In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, may take the form of strut, which act in compression or tension as the need arises, and/or wires, which act only in tension. In general, bracing allows a stronger, lighter structure than one, unbraced, but external bracing in particular adds drag which slows down the aircraft and raises more design issues than internal bracing. Another disadvantage of bracing wires is that they require routine checking and adjustment, or rigging when located internally. During the early years of aviation, bracing was a universal feature of all forms of aeroplane, including the monoplanes and biplanes which were equally common. Today, bracing in the form of lift struts is still used for some light commercial designs where a high wing and light weight are more important than ultimate performance. Bracing works by creating a triangulated truss structure which resists twisting.
By comparison, an unbraced cantilever structure bends unless it carries a lot of heavy reinforcement. Making the structure deeper allows it to be much lighter and stiffer. To reduce weight and air resistance, the structure may be made hollow, with bracing connecting the main parts of the airframe. For example, a high-wing monoplane may be given a diagonal lifting strut running from the bottom of the fuselage to a position far out towards the wingtip; this increases the effective depth of the wing root to the height of the fuselage, making it much stiffer for little increase in weight. The ends of bracing struts are joined to the main internal structural components such as a wing spar or a fuselage bulkhead, bracing wires are attached close by. Bracing may be used to resist all the various forces which occur in an airframe, including lift, weight and twisting or torsion. A strut is a bracing component stiff enough to resist these forces whether they place it under compression or tension. A wire is a bracing component able only to resist tension, going slack under compression, is nearly always used in conjunction with struts.
A square frame made of solid bars tends to bend at the corners. Bracing it with an extra diagonal bar would be heavy. A wire would stop it collapsing only one way. To hold it rigid, two cross-bracing wires are needed; this method of cross-bracing can be seen on early biplanes, where the wings and interplane struts form a rectangle, cross-braced by wires. Another way of arranging a rigid structure is to make the cross pieces solid enough to act in compression and to connect their ends with an outer diamond acting in tension; this method was once common on monoplanes, where the wing and a central cabane or a pylon form the cross members while wire bracing forms the outer diamond. Most found on biplane and other multiplane aircraft, wire bracing was common on early monoplanes. Unlike struts, bracing wires always act in tension The thickness and profile of a wire affect the drag it causes at higher speeds. Wires may be made of multi-stranded cable, a single strand of piano wire, or aerofoil sectioned steel.
Bracing wires divide into flying wires which hold the wings down when flying and landing wires which hold the wings up when they are not generating lift. Thinner incidence wires are sometimes run diagonally between fore and aft interplane struts to stop the wing twisting and changing its angle of incidence to the fuselage. In some pioneer aircraft, wing bracing wires were run diagonally fore and aft to prevent distortion under side loads such as when turning. Besides the basic loads imposed by lift and gravity, bracing wires must carry powerful inertial loads generated during manoeuvres, such as the increased load on the landing wires at the moment of touchdown. Bracing wires must be rigged to maintain the correct length and tension. In flight the wires tend to stretch under load and on landing some may become slack. Regular rigging checks are required and any necessary adjustments made before every flight. Rigging adjustments may be used to set and maintain wing dihedral and angle of incidence with the help of a clinometer and plumb-bob.
Individual wires are fitted with turnbuckles or threaded end fittings so that they can be adjusted. Once set, the adjuster is locked in place. Internal bracing was most significant during the early days of aeronautics when airframes were frames, at best covered in doped fabric which had no strength of its own. Wire cross-bracing was extensively used to stiffen such airframes, both in the fabric-covered wings and in the fuselage, left bare. Routine rigging of the wires was needed to maintain structural stiffness against bending and torsion. A particular problem for internal wires is access in the cramped interior of the fuselage. Providing sufficient internal bracing would make a design too heavy, so in order to make the airframe both light and strong the bracing is fitted externally; this was common in early aircraft due to the limited engine power available and the need for light weight in order to fly at all. As engine powers rose through the 1920s and 30s, much heavier airframes became practicable and most designers abandoned external bracing in order to allow for increased speed.
