bottom boats called Sea Sleds.
In 1919 the Boeing B-1 flying boat made its first flight. It accommodated two passengers and some mail. Over the course of eight years, it made international airmail flights from Seattle to Victoria, British Columbia. On May 24, 1920, the Boeing Model 8 made its first flight, it was the first plane to fly over Mount Rainier. In 1923, Boeing entered competition against Curtiss to develop a pursuit fighter for the U. S. Army Air Service. Although Curtiss finished its design first and was awarded the contract, Boeing continued to develop its PW-9 fighter; that plane, along with the Boeing P-12/F4B fighter, made Boeing a leading manufacturer of fighters over the course of the next decade. In 1925, Boeing built its Model 40 mail plane for the U. S. government to use on airmail routes. In 1927, an improved version of this plane was built, the Model 40A which won the U. S. Post Office's contract to deliver mail between San Chicago; the 40A had a passenger cabin that accommodated two. That same year, Boeing created an airline named Boeing Air Transport, which merged a year with Pacific Air Transport and the Boeing Airplane Company.
The first airmail flight for the airline was on July 1, 1927. In 1929 the company merged with Pratt & Whitney, Hamilton Aero Manufacturing Company, Chance Vought under the new title United Aircraft and Transport Corporation; the merge was followed by the acquisition of the Sikorsky Manufacturing Corporation, Stearman Aircraft Corporation, Standard Metal Propeller Company. United Aircraft purchased National Air Transport in 1930. On July 27, 1928, the 12-passenger Boeing 80 biplane made its first flight. With three engines, it was Boeing's first plane built with the sole intention of being a passenger transport. An upgraded version, the 80A, carrying eighteen passengers, made its first flight in September 1929. In the early 1930s Boeing became a leader in all-metal aircraft construction, in the design revolution t
Aeronautics is the science or art involved with the study and manufacturing of air flight capable machines, the techniques of operating aircraft and rockets within the atmosphere. The British Royal Aeronautical Society identifies the aspects of "aeronautical Art and Engineering" and "the profession of Aeronautics." While the term referred to operating the aircraft, it has since been expanded to include technology and other aspects related to aircraft. The term "aviation" is sometimes used interchangeably with aeronautics, although "aeronautics" includes lighter-than-air craft such as airships, includes ballistic vehicles while "aviation" technically does not. A significant part of aeronautical science is a branch of dynamics called aerodynamics, which deals with the motion of air and the way that it interacts with objects in motion, such as an aircraft. Attempts to fly without any real aeronautical understanding have been made from the earliest times by constructing wings and jumping from a tower with crippling or lethal results.
Wiser investigators sought to gain some rational understanding through the study of bird flight. An early example appears in ancient Egyptian texts. Medieval Islamic scientists made such studies; the founders of modern aeronautics, Leonardo da Vinci in the Renaissance and Cayley in 1799, both began their investigations with studies of bird flight. Man-carrying kites are believed to have been used extensively in ancient China. In 1282 the European explorer Marco Polo described the Chinese techniques current; the Chinese constructed small hot air balloons, or lanterns, rotary-wing toys. An early European to provide any scientific discussion of flight was Roger Bacon, who described principles of operation for the lighter-than-air balloon and the flapping-wing ornithopter, which he envisaged would be constructed in the future; the lifting medium for his balloon would be an "aether". In the late fifteenth century, Leonardo da Vinci followed up his study of birds with designs for some of the earliest flying machines, including the flapping-wing ornithopter and the rotating-wing helicopter.
Although his designs were rational, they were not based on good science. Many of his designs, such as a four-person screw-type helicopter, have severe flaws, he did at least understand that "An object offers as much resistance to the air as the air does to the object." His analysis led to the realisation that manpower alone was not sufficient for sustained flight, his designs included a mechanical power source such as a spring. Da Vinci's work was lost after his death and did not reappear until it had been overtaken by the work of George Cayley; the modern era of lighter-than-air flight began early in the 17th century with Galileo's experiments in which he showed that air has weight. Around 1650 Cyrano de Bergerac wrote some fantasy novels in which he described the principle of ascent using a substance he supposed to be lighter than air, descending by releasing a controlled amount of the substance. Francesco Lana de Terzi measured the pressure of air at sea level and in 1670 proposed the first scientifically credible lifting medium in the form of hollow metal spheres from which all the air had been pumped out.
