http://www.batechnics.com/ Brussels Airlines, Technics en http://blogs.law.harvard.edu/tech/rss GuppY v4.6.3 info@batechnics.com (webmaster) info@batechnics.com (webmaster) http://www.batechnics.com/articles.php?lng=en&pg=713 http://www.batechnics.com/articles.php?lng=en&pg=713 Documentary:Youtube.com, 25 min documentary about ejector seats can be found HERE  Introduction:It's important for many types of aircraft to have an ejection seat in case the plane is damaged in battle or during testing and the pilot has to bail out to save his or her life. Ejection seats are one of the most complex pieces of equipment on any aircraft, and some consist of thousands of parts. The purpose of the ejection seat is simple: To lift the pilot straight out of the aircraft to a safe distance, then deploy a parachute to allow the pilot to land safely on the ground.  An ejection seat being removed from an F-15C EagleTo understand how an ejection seat works, you must first be familiar with the basic components in any ejection system. Everything has to perform properly in a split second and in a specific sequence to save a pilot's life. If just one piece of critical equipment malfunctions, it could be fatal. Ejection seats are placed into the cockpit and usually attach to rails via a set of rollers on the edges of the seat. During an ejection, these rails guide the seat out of the aircraft at a predetermined angle of ascent. Like any seat, the ejection seat's basic anatomy consists of the bucket, back and headrest. Everything else is built around these main components. Here are key devices of an ejection seat:  Catapult  Rocket  Restraints Parachute  In the event of an ejection, the catapult fires the seat up the rails, the rocket fires to propel the seat higher and the parachute opens to allow for a safe landing. In some models, the rocket and catapult are combined into one device. These seats also double as restraint systems for the crewmembers both during an ejection and during normal operation.  Ejection seats are just one part of a larger system called the assisted egress system. "Egress" means "a way out" or "exit." Another part of the overall egress system is the plane's canopy, which has to be jettisoned prior to the ejection seat being launched from the aircraft. Not all planes have canopies. Those that don't will have escape hatches built into the roof of the plane. These hatches blow just before the ejection seat is activated, giving crewmembers an escape portal.  A pilot prepares to pull down the face curtain that will launch the ejection seat up the track of the ejection-seat trainer.Seats are activated through different methods. Some have pull handles on the sides or in the middle of the seat. Others are activated when a crew member pulls a face curtain down to cover and protect his or her face. In the next section, you will find out what happens once the seat is activated.   Bailing OutWhen a crewmember lifts the pull handle or yanks the face curtain down on the ejection seat, it sets off a chain of events that propels the canopy away from the plane and thrusts the crewmember safely out. Ejecting from a plane takes no more than four seconds from the time the ejection handle is pulled. The exact amount of time depends on the seat model and the crewmember's body weight. This ACES II ejection seat has a middle pull handle used to activate the ejection sequence.Pulling the ejection handle on a seat sets off an explosive cartridge in the catapult gun, launching the ejection seat into the air. As the seat rides up the guide rails, a leg-restraint system is activated. These leg restraints are designed to protect the crewmember's legs from getting caught or harmed by debris during the ejection. An underseat rocket motor provides the force that lifts the crewmember to a safe height, and this force is not outside normal human physiological limitations, according to documents from Goodrich Corporation, a manufacturer of ejection seats used by the U.S. military and NASA.  Prior to the ejection system launching, the canopy has to be jettisoned to allow the crewmember to escape the cockpit. There are at least three ways that the canopy or ceiling of the airplane can be blown to allow the crewmember to escape:  Lifting the canopy - Bolts that are filled with an explosive charge are detonated, detaching the canopy from the aircraft. Small rocket thrusters attached on the forward lip of the canopy push the transparency out of the way of the ejection path, according to Martin Herker, a former physics teacher who has written about ejection seats and maintains a Web site describing ejection seats. (Click here to go to Herker's site.)  Shattering the canopy - To avoid the possibility of a crewmember colliding with a canopy during ejection, some egress systems are designed to shatter the canopy with an explosive. This is done by installing a detonating cord or an explosive charge around or across the canopy. When it explodes, the fragments of the canopy are moved out of the crewmember's path by the slipstream.  Explosive hatches - Planes without canopies will have an explosive hatch. Explosive bolts are used to blow the hatch during an ejection. The seat, parachute and survival pack are also ejected from the plane along with the crewmember. Many seats, like Goodrich's ACES II (Advanced Concept Ejection Seat, Model II), have a rocket motor fixed underneath the seat. After the seat and crewmember have cleared the cockpit, this rocket will lift the crewmember another 100 to 200 feet (30.5 to 61 m), depending on the crewmember's weight. This added propulsion allows the crewmember to clear the tail of the plane. As of January 1998, there had been 463 ejections worldwide using the ACES II system, according to the U.S. Air Force. More than 90 percent of those ejections were successful. There were 42 fatalities.  The parachutes opening on a Martin-Baker ejection seat during a test. The small parachute at the top is called the drogue parachute.Once out of the plane, a drogue gun in the seat fires a metal slug that pulls a small parachute, called a drogue parachute, out of the top of the chair. This slows the person's rate of descent and stabilizes the seat's altitude and trajectory. After a specified amount of time, an altitude sensor causes the drogue parachute to pull the main parachute from the pilot's chute pack. At this point, a seat-man-separator motor fires and the seat falls away from the crewmember. The person then falls back to Earth as with any parachute landing. Modes of EjectionIn the ACES II ejection seat produced by Goodrich Corporation, there are three possible ejection modes. The one used is determined by the aircraft's altitude and airspeed at the time of ejection. These two parameters are measured by the environmental sensor and recovery sequencer in the back of the ejection seat. The environmental sensor senses the airspeed and altitude of the seat and sends data to the recovery sequencer. When the ejection sequence begins, the seat travels up the guide rails and exposes pitot tubes. Pitot tubes, named for physicist Henri Pitot, are designed to measure air-pressure differences to determine the velocity of the air. Data about the air flow is sent to the sequencer, which then selects from the three modes of ejections: Mode 1: low altitude, low speed - Mode 1 is for ejections at speeds of less than 250 knots (288 mph / 463 kph) and altitudes of less than 15,000 feet (4,572 meters). The drogue parachute doesn't deploy in mode 1. Mode 2: low altitude, high speed - Mode 2 is for ejections at speeds of more than 250 knots and altitudes of less than 15,000 feet. Mode 3: high altitude, any speed - Mode 3 is selected for any ejection at an altitude greater than 15,000 feet.  