Nearly all biplane aircraft have their upper and lower planes connected by interplane struts, with the upper wing running across above the fuselage and connected to it by shorter cabane struts. These struts divide the wings into bays which are brace
Elevators are flight control surfaces at the rear of an aircraft, which control the aircraft's pitch, therefore the angle of attack and the lift of the wing. The elevators are hinged to the tailplane or horizontal stabilizer, they may be the only pitch control surface present, sometimes located at the front of the aircraft or integrated into a rear "all-moving tailplane" called a slab elevator or stabilator. The horizontal stabilizer creates a downward force which balances the nose down moment created by the wing lift force, which applies at a point situated aft of the airplane's center of gravity; the effects of drag and changing the engine thrust may result in pitch moments that need to be compensated with the horizontal stabilizer. Both the horizontal stabilizer and the elevator contribute to pitch stability, but only the elevators provide pitch control, they do so by decreasing or increasing the downward force created by the stabilizer: an increased downward force, produced by up elevator, forces the tail down and the nose up.
At constant speed, the wing's increased angle of attack causes a greater lift to be produced by the wing, accelerating the aircraft upwards. The drag and power demand increase. At constant speed, the decrease in angle of attack reduces the lift, accelerating the aircraft downwards. On many low-speed aircraft, a trim tab is present at the rear of the elevator, which the pilot can adjust to eliminate forces on the control column at the desired attitude and airspeed. Supersonic aircraft have all-moving tailplanes, because shock waves generated on the horizontal stabilizer reduce the effectiveness of hinged elevators during supersonic flight. Delta winged aircraft combine ailerons and elevators –and their respective control inputs– into one control surface called an elevon. Elevators are part of the tail, at the rear of an aircraft. In some aircraft, pitch-control surfaces are in the front, ahead of the wing. In a two-surface aircraft this type of configuration is called a tandem wing; the Wright Brothers' early aircraft were of the canard type.
Some early three surface aircraft had front elevators. Several technology research and development efforts exist to integrate the functions of aircraft flight control systems such as ailerons, elevons and flaperons into wings to perform the aerodynamic purpose with the advantages of less: mass, drag, inertia and radar cross section for stealth; these may be used in 6th generation fighter aircraft. Two promising approaches are flexible wings, fluidics. In flexible wings, much or all of a wing surface can change shape in flight to deflect air flow; the X-53 Active Aeroelastic Wing is a NASA effort. The Adaptive Compliant Wing is a commercial effort. In fluidics, forces in vehicles occur via circulation control, in which larger more complex mechanical parts are replaced by smaller simpler fluidic systems where larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles. In this use, fluidics promises lower mass and low inertia and response times, simplicity.
Rudder Aileron Aircraft Pitch Motion
A flaperon on an aircraft's wing is a type of control surface that combines the functions of both flaps and ailerons. Some smaller kitplanes have flaperons for reasons of simplicity of manufacture, while some large commercial aircraft may have a flaperon between the flaps and aileron. In addition to controlling the roll or bank of an aircraft, as do conventional ailerons, both flaperons can be lowered together to function to a set of flaps. On a plane with flaperons, the pilot still has the standard separate controls for ailerons and flaps, but the flap control varies the flaperon's range of movement. A mechanical device called. While the use of flaperons rather than ailerons and flaps might seem to be a simplification, some complexity remains through the intricacies of the mixer; some aircraft, such as the Denney Kitfox, suspend the flaperons below the wing to provide undisturbed airflow at high angles of attack or low airspeeds. When the flaperon surface is hinged below the trailing edge of a wing, they are sometimes named "Junker Flaperons", from the doppelflügel type of trailing edge surfaces used on a number of Junkers aircraft of the 1930s, such as the Junkers Ju 52 airliner, Junkers Ju 87 Stuka iconic World War II dive bomber.
Current research seeks to coordinate the functions of aircraft flight control surfaces so as to reduce weight, drag and thereby achieve improved control response, reduced complexity, reduced radar visibility for stealth purposes. Beneficiaries of such research might include the latest fighter aircraft; these research approaches include flexible wings and fluidics: In flexible wings, much or all of a wing surface can change shape in flight to deflect air flow. The X-53 Active Aeroelastic Wing is a NASA effort; the Adaptive Compliant Wing is a commercial effort. This may be seen as a return to the wing warping patented by the Wright brothers. In fluidics, forces in vehicles occur via circulation control, in which larger, more complex mechanical parts are replaced by smaller simpler fluidic systems, where larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles. In this use, fluidics promises lower mass and low inertia and response times, as well as simplicity.
