Spoilers:Definition and Explanation Spoilers are devices, which are very important in an airplane. They help to increase lifts when you are flying. They are fitted to the wings of which increases the drag also. They usually consist of a long narrow strip of metal arranged span wise along the top surface of the airfoil. In some airplane, they are usually linked to the ailerons and work together with the ailerons for lateral control. As such, they open on the side of the up-going ailerons, spoil the lift on that wing and help drive the wing down and this helps in the roll into turn of the airplane. In some airplane, spoilers have taken the place of ailerons as a means of roll control. The later does not really help much again in roll control making way for the introduction of spoilers. The spoilers moves only upwards in contrast to the aileron that moves upwards to reduce lift and downward to increase lift. The spoilers for roll control full span flaps can be used to increase low speed.

Construction and attachment:Spoilers are hinged, rectangular plate-like structures installed flush along the top of an aircraft wing, just forward of the flaps. When the pilot activates the spoilers, the plates pivot up on their center hinge fittings into the airstream. As the name suggests, the airflow over the wing is disturbed (spoiled) and lift is decreased. Maximum deployment of the spoiler would be about 50 from the flush position. The spoiler is a multifunctional flight control surface with three main functions: in-flight airbraking for speed reduction; in-flight roll control (to augment the ailerons in turning); and airbraking on the ground, during lift dumping. The latter dispels the remaining lift as an aircraft touches down on a runway. This increases the efficiency of the wheel brakes by applying the full weight of the aircraft on the wheels.

Advantages and disadvantagesThere are a number of advantages to spoilers however. One is that spoilers are VERY effective. While this has been pointed out as a disadvantage, it becomes an advantage if you combine a spoiler with a small aileron. The aircraft designer would see to it that the aileron is used when only a gentle roll is commanded, but the spoilers kick in when more rapid roll is called for. By doing this the designer can give the pilot a lot of roll "authority" while using only a small amount of wing trailing edge for aileron. This makes it possible to use a large portion of the wing trailing edge for flaps. Combining spoilers with ailerons may be a great idea but it is rather complicated. As a result designers generally only do it if they need maximum possible flap. For most light aircraft a modest amount of flap is sufficient so the designer makes the ailerons as large as needed for good roll control and then uses whatever wingspan remains for flaps. But, in an airliner that may not be sufficient. Therefore, as mentioned above, many airliners have small ailerons with spoilers to assist in roll control, and thereby are able to have much larger flaps for reduced takeoff and landing speed. Their use is often limited, however, as turbulent airflow which develops behind them causes noticeable noise and vibration, which may cause discomfort to extra-sensitive passengers

Example Airbus A320

. The A320 has ground spoilers. These consist of the flight spoilers,plus four inboard ground spoiler panels. The purpose is to destroy lift above the wing. An autoamtic ground spoiler system may be armed. When the speed brake lever is pulled into the armed position and the thrust reversers are at idle, or when reverse thrust is selected on either engine, the surfaces will extend to 45 degrees, IF the airplane is on the ground and airspeeds are greater than 66 knots. It seems this limitation also applies to manual selection of the spoilers. If the airplane is in the air, spoilers are retracted at high AOA, or in full landing configuration. This could be relevant if the plane was floating, or didn't sense it was on the ground.

Horn balanceDefinition and Explanation: An aerodynamic balance for the ailerons, elevators, and rudders in which the area ahead of the hinge is concentrated on one part of the surface in the form of a horn. This horn produces a balancing moment, thus reducing the amount of force required to move the controls or the controls CG (center of gravity) forward of the hinge to reduce the likelihood of control flutter.

Advantages A: to obtain mass balancing. B: to prevent flutter. C: to decrease stick forces. D: to decrease the effective longitudinal dihedral of the aeroplane.

Insert Hinge Aerodynamic balancing is achieved in several ways, all of which decrease the the force required to move the control in flight. This form of balancing is generally done by hinging the control surface about a line set back from the leading edge. The effort required to move any control surface is determined by the aerodynamic force acting through the centre of pressure of the airfoil multiplied by the distance from the hinge line. This force is known as the hinge moment of the control surface: the smaller the hinge moment the less

is the effort required to move the surface through a given angle at a given speed.

Adjustable Stabilizer : Rather than using a movable tab on the trailing edge of the elevator, some aircraft have an adjustable stabilizer. With this arrangement, linkages pivot the horizontal stabilizer about its rear spar. This is accomplished by use of a jackscrew mounted on the leading edge of the stabilator. [Figure 5-23]

On small aircraft, the jackscrew is cable operated with a trim wheel or crank. On larger aircraft, it is motor driven. The trimming effect and flight deck indications for an adjustable stabilizer are similar to those of a trim tab.

