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FROM THE GROUND UP AVIATION BOOK

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From the Ground Up (FTGU) is a pilot's training book, and it covers almost every aspect of flying Chapter 6, Aviation Weather: Discusses various aspects of weather including cloud, precipitation, winds, and other natural phenomena. Chapter. From the Ground Up-Canada's primary aeronautical ground school reference manual for I purchased this book as a birthday gift and the recipient LOVES it!. For over 70 years, the content of From the Ground Up has stood as a literary benchmark for the Ships from and sold by Aircraft Technical Book Company.


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A celebrated book on the subject of aeronautics, this ground scho and procedures in general aviation, it includes discussions of the airplane, theory of flight. "A celebrated book on the subject of aeronautics, this ground school manual for and procedures in general aviation, it includes discussions of the airplane. Himalayan Books. Year: Edition: 1. Binding: Paperback. Page: Country Origin: India. Condition Type: New. Leadtime to ship in days (default).

Wing 6. Right Wing flap 8. Horizontal Stabilizer Rudder Left Wing Flap Door Windshield The wings or lifting surfaces The tail section, or empennage The propulsion system, i. It therefore includes the fuselage, wings, tail assembly and undercarriage. It is the structural body to which the wings, tail assembly, landing gear and engine are attached. The fuselage is usually classed according to its type of construction. Truss Type In the early days, the fuselage was a frame made up of wooden members, wire braced.

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These materials are now obsolete, having been replaced by metal. The modern truss type fuselage is made up of steel tubes, usually welded or bolted together to form the frame. Truss Type Fuselage. The longerons three, four or more long tubes running lengthways are the principle members and are braced, or held together, to form the frame by vertical or diagonal members, the whole assembly being in the form of a truss. The covering may be fabric, metal or composite.

Monocoque Stressed Skin Fuselage. Monocoque This type consists of a series of round or oval formers or bulkheads held together by stringers long strips running lengthwise.

The formers, or bulkheads, carry the loads, the stringers being merely superstructure. The early types of monocoque construction were of wood, plywood covered. Present monocoque construction is of metal, metal covered. Since the covering of the monocoque fuselage must be made stiff, the skin is capable of carrying some of the load.

This is known as a stressed skin structure. A perfect stressed skin structure would be one in which the skin, in addition to providing the covering and forming the shape, would be capable of carrying all the load, without any internal bracing. THE WING Most airplanes in use in general aviation today are monoplanes; that is, they have one pair of wings, Biplanes, those with two pairs of wings, are also to be found. They are usually restored antiques, agricultural spray planes, or sport and acrobatic airplanes.

Wings come in a variety of shapes: rectangular, tapered from wing root to wing tip, elliptical, delta. They may be attached in different positions on the fuselage: at the top of the fuselage, known as high wing; at the bottom of the fuselage, low wing; or in the middle, mid wing.

High wing airplanes may be externally braced with wing struts or may be fully cantilevered. Five general systems of wing construction are now in use on modern airplanes.

These are: 1. Metal frame, metal covered main strength in the covering, or skin, i. Metal frame, metal covered main strength in the frame. Metal frame, fabric covered. Wooden frame, fabric covered. Wooden frame, plywood covered. Two-Spar, Fabric-covered Wing. The main members in a wing are the spars. These are beams, running the length of the wing from wing root to wing tip, which carry most of the load.

The spars are intended to stiffen the wing against torsion, or twisting. Some wings are constructed with two or more spars multispar and some with only one main spar monospar. The latter type of single spar construction is found in certain models of modern airplanes which use a laminar flow airfoil wing design. The ribs run from the leading to the trailing edge. They are cambered to form an airfoil section and their purpose is to give the wing its shape and to provide a framework to which the covering is fastened.

To strengthen the leading edge, nose ribs are sometimes installed between the front spar and leading edge. These are generally known as false ribs. Compression struts are spaced at regular intervals between the front and rear spars.

