* Longitudinal axis (Aviation) - Definition,meaning - Online Encyclopedia The characteristic of returning to the trimmed angle of attack after a displacement ... longitudinal axis An imaginary line running from the nose to the tail of an aircraft ; one of the three axes of an aircraft . Rotation about the longitudinal axis is called " roll " and is controlled using the ailerons . Longitudinal Axis Straight line through the centre of gravity that runs parallel with the line that would run from nose to tail Magnetic Course The angle (measured in a clockwise direct ion) between the course of an aeroplane and Magnetic North ... Rotation about the longitudinal axis is called roll and is controlled by the outboard movable portions of each wing : the ailerons . The term " aileron " is the French word for "little wing ." Ailerons are located on the trailing (rear) edge of each wing near the outer tips. Bank : Aspect of Rotation of airplane about its longitudinal axis. Barrel Roll : Airplane rolled about a line offset but parallel to its longitudinal axis. BC: Bomber Command BD or Bomb. Div.: Bombardment Division Beat up the field: Unauthorized high- speed "buzz" over friendly airfield.

Aircraft perform much better if their longitudinal axis is accurately aligned, in plan view, with the flight path ; i.e. with the relative airflow. Also, an aircraft flying with a constant angle of slip is part way to ending up in an unusual flight attitude . Rotation about the longitudinal axis is called roll and is controlled by the ailerons . The rotation is similar to a barbecue rotisserie, in which the spit is the longitudinal axis. The angle between the airplane 's wings and the horizon is known as the airplane 's bank . It is a plane at right angles to the longitudinal axis of the aircraft . For each aircraft make and model, all locations of equipment, tanks , baggage compartments, seats, engine s, propeller s, etc. They refer to the Y axis as the lateral axis and the X axis as the longitudinal axis, which are sensible enough, but then they refer to Y-axis stability as longitudinal stability and X-axis stability as lateral stability — which seems completely reversed and causes needless confusion. Angle of Incidence : The angle of incidence is the angle formed by the longitudinal axis of the airplane and the chord of the wing . The longitudinal axis is an imaginary line that extends lengthwise through the fuselage from nose to tail.

The pilot should realize that if the CG of an airplane is displaced too far forward on the longitudinal axis, a nose- heavy condition will result. Conversely, if the CG is displaced too far aft on the longitudinal axis, a tail- heavy condition will result. The two ailerons , one at the outer trailing edge of each wing , are movable surfaces that control movement about the longitudinal axis. The movement is roll . Lowering the aileron on one wing raises the aileron on the other. Calculations for the longitudinal axis of the guidance modes. The control law longitudinal axis input data are: Reference Acceleration, Reference Acceleration Gain, Desired Velocity , Velocity Error Scale Factor. Thus the longitudinal axis of the aircraft is at an angle to the runway while its ground track is along the extended centerline of the runway . Buttock line (BL) - The longitudinal axis of the aircraft that serves as the reference location for positions to the left and right of center. The positions are usually dimensioned in inches. Related Definitions from Aviation Glossary ... TAILWIND - Any wind more than 90 degrees to the longitudinal axis of the runway . The magnetic direct ion of the runway shall be used as the basis for determining the longitudinal axis.

This is borrowed from full sized helicopters , and is a rotor head which allows the blades to flap , drag and feather. ROLL - Movement of an aircraft about its longitudinal axis, representing a wing -over rolling action. ROTARY ENGINE - Cylinders disposed as for radial engine , but in this case the crankshaft is fixed, and cylinders and crankcase rotate around it. ANGLE OF INCIDENCE - The angle at which an airfoil is normally fixed in relation to the longitudinal axis of an aircraft . ANHEDRAL - The downward angle of a wing in relation to a horizontal cross-section line; aka CATHEDRAL . SEE DIHEDRAL . APPROACH CONTROL SEE RADIO NAVIGATION ... This is the angle that is measured between the longitudinal axis, running through the length of the aircraft , and the chord line of the wing . On most aircraft s, the wing is inclined relative to its fuselage , so there is a slight positive angle of incidence . The direct ion in which the longitudinal axis of an aircraft is pointed, usually expressed in degrees from North (True, Magnetic, Compass or Grid). inclination of the longitudinal axis to the horizontal in the steady state (+ve upwards) ...

chord Distance from leading-edge to trailing-edge measured parallel to longitudinal axis. CIA Central Intelligence Agency. CIS Commonwealth of Independent [ex-USSR] State s. See also RFAS. The operator holds the scribe by the end of the long handle and pressing the point of the pin into the grain, pulls the scribe in the direct ion of the longitudinal axis or what appears to be the grain direct ion. TAIL NUMBER An airplane 's registration number. TAIL WIND Winds that are more than 90 degrees to the longitudinal axis of the runway . TARMAC An airport surface paved with the substance, especially a runway or an apron at a hangar . Rotation about an axis aligned with the direct ion in which the aircraft is flying. This axis is also known as the longitudinal axis. rotorcraft An aircraft that derives its lift from rotating lifting surfaces (usually called blades) ... Direct ion is indicated to the pilot as a magnetic bearing or as a relative bearing to the longitudinal axis of the aircraft depending on the type of indicator installed in the aircraft . Ailerons . Primary flight control surface s mounted on the trailing edge of an airplane wing , near the tip. Ailerons control roll about the longitudinal axis. Aircraft .

A device that is used, or intended to be used, for flight . Preliminary examination revealed substantial damage to the engine firewall and left wing . Tire skid marks on the runway were consistent with the nose landing gear tire contacting the runway at an approximate 90-degree angle to the airplane 's longitudinal axis. factors affecting aircraft stability aerodynamics Your browser does not support inline frames or is currently configured not to display inline frames. stability of an airplane The aircraft's response to disturbance is associated with the inherent degree of stability built in by the designer, in each of the three axes; and eventuating without any reaction from the pilot. Another condition affecting flight is the aircraft's state of trim ï¿½ or equilibrium where the net sum of all forces equals zero. Some aircraft can be trimmed by the pilot to fly 'hands off' for straight and level flight, for climb or for descent. If the trim is wrong, and perhaps it flies with one wing low, inherent stability will maintain that wing-low attitude and not restore the aircraft to a wings-level attitude. It is desirable that longitudinal trim doesn't change significantly with alterations in power, nor does directional trim change significantly with alterations in airspeed.

An aircraft's stability is expressed in relation to each axis: lateral stability ï¿½ stability in roll, directional stability ï¿½ stability in yaw and longitudinal stability ï¿½ stability in pitch. The latter is the most important stability characteristic. Lateral and directional stability are inter-dependent. Degrees of stability An aircraft will have differing degrees of stability around each axis; here are a few examples: A totally stable aircraft will return, more or less immediately, to its trimmed state without pilot intervention; however such an aircraft is rare ï¿½ and undesirable. We usually want an aircraft just to be reasonably stable so it is easy to fly: if it is too stable they tend to be sluggish in manoeuvring and heavy on the controls. If it tends toward instability the pilot has to continually watch the aircraft's attitude and make the restoring inputs, which becomes tiring, particularly when flying by instruments. Some forms of instability make an aircraft unpleasant to fly in bumpy weather. The normally or positively stable aircraft, when disturbed from its trimmed flight state will ï¿½ without pilot intervention ï¿½ commence an initial movement back towards the trimmed flight state but over-run it, then start a series of diminishing damping oscillations about the original flight state.