These would be able to lift an airship. His proposed methods of controlling height are still in use today. In practice de Terzi's spheres would have collapsed under air pressure, further developments had to wait for more practicable lifting gases. From the mid-18th century the Montgolfier brothers in France began experimenting with balloons, their balloons were made of paper, early experiments using steam as the lifting gas were short-lived due to its effect on the paper as it condensed. Mistaking smoke for a kind of steam, they began filling their balloons with hot smoky air which they called "electric smoke" and, despite not understanding the principles at work, made some successful launches and in 1783 were invited to give a demonstration to the French Académie des Sciences. Meanwhile, the discovery of hydrogen led Joseph Black in c. 1780 to propose its use as a lifting gas, though practical demonstration awaited a gas tight balloon material. On hearing of the Montgolfier Brothers' invitation, the French Academy member Jacques Charles offered a similar demonstration of a hydrogen balloon.
Charles and two craftsmen, the Robert brothers, developed a gas tight material of rubberised silk for the envelope. The hydrogen gas was to be generated by chemical reaction during the filling process; the Montgolfier designs had several shortcomings, not least the need for dry weather and a tendency for sparks from the fire to set light to the paper balloon. The manned design had a gallery around the base of the balloon rather than the hanging basket of the first, unmanned design, which brought the paper closer to the fire. On their free flight, De Rozier and d'Arlandes took buckets of water and sponges to douse these fires as they arose. On the other hand, the manned design of Charles was modern; as a result of these exploits, the hot-air balloon became known as the Montgolfière type and the hydrogen balloon the Charlière. Charles and the Robert brothers' next balloon, La Caroline, was a Charlière that followed Jean Baptiste Meusnier's proposals for an elongated dirigible balloon, was notable for having an outer envelope with the gas contained in a second, inner ballonet.
On 19 September 1784, it completed the first flight of over 100 km, between Pa
The cruciform tail is an aircraft empennage configuration which, when viewed from the aircraft's front or rear, looks much like a cross. The usual arrangement is to have the horizontal stabilizer intersect the vertical tail somewhere near the middle, above the top of the fuselage; the design is used to locate the horizontal stabilizer away from jet exhaust and wing wake, as well as to provide undisturbed airflow to the rudder. Avro Canada CF-100 Canuck British Aerospace Jetstream 31/32 British Aerospace Jetstream 41 Britten-Norman Trislander Canadair CL-215 Cessna A-37 Dragonfly Cessna Citation - Excel and Latitude variants only Cessna T303 Crusader Cessna T-37 Tweet Consolidated PBY Catalina Dassault Falcon 10/100 Dassault Falcon 20/200 Dassault Falcon 50 Dassault Falcon 5X Dassault Falcon 7X Dassault Falcon 8X Dassault Falcon 900 Dassault Falcon 2000 de Havilland Canada DHC-3 Otter Dornier Do 335 Douglas A-4 Skyhawk Fairchild C-26 Metroliner Fairchild Swearingen Metroliner Gloster Meteor Handley Page Jetstream Hawker Hunter Ivanov ZJ-Viera Lake Buccaneer Lockheed JetStar McDonnell FH Phantom McDonnell F2H Banshee - early variants only Messerschmitt 262 Mikoyan-Gurevich MiG-15 Northrop YC-125 Raider Piccard Eureka PZL Bielsko SZD-50 Puchacz Republic F-84 Thunderjet Republic F-84F Thunderstreak/RF-84F Thunderflash Republic XF-84H Thunderscreech Roberts Cygnet Rockwell B-1 Lancer Rockwell Commander 112/114 Scaled Composites White Knight Two Stratos 714 Sud Aviation Caravelle Swearingen Merlin US Aviation Cumulus Westland Whirlwind Pelikan tail T-tail Twin tail V-tail
Northrop P-61 Black Widow
The Northrop P-61 Black Widow, named for the American spider, was the first operational U. S. warplane designed as a night fighter, the first aircraft designed to use radar. The P-61 had a crew of three: pilot and radar operator, it was armed with four 20 mm Hispano M2 forward-firing cannon mounted in the lower fuselage, four.50 in M2 Browning machine guns mounted in a remote-controlled dorsal gun turret. It was an all-metal, twin-engine, twin-boom design developed during World War II; the first test flight was made on May 26, 1942, with the first production aircraft rolling off the assembly line in October 1943. The last aircraft was retired from government service in 1954. Although not produced in the large numbers of its contemporaries, the Black Widow was operated as a night-fighter by United States Army Air Forces squadrons in the European Theater, Pacific Theater, China Burma India Theater, Mediterranean Theater during World War II, it replaced earlier British-designed night-fighter aircraft, updated to incorporate radar when it became available.