Physics of Ejecting Ejecting from an airplane is a violent sequence of events that places the human body under an extreme amount of force. The primary factors involved in an aircraft ejection are the force and acceleration of the crewmember, according to Martin Herker, a former physics teacher. To determine the force exerted on the person being ejected, we have to look at Newton's second law of motion, which states that the acceleration of an object depends on the force acting upon it and the mass of the object.   An ejection seat is test-fired at NASA to analyze the seat's ability to perform a zero-altitude, zero-velocity ejection.Newton's second law is represented as:  Force = Mass x Acceleration(F=MA)Regarding a crewmember ejecting from a plane, M equals his or her body mass plus the mass of the seat. A is equal to the acceleration created by the catapult and the underseat rocket. Acceleration is measured in terms of G, or gravity forces. Ejecting from an aircraft is in the 5-G to 20-G range, depending on the type of ejection seat. As mentioned in the introduction, 1 G is equal to the force of Earth's gravity and determines how much we weigh. One G of acceleration is equal to 32 feet/second2 (9.8 m/s2). This means that if you drop something off of a cliff, it will fall at a rate of 32 feet/second2. It's simple to determine the mass of the seat and the equipment attached to the seat. The pilot's mass is the largest variable. A 180-pound person normally feels 180 pounds of force being applied to him when standing still. In a 20-G impact, that same 180-pound person will feel 3,600 pounds of force being exerted.  "To determine the speed of the [ejection] seat at any point in time, one solves the Newton equation knowing the force applied and the mass of the seat/occupant system. The only other factors that are needed are the time of the force to be applied and the initial velocity present (if any)," writes Herker on his Web site describing the physics for understanding ejections. Herker provides this equation for determining the speed of the seat:   Speed = Acceleration x Time + Initial speedV(f) = AT + V(i)Initial speed refers to either the climb or the sink rate of the aircraft. It may also be determined by the initial step of the ejection process in a seat that combines an explosive catapult and an underseat rocket. The seat speed must be high enough to allow separation of the seat and person from the aircraft as quickly as possible in order to clear the entire aircraft.  The use of an ejection seat is always a last resort when an aircraft is damaged and the pilot has lost control. However, saving the lives of pilots is a higher priority than saving planes, and sometimes an ejection is required in order to save a life. http://www.batechnics.com/articles.php?lng=en&pg=700 http://www.batechnics.com/articles.php?lng=en&pg=700 Empennage is an aviation term used to describe the tail portion of an aircraft. ("Empennage", "tail", and "tail assembly" may be interchangeably used.) The empennage gives stability to the aircraft and controls the flight dynamics: pitch and yaw. In simple terms the empennage may be compared to the feathers of an arrow, colloquially; "Tail Feathers"Structurally, the empennage consists of the entire tail assembly, including the fin, tailplane and the part of the fuselage to which these are attached. On an airliner this would be everything behind the rear pressure bulkhead.The front, usually fixed section of the tailplane is called the horizontal stabilizer and is used to balance and share lifting loads of the mainplane dependant on centre of gravity considerations by limiting oscillations in pitch. The rear section is called the elevator and is usually hinged to the horizontal stabilizer. The elevator is a movable airfoil that controls changes in pitch, the up-and-down motion of the aircraft's nose.On some aircraft, the horizontal stabilizer and elevator are combined into one movable unit called the stabilator or sometimes "flying tail". In all cases some arrangement is made for the provision of trim to allow minor adjustment of airflow over the control surface and to unload the pilot from the need to maintain constant pressure on the elevator control. The trim may take the form of trim tabs on the rear of the elevators which act to force the elevator in the desired direction, or the stabilizer may be hinged at its trailing edge, forward of the elevator and adjustably jacked a few degrees in incidence either up or down. Early aircraft had a spring in the control circuit which provided an adjustable preload in the desired direction.The vertical tail structure, or fin, also has a fixed front section called the vertical stabilizer, used to prevent the aircraft from yawing from side to side. The rear section of the vertical fin is the rudder, a movable airfoil that is used to turn the aircraft in combination with the ailerons.Occasionally the horizontal stabilizer may carry more than one fin and rudder (Avro Lancaster, Lockheed Constellation) or the stabilizer and fin may be combined into a "V" shaped structure (Ruddervators) with each of the angled airfoils performing both functions (Beechcraft Bonanza 35, Fouga Magister). Frequently the horizontal stabilizer is mounted atop the fin (Boeing 727, Piper Tomahawk) Additional fin area may be added to aircraft fitted with floats (seaplanes) usually beneath the horizontal stabilizer (ventral fin) and sometimes at the stabilizer extremities.Multi engined and some light aircraft also include trim tabs on the rudder when asymmetric forces would impose unusual loads on the pilot's rudder controls.  