This damping process is usually referred to as dynamic stability and the initial movement back towards the flight state is called static stability. The magnitude of the oscillation and the time taken for the oscillations to completely damp out is another aspect of stability. Unfortunately a statically stable aircraft can be dynamically unstable in that plane i.e. the oscillations do not damp out. The neutrally dynamically stable aircraft will continue oscillating after disturbance but the magnitude of those oscillations will neither diminish nor increase. If these were oscillations in pitch the aircraft will just continue 'porpoising' ï¿½ if there were no other disturbances and the pilot did not intervene. The negatively stable or fully unstable aircraft may be statically unstable and never attempt to return towards the trimmed state. Or it can be statically stable but dynamically unstable, where it will continue oscillating after disturbance with the magnitude of those oscillations getting larger and larger. Significant instability is an undesirable characteristic, except where an extremely manoeuvrable aircraft is needed and the instability can be continually corrected by on-board 'fly-by-wire' computers rather than the pilot ï¿½ for example, a supersonic air superiority fighter.

The best piston-engined WW2 day fighters were generally designed to be just stable longitudinally, neutrally stable laterally and positively stable directionally. Longitudinal stability Longitudinal stability is associated with the restoration of aoa to the trimmed aoa after a disturbance changes it. Angle of incidence Angle of incidence is a term which is sometimes confusingly used as being synonymous with wing angle of attack, however the former cannot be altered in flight. Angle of incidence, usually just expressed as incidence, is within the province of the aircraft designer who calculates the wing aoa to be employed in the main role for which the aircraft is being designed, probably the aoa in performance cruise mode. The designer might then plan the fuselage wing mounting so that the fuselage is aligned to produce the least drag when the wing is flying at the cruise aoa. Wings which incorporate washout will have differing angles of incidence at the wing root and at the outer section. A notional horizontal datum line is drawn longitudinally through the fuselage and the angle between that fuselage reference line (FRL) and the wing chord line is the angle of incidence. Incidence should be viewed as the mounting angle of the fuselage rather than the mounting angle of the wings.

Incidence may also be called the 'rigger's incidence' or some similar expression carried over from the earlier days of aviation. Longitudinal dihedral An angle of incidence is also calculated for the horizontal stabiliser with reference to the FRL and the angular difference between wing and stabiliser angles is called the longitudinal dihedral, although it is probably more correct to say that the longitudinal dihedral is the angular difference between the two surfaces at their zero lift aoa. Incidentally the angle of the line of thrust is also expressed relative to the FRL. It is the longitudinal dihedral, combined with the horizontal stabiliser area and moment arm, which provides the restoring moment to return aoa to the trimmed state. However bear in mind that the moment arm, which supplies the restoring leverage and thus the stability, is affected by the cg position and if the cg lies outside its limits the aircraft will be longitudinally unstable. When flying with level wings, at a particular weight, each aoa is associated with a particular IAS. We might as well take advantage of that by arranging the longitudinal dihedral so that the built-in state of trim produces a particular indicated airspeed.

Directional stability Directional stability is associated with the realigning of the longitudinal axis with the flight path (the angle of zero slip) after a disturbance causes the aircraft to yaw out of alignment and produce slip; remember yaw is a rotation about the normal (vertical) axis. The restoring moment ï¿½ the static stability ï¿½ provided by the fin is the product of the fin area and the moment arm and the moment arm leverage will vary according to the cg position ï¿½ the aircraft's balance. The area required for the fin has some dependency on the net sum of all the restoring moments associated with the aircraft fuselage and undercarriage side surfaces fore (negative moments) and aft (positive moments) of the cg. Some aircraft have ventral or dorsal fins added to increase their directional stability. The areas of side surface above and below the cg also affect other aspects of stability. The similar term 'weathercocking' refers to the action of an aircraft, moving on the ground, attempting to swing into wind. It is brought about by the pressure of the wind on the rear keel surfaces, fin and rudder causing the aeroplane to pivot about one or both of its main wheels.

It is usually more apparent in tailwheel aircraft because of the longer moment arm between the fin and the main wheels: although if a nosewheel aircraft is 'wheelbarrowing' with much of the weight on the nose wheel, then there will be a very long moment arm between the nose wheel pivot point and the fin. Lateral stability Lateral stability refers to roll stability about the longitudinal axis and ailerons provide the means whereby the aircraft is rolled in the lateral plane. However, unlike the longitudinal and normal planes where the horizontal and vertical stabilisers provide the restoring moments necessary for pitch and yaw stability, no similar restoring moment device exists in the lateral plane. But let's imagine that some atmospheric disturbance has prompted the aircraft to roll to the left, thus the left wingtip will be moving forward and down, the right wingtip will be moving forward and up. Now think about the aoa for each wing ï¿½ the wing that is moving down will be meeting a relative airflow coming from forward and below and consequently has a greater aoa than the rising wing.

A greater aoa, with the same airspeed, means more lift generated on the downgoing side and thus the left wing will stop going further down or perhaps even rise and return to a wings level state. This damping of the roll is known as lateral damping. So roll stability, except at or very close to the stall, is intrinsic to practically all single-engined light aircraft. (When the aircraft is flying close to the stall the aoa of the downgoing wing could exceed the critical aoa and thus stall, which will exacerbate the wing drop and might lead to an incipient spin condition. But, and there always seems to be a 'but', when the aircraft is banked other forces come into play and affect the process. If you re-examine the turn forces diagram in the manoeuvring forces module you will see that when an aircraft is banked the lift vector has a substantial sideways component, in fact for bank angles above 45ï¿½ that sideways force is greater than weight. So we can say that any time the aircraft is banked, with the rudder and elevators in the neutral position, an additional force will initiate a movement in the direction of bank i.e. creating a slip.

The aircraft's directional stability will then yaw the nose to negate the slip and the yaw initiates a turn, which will continue as long as the same bank angle is maintained. There are several design features that stop that slip and level the wings thus promoting lateral stability, for instance placing the wing as high as possible above the cg promotes 'pendulum' stability; the feature usually employed with low wing monoplanes is wing dihedral, where the wings are tilted up from the wing root a few degrees. Another design method is anhedral where the wings are angled down from the wing root, but it is unlikely to be used in light aircraft. Spiral instability An aircraft with positive spiral stability tends to roll out of a turn by itself if the controls are centred. Some light aircraft with little or no wing dihedral and a large fin tend to have strong static directional stability but are not so stable laterally. If a sideslip is introduced by turbulence ï¿½ and left to their own devices ï¿½ such aircraft will gradually start to bank and turn, with increasing slip and hence increasing turn rate and rapid increase in height loss.

The condition is spiral instability and the process is spiral divergence which, if allowed to continue and given sufficient height, will turn into a high speed spiral dive. Neutral spiral stability is the usual aim of the designer. It is evident that directional stability and lateral stability are coupled and to produce a balanced turn, i.e. with no slip or skid, the aileron, rudder and elevator control movements and pressures must be balanced and co-ordinated. Your browser does not support inline frames or is currently configured not to display inline frames.