They are usually steel tubes and are intended to take compression loads. Further internal bracing is secured by drag and anti-drag wires. These are wires running diagonally from the front to the rear spars, the drag wires taking drag loads and the anti-drag wires anti-drag loads, as their names imply.

External bracing is secured in monoplane types by wing bracing struts which extend out from the fuselage to about the mid-section of the wing. In biplanes, struts are placed between the wings, well out towards the tips. These are braced by incidence wires which run diagonally between the struts, and by flying and landing wires which run diagonally between the struts and the fuselage. The flying wires transmit part of the load to the fuselage in flight and the landing wires support the weight of the wing on the ground.

Some wings are constructed with no external bracing at all. These are known as cantilever wings. Since there is no external support to such a wing, the spars must be made sufficiently strong to carry the load into the fuselage internally with no outside assistance.

Transmission of Loads - Internally.

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The load on a wing comes first on the skin. It is then transmitted to the ribs and from these to the spars and thence carried into the fuselage. In an externally braced wing, part of the load is taken by the bracing struts or the flying or landing wires, as the case may be, and thence transmitted to the fuselage. These are surfaces, usually of airfoil section, hinged to the trailing edge of the wing towards each wing tip for the purpose of lateral control.

Their internal construction is much like that of the wing itself. They are usually hinged to the rear spar. When fitted, these form a part of the wing structure.

Like the ailerons, they are usually hinged to the rear spar. A full description of flaps and their function will be found in the Chapter Theory of Flight. This is a section of the wing nearest the fuselage.

On low wing airplanes, it is reinforced to permit the passengers and crew to walk on it. The fittings which attach the wing. Or the separate wing panels, to the fuselage. A small nearly vertical wing like surface usually of airfoil section, attached to the wing tip.

The winglet is incorporated into the design of some modern airplanes. It is usually located rearward above the wing tip and is effective in reducing Induced drag. See Chapter Theory of Flight. An imaginary straight line joining the leading and trailing edges of the wing. The mean aerodynamic chord MAC is the average chord of the wing.

The maximum distance from wing tip to wing tip of an airfoil, wing or stabilizer. Instead of a fixed stabilizer and movable elevators. Some airplanes have a one piece pivoting, horizontal stabilizer that is known as a stabilator. An airfoil placed at the rear end of the fuselage to balance the airplane and hence provide longitudinal stability. The Tail Section. Surfaces hinged on the trailing edge of the stabilizer to give longitudinal control. A fixed vertical surface placed ahead of the stern post to provide directional stability.

The fin is usually offset from the centre to compensate for the corkscrew motion of the slipstream from the revolving propeller.

A movable surface hinged to the fin to give directional control. An adjustable tab either fixed or hinged to a control surface rudder, elevators and ailerons that helps the pilot by eliminating the need to exert excessive pressure on the cockpit flight controls during the various phases of flight. A single airfoil section that replaces the combination of stabilizer and elevator. It is attached to the fuselage at a point around which it pivots.

A few airplanes of modern design have replaced the familiar tail section with a canard that incorporates a horizontal stabilizer assembly at the front of the airplane. The arrangement, though much more streamlined, is reminiscent of the original Wright airplanes. The airfoils comprising the tail unit assembly are similar to, but of lighter construction, than those of the main structure.

The tail unit is positioned so that it is in the airflow and not blanketed by the main planes or other parts of the structure. Many of the new business airplanes are jet powered as are most of the large transport type airplanes.

The gas turbine, or jet, engine can also be used to drive a propeller and, in this configuration, is known as a turboprop engine. Power plants and propellers are discussed in detail in the Chapter Aero Engines. The Cowling The cowling encloses the engine and streamlines the front of the airplane to reduce drag.

The cowling provides cooling of the engine by ducting the cooling air around the engine. On high performance airplanes, adjustable openings called cowl flaps are incorporated into the cowling to control the amount of cooling air circulating around the engine. Engine Mountings The engine is supported by a structure, usually of steel tubing welded together, called the engine mount, which is made flexible to absorb vibration from the engine and prevent it being transmitted to the fuselage.