http://www.batechnics.com/articles.php?lng=en&pg=699 http://www.batechnics.com/articles.php?lng=en&pg=699 The fuselage (from the French fuselé "spindle-shaped") is an aircraft's main body section that holds crew and passengers or cargo. In single engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage. The fuselage also serves to position control and stabilization surfaces in specific relationships to lifting surfaces, required for aircraft stability and maneuverability. The structural elements resemble those of a bridge, with emphasis on using linked triangular elements. The aerodyamic shape is completed by additional elements called formers and stringers and is then covered with fabric and painted. Most early aircraft used this technique with wood and wire trusses and this type of structure is still in use in many lightweight aircraft using welded steel tube trusses. This method is especially suitable for amateur-built aircraft kits, where a complete welded truss structure is delivered with the fitting of other components, covering, and finishing completed by the user, as it ensures that a robust, uniform load bearing structure is within the completed aircraft.Geodesic construction structural elements were used by Barnes Wallis for British Vickers between the wars and into World War II to form the whole of the fuselage, including its aerodynamic shape. In this type of construction multiple flat strip stringers are wound about the formers in opposite spiral directions, forming a basket-like appearance. This proved to be light, strong, and rigid and had the advantage of being made almost entirely of wood. The structure is also redundant and so can survive localized damage without catastrophic failure. A fabric covering over the structure completed the aerodynamic shell. The logical evolution of this is the creation of fuselages using molded plywood, in which multiple sheets are laid with the grain in differing directions to give the monocoque type below. The exterior surface of the fuselage is also the primary structure. A typical early form of this was built using moulded plywood, where the layers of plywood are formed over a "plug" or within a mold, A later form of this structure uses fiberglass cloth impregnated with polyester or epoxy resin. A simple form of this used in some amateur-built aircraft uses rigid expanded foam plastic with a fiberglass covering, eliminating the necessity of fabricating molds, but requiring more effort in finishing. An example of a moulded plywood aircraft is the de Havilland Mosquito fighter/light bomber of World War II. The use of molded fiberglass using negative molds (which give a nearly finished product) is prevalent in the series production of many modern sailplanes. The use of molded composites for fuselage structures is being extended to large passenger aircraft such as the Boeing 787 Dreamliner.Semi Monocoque  is the preferred method of constructing an all-aluminum fuselage. First, a series of frames in the shape of the fuselage cross sections are held in position on a rigid fixture. These frames are then joined with lightweight longitudinal elements called stringers. These are in turn covered with a skin of sheet aluminum, attached by riveting or by bonding with special adhesives. The fixture is then disassembled and removed from the fuselage, which is then fitted out with wiring, controls, and interior equipment such as seats and luggage bins. Most modern large aircraft are built using this technique, but use several large sections constructed in this fashion which are then joined with fasteners to form the complete fuselage. As the accuracy of the final product is determined largely by the costly fixture, this form is suitable for series production, where a large number of identical aircraft are to be produced. Early examples of this type include the Douglas Aircraft DC-2 and DC-3 civil aircraft and the Boeing B-17 Flying Fortress.Both monocoque and semi-monocoque are referred to as "stressed skin" structures as all or a portion of the load is taken by the surface covering. http://www.batechnics.com/articles.php?lng=en&pg=697 http://www.batechnics.com/articles.php?lng=en&pg=697 A vortex generator is an aerodynamic surface, consisting of a small vane that creates a vortex. They can be found in many devices, but the term is most often used in aircraft design.Vortex generators are added to the leading edge of a swept wing in order to maintain steady airflow over the control surfaces at the rear of the wing. They are typically rectangular or triangular, tall enough to protrude above the boundary layer, and run in spanwise lines near the thickest part of the wing. They can be seen on the wings and vertical tails of many airliners. Vortex generators are positioned in such a way that they have an angle of attack with respect to the local airflow.A vortex generator creates a tip vortex which draws energetic, rapidly-moving air from outside the slow-moving boundary layer into contact with the aircraft skin. The boundary layer normally thickens as it moves along the aircraft surface, reducing the effectiveness of trailing-edge control surfaces; vortex generators can be used to remedy this problem, among others, by re-energizing the boundary layer. Vortex generators delay flow separation and aerodynamic stalling; they improve the effectiveness of control surfaces (e.g Embraer 170 and Symphony SA-160); and, for swept-wing transonic designs, they alleviate potential shock-stall problems (e.g. Harrier, Blackburn Buccaneer, Gloster Javelin).Many aircraft carry vane vortex generators from time of manufacture, but there are also after-market suppliers who sell VG kits to improve the STOL performance of some light aircraft. http://www.batechnics.com/articles.php?lng=en&pg=696 http://www.batechnics.com/articles.php?lng=en&pg=696 Spoiler In aeronautics (sometimes called a lift dumper) is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the smooth airflow and spoiling it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag while making little change to lift, while spoilers greatly reduce lift while making only a moderate increase in drag.Spoilers are used by gliders to control their rate of descent, and thus achieve a controlled landing at a desired spot. Spoilers are necessary because while an increased rate of descent can be achieved by angling the nose of an aircraft downwards, this may result in a significant increase in speed, possibly exceeding safe limits.Airliners too are usually fitted with spoilers. Spoilers are sometimes used when descending from cruise altitudes, to assist the aircraft in descending to lower altitudes without picking up speed. Their use is often limited, however, as turbulent airflow which develops behind them causes noticeable noise and vibration, which may cause discomfort to passengers. The spoilers may also be differentially operated to provide roll control. On landing, however, the spoilers are nearly always used at full effect to assist in slowing 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 much less chance of skidding. Reverse thrust is also often used to help slow the aircraft on landing.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 rapidly, 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 excessively rapid cooling. (This is particularly true in turbocharged piston engines, which generate higher temperatures than normally aspirated engines.)Some aircraft use spoilers in combination with or in lieu of ailerons for roll control. 