Aerodynamics and Theory of Flight, Forces of Flight, Lift, Weight, Thrust, Drag, Generating Lift, Airfloils, Angle of Attack, Parasitic Drag, Induced Drag, Groiund Effect, Boundary Layer, Stalls, Factors Affecting Aircraft Stalls, Spins, Aircraft Lift and Drag Concepts, Drag Curve, Maximum-distance Glide, Maximum lift-drag Ratio, Wing Design, Laminar and conventional airfoils, Angle of Incidence, Washoiut, Stall Strips, Airfoil Variation, Wing Fences, Winglets, Slots and Slats, Aircraft Spoiler and Speed Brakes, Aircraft Flap Variations, Aircraft Stability, Longitudinal Stability, Lateral Stability, Dihedral, Directional Stability, Dutch Roll, Forces during Takeoff, Critical Engine, High-speed Flight, Compressibility, Transonic Flight, Langley Flying School Students / Resources / Classroom / Commercial Pilot Groundschool / Aerodynamics and Theory of Flight AERODYNAMICS AND THEORY OF FLIGHT Forces of Flight Lift Lift is an artificial force manipulated by pilot; it is generated through the wings, acts perpendicular to the relative wind and wingspan.

The theoretical concept that summarizes the direction and force of lift is the centre of pressure. Lift opposes weight—during level cruise, lift equals weight; during climb, lift is greater than weight; and during descent, weight is greater that lift. Weight Weight is a natural (uncontrollable) force generated by gravity (g force) that acts perpendicular to earth’s surface; theoretically, weight is exerted through the centre of gravity, and opposes lift. Thrust Thrust is an artificial force manipulated by pilot and generated through engine(s) that acts horizontally, parallel to flight path; thrust opposes drag—when airspeed constant, thrust equals drag; when airspeed accelerating, thrust is greater than drag; and when decelerating, drag is greater than thrust. Drag Drag is the natural resistance of an aeroplane while it is moving through air; it is partially controlled by pilot. Drag is a horizontal force acting parallel to flight path, and is opposed to thrust. Generating Lift Airfoils As viewed as a cross-section, the upper surface of an airfoil has more camber (curve) than lower surface. A straight line from leading edge to trailing edge is referred to as the chord.

With this structure, lift is generated by two process—what are referred to as pressure differential and ram air. Lift by pressure differential is based on the theory of Daniel Bernoulli (Bernoulli’s Theorem)—the faster a fluid flows (including air), the lower will be the pressure surrounding it; given the difference of the camber of the upper and lower surfaces, the air passing over the foil has greater distance to travel than the air passing under the airfoil; the air passing over must therefore travel faster than the air passing under the foil; a low air-pressure region is created above the accelerated air flow; the foil is displaced toward the lower pressure (upward) above the wing. This pressure differential accounts for about 50% of the lift, while the remaining lift is generated by ram air. With ram air, air is rammed under the foil, creating downwash and resultant upward pressure—this is based on Isaac Newton’s Third Law (the application of force causes an equal opposite force). Angle of Attack Lift varies with the angle of attack—the angle between the relative wind (parallel to flight path) and the chord line (line between leading and trailing edge).

Generally, the greater the angle of attack, the greater the lift—lift increases because the distance the air must flow along the upper camber increases, and the ram air and downwash increase. An excessive angle of attack, referred to as the critical angle of attack (usually about 20°) will produce a stalled condition—laminar airflow above the wing is displaced by turbulent airflow, and differential pressure collapses. Parasitic Drag Parasitic drag is drag created by those parts of an aeroplane that do not contribute to lift—e.g., the tires, windshield, rivets, etc. There are, in turn, three forms of parasitic drag—form drag, skin-friction drag, and interference drag. Form drag is caused by the frontal areas of the aeroplane, and is reduced by streamlining. Skin-friction drag is caused by the air passing over the aeroplane surfaces, and is reduced by smoothing the surfaces (flush riveting, smooth paints, and waxing). Interference drag is caused by the interference of airflow between parts of an aeroplane (wings and fuselage or fuselage and empennage) and is reduced by filleting interference areas.

Induced drag Induced drag is created by those parts of the aeroplane that create lift—the wings and the horizontal tail surface; induced drag is said to be the by-product or cost of lift—that is, the greater the angle of, attack, the greater the induced drag. Induced drag does not increase with speed; instead, as speed decreases induced drag increases. Induced drag is associated with difference in pressure that exists above and below a wing surface—as airspeed decreases, an airfoil must produce an increased low pressure above the wing, and an increased high pressure below the wing. At the wingtip these disparate pressures meet in the form of a vortex as the high pressure flow around the wingtip is sucked into the low pressure above the wing; the greater the pressure differences (such as in the case in slower flight), the greater the vortices are at each wing tip, and the greater the drag caused by these vortices.

1 Ground Effect Ground effect is a term used to describe the reduced drag and increased lift experience when an aircraft is flying close to the ground—as is the case, for example, during landings and takeoffs; the reduce drag associated with ground effect is the result of the ground interfering with the formation of the wingtip vortices. Ground effect exists when the aircraft is within one wingspan distance from the ground, but is most effective at distances equal or less than ½ wingspan (i.e., ½ the distance between the wingtips). Boundary Layer During flight, there are two types of airflow along the upper camber of an airfoil—turbulent and laminar (smooth). Turbulent and laminar flow are separated by a point of transition or separation point; as the angle of attack is increased, the portion of the upper airflow that is turbulent also increases (it migrates forward from the trailing edge) and therefore produces increased drag.

Vortex generators are small fins (approximately 1 inch tall) that are placed along the leading edge of an air foil; the vortex generators are themselves small air foils that are placed perpendicular to the upper wing surface, and are positioned so as to meet the laminar flow coming over the wing with a slight angle attack; the vortex generators, as the name implies, generate vortices which regenerate the boundary layer and delay turbulent flow (boundary layer separation). Stalls Stalls occur at the critical angle of attack, where induced drag (airfoil drag) exceeds lift—the wing can no longer produce sufficient lift to counteract weight. As the airfoil approaches the critical angle of attack, the point of transition, or separation point, moves forward enough to exceed the design factor of the wing. In contrast, the centre of pressure moves forward as the angle of attack is increased until the critical angle of attack is achieved; when a stall occurs, the centre of pressure moves rearward, causing the instability associated with stall phenomena. As said earlier, the stalling angle is usually 20°. Since most aircraft lack angle-of-attack indicators, airfoil angle is measured by indicated airspeed (IAS)—our best estimate of the actual angle of attack.