FLAPERON:Definition and explanation: A flaperon is a type of aircraft control surface that combines aspects of both flaps and ailerons. In addition to controlling the roll or bank of an aircraft as do conventional ailerons, both flaperons can be lowered together to function similarly to a dedicated set of flaps. Both ailerons could also be raised, which would give spoilerons. The pilot has separate controls for ailerons and flaps. A mixer is used to combine the separate pilot input into this single set of control surfaces called flaperons. The use of flaperons instead of separate ailerons and flaps can reduce the weight of an aircraft. The complexity is transferred from having a double set of control surfaces (flaps and ailerons) to the mixer.

Many designs that incorporate flaperons mount the control surfaces away from 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 doppelflgel type of trailing edge surfaces used on a number of Junkers aircraft of the 1930s, such as the Junkers Ju 52 airliner, and Junkers Ju 87 Stuka iconic World War II dive bomber.

Advantages: Flaperons produce a much quicker roll rate than ailerons but when drooped too far with the flap handle the roll rate suffers. They are very effective in cross wind landing. Drooping them causes a nose down pitch in the kitfox. In the Kitfox models 1 through 4 they are used to trim the pitch.

They can be rigged with a few degrees of reflex in the down flap handle position. This position spills lift off the wing and can be used to lose altitude in a hurry when you want to. When installed below the trailing edge of the wing...like a kitfox...flaperons do not suffer from flow separation when the wing stalls so roll control is maintained well into the stall. Their primary purpose is to produce lift not drag. On my Kitfox 90% of the stall speed reduction is achieved with the flap handle about half way up. Beyond that they produce some drag but start to feedback into the ailerons and reduce the roll effectiveness. The design is simple with few parts. There is only one control rod to connect to each wing, which simplifies the wing folding process. I think this is one reason kitfox continues to use them.

ElevonDefinition and explanation: Elevons are aircraft control surfaces that combine the functions of the elevator (used for pitch control) and the aileron (used for roll control), hence the name. They are frequently used on tailless aircraft such as flying wings. An elevon that is not part of the main wing, but instead is a separate tail surface, is a stabilator. The word "elevon" is a portmanteau of elevator and aileron.

Elevons at the wing trailing edge are used for pitch and roll control. Top: on the F-102A Delta Daggerof 1953, an early use. Bottom: on the F-117A Nighthawk of 1981. Elevons are installed on each side of the aircraft at the trailing edge of the wing. When moved in the same direction (up or down) they will cause a pitching force (nose up or nose down) to be applied to the airframe. When moved differentially, (one up, one down) they will cause a rolling force to be applied. These forces may be applied simultaneously by appropriate

positioning of the elevons e.g. one wing's elevons completely down and the other wing's elevons partly down. An aircraft with elevons is controlled as though the pilot still has separate aileron and elevator surfaces at his disposal, controlled by the yoke or stick. The inputs of the two controls are mixed either mechanically or electronically to provide the appropriate position for each elevon.

RuddervatorDefinition and Explanation: A pair of control surfaces on the tail of an aircraft arranged in the form of a V. These surfaces, when moved together by the control wheel, serve as elevators, and when moved differentially by the rudder pedals, serve as a rudder. Ruddevators provide the same control effect as conventional control surfaces, but through a more complex control system that actuates the control surfaces in unison. Yaw moving the nose to the the left is produced on an upright V tail by moving the pedals left which deflects the left-hand ruddervator down and left and the right-hand ruddervator up and left. The opposite produces yaw to the right. Pitch nose up is produced by moving the control column or stick back which deflects the left-hand ruddervator up and right and the right-hand ruddervator up and left. Pitch nose down is produced by moving the control column or stick forward which induces the opposite ruddervator movements Advantages The theoretical advantage of this design is the reduced interference drag associated with two surfaces instead of three. On the V-tail the combined rudders and elevators are known as Ruddervators. The engineering is more complicated in this system