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, thus decreasing lift and speed causing roll and yaw.Spoilers increase drag and reduce lift on the wing. If raised on only one wing, they aid roll control causing that wing to drop. If the spoilers raise symmetrically in flight, the aircraft can either be slowed in level flight or can descend rapidly without an increase in airspeed. When the spoilers rise on the ground at high speeds, they destroy the wing's lift which puts more of the aircraft's weight on the wheels.The flight spoilers are available both in flight and on the ground. However, the ground spoilers can only be raised when the weight of the aircraft is on the landing gear. When the spoilers deploy on the ground, they decrease lift and make the brakes more effective. In flight a ground sensing switch on the landing gear prevents deployment of the ground spoilers. http://www.batechnics.com/articles.php?lng=en&pg=695 http://www.batechnics.com/articles.php?lng=en&pg=695 Ailerons are hinged control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. They are used to control the aircraft in roll. The two ailerons are interconnected so that one goes down when the other goes up: the down-going aileron increases the lift on its wing while the up-going aileron reduces the lift on the other wing, producing a rolling moment about the aircraft's longitudinal axis. The word aileron is French for "little wing."An unwanted side-effect of aileron operation is adverse yaw — a yawing moment in the opposite direction to the turn generated by the ailerons. In other words, using the ailerons to roll an aircraft to the right would produce a yawing motion to the left. As the aircraft rolls, adverse yaw is caused primarily by an increase in induced drag on the rising wing, and a decrease in induced drag on the falling wing. One wing is rising in response to increased lift caused by the greater effective camber of the wing and downward-deflected aileron, and the other wing is falling in response to reduced lift caused by the reduced effective camber of the wing and upward-deflected aileron. Increased lift causes increased induced drag, and reduced lift causes reduced induced drag. A secondary contribution to adverse yaw is caused by the wing on the outside of the turn traveling faster than the inside wing and thus the outer wing experiences more parasitic drag than the inner wing. Modern aileron systems have minimal adverse yaw, such that it is barely noticeable in most powered aircraft. This may be accomplished by the use of differential ailerons, which have been rigged such that the down-going aileron deflects less than the upward-moving one. Frise ailerons achieve the same effect by protruding beneath the wing of an upward-deflected aileron, most often by being hinged slightly behind the leading edge and near the bottom of the surface, with the lower section of the leading edge protruding slightly below the wing's undersurface when the aileron is deflected upwards, increasing drag on that side. Ailerons may also use a combination of these methods.With ailerons in the neutral position the wing on the outside of the turn develops more lift than the opposite wing due to the variation in airspeed across the wing span, and this tends to cause the aircraft to continue to roll. Once the desired angle of bank (degree of rotation on the longitudinal axis) is obtained, the pilot uses opposite aileron to prevent the aircraft from continuing to roll due to this variation in lift across the wing span. This minor opposite use of the control must be maintained throughout the turn. The pilot also uses a slight amount of rudder in the same direction as the turn to counteract adverse yaw and to produce a "coordinated" turn where the fuselage is parallel to the flight path. A simple gauge on the instrument panel called the inclinometer, also known as "the ball", indicates when this coordination is achieved.The device first appeared on a monoplane, built by New Zealand inventor Richard Pearse in 1902, but most researchers believe the aircraft achieved no more than short, poorly controlled flights. The first aircraft accepted to have had a fully controlled flight using an aileron was 14 Bis by Santos Dumont. It was later developed independently by the Aerial Experiment Association, headed by Alexander Graham Bell, and by Robert Esnault-Pelterie, a French aircraft builder. Ailerons superseded the earlier wing warping technique, developed by the Wright Brothers.Combination with other surfacesA control surface that combines an aileron and flap is called a flaperon. A single surface on each wing serves both purposes: used as an aileron, the flaperons left and right are actuated differentially; when used as a flap, both flaperons are actuated downwards. When a flaperon is actuated downwards (i.e. used as a flap) there is enough freedom of movement left to be able to still use the aileron function. A further form of roll control, common on modern jet transport aircraft, utilises spoilers in conjunction with ailerons. This is called a spoileron. In a delta-winged aircraft, the ailerons are combined with the elevators to form an elevon. Modern military aircraft may have no ailerons on the wings at all, and combine roll control with an all-moving tailplane. This is a taileron or a rolling tail. http://www.batechnics.com/articles.php?lng=en&pg=691 http://www.batechnics.com/articles.php?lng=en&pg=691 Flaps are hinged surfaces on the trailing edge of the wings of a fixed-wing aircraft. As flaps are extended the stalling speed of the aircraft is reduced. Flaps are also used on the leading edge of the wings of some high-speed jet aircraft, where they may be called slats.Flaps reduce the stalling speed by increasing the camber of the wing and thereby increasing the maximum lift coefficient. Some trailing edge flaps also increase the area of the wing and, for any given aircraft weight, this reduces the stalling speed. The Fowler flap is an example of one which increases the area of the wing.Extending the flaps also increases the drag coefficient of the aircraft so, for any given weight and airspeed, flaps cause higher drag. Flaps increase the drag coefficient of an aircraft because of higher induced drag caused by the distorted planform of the wing with flaps extended. (Induced drag is a minimum on a wing with elliptical planform.) Some flaps increase the wetted area of the wing and, for any given speed, this also increases the parasitic drag component of total drag.Depending on the aircraft type, flaps may be partially extended for takeoff. With light aircraft, use of flaps for takeoff may be optional and will depend on the method of takeoff (e.g., short field, soft field, normal, etc.) When flaps are partially extended for takeoff it is to give the aircraft a slower stalling speed but with little increase in drag. A slower stalling speed allows the aircraft to takeoff in a shorter runway distance. Flaps are usually fully extended for landing to give the aircraft a slower stalling speed so the approach to landing can be flown more slowly, allowing the aircraft to land in a shorter runway distance. The higher drag associated with fully extended flaps allows a steeper approach to the landing site. This