As a rule, aircraft will usually stall near the stalling speed published in the Pilot Operating Handbook; however, IAS does not always accurately indicate angle of attack, as in the case of a high-speed stall. Factors that affect the Stall Contaminants. Snow, frost, ice and dirt—all of these disrupt the laminar flow and therefore reduce airfoil lift capability. It is illegal to fly with snow, frost, or ice adhering to critical surfaces of the aircraft—“wings, control surfaces, rotors, propellers, horizontal stabilizers, vertical stabilizers or any other stabilising surface of an aircraft (CAR 602.11).” Contamination to the extent of medium to coarse sandpaper will reduce lift by 30% and increase drag by 40%. Weight. Increased weight requires increased lift and an increased angle of attack; therefore the critical angle of attack (stall) will occur at higher airspeeds. Stated another way, if two aircraft are travelling at the same airspeed, but one is heavier than the other, the angle of attack of the heavier aircraft is greater than the lighter aircraft and therefore that much closer to the critical angle of attack. Centre of Gravity.

Stalling speed increases as the aircraft C of G moves forward. As the C of G moves forward, the negative lift generated by the horizontal tail surface will have to be increased. Any increase in the negative lift produced by the tail will effectively increase the aerodynamic weight of the aircraft—producing the same effect as described above with respect to weight. Conversely, stalling speeds decrease as the C of G moves aft as less negative lift is required from the tail and the aircraft is aerodynamically lighter. While the benefits of a rearward C of G is a lower stall speed, the adverse result of a rearward C of G is less stability as there is less tail force that can be manipulated by the pilot through elevator or stabilator control. Turbulence. Upward vertical gusts abruptly increase the angle of attack beyond the stalling angle, irrespective of airspeed. Turns. During a turn in level flight, greater lift is required to offset increased load factor; the critical angle of attack is therefore reached at higher airspeeds.

The formula is as follows—normal stalling speed times the square root of the load factor equals banked stall speed; accordingly, an aircraft with a stall speed of 50 KTS in a 60°-banked turn (load factor of 2.0) will stall at 71 KTS. During a climbing turn, the inner wing has a smaller angle of attack than the outer wing; the outer wing will therefore stall first. The reverse is the case for descending turn, where the inner wing has a larger angle of attack and will therefore stall first. 2 Flaps. An increase in airfoil lift is produced by the use of flaps, and the stall speed is decreased by their use. Spins Spinning is defined as autorotation that develops after an asymmetrical or aggravated stall (a wing dropping during a stall)—the downward moving wing has a higher angle of attack and more induced drag than the upward moving wing and therefore acquires a greater stalled condition. Spinning involves simultaneous roll, yaw, and pitch as it develops a helical or corkscrew path nose down. An incipient spin is the autorotation prior to a vertical descent path, while a fully developed spin begins once the vertical path is achieved.

Lift and Drag Concepts Factors that affect lift and drag can be expressed in the following formulas: Lift = CL × ½ pV2 × S Drag = CD × ½ pV2 × S In these formula, CL = lift coefficient (angle of attack) CD = drag coefficient S = the plan area (or wing area) of an airfoil V= the TAS or an aircraft’s velocity squared p = the density of the air. Don’t be alarmed by the esoteric appearance of these formulas. Coefficient simply means a value that is constant or predictable, and in this case it is by virtue of the shape and design of the airfoil—the coefficient (whether for drag or lift) will vary with the angle of attack of the airfoil. Therefore, think of CL or CD as “angle of attack”. Note, however, that the rest of the equation is the same for both lift and drag, and further note that air density and TAS, and wing area are concepts which you are likely already familiar with. So what is the big deal with these formulas? The answer is this: V2. Lift and drag increase exponentially with speed—if speed is doubled, drag or lift will be quadrupled.

In contrast the relationship between lift or drag and air density is a direct relationship such that an increase or decrease in air density will cause an increase or decrease in both drag and lift. The relationship between drag and speed is of special interest with respect to the concepts of flight for maximum endurance (VME) and maximum range (VMR), as well as the concept of slow flight. As speed increases, parasitic drag increases exponentially, and as speed decreases, induced drag increases exponentially. This is referred to as the drag curve. At the bottom of the drag curve—that is, the position at where drag is at the combined minimum value—is the speed for maximum range—i.e., the speed at which the maximum amount of speed (or distance) is obtained per unit of fuel. To decrease speed from VMR would increase fuel consumption as a result of increased induced drag, while to increase speed from VMR would increase fuel consumption as a result of increased parasitic drag. The bottom of the drag curve is the most efficient speed at which the airfoil can generate maximum lift and minimum drag—this is the speed at which you will maximum-distance glide. If you were to express lift and drag as a ratio, this position would be referred to as the maximum lift-drag ratio.

In contrast, we can also produce a curve—again relative to changes in speed—representing the minimum amount of power necessary to offset drag; this power curve would be quite similar in shape to the drag curve. The bottom of the power curve would be the maximum endurance speed (VME). If we could compare the two curves—power and drag—we would note that VME is slightly less that VMR. Flight between VME and VSO is the slow flight range. Wing Design Laminar and conventional airfoils Two types of airfoils commonly used are the laminar and conventional airfoils; as a rule, the laminar foil is faster, but the cost is more adverse stalling characteristics. The two types differ with respect to location of the maximum camber—while the maximum camber on a conventional airfoil is located 25% behind the leading edge, the laminar maximum camber is located at 50% chord. On the laminar foil, a greater portion of the upper camber is dedicated to laminar airflow; there is therefore less surface friction drag. The cost of this, however, is that the transition or separation point jumps rapidly forward at the approach of a stall.

Additionally, the laminar foil is more susceptible to surface contamination. Angle of incidence The angle of incidenceis defined as the angle between the chord line and the longitudinal axis of the aeroplane; designers select an angle that provides optimum lift/drag ratio. Washout Washout is a design trait that pacifies or softens the stall characteristics of an aeroplane whereby the wings are twisted such that the wing tips have a lower angle of incidence than the wing root. This means that the entire wing will not stall simultaneously; instead, the stall will progressively move from the roots to the tips. Since the wing tips are the last to stall, the ailerons will remain effective longer during the stall. Stall Strips Stall strips are triangular strips placed on a portion of the leading edge of wing; they also have the effect of pacifying the stall characteristic of an aircraft—instead of the entire wing surface stalling uniformly, stall strips create a two-phase stall whereby those portions of the wing behind the strips stall first as the angle of attack is increased. Airfoil Variation Airfoil variation is in fact span-wise airfoil variation whereby a thin high-speed airfoil is designed near the roots, and a thick low-speed airfoil near the tips.

The result is that the high-speed roots stall before the low-speed tips—again, this prolongs aileron control. Wing Fences Wing fencesare vertical fins that are attached to the upper wing surface and serve the function of reducing the out-flow of air over the upper camber and therefore reduce induced drag. Winglets Winglets 3 are vertical wing-like surfaces attached to the wingtips; they serve the function of inhibiting the development of wingtip vortices, and therefore reduce induced drag. Slots and Slats These are two leading-edge devicesused to enhance lift in high angle of attack attitudes. Slots are passageways located just aft of the wing’s leading edge, through which air flows through the wing and becomes laminar flow along the upper surface without having to transition over the leading edge; turbulent flow over the upper surface is therefore reduced by slots. In contrast, slats are auxiliary airfoils attached to the leading edge and which move ahead of the main airfoil at high angles of attack and enhance laminar flow; the enhancement of laminar flow is caused by the reduced angle of attack of the auxiliary airfoil, when compared to the main airfoil. The space between the two airfoils is considered to be a slot.