This is usually accomplished by engine mount bushings which are made springy in the direction of the engine rotation but rigid otherwise, in order to hold the engine steady fore and aft. Fire Wall Between the main structure and the engine is the fire wall. This is made of a heavy sheet of stainless steel or often a sandwich of asbestos-between two sheets of dural.

Openings for fuel and control lines are made small, with bushings to ensure a snug fit. The fuel tank must be behind the fire wall, whereas the oil tank may be ahead of it - oil being less inflammable than gasoline. Tank Installations Fuel tanks may be carried in the wings or in the fuselage. The earliest type of main landing gear was a through axle, similar to the wheel and axle arrangement on a cart or wagon. This is now completely obsolete, having been replaced with more sophisticated, shock absorbing landing gear systems.

The landing gear on modern airplanes is either of the fixed gear type or retractable. Fixed Undercarriage On land airplanes, there are two basic classes of fixed gear undercarriage: main gear with a nose wheel, commonly called a tricycle gear, and main gear with a tail wheel.

There are several types of undercarriage in use for the main gear. These are used with both the tail wheel and the tricycle gear configuration. They are split axle, tripod, single spring leaf cantilever and single strut.

The split axle type has the axle bent upwards and split in the centre to enable it to clear obstructions on the ground Fig. This type is used on airplanes such as the Piper PA It is suspended on shock cords wound around a fuselage member which enables the whole assembly to spread when loads come on it. A strut or tie rod is usually incorporated to brace the structure against side loads. Tripod Landing Gear. Split Axle. The tripod landing gear is illustrated in Fig. This gear consists of three members hinged so as to form a triangle.

Two of these are rigid. The third is an oleo leg, designed to telescope and hence shorten its length when the load comes on the wheel. On landing, the whole assembly spreads outwards and upwards until springs, rubber discs, or other devices take the weight. The single leaf cantilever spring steel type of main landing gear is used extensively on Cessna airplanes.

The gear consists of a single strap of chrome vanadium steel bent to form the shape of the complete undercarriage structure.

It is attached to the fuselage in a cradle bulkhead by bolts. It is capable of storing energy in initial impact, thereby producing quite low load factors.

Low maintenance, simplicity and long service life characterize this gear type Fig. On the Cessna Cardinal, a spring steel tubular gear replaces the more familiar single leaf gear described here. The spring steel tubular gear has the same characteristics as the single leaf type. Single Strut Gear. The single strut type is used on several modern, low wing, fixed gear airplanes such as the Piper Cherokee and the Beech Musketeer. This gear consists of a single leg or strut extending downward from its attachment point on the main spar.

The strut usually incorporates a hydraulic cylinder or rubber biscuits for the purpose of absorbing the shock Fig. Retractable Gear Retractable gears are made to retract or fold up into the wing or fuselage in flight. The mechanical means and methods for accomplishing this are many and varied.

The wheel may fold sideways outwards towards the wing or inwards towards the fuselage. The latter is most common on high speed military airplanes when the wing camber is shallow. On some multi-engine airplanes the wheel folds straight back or forward into the nacelle and is left partly projecting in order to protect the belly of the ship in the case of a wheels-up landing. Some retractable undercarriages are made to turn through 90 degrees as they travel up and so fold into the side of the fuselage.

Most retractable undercarriage legs are cantilever, being a single oleo leg, with no external bracing. They are hinged at the top to permit them to fold. The means of retraction may be a hand gear, electric motor, or motor-driven hydraulic pump. Where mechanical means are used, a hand gear is also provided to allow for lowering the gear in an emergency.

Making the undercarriage retractable is a common practice with both the tricycle and tail wheel configuration. In the case of tricycle gear, the nose wheel is also made retractable. In the case of a tail wheel, however, because it is small and causes little drag, it is fixed. Nose Wheel Versus Tail Wheel The practice of placing a steerable third wheel forward of the main gear has found universal acceptance in modern airplane design and is referred to as being a tricycle gear arrangement.