is the benefit of the higher drag coefficient of fully extended flaps.Some gliders not only use flaps when landing but also in flight to optimize the camber of the wing for the chosen speed. When thermalling, flaps may be partially extended to reduce the stalling speed so that the glider can be flown more slowly and thereby turn in a smaller circle to make best use of the core of the thermal. At higher speeds a negative flap setting is used to reduce the nose-down pitching moment. This reduces the balancing load required on the horizontal stabilizer which in turn reduces the trim drag - drag associated with keeping the glider in longitudinal trim. Negative flap may also be used during the initial stage of an aerotow launch and at the end of the landing run in order to maintain better control by the ailerons.Types of flap systems include:Krueger flap - hinged flap on the leading edge. Often called a "droop." Plain flap — rotates on a simple hinge. Split flap — upper and lower surfaces are separate, the lower surface operates like a plain flap, but the upper surface stays immobile or moves only slightly. Fowler flap — slides backwards before hinging downwards, thereby increasing both camber and chord, creating a larger wing surface better tuned for lower speeds. Fairey-Youngman flap - moves bodily down before moving aft and rotating. Slotted flap — a slot (or gap) between the flap and the wing enables high pressure air from below the wing to re-energize the boundary layer over the flap. This helps the airflow to stay attached to the flap, delaying the stall. Blown flaps — systems that blow engine air over the upper surface of the flap at certain angles to improve lift characteristics.There are several technology development efforts to incorporate the function of the flaps into a flexible wing, so that the aerodynamic purpose is accomplished without the weight and mechanical complexity of a flap system. The X-53 Active Aeroelastic Wing is a NASA effort to incorporate this technology, and the Adaptive Compliant Wing is commercial development effort.Slats, also known as leading-edge flaps, have a similar purpose to trailing-edge flaps, except that they are located on the leading edge of the wing. Note that a Krueger flap and a leading-edge slat differ in how they are extended (and retracted), but their aerodynamic function is the same http://www.batechnics.com/articles.php?lng=en&pg=690 http://www.batechnics.com/articles.php?lng=en&pg=690 A wing is a surface used to produce lift and therefore flight, for travel in the air or another gaseous medium. The wing shape is usually an airfoil. The first use of the word was for the foremost limbs of birds, but has been extended to include the wings of insects, bats and pterosaurs and also man-made devices.A wing is a device for generating lift. Its aerodynamic quality, expressed as a Lift-to-drag ratio, can be up to 60 on some gliders. This means that a significantly smaller thrust force can be applied to propel the wing through the air in order to obtain a specified lift.UseA common use of wings is in flight, using forward motion to create vertical lift, but wings are also used to produce downforce. A sail boat moves by using sails and a keel like a vertical wings to produce lift (in the horizontal plane). Here are main wing terms:Leading edge: the front edge of the wingTrailing edge: the back edge of the wingSpan: distance from wing tip to wing tipChord: distance from wing leading edge to wing trailing edge, usually measured parallel to the long axis of the fuselageAspect ratio: ratio of span to standard mean chordAerofoil (or Airfoil in US English): the shape of the top and bottom surfaces when viewed as cross sections cut from leading edge to trailing edge.Sweep angle: the angle between the perpendicular to the design centreline of the wing in the wing plane, and either the leading edge or ¼ chord line.Twist: gradual change of the airfoil (aerodynamic twist) and/or angle of incidence of the wing cross-sections (geometrical twist) along the span.Aeroplane wings may feature some of the following:A rounded (rarely sharp) leading edge cross-sectionA sharp trailing edge cross-sectionLeading-edge devices such as slats, slots, or extensionsTrailing-edge devices such as flapsAilerons (usually near the wingtips) to provide roll controlSpoilers on the upper surface to disrupt lift and additional roll controlVortex generators to help prevent flow separationWing fences to keep flow attached to the wingDihedral, or a positive wing angle to the horizontal. This gives inherent stability in roll. Anhedral, or a negative wing angle to the horizontal, has a destabilising effectFolding wings allow more aircraft to be carried in the confined space of the hangar of an aircraft carrier. The wings of a Boeing 737-800 equipped with performance-enhancing winglet. The wing of a landing BMI AirbusA319-100. The slats at the leading edge and the flaps at the trailing edge are extended. Wing typesSwept wings are wings that are bent back at an angle, instead of sticking straight out from the fuselage.Forward-swept wings are bent forward, the reverse of a traditional swept wing. Forward swept wings have been used in some two seat gliders, and in the experimental X-29.Elliptical wings (technically wings with an elliptical lift distribution) are theoretically optimum for efficiency at subsonic speeds. A good example of this wing type can be seen on the British Supermarine Spitfire World War II fighter aircraft.Delta wings have reasonable performance at subsonic and supersonic speeds and are good at high angles of attack. For examples see the F-102, F-106, Avro Vulcan and B-58.Waveriders are efficient supersonic wings that take advantage of shock waves. For an example, see the XB-70.Rogallo wings are two partial cone sections arranged with the apexes together and the convex side up. One of the simplest wings to construct using cloth or other membrane material and a frame.Variable geometry wings (or Swing-wings) are able to move in flight to give the benefits of dihedral and delta wing. Although they were originally proposed by German aerodynamicists during the 1940s, they are now only found on military aircraft such as the Grumman F-14, Panavia Tornado, General Dynamics F-111, B-1 Lancer, Tupolev Tu-160, MiG-23 and Sukhoi Su-24.Ring wings are optimally loaded closed lifting surfaces with higher aerodynamic efficiency than planar wings having the same aspect-ratios. Other nonplanar wing systems display an aerodynamic efficiency intermediate between ring wings and planar wings.Science of wingsThe science of wings is one of the principal applications of the science of aerodynamics. However, at the simplest level, a wing operates by generating a greater pressure below the wing than above it. Pressure and force are directly related; higher pressure equals higher force. When enough force is applied below the wing, flight can take place. This, however is not due to the unequal path explanation commonly given. Despite popular belief, flat plates