Spoilers and Speed Brakes Spoilers are designed to spoil lift and increase drag in the portion of the upper wing surface where they are located. Spoilers may be designed only to operate during roll movements, in which case they are referred to as roll spoilers. On some aircraft such as the Mitsubishi MU-2, only roll spoilers create roll as there are no ailerons; on the Dash 8, two roll spoilers are automatically activated on the down-going wing to assist aileron deflection at speeds below 140 KTS, while only one roll spoiler operates on the down-going wing at airspeeds greater than 140. 4 Spoilers may be used symmetrically on both wings during flight or during touchdown to produce decreased lift and increased drag; if used in the air they are referred to as flight spoilers, while if used on the ground at touchdown, they are referred to as ground spoilers. In contrast, speed brakes are not designed to undermine or spoil lift, but are instead simply designed to increase drag; speed brakes can be mounted on the fuselage or the wing, and incorporate plates that extend into the airflow. Unlike spoilers, speed brakes do not increase the sink-rate of an aircraft, but simply decrease airspeed.

Flap Variations There are six types of flaps commonly used: Stability Aeroplane movement is based on three axes: the vertical (normal) axis, the lateral axis, and the longitudinal axis; all three axes pass through the aircraft C of G; stability is defined as the tendency of an aircraft to return to, stay at, or move farther from its original attitude after it has been displaced. There is positive, neutral, and negative stability, and stability is separated into static and dynamic categories Longitudinal Movement around the longitudinal axis is roll, which produces bank, and is produced by the ailerons; longitudinal stability (of the axis) is provided by a nose-heavy design and a negative-lift tail. Lateral Movement around the lateral axis is pitch, and is produced by the elevator; lateral stability (of the axis) is provided by dihedral, which lowers C of G relative to the lifting surfaces (wing tips are positioned higher than the wing roots); in short, the downward moving wing has greater lift than an upward moving wing.

Directional Movement around the vertical (normal) axis is yaw, and is “controlled” by the rudder; adverse yaw takes place during rolling movement because of aileron drag, and is controlled by rudder; stability of the vertical axis is referred to as directional stability, and is produced by the vertical stabilizer and sweptback (sweepback) wing design. Dutch Roll The term Dutch roll refers to a tendency for an aircraft to roll whenever there is yaw. Swept wing aircraft are particularly susceptible, and many are equipped with yaw damper, which is an automatic device that senses yaw and counters it with corrective control inputs before the Dutch roll oscillations can develop. Gregory N. Brown and Mark J. Holt describe the phenomena as follows: Dutch roll is caused by an aircraft’s tendency to sideslip slightly when the aircraft yaws. One wing yawing forward in this situation changes the effective span between left and right wings. The wing yawed forward momentarily creates more lift than the one of the other side. The result is that the forward wing rises and starts a rolling movement.

The problem is aggravated by the fact that the forward wing, due to its increased lift, also has more drag, pulling that wing back once again and starting an oscillation in the other direction. 5 Forces during Takeoff There are many forces that produce left yaw tendencies in most aircraft and must be controlled by rudder, Torque—caused by prop and engine: movement in one direction causes movement in another. Precession—a gyroscopic force whereby pressure exerted on a spinning mass will cause a reaction 90° along the direction of rotation. Asymmetric thrust or P-factor—during high-pitch attitudes (climbs), the downward moving side of the prop disk produces greater lift than the upward moving side. Viewed from the pilot seat, the right side of the prop disc is the down-going side and therefore produces greater thrust than the up-going left side (in most conventional engines). Slipstream—propeller slipstream spirals around the fuselage and strikes the vertical stabilizer on the port side. Critical Engine The effect of asymmetric thrust in multi-engine aeroplanes is to create what is referred to the critical engine. The critical engine is defined as the engine that, should a failure occur, will most adversely affect aircraft performance and control.

On a twin-engine aircraft when both propellers turn clockwise (as viewed from the rear of the aircraft), the failure of the left engine will have the more adverse effect because the remaining thrust from the right engine, owing to asymmetric thrust, would be further from the longitudinal axis than would be the case if the right engine failed and only the left were producing thrust. Note that some twin-engine aircraft do not have a critical engine as the right engine has a counter-rotating propeller. High-speed Flight Compressibility High-speed flight is flight near, but below the speed of sound. Below high-speed—what is regarded as slow-speed flight—the movement of air around an aircraft during flight does not involve compression of the airflow—what is referred to as compressibility. Instead, the behaviour of slow-speed airflow entails the rules of aerodynamics discussed thus far—the flow of air is like the flow of water around rocks in a stream, where the flow accelerates or slows, based on size and surface features of obstructions to the flow of water. In contrast, high-speed flight is different.

Because of the speed of the airframe and wings, etc., the air cannot move out of the way; instead of flowing around the wing, for example, the air cannot get out of the way fast enough, resulting in a compression of the air particles. Compressibility introduces radical changes in aerodynamic principles of high-speed flight. As the aircraft moves through the air, a pressure wave is propagated ahead of the aircraft, 6 which, as Linda D. Pendleton describes, effectively warns the air molecules that lie in the path of the aircraft that the wings, fuselage, etc., are coming, enabling them to organize and smoothly streamline around the structure of the aircraft. As the aircraft speed increases and approaches the speed of the propagated pressure wave, less and less warning is provided and smooth orderly flow is lost. Linda D. Pendleton describes the situation as follows: As speed increases, the aircraft comes closer and closer to the air particles before they are “warned” by the advancing pressure wave and can change direction. The greater the aircraft speed, the fewer air particles will be able to move out of its path. As a consequence, the air particles begin to pile up in front of the aircraft, and the air density increases.

7 The pressure wave, then, conditions the air particles, allowing them to get out of the way of the airframe; as the aircraft approaches high-speed flight, the pressure wave can no longer radiate in front of the aircraft structure, and the air particles begin to compress—i.e, the phenomenon of compressibility develops. The speed of the pressure wave is, of course, the speed of sound, and compressibility occurs when the aircraft itself approaches the speed of sound. The concept of compressibility goes a long way to explain the thin design of leading edges of high-speed wings and fuselage designs, and aeronautical engineers attempt to reduce as much as possible the effects of compressibility. Essentially, compressibility inhibits laminar flow, and instead of the air particles accelerating smoothly, the speed of airflow decreases dramatically. Transonic Flight The speed of air flow over the upper camber of a wing varies, and it follows, therefore, that portions of the air flowing over the wing will attain the speed of sound—Mach 1.0 (M 1.0)—first, while other portions of airflow remain subsonic. As indicated in the depiction to the right, supersonic speed first develops at the area of maximum airfoil thickness.

While this portion has attained M 1.0, remaining portions of the wing, as well as the airframe, remain subsonic. When this happens, an aircraft is said to have reached its critical Mach number (MCRIT), and this marks the beginning of the transonic speed range. Pendleton writes as follows: Critical Mach number . . is an aircraft limitation to be heeded. If the aircraft is flown at speeds in excess of its critical Mach number, numerous unsettling and potentially disastrous events occur. . . Boundary layer separation on the control surfaces might cause the surfaces to rapidly oscillate, which is called buzz. This can cause metal fatigue problems in both the control surfaces and the hinge fittings joining the control surface to the wing . . Shock-induced separation of the airflow over the control surfaces causes them to be in an area of turbulent, nonstreamlined air that causes a loss of effectiveness. When there is a shock wave in front of the control surface, deflection of the surface cannot influence the airflow in front of the shock wave . . The wings might begin to twist due to compressibility effects.