CanardThe term canard refers to a control surface that functions as a horizontal stabilizer but is located in front of the main wings. The term also is used to describe an airplane equipped with a canard. In effect, it is an airfoil similar to the horizontal surface on a conventional aft-tail design. The difference is that the canard actually creates lift and holds the nose up, as opposed to the aft-tail design which exerts downward force on the tail to prevent the nose from rotating downward. Although the Wright Flyer was configured as a canard with the horizontal surfaces in front of the lifting surface, it was not until recently that the canard configuration began appearing on newer airplanes. Canard designs

include two typesone with a horizontal surface of about the same size as a normal aft-tail design, and the other with a surface of the same approximate size and airfoil of the aft-mounted wing known as a tandem wing configuration. Theoretically, the canard is considered more efficient because using the horizontal surface to help lift the weight of the aircraft should result in less drag for a given amount of lift. The canards main advantage is in the area of stall characteristics. A properly designed canard or tandem wing will run out of authority to raise the nose of the aircraft at a point before the main wing will stall. This makes the aircraft stall-proof and results only in a descent rate that can be halted by adding power. Ailerons on the main wing remain effective throughout the recovery. Other canard configurations are designed so the canard stalls before the main wing, automatically lowering the nose and recovering the aircraft to a safe flying speed. Again, the ailerons remain effective throughout the stall. The canard design has several limitations. First, it is important that the forward lifting surface of a canard design stalls before the main wing. If the main wing stalls first, the lift remaining from the forward wing or canard would be well ahead of the CG, and the airplane would pitch up uncontrollably. Second, when the forward surface stalls first, or is limited in its ability to increase the angle of attack, the main wing never reaches a point where its maximum lift is created, sacrificing some performance. Third, use of flaps on the main wing causes design problems for the forward wing or canard. As lift on the main wing is increased by extension of flaps, the lift requirement of the canard is also increased. The forward wing or canard must be large enough to accommodate flap use, but not so large that it creates more lift than the main wing. Finally, the relationship of the main wing to the forward surface also makes a difference. When positioned closely in the vertical plane, downwash from the forward wing can have a negative effect on the lift of the main wing. Increasing vertical separation increases efficiency of the design. Efficiency is also increased as the size of the two surfaces grows closer to being equal.

Speed Brakes: In aeronautics, air brakes or speedbrakes are a type of flight control surface used on an aircraft to increase drag or increase the angle of approach during landing. The earliest known air brake was developed in 1931 and deployed on the wing support struts.[1] Not long after air brakes located on the bottom of the wing's trailing edge were developed and became the standard type of aircraft air brake for decades. Air brakes differ from spoilers in that air brakes are designed to increase drag while making little change to lift, whereas spoilers reduce the lift-to-drag ratio and require a higher angle of attack to maintain lift, resulting in a higher stall speed. Most gliders are equipped with spoilers on the wings in order to adjust their angle of descent during approach to landing. Often, characteristics of both spoilers and air brakes are desirable and are combined - most modern airliner jets feature combined spoiler and air brake controls. On landing, the deployment of these spoilers causes 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. In addition, the form

drag created by the spoilers directly assists the braking effect. Reverse thrust is also used to help slow the aircraft after landing. The British Blackburn Buccaneer naval strike aircraft designed in the 1950s had a tail cone that was split and could be hydraulically opened to the sides to act as a variable air brake. It also helped to reduce the length of the aircraft in the confined space on an aircraft carrier. The F-15 Eagle, Sukhoi Su-27 and other fighters have an air brake just behind the cockpit.

Wingtip devices are usually intended to improve the efficiency of fixedwing aircraft. There are several types of wingtip devices, and though they function in different manners, the intended effect is always to reduce the aircraft's drag by partial recovery of the tip vortex energy. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without materially increasing the wingspan. An extension of span would lower lift-induced drag, but would increase parasitic dragand would require boosting the strength and weight of the wing. At some point, there is no net benefit from further increased span. There may also be operational considerations that limit the allowable wingspan (e.g., available width at airport gates).

Wingtip devices increase the lift generated at the wingtip (by smoothing the airflow across the upper wing near the tip) and reduce the lift-induced drag caused by wingtip vortices, improving lift-to-drag ratio. This increases fuel efficiency in powered aircraft and increases cross-country speed in gliders, in both cases increasing range.[1] U.S. Air Force studies indicate that a given improvement in fuel efficiency correlates directly with the causal increase in the aircraft's lift-to-drag ratio.

A vortex generator (VG) is an aerodynamic surface, consisting of a small vane or bump that creates a vortex. Vortex generators can be found on many devices, but the term is most often used in aircraft design.[1] Vortex generators delay flow separation and aerodynamic stalling, thereby improving the effectiveness of wings and control surfaces (e.g.,Embraer 170 and Symphony SA-160). For swept-wing transonic designs, they alleviate potential shock-stall problems (e.g., Harrier, Blackburn Buccaneer, Gloster Javelin).