at angles and curved airfoils do not generate lift in different ways. They both, in fact, use Bernoulli's principle and the Coanda effect to generate lift. On a flat plate, there is a dividing point on the bottom surface, forward of which, the air must curl back and over the leading edge of the airfoil. This, in incompressible flow (a good approximation below Mach .6) results in the airflow over the top moving faster, at the same density, inducing a lower relative pressure. In aerodynamics the actual lift generated by an airfoil is found by integrating the area between the upper surface Cp and lower surface Cp from the front of the wing to the back. Each Cp is the relative pressure (pressure at some infinitely small point) minus the pressure of the free stream air (the condition before the air is affected by the airfoil) divided by dynamic pressure. It was at one point believed that lift over a wing would be produced through the molecules of air colliding with the surface, and imparting some of their momentum to it, having been deflected somewhat downward from their initial path. This theory, however, also proves, conclusively, that flight is impossible, as the lift created would be insignificant when compared to the drag induced. The equation arrived at through a Newtonian model of lift is L=ρ*V²*sin² α*cos α. (see Newton's Third Law). The fundamental flaw with this being that it does not account for upstream effects seen in airflows.The science of wings applies in other areas beyond conventional fixed-wing aircraft, including:Helicopters which use a rotating wing with a variable pitch or angle to provide a directional forceThe space shuttle which uses its wings only for lift during its descentSome racing cars, especially Formula One cars, which use upside-down wings to give cars greater adhesion at high speedsSailing boats which use sails as vertical wings with variable fullness and direction to move across water.Structures with the same purpose as wings, but designed to operate in liquid media, are generally called fins or hydroplanes, with hydrodynamics as the governing science. Applications arise in craft such as hydrofoils and submarines. Sailing boats use both fins and wings. http://www.batechnics.com/articles.php?lng=en&pg=652 http://www.batechnics.com/articles.php?lng=en&pg=652 FADECIs the acronym for Full Authority Digital Engine Control (sometimes incorrectly interpreted as Full Authority Digital Electronics Control). It is a system consisting of a digital computer (called EEC /Electronic Engine Control/ or ECU /Electronic Control Unit/) and its related accessories which control all aspects of aircraft engine performance. FADECs have been produced for both piston engines and jet engines, their primary difference due to the different ways of controlling the engines.The goal of any engine control system is to allow the engine to perform at maximum efficiency for a given condition. The complexity of this task is proportional to the complexity of the engine. To accurately explore the roots of today’s FADEC, one should first understand the evolution of the control interface of an aircraft engine. The original engine control system is simple mechanical linkages controlled by the pilot. By moving throttle levers directly connected to the engine, the pilot could control fuel flow, power output, and many other engine parameters. Following mechanical means of engine control was the introduction of analog electronic engine control. Analog electronic control varies an electronic signal to communicate the desired engine settings. The system was an obvious improvement over mechanical control but had its drawbacks including the common electronic noise interference. This system was pioneered in the 1960s and first introduced as a component of the Rolls Royce Olympus 593 engine. The 593 is the choice engine for the famous supersonic transport aircraft, Concorde. Following analog electronic control, the clear path was digital electronic control. Later in the 1970s NASA and Pratt and Whitney experimented with the first experimental FADEC, first flown on an F-111 fitted with a highly modified Pratt & Whitney TF30 left engine. The experiments led to Pratt & Whitney F100 and Pratt & Whitney PW2000 being the first military and civil engines respectively fitted with FADEC and later the Pratt & Whitney PW4000 as the first commercial "Dual FADEC" engine.To be a true, 100%, Full Authority Digital Engine Control, there must not be any form of manual override available. This literally places full authority to the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails. If the engine is controlled digitally and electronically but allows for manual override, it is considered solely an Electronic Engine Control or Electronic Control Unit. An EEC, though a component of a FADEC, is not by itself FADEC. When standing alone, the EEC makes all of the decisions until the pilot wishes to intervene. FADEC works by receiving multiple input variables of the current flight condition including air density, throttle lever position, engine temperatures, engine pressures, and many others. The inputs are received by the EEC and analyzed up to 70 times per second. Engine operating parameters such as fuel flow, stator vane position, bleed valve position, and others are digitally computed based off this data and applied as appropriate. FADEC also controls engine starting and restarting. The FADEC's basic purpose is to provide optimum engine efficiency for a given flight condition. FADEC not only provides for efficient engine operation, it also allows the manufacturer to program engine limitations, receive engine health reports, and receive maintenance reports. For example, in order to not exceed a certain engine temperature, the FADEC can be programmed to automatically take the necessary measures without pilot intervention.Safety With the operation of the engines so heavily relying on automation, safety is a great concern. Redundancy is provided in the form of two, separate identical digital channels. Each channel may provide all engine functions without restriction. FADEC also monitors a variety of analog, digital and discrete data coming from the engine subsystems and related aircraft systems, providing for fault tolerant engine control.Application To perhaps more clearly illustrate the function of a FADEC, explore a typical civilian transport aircraft flight. The flight crew first enters the data appropriate to the day’s flight in the flight management system or FMS. The FMS takes environmental data such as temperature, wind, runway length, runway condition, cruise altitude etc. and calculates power settings for different phases of flight. For takeoff, the flight crew advances the throttle (which contains no mechanical linkage to the engine) to a takeoff detent or opts for an auto-throttle takeoff if available. The FADECs know the calculated takeoff thrust setting and apply it. The flight crew notes that they have merely sent an electronic signal to the engines, no direct linkage