The airfoil shape over the length of the wing is seldom constant, and the differing onset of formation of shock waves and movements of centers of pressure cause this effect. This effect is unnerving at the least. . . Severe buffeting will almost surely be the next compressibility effect that is sure to show up. The extremely turbulent airflow separated from the wings begins to bang against the tail surfaces in a manner that is violent and irregular and disturbs the flow patterns around these surfaces causing them to buffet . . This buffeting, if allowed to continue, has been known to cause separation of the tail from the aircraft . . . If all this has not caused the pilot to slow down and escape compressibility effect by now, a more violent effect is about to occur. Loss of longitudinal stability will cause the aircraft to “tuck under” . . The important point is that the first signs of compressibility effects call for immediate pilot action. The airspeed must be reduced, and the nose must be eased up. The power reduction has to be fast, for when the tuck starts and the aircraft starts into a dive, the situation is going to get rapidly worse.

The increased speed will cause the separation of the airflow to become more pronounced, and the severity of the buffet will become greater. The greater the turbulence over the tail, the greater will be the elevator angle and the stick force required to pull out of the dive. Some have not been successful in this manoeuvre, and some have lost the tail of the aircraft before they had time to begin recovery. 8 Generally speaking, corporate jets and airline jets are designed to cruise at speeds between M .7 and M .9. Exceeding these speed will produce Mach tuck and the other rather unpleasant flight characteristic described by Pendleton. So the question arises as to how the pilot is advised as to the proximity of the aircraft’s speed relative to MCRIT. Effective communication is complicated by variations in Mach 1.0, based on altitude and temperature. While slow-speed aircraft are speed-limited by Vne, high-speed aircraft are speed limited by the expression MMO—the maximum operating speed relative to the speed of sound. MMO is displayed automatically on the airspeed indicators of high speed by what is referred to as the barber pole—a self-adjusting needle that predicts the MMO based on ambient temperature and pressure altitude.

An aural over-speed warning device is also wired to the system—referred to as a clacker. References 1 Of course, we know these vortices as wake turbulence, which is greatest with large, slow speed, clean configuration aircraft—all features of flight in which the angle of attack is at its greatest. 2 From the Ground Up, P. 33 (Theory of Flight, Turns) 3 Also referred to as topsails. 4 Gregory N. Brown and Mark J. Hold, The Turbine Pilot’s Flight Manual (1995, Ames: Iowa State University Press), p. 66. 5 The Turbine Pilot’s Flight Manual (1995, Ames, Iowa State University Press), P. 150. 6 This pressure wave, incidentally, is what we refer to as sound—sound is simply a pressure wave (noise) that is detected by our eardrums. 7 Flying Jets (Toronto, McGraw-Hill, 1996), P. 42. 8 Flying Jets (Toronto, McGraw-Hill, 1996), Pp.

43-48 Booking Sheet | Contact Form | Address & Map | Standard Operating Procedures | Anonymous Safety Reporting | People & Places © 2016 Langley Flying School, Inc. The content of this website is protected by copyright and reproduction in whole or in part is only authorized with the written consent of Kamy Farrd, Chief Flying Instructor, Langley Flying School. "Choose a job you love, and you will never have to work a day in your life." Confucius Aerodynamics and Theory of Flight, Langley Flying School. Includes Forces of Flight, Generation of Aircraft Lift, Bernoulli's Theorem, Ram Air, Angle of Attack, Parasitic Drag, Induced Drag, Aileron Drag, Stalls, Factors that affect Stalls, Turns, Flaps, Spins, Lift-drag Ratio, Wing Design, Aircraft Stability, Forces on aircraft during takeoff, Best Rate and Best Angle Climb. Acts perpendicular to the relative wind and wingspan. Lift is exerted through the centre of pressure. Opposes weight: during level cruise, lift equals weight; during climb, lift is greater than weight; and during descent, weight is greater that lift.

Weight Natural (uncontrollable) force generated by gravity (g force) that acts perpendicular to earth’s surface. Weight is exerted through the centre of gravity. Opposes lift (see above). Thrust Artificial force manipulated by pilot and generated through engine(s) that acts horizontally, parallel to flight path. Opposes drag: when airspeed constant, thrust equals drag; when airspeed accelerating, thrust is greater than drag; and when decelerating, drag is greater than thrust. Drag Viewed as a cross-section: upper surface has more camber (curve) than lower surface. Chord line: straight line from leading edge to trailing edge. The airfoil generates lift by two means: pressure differential and ram air. Bernoulli’s Theorem Lift by pressure differential is based on the theory of Daniel Bernoulli: the faster a fluid flows (including air), the lower will be the pressure surrounding it. Given the difference of the camber of the upper and lower surfaces, the air passing over the foil has greater distance to travel than the air passing under the airfoil. The air passing over must therefore travel faster than the air passing under the foil. A low air-pressure region is created above the accelerated air flow.

The foil is displaced toward the lower pressure (upward) above the wing. Ram Air The pressure differential accounts for about 50% of the lift, while the remaining lift is generated by ram air. Air is rammed under the foil, creating downwash, and upward pressure (Isaac Newton’s Third Law: the application of force causes an equal opposite force). Angle of Attack Lift varies with the angle of attack. The angle of attack is the angle between the relative wind (parallel to flight path) and the chord line (line between leading and trailing edge). Generally, the greater the angle of attack, the greater the lift. Lift increases because the distance the air must flow along the upper camber increases, and the ram air and downwash increase. An excessive angle of attack, referred to as the critical angle of attack, will produce a stall, where air-foil drag (induced drag) exceeds airfoil lift (usually 20°). Drag There are two types of drag: parasitic and induced. Parasitic Drag Parasitic drag is drag created by those parts of an aeroplane that do not contribute to lift—e.g., the tires, windshield, rivets, etc.

There are three forms of parasitic drag: form drag, skin-friction drag, and interference drag. Form drag is caused by the frontal areas of the aeroplane, and is reduced by streamlining. Skin-friction drag is caused by the air passing over the aeroplane surfaces, and is reduced by smoothing the surfaces (flush riveting, smooth paints, and waxing). Interference drag is caused by the interference of airflow between parts of an aeroplane (wings and fuselage or fuselage and empennage) and is reduced by “filleting” interference areas). Induced drag Induced drag is created by those parts of the aeroplane that creates lift—the wings and the horizontal tail surface. Induced drag is said to be the by-product of lift. The greater the angle of attack, the greater the induced drag. Induced drag does not increase with speed; instead, as speed decreases induced drag increases.