The empennage known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow. The term derives from the French language word empenner which means "to feather an arrow". Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the flight dynamics of yaw and pitch, as well as housing control surfaces. In spite of effective control surfaces, many early aircraft that lacked a stabilising empennage were unflyable. So-called "tailless aircraft" have a tail fin. Heavier-than-air aircraft without any kind of empennage are rare. Structurally, the empennage consists of the entire tail assembly, including the tailfin, the tailplane and the part of the fuselage to which these are attached. On an airliner this would be all the flying and control surfaces behind the rear pressure bulkhead; the front section of the tailplane is called the tailplane or horizontal stabiliser and is used to provide pitch stability.
The rear section is called the elevator, is hinged to the horizontal stabiliser. The elevator is a movable aerofoil that controls changes in pitch, the up-and-down motion of the aircraft's nose; some aircraft employ an all-moving stabiliser and elevators in one unit, known as a stabilator or "full-flying stabiliser". The vertical tail structure has a fixed front section called the vertical stabiliser, used to restrict side-to-side motion of the aircraft; the rear section of the vertical fin is the rudders, a movable aerofoil, used to turn the aircraft's nose to one side or the other. When used in combination with the ailerons, the result is a banking turn referred to as a "coordinated turn"; some aircraft are fitted with a tail assembly, hinged to pivot in two axes forward of the fin and stabiliser, in an arrangement referred to as a movable tail. The entire empennage is rotated vertically to actuate the horizontal stabiliser, sideways to actuate the fin; the aircraft's cockpit voice recorder, flight data recorder and Emergency locator transmitter are located in the empennage, because the aft of the aircraft provides better protection for these in most aircraft crashes.
In some aircraft trim devices are provided to eliminate the need for the pilot to maintain constant pressure on the elevator or rudder controls. The trim device may be: a trim tab on the rear of the elevators or rudder which act to change the aerodynamic load on the surface. Controlled by a cockpit wheel or crank. an adjustable stabiliser into which the stabiliser may be hinged at its spar and adjustably jacked a few degrees in incidence either up or down. Controlled by a cockpit crank. A bungee trim system. Controlled by a cockpit lever. An anti-servo tab used to trim some elevators and stabilators as well as increased control force feel. Controlled by a cockpit wheel or crank. A servo tab used to move the main control surface, as well as act as a trim tab. Controlled by a cockpit wheel or crank. Multi-engined aircraft have trim tabs on the rudder to reduce the pilot effort required to keep the aircraft straight in situations of asymmetrical thrust, such as single engine operations. Aircraft empennage designs may be classified broadly according to the fin and tailplane configurations.
The overall shapes of individual tail surfaces are similar to wing planforms. The tailplane comprises the tail-mounted fixed horizontal movable elevator. Besides its planform, it is characterised by: Number of tailplanes - from 0 to 3 Location of tailplane - mounted high, mid or low on the fuselage, fin or tail booms. Fixed movable elevator surfaces, or a single combined stabilator or flying tail; some locations have been given special names: Cruciform tail - The horizontal stabilisers are placed midway up the vertical stabiliser, giving the appearance of a cross when viewed from the front. Cruciform tails are used to keep the horizontal stabilisers out of the engine wake, while avoiding many of the disadvantages of a T-tail. Examples include Douglas A-4 Skyhawk. T-tail - The horizontal stabiliser is mounted on top of the fin, creating a "T" shape when viewed from the front. T-tails keep the stabilisers out of the engine wake, give better pitch control. T-tails have a good glide ratio, are more efficient on low speed aircraft.