After the war, the P-61—redesignated the F-61—served in the United States Air Force as a long-range, all-weather, day/night interceptor for Air Defense Command until 1948, Fifth Air Force until 1950. On the night of 14 August 1945, a P-61B of the 548th Night Fight Squadron named Lady in the Dark was unofficially credited with the last Allied air victory before VJ Day; the P-61 was modified to create the F-15 Reporter photo-reconnaissance aircraft for the United States Army Air Forces and subsequently used by the United States Air Force. In August 1940, 16 months before the United States entered the war, the U. S. Air Officer in London, Lieutenant General Delos C. Emmons, was briefed on British research in radar, underway since 1935 and had played an important role in the nation's defense against the Luftwaffe during the Battle of Britain. General Emmons was informed of the new Airborne Intercept radar, a self-contained unit that could be installed in an aircraft and allow it to operate independently of ground stations.
In September 1940, the Tizard Mission traded British research, including the cavity magnetron that would make self-contained interception radar installations practicable, for American production. The British Purchasing Commission evaluating US aircraft declared their urgent need for a high-altitude, high-speed aircraft to intercept the Luftwaffe bombers attacking London at night; the aircraft would need to patrol continuously over the city throughout the night, requiring at least an eight-hour loiter capability. The aircraft would carry one of the early AI radar units, mount its specified armament in "multiple-gun turrets"; the British conveyed the requirements for a new fighter to all the aircraft designers and manufacturers they were working with. Jack Northrop was among them, he realized that the speed, fuel load and multiple-turret requirements demanded a large aircraft with multiple engines. General Emmons returned to the U. S. with details of the British night-fighter requirements, in his report said that the design departments of the Americans' aviation industry's firms could produce such an aircraft.
The Emmons Board developed basic requirements and specifications, handing them over towards the end of 1940 to Air Technical Service Command at Wright Field, Ohio. After considering the two biggest challenges—the high weight of the AI radar and the long loiter time of eight hours minimum—the board, including Jack Northrop, realized the aircraft would need the considerable power and resulting size of twin engines, recommended such parameters; the United States had two twin-row radials of at least 46 liters displacement in development since the late 1930s. These engines had been airborne for their initial flight tests by the 1940/41 timeframe, were each capable, with more development, of exceeding 2,000 hp. Vladimir H. Pavlecka, Northrop Chief of Research, was present on unrelated business at Wright Field. On 21 October 1940, Colonel Laurence Craigie of the ATSC phoned Pavlecka, explaining the U. S. Army Air Corps' specifications, but told him to "not take any notes,'Just try and keep this in your memory!'"
What Pavlecka did not learn was radar's part in the aircraft. The mission, Craigie explained, was "the interception and destruction of hostile aircraft in flight during periods of darkness or under conditions of poor visibility." Pavlecka met with Jack Northrop the next day, gave him the USAAC specification. Northrop compared his notes with those of Pavlecka, saw the similarity between the USAAC's requirements and those issued by the RAF, pulled out the work he had been doing on the British aircraft's requirements, he was a month along, a week Northrop pounced on the USAAC proposal. On 5 November and Pavlecka met at Wright Field with Air Material Command officers and presented them with Northrop's preliminary design. Douglas' XA-26A night fighter proposal was the only competition, but Northrop's design was selected and the Black Widow was conceived. Following the USAAC acceptance, Northrop began comprehensive design work on the aircraft to become the first to design a dedicated night fighter.