Induced drag is associated with difference in pressure that exists above and below a wing surface; as airspeed decreases, and airfoil must produce an increased low pressure above the wing, and an increased high pressure below the wing; at the wing tip these disparate pressures meet in the form of a vortex as the high pressure flows around the wing tip is sucked into the low pressure above the wing; the greater the pressure differences (such as in the case in slower flight), the greater the vortices are at each wing tip, and the greater the drag caused by these vortices. Ground effect is a term used to described the reduced drag and increased lift experience when an aircraft is flying close to the ground—as is the case, for example, during landings and takeoffs; the reduced drag associated with ground effect is the result of the ground interfering with the formation of the wing tip vortices. Ground effect exists when the aircraft is within one wingspan distance from the ground, but is most effective at distances equal or less than ½ wingspan (i.e., ½ the distance between the wingtips). Wing tip vortices can produce extremely hazardous turbulence and there are crucial operational considerations (see page 70).

Boundary Layer Along the upper camber of an airfoil, there are two types of airflow: turbulent and laminar (smooth). The turbulent and laminar flows are separated by a point of transition, or separation point. As the angle of attack is increased the portion of the upper airflow that is turbulent also increases (it migrates forward from the trailing edge). Aileron Drag A type of adverse or undesirable yaw is aileron drag; aileron drag is created when a pilot manipulates the ailerons when rolling into a turn. When the pilot induces a roll, one aileron is deflected upward so as to decrease the angle of attack associated with that portion of the wing, the same portion of the opposite wing is subject to an increase in the angle of attack as the aileron is deflected downward. As the downward deflected aileron enters the high-pressure airflow below the wing it creates drag that causes the wing to move rearward; the upward moving aileron enters low-pressure airflow and is subject to less drag and allowing this wing to move forward.

Aileron drag can be reduced by flap design, including Differential Ailerons (in which the movement of the downward aileron is reduced relative to the aileron that is deflected upward), and Frise Ailerons (in which the upward deflected aileron projects the forward portion of the aileron structure into the airflow below the wing). Aileron drag can be controlled by the use of sufficiently adequate opposite rudder during the rolling movement. Stalls Stalls occur at the critical angle of attack, at which point the airflow over the wing becomes chaotic and the wings can no longer produce sufficient lift to counteract weight. As the airfoil approaches the stalling speed, the point of transition, or separation point, moves forward enough to exceed the design factor of the wing. The stalling angle is usually 20°. Since most aircraft lack angle-of-attack indicators, airfoil angle is measured by indicated airspeed (IAS). As a rule, aircraft will usually stall near the stalling speed published in the Pilot Operating Handbook (bottom of green line on an Airspeed Indicator); however, IAS does not always indicate angle of attack, as in the case of a high-speed stall.

Factors that affect the Stall Snow, frost, ice and dirt: All of these disrupt the laminar flow and therefore reduce airfoil lift capability. It is illegal to fly with snow, frost, or ice adhering to “critical surfaces” of the aircraft 1 — “wings, control surfaces, rotors, propellers, horizontal stabilizers, vertical stabilizers or any other stabilizing surface of an aircraft.” Contamination to the extent of medium to coarse sandpaper will reduce lift by 30% and increase drag by 40%. Weight Increased weight requires increased lift; therefore the critical angle of attack (stall) will occur at higher airspeeds. Stated another way, if two aircraft are travelling at the same airspeed, but one is heavier than the other, the angle of attack of the heavier aircraft is greater than the lighter aircraft and therefore that much closer to the critical angle of attack. Centre of Gravity Stalling speed increases as the aircraft C of G moves forward. As the C of G moves forward, the negative lift generated by the horizontal tail surface will have to be increased.

Any increase in the negative lift produced by the tail will effectively increase the aerodynamic weight of the aircraft—producing the same effect as described above with respect to weight. Conversely, stalling speeds decrease as the C of G moves aft as less negative lift is required from the tail and the aircraft is aerodynamically lighter. While the benefits of a rearward C of G is a lower stall speed, the adverse result of a rearward C of G is less stability as there is less tail force that can be manipulated by the pilot through elevator or stabilator control. Turbulence Upward vertical gusts abruptly increase the angle of attack beyond the stalling angle, irrespective of airspeed. Turns During a turn in level flight, greater lift is required to offset increased effective aerodynamic weight of the aircraft in the turn. Because the angle of attack of an aircraft must be increased to offset the increased aerodynamic weight (resultant force of a turn), the wing is closer to the critical angle of attack and therefore closer to a stall, despite a constant airspeed. Accordingly, there is an increase in the relative stall speed of an aircraft in a level turn.

The formula to determine increased stall speed is as follows: normal stalling speed times the square root of the load factor equals banked stall speed. Thus, an aircraft with a stall speed of 50 KTS and in a 60°-bank turn (load factor of 2.0) will stall at 71 KTS. Flaps An increase in airfoil lift is produced by the use of flaps, and the stall speed is decreased by their use (bottom of white line on an Airspeed Indicator). The extension of flaps has the effect of increasing the relative angle of attack of the airfoil. Induced drag is also increased. Some flap designs incorporated slots, which permit the compressed air under the wing to migrate through the slot to the upper surface of the flaps. These are referred to as slotted flaps. Some flap designs allow the flap surface to move rearward as it extends—the feature is referred to as a Fowler Flap. Spins Spinning is defined as autorotationthat develops after an aggravated stall (a wing dropping during a stall). The downward moving wing has a higher angle of attack and more induced drag than the upward moving wing and therefore acquires a greater stalled condition.

Spinning involves simultaneous roll, yaw and pitch as it develops a helical or corkscrew path nose down. An incipient spin is the autorotation prior to a vertical descent path, while a fully developed spin begins once the vertical helical or corkscrew path is achieved. Lift-drag ratio The amount of lift/induced drag can be graphically plotted (lift/drag coefficients vs. angle of attack). As the angle of attack increases, lift increases to the critical angle of attack, and then falls off suddenly. As the angle of attack increases, induced drag increases slowly at first, and then in ever increasing proportions. The lift-drag ratio defines the proportion of lift to drag at given angles of attack. The study of an aircraft’s lift-drag ratio helps engineers map out the maximum range and maximum glide-distance configurations. Wing Design There are numerous wing-design features that affect performance: laminar versus conventional airfoils, angle of incidence, washout, stall strips, and airfoil variation. Laminar and conventional airfoils There are two types of airfoils commonly used in wing design: laminar and conventional. As a rule, the laminar foil is faster, but the cost is more adverse stalling characteristics.

They differ with respect to location of the maximum camber: while the maximum camber on a conventional airfoil is located 25% behind the leading edge, the laminar maximum camber is located at 50% chord. On the laminar foil, a greater portion of the upper camber is dedicated to laminar airflow, and there is therefore less drag; the cost of this, however, is that the transition or separation point “jumps” rapidly forward at the approach of a stall; additionally, the laminar foil is more susceptible to surface contamination. Angle of incidence Defined as the angle between the chord line and the longitudinal axis of the aeroplane; designers select an angle that provides optimum lift/drag ratio. Washout A design trait that pacifies or softens the stall characteristics of an aeroplane whereby the wings are “twisted” such that the wing tips have a lower angle of incidence than the wing root. The effect is that the entire wing will not stall simultaneously; instead, the stall will progressively move from the roots to the tips. Because the wing tips are the last to stall, the ailerons will remain effective longer during the stall.