However, the T-tail has several disadvantages. It is more to enter a deep stall, is more difficult to recover from a spin. For this reason a small secondary stabiliser or tail-let may be fitted lower down where it will be in free air when the aircraft is stalled. A T-tail must be stronger, therefore heavier than a conventional tail. T-tails tend to have a larger radar cross section. Examples include the Gloster Javelin and McDonnell Douglas DC-9; the fin comprises rudder. Besides its profile, it is characterised by: Number of fins - one or two. Location of fins - on the fuselage, tail booms or wingsTwin fins may be mounted at various points: Twin tail A twin tail called an H-tail, consists of two small vertical stabilisers on either side of the horizontal stabiliser. Examples include the Antonov An-225 Mriya, B-25 Mitchell, Avro Lancaster, ERCO Ercoupe. Twin boom A twin boom has two fuselages or booms, with a vertical stabiliser on each, a horizontal stabiliser between them. Examples include the P-38 Lightning, de Havilla
A rudder is a primary control surface used to steer a ship, submarine, aircraft, or other conveyance that moves through a fluid medium. On an aircraft the rudder is used to counter adverse yaw and p-factor and is not the primary control used to turn the airplane. A rudder operates by redirecting the fluid past the hull or fuselage, thus imparting a turning or yawing motion to the craft. In basic form, a rudder is a flat plane or sheet of material attached with hinges to the craft's stern, tail, or after end. Rudders are shaped so as to minimize hydrodynamic or aerodynamic drag. On simple watercraft, a tiller—essentially, a stick or pole acting as a lever arm—may be attached to the top of the rudder to allow it to be turned by a helmsman. In larger vessels, pushrods, or hydraulics may be used to link rudders to steering wheels. In typical aircraft, the rudder is operated by pedals via mechanical hydraulics. A rudder is "part of the steering apparatus of a boat or ship, fastened outside the hull", denoting all different types of oars and rudders.
More the steering gear of ancient vessels can be classified into side-rudders and stern-mounted rudders, depending on their location on the ship. A third term, steering oar, can denote both types. In a Mediterranean context, side-rudders are more called quarter-rudders as the term designates more the place where the rudder was mounted. Stern-mounted rudders are uniformly suspended at the back of the ship in a central position. Although some classify a steering oar as a rudder, others argue that the steering oar used in ancient Egypt and Rome was not a true rudder and define only the stern-mounted rudder used in ancient Han China as a true rudder; the steering oar has the capacity to interfere with handling of the sails while it was fit more for small vessels on narrow, rapid-water transport. In regards to the ancient Phoenician use of the steering oar without a rudder in the Mediterranean, Leo Block writes: A single sail tends to turn a vessel in an upwind or downwind direction, rudder action is required to steer a straight course.
A steering oar was used at this time. With a single sail, a frequent movement of the steering oar was required to steer a straight course; the second sail, located forward, could be trimmed to offset the turning tendency of the main sail and minimize the need for course corrections by the steering oar, which would have improved sail performance. The steering oar or steering board is an oversized oar or board to control the direction of a ship or other watercraft prior to the invention of the rudder, it is attached to the starboard side in larger vessels, though in smaller ones it is if attached. Rowing oars set aside for steering appeared on large Egyptian vessels long before the time of Menes. In the Old Kingdom as many as five steering oars are found on each side of passenger boats; the tiller, at first a small pin run through the stock of the steering oar, can be traced to the fifth dynasty. Both the tiller and the introduction of an upright steering post abaft reduced the usual number of necessary steering oars to one each side.
Single steering oars put on the stern can be found in a number of tomb models of the time during the Middle Kingdom when tomb reliefs suggests them employed in Nile navigation. The first literary reference appears in the works of the Greek historian Herodotus, who had spent several months in Egypt: "They make one rudder, this is thrust through the keel" meaning the crotch at the end of the keel. In Iran, oars mounted on the side of ships for steering are documented from the 3rd millennium BCE in artwork, wooden models, remnants of actual boats. Roman navigation used sexillie quarter steering oars that went in the Mediterranean through a long period of constant refinement and improvement, so that by Roman times ancient vessels reached extraordinary sizes; the strength of the steering oar lay in its combination of effectiveness and simpleness. Roman quarter steering oar mounting systems survived intact through the medieval period. By the first half of the 1st century AD, steering gear mounted on the stern were quite common in Roman river and harbour craft as proved from reliefs and archaeological finds.