The result was the largest and one of the deadliest pursuit-class aircraft flown by the U. S. during the war. Jack Northrop's first proposal was a long fuselage gondola between two engine nacelles and tail booms. Engines were Pratt & Whitney
An aircraft canopy is the transparent enclosure over the cockpit of some types of aircraft. An aircraft canopy provides a controlled and sometimes pressurized environment for the aircraft's occupants, allows for a greater field of view over a traditional flight deck. A canopy's shape is a compromise designed to minimize aerodynamic drag, while maximizing visibility for pilots and other crewmembers. Early aircraft had no canopies at all; the pilots were exposed to the weather, although most flying was done in good weather. Through World War I most aircraft had no canopy, although they had a small windshield to deflect the prop wash and wind from hitting the pilot in the face. In the 1920s and 1930s, the increasing speed and altitude of airplanes necessitated a enclosed cockpit and canopies became more common. Early canopies were made of numerous pieces of flat glass held in position by muntins; the muntins reduced visibility, problematic for military aircraft. Glass canopies were much heavier than acrylic canopies, which were first introduced shortly before World War II.
The acrylic bubble canopy was used on aircraft such as the Supermarine Spitfire and Westland Whirlwind, which gave better all-round visibility and reduced weight. It is still being used today on most fighter aircraft. In the 1970s, US aviation artist Keith Ferris invented a false canopy to paint on the underside of military aircraft, directly underneath the front of the plane, the purpose of, to confuse an enemy so they do not know in what direction the aircraft is headed; this ruse was inspired by animals and fishes that have similar markings on the head and tail, so they can confuse other creatures. Pilots remain skeptical of this feature, asserting that if the enemy is close enough to see the marking, they are too close to be fooled by it. On many high-performance military aircraft, the canopy is an integral part of the ejection seat system; the pilot cannot be ejected from the aircraft until the canopy is no longer in the path of the ejection seat. In most ejection seat equipped aircraft, the canopy is blown upwards and rearwards by explosive charges.
The relative wind blows the canopy away from the ejection path. However, on some aircraft, such as the McDonnell Douglas AV-8B Harrier II, the pilot may be forced to eject when in a hover, or when going too slow for the relative wind to move the canopy out of the path of the ejection seat. In that situation, the pilot could impact the canopy when ejecting. To overcome that possibility, some aircraft have a thin cord of plastic explosive zig-zagging across the canopy over the pilot's head. In the event of an ejection, the explosive cord is activated first; the ejection seat and pilot is launched through the shattered canopy. Most modern acrylic canopies are vacuum formed. A sheet of acrylic is secured to a female mould the entire assembly is heated in an oven until the acrylic is pliable; the air is removed from the mould and the acrylic sheet is drawn into it, forming the shape of the canopy. The acrylic is trimmed to the appropriate shape and attached to an aluminum or composite frame; some one-off canopies are made in a similar fashion, but since a mould would be too time-consuming to make, the acrylic is heated and vacuum formed until it approximates the shape the builder is seeking.
This type of construction is less precise and each canopy is unique. If multiple canopies will be needed, a mould is always used. Have Glass is the code name for a series of RCS reduction measures for the F-16 fighter, its primary aspect is the addition of an indium-tin-oxide layer to the gold tinted cockpit canopy, reflective to radar frequencies. An ordinary canopy would let radar signals straight through where they would strike the many edges and corners inside and bounce back to the radar source, the reflective layer dissipates these signals instead. Overall, Have Glass reduces an F-16's RCS by some 15 percent; the gold tint reduces glare from the sun to improve the pilot's visibility. The Malcolm Hood is a type of aircraft canopy developed for the Supermarine Spitfire, its concept proved valuable for other aircraft such as the North American Aviation-produced P-51B & C Mustangs as retrofit items, standard on versions of the Vought F4U Corsair, somewhat emulated on the models of the Luftwaffe's Focke-Wulf Fw 190 fighter.