has been moved to open fuel flow. This procedure is the same for climb, cruise, and all phases of flight. The FADECs compute the appropriate thrust settings and apply them. During flight, small changes in operation are constantly being made to maintain efficiency. Maximum thrust is available for emergency situations if the throttle is advanced to full, but remember, limitations can’t be exceeded. The flight crew has no means of manually overriding the FADECs, so if they make a decision the crew doesn’t like, it will have to be accepted. FADECs today are employed by almost all current generation jet engines and increasingly in newer piston engines, on fixed-wing aircraft and helicopters.Advantages Better fuel efficiencyAutomatic engine protection against out-of-tolerance operationsSafer as the multiple channel FADEC computer provides redundancy in case of failureCare-free engine handling, with guaranteed thrust settingsAbility to use single engine type for wide thrust requirements by just reprogramming the FADECsProvides semi-automatic engine startingBetter systems integration with engine and aircraft systemsCan provide engine long-term health monitoring and diagnosticsNumber of external and internal parameters used in the control processes increases by one order of magnitudeReduces the number of parameters to be monitored by flight crewsDue to the high number of parameters monitored, the FADEC makes possible "Fault Tolerant Systems" (where a system can operate within required reliability and safety limitation with certain fault configurations)Can support automatic aircraft and engine emergency responses (e.g. in case of aircraft stall, engines increase thrust automatically). Disadvantages Engineering processes used to design, manufacture, install and maintain the sensors which measure and report flight and engine parameters to the control system itselfIntegrity and reliability of the materials and the path over which this data flowsSoftware engineering processes used in the design, implementation and testing of the software used in these safety-critical control systems. This led to the development and use of specialized software such as SCADE.Inability of the display subsystem to provide clear and unambiguous information to the crew, under conditions of high stress and intensive cockpit workload (for example, in an emergency)Responsiveness of both the FADEC software and its acceptance of "human input" under dangerous flight envelopes, for instance at low airspeed, close to terrain, high gross weight, low fuel state, unusual airframe attitude, other systems reporting "anomalous behaviour" (typically, after combat damage or other component failure)Completeness of the flight simulations and parameters used to populate the rulebase against which some FADEC systems compare for "valid" control inputs in prevailing flight conditions. http://www.batechnics.com/articles.php?lng=en&pg=642 http://www.batechnics.com/articles.php?lng=en&pg=642 Pilot Orientation Guide to using the Wide Area Augmentation System    (WAAS)The WAAS is an extremely accurate navigation system developed for civil aviation by the Federal Aviation Administration (FAA), a division of the United States Department of Transportation (DOT). The system augments the Global Positioning System (or GPS) to provide the additional accuracy, integrity, and availability necessary to enable users to rely on GPS for all phases of flight, from en route through GLS approach for all qualified airports within the WAAS coverage area.[1] Before WAAS, the U.S. National Airspace System (NAS) did not have the ability to provide horizontal and vertical navigation for precision approaches for all locations, as ground-based systems are quite expensive.The worst-case accuracy is within 7.6 meters of the true position 95% of the time, and it provides integrity information equivalent to or better than receiver autonomous integrity monitoring (RAIM). This is achieved via a network of ground stations located throughout North America which monitor and measure the GPS signal. Measurements from the reference stations are routed to two master stations which generate and send the correction messages to geostationary satellites. Those satellites broadcast the correction messages back to Earth, where WAAS-enabled GPS receivers apply the corrections to their computed GPS position.The International Civil Aviation Organization (ICAO) calls this type of system a Satellite Based Augmentation System (SBAS). Europe and Asia are developing their own SBASs by way of the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-functional Satellite Augmentation System (MSAS), respectively. Commercial systems include StarFire and OmniSTAR.AccuracyThe WAAS specification requires it to provide a position accuracy of 7.6 meters or better (for both lateral and vertical measurements), at least 95% of the time. Actual performance measurements of system at specific locations have shown it typically provides better than 1.0 meters laterally and 1.5 meters vertically throughout most of the contiguous United States and large parts of Canada and Alaska. With these results, WAAS is capable of achieving the required Category I precision approach accuracy of 16 m laterally and 4.0 m vertically.IntegrityIntegrity is the ability of a navigation system to provide timely warnings when its signal is providing misleading data that could potentially create hazards. The WAAS specification requires the system detect errors in the GPS or WAAS network and notify users within 5.2 seconds. Certifying that WAAS is safe for IFR flight requires proving there is only an extremely small probability that an error exceeding the requirements for accuracy will go undetected. Specifically, the probability is stated as 1×10-7, and is equivalent to no more than 3 seconds of bad data per year.AvailabilityAvailability is the probability that a navigation system meets the accuracy and integrity requirements. Without the WAAS improvement, GPS could be unavailable for up to a total time of 4 days per year.