Method of operationVortex generators are most often used to delay flow separation. To solve this problem, they are often placed on the external surfaces of vehicles. On aircraft they are installed on the front third of a wing in order to maintain steady airflow over the control surfaces at the trailing edge. They are typically rectangular or triangular, about 80% as tall as 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 obliquely so that they have an angle of attack with respect to the local airflow. A vortex generator creates a tip vortex which draws energetic, rapidlymoving 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".

After-market installationMany aircraft carry vane vortex generators from time of manufacture, but there are also after-market suppliers who sell VG kits to improve the STOLperformance of some light aircraft.[4] After-market suppliers claim (i) that VGs lower stall speed and reduce take-off and landing speeds, and (ii) that VGs increase the effectiveness of ailerons, elevators and rudders, thereby improving controllability and safety at low speeds. For home-built and experimentalkitplanes, VGs are cheap, cost-effective and can be installed quickly; but for certified aircraft installations, certification costs can be high, making the kits relatively expensive. Owners fit after-market VGs primarily to gain benefits at low speeds, but a downside is that such VGs may reduce cruise speed slightly. In tests performed on a Cessna 182 and a Piper PA-28-235 Cherokee, independent reviewers have documented a loss of cruise speed of 1.5 to 2.0 kn (2.8 to 3.7 km/h) . However, these losses are relatively minor, since an aircraft wing at high speed has a small angle of attack, thereby reducing VG drag to a minimum.

Owners have reported that on the ground, it can be harder to clear snow and ice from wing surfaces with VGs than from a smooth wing, but VGs are not generally prone to in-flight icing as they reside within the boundary layer of airflow. VGs may also have sharp edges which can tear the fabric of airframe covers and may thus require special covers to be made. For twin-engined aircraft, manufacturers claim that VGs reduce single engine control speed (Vmca), increase zero fuel and gross weight, improve the effectiveness of ailerons and rudder, provide a smoother ride in turbulence and make the aircraft a more stable instrument platform.

Increase in maximum takeoff weightMany of the vortex generator kits available for light twin-engine airplanes bring with them the added benefit of an increase in maximum takeoff weight.[4] This might seem paradoxical because installation of vortex generators does not increase the strength of the wing. The maximum takeoff weight of a twin-engine airplane is determined by structural requirements and single-engine climb performance requirements (which are lower for a lower stall speed). For many light twin-engine airplanes, the single-engine climb performance requirements determine a lower maximum weight rather than the structural requirements. Consequently, anything that can be done to improve the single-engineinoperative climb performance will bring about an increase in maximum takeoff weight. In the USA from 1945 until 1991, the one-engine-inoperative climb requirement for multi-engine airplanes with a maximum takeoff weight of 6,000 lb (2,700 kg) or less was as follows: All multiengine airplanes having a stalling speed greater than 70 miles per hour shall have a steady rate of climb of at least in feet per minute at an altitude of 5,000 feet with the critical engine inoperative and the remaining engines operating at not more than maximum continuous power, the inoperative propeller in the minimum drag position, landing gear retracted, wing flaps in the most favorable position where hour. is the stalling speed in the landing configuration in miles per

Installation of vortex generators can usually bring about a slight reduction in stalling speed of an airplane[3] and therefore reduce the required one-

engine-inoperative climb performance. The reduced requirement for climb performance allows an increase in maximum takeoff weight, at least up to the maximum weight allowed by structural requirements.[6] An increase in maximum weight allowed by structural requirements can usually be achieved by specifying a maximum zero fuel weight or, if a maximum zero fuel weight is already specified as one of the airplane's limitations, by specifying a new higher maximum zero fuel weight.[6] For these reasons, vortex generator kits for many light twin-engine airplanes are accompanied by a reduction in maximum zero fuel weight and an increase in maximum takeoff weight.[6] The one-engine-inoperative rate-of-climb requirement does not apply to single-engine airplanes, so gains in the maximum takeoff weight (based on stall speed or structural considerations) are less significant compared to those for 19451991 twins. After 1991, the airworthiness certification requirements in the USA specify the one-engine-inoperative climb requirement as a gradient independent of stalling speed, so there is less opportunity for vortex generators to increase the maximum takeoff weight of multi-engine airplanes whose certification basis is FAR 23 at amendment 23-42 or later.