A tomb plaque of Hadrianic age shows a harbour tug boat in Ostia with a long stern-mounted oar for better leverage. The boat featured a spritsail, adding to the mobility of the harbour vessel. Further attested Roman uses of stern-mounted steering oars includes barges under tow, transport ships for wine casks, diverse other ship types; the well-known Zwammerdam find, a large river barge at the mouth of the Rhine, featured a large steering gear mounted on the stern. According to new research, the advanced Nemi ships, the palace barges of emperor Caligula, may have featured 14 m long rudders; the world's oldest known depiction of a sternpost-mounted rudder can be seen on a pottery model of a Chinese junk dating from the 1st century AD during the Han Dynasty, predating their appearance in the West by a thousand years. In China, miniature models of ships t
A former is an object, such as a template, gauge or cutting die, used to form something such as a boat's hull. A former gives shape to a structure that may have complex curvature. A former may become an integral part of the finished structure, as in an aircraft fuselage, or it may be disposable, being using in the construction process and discarded. Here, a former is a structural member of an aircraft fuselage, of which a typical fuselage has a series from the nose to the empennage perpendicular to the longitudinal axis of the aircraft; the primary purpose of formers is to establish the shape of the fuselage and reduce the column length of stringers to prevent instability. Formers are attached to longerons, which support the skin of the aircraft; the "former-and-longeron" technique was adopted from boat construction, was typical of light aircraft built until the advent of structural skins, such as fiberglass and other composite materials. Many of today's light aircraft, homebuilt aircraft in particular, are still designed in this way.
A former may instead be a temporary shape over which a structure is built, the former subsequently being discarded in whole or part, as follows: Strip-built boat construction uses formers over which thin plank strips are applied and glued. in some cases, some of the formers may be incorporated as structural ribs. In civil engineering, bridge building, architecture, arches may be built upon a wooden former, removed once the keystone is securely in place
The fuselage is an aircraft's main body section. It holds crew and cargo. In single-engine aircraft it will contain an engine, as well, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage, which in turn is used as a floating hull; the fuselage serves to position control and stabilization surfaces in specific relationships to lifting surfaces, required for aircraft stability and maneuverability. This type of structure is still in use in many lightweight aircraft using welded steel tube trusses. A box truss fuselage structure can be built out of wood—often covered with plywood. Simple box structures may be rounded by the addition of supported lightweight stringers, allowing the fabric covering to form a more aerodynamic shape, or one more pleasing to the eye. Geodesic 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 and rigid and had the advantage of being made entirely of wood. A similar construction using aluminum alloy was used in the Vickers Warwick with less materials than would be required for other structural types; the geodesic structure is 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. In this method, the exterior surface of the fuselage is the primary structure. A typical early form of this was built using molded plywood, where the layers of plywood are formed over a "plug" or within a mold. A form of this structure uses fiberglass cloth impregnated with polyester or epoxy resin, instead of plywood, as the skin. A simple form of this used in some amateur-built aircraft uses rigid expanded foam plastic as the core, with a fiberglass covering, eliminating the necessity of fabricating molds, but requiring more effort in finishing.
An example of a larger molded plywood aircraft is the de Havilland Mosquito fighter/light bomber of World War II. No plywood-skin fuselage is monocoque, since stiffening elements are incorporated into the structure to carry concentrated loads that would otherwise buckle the thin skin; the use of molded fiberglass using negative molds 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; this 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 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 disassembled and removed from the completed fuselage shell, fitted out with wiring 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 joined with fasteners to form the complete fuselage. As the accuracy of the final product is determined 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. Most metal light aircraft are constructed using this process. Both monocoque and semi-monocoque are referred to as "stressed skin" structures as all or a portion of the external load is taken by the surface covering. In addition, all the load from internal pressurization is carried by the external skin; the proportioning of loads between the components is a design choice dictated by the dimensions and elasticity of the components available for construction and whether or not a design is intended to be "self jigging", not requiring a complete fixture for alignment.
Early aircraft were constructed of wood frames covered in fabric. As monoplanes became popular, metal frames improved the strength, which led to all-metal-structure aircraft, with metal covering for all its exterior surfaces - this was first pioneered in the second half of 1915; some modern aircraft are constructed with composite materials for major control surfaces, wings, or the entire fuselage such as the Boeing 787. On the 787, it makes possible higher pressurization levels and larger windows for passenger comfort as well as lower weight to reduce operating costs; the Boeing 787 weighs 1500 lb less than. Cockpit windshields on the Airbus A320 must withstand bird strikes up to 350 kt and are made of chemically strengthened glass, they are composed of three layers or plies, of glass or plastic: the inner two are 8 mm thick each and are structural, while the outer ply, about 3 mm thick, is a barrier against foreign object damage and abrasion, with a hydrophobic coating. It m