[3] The WAAS specification mandates availability as 99.999% (five nines) throughout the service area.Ground SegmentThe Ground Segment is composed of multiple Wide-area Reference Stations (WRS). These precisely surveyed ground stations monitor and collect information on the GPS signals, and then send their data to the two Wide-area Master Stations (WMS) using a terrestrial communications network. The reference stations also monitor the signal from the WAAS geostationary satellites, providing integrity information regarding them as well. As of November 2006 there are 29 WRS's, twenty in the contiguous United States (CONUS), seven in Alaska, one in Hawaii, one in Puerto Rico. Using the data from the WRS sites, the WMSs generate two different sets of corrections: fast and slow. The fast corrections are for errors which are changing rapidly and primarily concern the GPS satellites' instantaneous positions and clock errors. These corrections are considered user position independent, which means they can be applied instantly by any receiver in the WAAS broadcast footprint. The slow corrections include long-term ephemeric and clock error estimates, as well as ionospheric delay information. WAAS supplies ionospheric delay corrections for a number of points (organized in a grid pattern) across the WAAS service area (See the User Segment, below, to understand how these corrections are used). Once these corrections are generated, the WMSs then send them to the two pairs of Ground Uplink Stations (GUS) which transmit them to the satellites in the Space segment for broadcast to the User segment.Space SegmentThe space segment consists of multiple geosynchronous communication satellites which broadcast the correction messages generated by the Wide-area Master Stations for reception by the User segment. The satellites also broadcast the same type of range information as normal GPS satellites, effectively increasing the number of satellites available for a position fix. Currently, the Space segment consists of two satellites named Galaxy XV and Anik F1R.The original two WAAS satellites, named Pacific Ocean Region (POR) and Atlantic Ocean Region-West (AOR-W), were leased space on Inmarsat III satellites. These satellites ceased WAAS transmissions on July 31, 2007. With the end of the Inmarsat lease approaching, two new satellites (Galaxy XV and Anik F1R) were launched in late 2005. Galaxy XV is a PanAmSat, and Anik F1R is a Telesat. As with the previous satellites, these are leased services under the FAA's Geostationary Satellite Communications Control Segment contract with Lockheed Martin for WAAS geostationary satellite leased services, who is contracted to provide up to three satellites through the year 2016.As of August, 2007, the new satellites are in an operational mode, however they are not yet full replacements. While both new satellites transmit correction messages, their GPS-like signals are still being improved. Galaxy XV's ranging data is flagged as "Not Monitored" and Anik F1R's is flagged "Non Precision Approach." Both are expected to improve to "Precision Approach" during the second half of 2007.Satellite Name & Details SVN / PRN Location Galaxy XV ID #48 / PRN #135 133°W Anik F1R ID #51 / PRN #138 107°W Pacific Ocean Region (POR)Ceased WAAS transmissions ID #47 / PRN #134 178°E Atlantic Ocean Region-WestCeased WAAS transmissions ID #35 / PRN #122 142°WUser Segment The User segment is the GPS and WAAS receiver, which uses the information broadcast from each GPS satellite to determine its location and the current time, and receives the WAAS corrections from the Space segment. The two types of correction messages received (fast and slow) are used in different ways. The GPS receiver can immediately apply the fast type of correction data, which includes the corrected satellite position and clock data, and determines its current location using normal GPS calculations. Once an approximate position fix is obtained the receiver begins to use the slow corrections to improve its accuracy. Among the slow correction data is the ionospheric delay. As the GPS signal travels from the satellite to the receiver, it passes through the ionosphere. The receiver calculates the location where the signal pierced the ionosphere and, if it has received an ionospheric delay value for that location, corrects for the error the ionosphere created. While the slow data can be updated every minute if necessary, ephemeris errors and ionosphere errors do not change this frequently, so they are only updated every two minutes and are considered valid for up to six minutes.A comparison of various radionavigation system accuracies System 95% Accuracy (Lateral / Vertical) Details LORAN-C 460 meters / 460 meters The specified absolute accuracy of the LORAN-C system. Distance Measuring Equipment (DME) 185 meters / 185 meters DME is a radionavigation aid that can calculate the distance from an aircraft to ground equipment. GPS 100 meters / 150 meters The specified accuracy of the GPS system with the Selective Availability (SA) option turned on. SA was employed by the U.S. Government until May 1, 2000. LORAN-C 50 meters / 50 meters The U.S. Coast Guard reports "return to position" accuracies of 50 meters in time difference mode. eLORAN 10 meters / 10 meters Modern LORAN-C receivers, which use all the available signals simultaneously and H-field antennas. Differential GPS 10 meters / 10 meters This is the Differential GPS (DGPS) worst-case accuracy. According to the 2001 Federal Radionavigation Systems (FRS) report published jointly by the U.S. DOT and Department of Defense (DoD), accuracy degrades with distance from the facility; it can be < 1 m but will normally be < 10 m. Wide Area Augmentation System (WAAS) Specification 7.6 meters / 7.6 meters The worst-case accuracy that the WAAS must provide to be used in precision approaches. GPS Measured 2.5 meters / 4.7 meters The actual measured accuracy of the system (excluding receiver errors), with SA turned off, based on the NSTB's findings. WAAS Measured 0.9 meters / 1.3 meters The actual measured accuracy of the system (excluding receiver errors), based on the NSTB's findings. Local Area Augmentation System (LAAS) Specification 1.0 meter / 1.0 meter  The goal of the LAAS program is to provide Category III ILS capability. This allows aircraft to land with zero visibility utilizing 'autoland' systems and indicates a very high accuracy of < 1 m.Drawbacks and Limitations For all its benefits, WAAS is not without drawbacks and critical limitations. The broadcasting satellites are geostationary, which causes them to be less than 10° above the horizon for locations north of 71.4° latitude. This means aircraft in areas of Alaska or northern Canada may have difficulty maintaining a lock on the WAAS signal.To calculate an ionospheric grid point's delay, that point must be located between a satellite and a reference station. The low number of satellites and ground stations limit the number of points which can be calculated. This ultimately limits the operational area and accuracy due to undersampling.Aircraft conducting WAAS approaches must possess certified receivers, which are much more expensive than commercial units. Garmin's least expensive receiver, the GNS 430W, has a suggested retail price of US$­­­10,750.WAAS is not capable of the accuracies required for Category II or III ILS approaches. Thus, WAAS is not a sole-solution and either existing ILS equipment must be maintained or it must be replaced by new systems, such as the Local Area Augmentation System (LAAS).WAAS LPV approaches with 200 foot minimums can not be used at airports without medium intensity lighting, runway markings and a parallel taxiway. Smaller airports may not have these, and therefore require pilots to use higher minimums or pay to upgrade the airport.The 2004 baseline estimates the final program cost to the US Federal government as over US$­­­3.3 billion when delivered in 2013; more than 3.7 times the original budget and 12 years behind schedule.