Maximum landing weightBecause most light twin engined aircraft landing weights are determined by structural considerations and not stall speed, most VG kits only increase the take-off weight available and not the landing weight. In these cases increasing the landing weight requires either structural modifications or else re-testing the aircraft to demonstrate that the certification requirements are still met at the higher landing weight.[6]

Wing fences, also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings. Not to be confused with wingtip fences, wing fences are flat plates fixed to the upper surfaces (and often wrapping around the leading edge) parallel to the airflow. They are often seen on swept-wing aircraft. They obstruct spanwise airflow along the wing, and prevent the entire wing from stallingat once. As a swept-wing aircraft slows toward the stall speed of the wing, the angle of the leading edge forces some of the airflow sidewise, toward the wing tip. This process is progressive, airflow near the middle of the wing is affected not only by the leading edge angle, but also the spanwise airflow from the wing root. At the wing tip the airflow can end up being almost all spanwise, as opposed to front-to-back over the wing, meaning that the effective airspeed drops well below the stall. Because the geometry of swept wings typically places the wingtips of an aircraft aft of itscenter of gravity, lift generated at the wingtips tends to create a nose-down pitching moment. When the wingtips stall, both the lift and the associated nose-down pitching moment rapidly diminish. The loss of the nose-down

pitching moment leaves the previously balanced aircraft with a net nose-up pitching moment. This forces the nose of the aircraft up, increasing the angle of attack and leading to stall over a greater portion of the wing. The result is a rapid and powerful pitch-up followed by a complete stall, a difficult situation for a pilot to recover from. The "Sabre dance" (which caused many F-100 Super Sabres to crash) is a notable example of this behavior.

A Polish Sukhoi Su-20, showing the wing fences in relation to its wings Wing fences delay, or eliminate, this effect by preventing the spanwise flow from moving too far along the wing and gaining speed. When meeting the fence, the air is directed back over the wing surface. Similar solutions included a notch in the leading edge, as seen on the Avro Arrow, or the use of slats, as on the later versions of the F-86. Slats can act as fences directly, in the form of their actuators, but also reduce the problem by improving the angle of attackresponse of the wing and moving the stall point to a lower speed. Wolfgang Liebe, who is generally credited with inventing wing fences, filed a patent[1] for it in 1938 while working on the Messerschmitt Me.109B. After World War II, Soviet military aircraft designers became known for their habit of using wing fences, using them on aircraft as varied as Mikoyan MiG-15s and Tupolev Tu-22Ms.

Stall strips

A stall strip factory installed on an American Aviation AA-1 Yankee A stall strip is a fixed aerodynamic device employed on fixedwing aircraft to modify the airfoil used.[1] They are usually factory-installed or, on rarer occasion, an after-market modification. Stall strips are almost always employed in pairs, symmetrically on both wings. In rare installations they are employed as a single strip on one wing to correct aberrant stall behaviour. Operation A stall strip alters the wings stall characteristics and ensures that the wing root stalls before the wing tips. This is usually as a result of initial aircraft flight testing which shows that the existing stall characteristics are unacceptable for certification. In some cases, such as the American Aviation AA-1 Yankee, stall strips are planned to be used on the wing from the start. In the case of the AA-1 the left and right wings were identical, interchangeable and built on a single wing jig, thus the more traditional use of washout in the wing design was not possible. Stall strips can be an alternative to washout in aircraft design or they can be used as well as washout to improve stall performance.

Stall strips typically consist of a small piece of material, usually aluminium, triangular in cross section and often 6-12 inches (1530 cm) in length. It is riveted or bondedon the point of the wings leading edge, usually at the wing root. Here it acts to trip the boundary layer air flow at higher angles of attack, causing turbulent flow and air flow separation. This has the effect of causing the wing root to stall before the outer portions of the wing, ensuring a progressive outward stall, minimizing the risk ofspinning and giving maximum aileron control throughout the stall.

References http://www.ultraligero.net/Cursos/mecanica/fundamentos_de_la_mecanica _de_vuelo.pdf http://en.wikipedia.org/wiki/Vortex_generator http://en.wikipedia.org/wiki/Wingtip_device http://en.wikipedia.org/wiki/Wing_fence http://en.wikipedia.org/wiki/Stall_strips http://www.vortexgenerator.net/

http://answers.yahoo.com/question/index?qid=20080128151003AApiZqI http://www.mitsubishimotors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf http://selair.selkirk.bc.ca/training/aerodynamics/roll.htm