The canopy was manufactured by the British company R Co which gave its name. Instead of taking a straight line between the canopy frames, the hood was bulged outward; this gave the pilot a better view to the rear....the Corsair's initial deficiencies were being worked out on a concurrent basis... The 689th production F4U-1 featured a number of significant changes; the most noticeable was that the cockpit was raised 18 centimeters to improve the pilot's forward view, a bulged canopy, along the lines of the "Malcolm Hood" used on Spitfires, replaced the original "birdcage" framed canopy to provide better all-round field of view. Bubble canopy
In aeronautics, a spoiler is a device intended to intentionally reduce the lift component of an airfoil in a controlled way. Most spoilers are plates on the top surface of a wing that can be extended upward into the airflow to spoil it. By so doing, the spoiler creates a controlled stall over the portion of the wing behind it reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag without affecting lift, while spoilers reduce lift as well as increasing drag. Spoilers fall into two categories: those that are deployed at controlled angles during flight to increase descent rate or control roll, those that are deployed on landing to reduce lift and increase drag. In modern fly-by-wire aircraft, the same set of control surfaces serve both functions. Spoilers are used by nearly every glider to control their rate of descent and thus achieve a controlled landing. An increased rate of descent can be achieved by lowering the nose of an aircraft, but this would result in increased speed.
Spoilers enable the approach to be made at a safe speed for landing. Airliners are always fitted with spoilers. Spoilers are used to increase descent rate without increasing speed, their use is limited, however, as the turbulent airflow that develops behind them causes noise and vibration, which may cause discomfort to passengers. Spoilers may be differentially operated for roll control instead of ailerons. On landing, the spoilers are nearly always deployed to help slow the aircraft; the increase in form drag created by the spoilers directly assists the braking effect. However, the real gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with less tendency to skid. In air-cooled piston engine aircraft, spoilers may be needed to avoid shock cooling the engines. In a descent without spoilers, air speed is increased and the engine will be at low power, producing less heat than normal.
The engine may cool too resulting in stuck valves, cracked cylinders or other problems. Spoilers alleviate the situation by allowing the aircraft to descend at a desired rate while letting the engine run at a power setting that keeps it from cooling too quickly. Spoiler controls can be used for descent control; some aircraft use spoilers in combination with or in lieu of ailerons for roll control to reduce adverse yaw when rudder input is limited by higher speeds. For such spoilers the term spoileron has been coined. In the case of a spoileron, in order for it to be used as a control surface, it is raised on one wing only, thus decreasing lift and increasing drag, causing roll and yaw. Spoilerons avoid the problem of control reversal that affects ailerons. All modern jet airliners are fitted with inboard lift spoilers which are used together during descent to increase the rate of descent and control speed; some aircraft use lift spoilers on landing approach to control descent without changing the aircraft's attitude.
One jet airliner not fitted with lift spoilers was the Douglas DC-8 which used reverse thrust in flight on the two inboard engines to control descent speed. The Lockheed Tristar was fitted with a system called Direct Lift Control using the spoilers on landing approach to control descent. Airbus aircraft with fly-by-wire control utilise wide-span spoilers for descent control, gust alleviation, lift dumpers. On landing approach, the full width of spoilers can be seen controlling the aircraft's descent rate and bank. Lift dumpers are a special type of spoiler extending along much of the wing's length and designed to dump as much lift as possible on landing. Lift dumpers have only two positions and retracted. Lift dumpers have three main functions: putting most of the weight of the aircraft on the wheels for maximum braking effect, increasing form drag, preventing aircraft'bounce' on landing. Lift dumpers are always deployed automatically on touch down; the flight deck control has three positions: off and manual.
On landing approach'automatic' is selected and, at the moment of touchdown, lift dumpers are deployed in a fraction of a second, with flight control spoilers being raised automatically as additional lift dumpers. All modern jet aircraft are fitted with lift dumpers; the British Aerospace 146 is fitted with wide span spoilers to generate additional drag and make reverse thrust unnecessary. A number of accidents have been caused either by inadvertently deploying lift dumpers on landing approach, or forgetting to set them to'automatic'. Air Canada Flight 621 – Premature deployment of the spoilers at low altitude contributed to this crash in Toronto on 5 July 1970. United Airlines Flight 553 – Forgetting to deactivate the spoilers contributed to crash at Chicago Midway International Airport on 8 December 1972. Loftleiðir Icelandic Airlines Flight 509 – Deployment of lift dumpers while attempting to arm them 40 feet above the runway caused this accident at John F Kennedy International Airport on 23 June 1973.
American Airlines Flight 965 – Forgetting to deactivate the spoilers while climbing to avoid a mountain contributed to this crash on 20 December 1995. American Airlines Flight 1420 – Forgetting to deploy the s