Stall Strips Stall strips are triangular strips placed on a portion of the leading edge of wing. Stall strips create a gentle stall because the portions of the wing behind the strips stall first. Airfoil Variation This involves spanwise airfoil variation whereby a thin high-speed airfoil is designed near the roots, and a low-speed airfoil near the tips. The high-speed roots stall before the low-speed tips. Stability Aeroplane movement is based on 3 axes: the vertical (normal) axis, the lateral axis, and the longitudinal axis. All three axes pass through the aircraft C of G. Stability is defined as the tendency of an aircraft to return to, stay at, or move farther from its original attitude after it has been displaced. There is positive, neutral, and negative stability. Longitudinal Movement around the longitudinal axis is roll, which produces bank, and is produced by the ailerons. Longitudinal stability (of the axis) is provided by a nose-heavy design and a “negative-lift” tail. Lateral Movement around the lateral axis is pitch, and is produced by the elevator.

Lateral stability (of the axis) is provided by dihedral, which lowers C of G relative to the lifting surfaces (wing tips are positioned higher than the wing roots). Additionally, the lower wing produces more effective lift than the raised wing, causing the lower wing to naturally rise, and higher wing to descend. Directional Movement around the vertical (normal) axis is yaw, and is “controlled” by the rudder. Adverse yaw takes place during rolling movement because of aileron drag, and is controlled by rudder. Stability of the vertical axis is referred to as directional stability, and is produced by the vertical stabilizer and sweptback (sweepback) wing design. When a sweptback wing moves forward, it acquires increased lift, as the airflow is more perpendicular to the wing’s leading edge. This increased lift simultaneously produces increased induced drag, which encourages the wing to migrate back to is original position. The effect is the reverse for the opposite wing. Forces during Takeoff There are a number of forces exerted on the aircraft during the take-off roll and climb, and they all contribute (in single-engine aircraft) to left yaw tendencies, which must be controlled by the pilot with the used of rudder pedals.

Torque The force of Torque is based on the principle of physics that a movement in one direction will cause a movement in the opposite direction. The force referred to here is the force of the spinning propeller which, from the pilot perspective in the cockpit, rotates clockwise. This movement of the propeller produces an opposite rotation of the aircraft—from the pilot perspective, counter-clockwise. This translates during the takeoff roll as a left-yaw tendency, and requires the pilot to exert right-rudder pressure. Precession Precession is a gyroscopic force, which again originates from the movement of the propeller. According to the law of precession, a pressure exerted on a spinning mass will cause a reaction 90° along the direction of rotation. The force of precession during takeoff is primarily associated with conventional-gear (“tail-dragger”) aircraft, with the pilot exerting nose-down pressure on the control column to raise the tail wheel off the ground—when this happens, the spinning propeller converts this force into a left-yaw movement, which again must be countered by the pilot with right-rudder input.

Slipstream Slipstream refers to the spiral-like movement of the air flowing from the propeller over the fuselage of the aircraft. The spiral flow migrates around the fuselage as it travels rearward and strikes the left side of the vertical fin. This again translates to the pilot as left-yaw tendency, which must also be countered with right rudder. Asymmetric thrust The force referred to as asymmetric thrust must be managed by the pilot whenever a single-engine aircraft is in a climb or nose-up attitude. When the longitudinal axis of the aircraft is inclined upward, the propeller produces different levels of thrust whereby the down-going blade (the right side of the spinning propeller disk, as viewed by the pilot) produces more thrust than the up-going blade (the left side of the propeller disk). The relative wind (or flight path) of the aircraft with a nose-up attitude means that the down-going blade has a greater angle of attack (and therefore greater thrust) than the down-going blade (which has a less angle of attack). A pilot learns that whenever the aircraft is in a nose-up attitude—whenever the aircraft is climbing—compensating right rudder must be used to counter the resultant left-yaw tendency.

Climbs There are three climb configurations commonly used in flying. The climb configurations are flown on the basis of air speeds (the pilot’s indication of angle of attack), and these speeds, as well as the associated flap configurations, are specified by the aircraft manufacturer in the Pilot Operating Handbook. 2 They are summarized as follows: Best Angle Climb (Vx) The best angle climb speed provides the greatest gain in altitude over a given distance. This speed would be used, for example, when the pilot must clear obstacles that exist off the end of a runway. An aircraft manufacturer usually specifies that partial flap settings must be used when flying best angle speed—with the Piper Cherokee, 25° flaps are required. 3 Best Rate Climb (Vy) The best rate climb speed provides the greatest gain in altitude over a given period of time—it will get you to the highest altitude the quickest. This speed is typically flown immediately after rotation during a takeoff where pilots, not faced with obstacle clearance concerns, typically seek to get safely clear of the ground as quickly as possible during a departure.

Normal or Cruise Climb The normal climb speed is usually specified by the manufacturer to combine efficiency in climb performance with effective cooling of the engine (the steeper the angle of attack, the less effective the airflow over the engine). This speed is usually flown after the airport departure is completed—say 1000’ AAE 4 —and obstacles are no longer a factor. The total time en route is decreased when a normal or cruise climb is flown. References how to control an aircraft The ailerons are controlled by turning the control yoke. secondary effect of aileron actuation The ailerons primarily control bank. However because the air underneath a wing is denser than that above it, the lowering aileron causes more drag on its side than the rising aileron. Using ailerons causes a small amount of yaw to occur. This is more pronounced for light aircraft with long wings, such as gliders. It is usually counteracted by the pilot with the rudder. Another most import consideration is that the stall speed of the aircraft increases with the angle of roll. Large angles of bank at slow speed may very well result in a stall and spin.

click arrows to operate movie Your browser does not support inline frames or is currently configured not to display inline frames. Vertical (yaw) axis -- an imaginary line extending vertically through the intersection of the lateral and longitudinal axes Rotation about the vertical axis is called yaw and is controlled by the rudder. This rotation is referred to as directional control or directional stability. The rotation is similar to a weather vane, in which the post holding the vane is the vertical axis but the rotation is directional. Rudder The rudder is attached to the vertical stabilizer. Controlled by the rudder pedals, the rudder is used by the pilot to control the direction (left or right) of yaw about the airplane's vertical axis for minor adjustments. It is NOT used to make the airplane turn, as is often erroneously believed. Banking the airplane makes it turn. When the foot pressure on the left rudder pedal moves the rudder to the left, causing the nose of the airplane to move to the left. When the foot pressure on the right rudder pedal moves the rudder to the right, causing the nose of the airplane to move to the right. secondary effect of rudder actuation Using the rudder causes one wing to move forward faster than the other.

Increased speed means increased lift, and hence rudder use causes a small roll effect. For this reason ailerons and rudder are generally used together on light aircraft. click arrows to operate movie Your browser does not support inline frames or is currently configured not to display inline frames. Power The application of power will increase the aircraft speed with a secondary effect of climb. A reduction in power will reduce speed with a secondary effect of descent. Your browser does not support inline frames or is currently configured not to display inline frames.

Question: What is the term given to the tilt of an aeroplane about its longitudinal axis?
Answer: Bank