The landing gear arrangement in which the third wheel is rearward of the main gear i. The recent trend to tricycle gear arranger by most manufacturers is this result of certain advantages that this type of landing gear has over the tail wheel arrangement. These advantages are: 1 Nose-over tendencies are reduced greatly.

Therefore, tricycle geared airplanes can use single runway airports which are becoming more numerous with greater safety in cross wind conditions than can tail wheel airplanes. Tail wheel airplanes have advantages too. These are: 1 The tail wheel has less parasite drag than a nose wheel due to its smaller size. The main undercarriage which hits the bumps first is attached to a primary structure and is therefore stronger and more rigid than a nose gear which in the tricycle gear arrangement is the first to hit the bump which is usually fastened to a weaker or nonprimary part of the airframe.

A tail wheel will easily absorb bumps that may be severe enough to damage a nose gear. On most modern airplanes, regardless of whether they have a fixed or retractable undercarriage, the nose wheel and the tail wheel are steerable by the pilots controls. Shock Absorbers The purpose of the shock absorber is to prevent landing shock damage to the fuselage or body of the airplane. Pilots may accidentally impose heavy stresses due to faulty landings.

If these stresses were not properly absorbed by the landing gear, they could easily cause failure in the airplane structure. Shock absorbers generally are divided into four classes: 1. Low Pressure Tyres: On some types of light airplanes these are the sole means provided for absorbing shocks.

The principal difficulty with tires and some of the other shock absorbing devices is that they do not dissipate the shock but store it and kick the airplane back into the air after a rough landing. Oleo: When the airplane hits the ground the momentum must be absorbed in the undercarriage. To absorb this energy on springs or rubber alone would result in the aircraft being bounced into the air again.

On practically all modern airplanes, the energy produced on landing is dissipated by forcing oil an incompressible fluid from one side of a piston to the other through a small orifice. The displacement of the oil is thus delayed, cushioning the shock of landing for the reason that the bulk of the energy is absorbed in forcing the oil through the restricted orifice. The simple oleo Fig. On landing, these will telescope, and the oil will be displaced from the lower to the upper, but is delayed in doing so by the restricted orifice.

Since the oil, once displaced, will not return until the airplane again leaves the ground, the oleo leg serves only to absorb the shock of landing. Further shocks experienced while taxiing or taking off are handled by devices such as the spring shown in Fig. Rubber: Two types of rubber shock absorbers are in use, usually in conjunction with the oleo, to cushion further shocks after landing.

These take the form of rubber discs or doughnuts, and shock cord, which is an elastic cord wound around two moving members. Spring Steel: The spring steel type of landing gear, as described above, is in itself a shock absorber capable of storing energy. Brakes The advantage of the use of brakes on airplanes is two-fold: 1. They provide quick deceleration, or pull-up, after landing.

For heavy and high speed airplanes that land with faster initial, or hotter, speeds, such quick deceleration is important, especially when landing on short runways.

Differential or individually operated brakes, ensure better control after landing, to prevent ground loops, etc. They also provide better manoeuvrability on the ground. On some models of airplanes, steering while taxiing is accomplished only by the use of the brakes. They are needed to perform short radius turns. Due to the much higher landing speeds of modern airplanes, brakes have to be powerful, reliable and capable of dissipating heat very rapidly.

Nearly all airplanes use disc brakes operated by hydraulic pressure, sandwiching a rotating disc between two brake linings called pucks. These pucks are located in a fixed cast unit, grooved to permit the disc to float freely.

Attachment of the disc is attained by splitting tie periphery into the wheel hub. This floating action allows the disc to move laterally during braking and permits the use of one moving puck. The fixed puck is called the anvil; the moving one is called the piston puck. Pressure applied against the brakes that usually are part of the rudder pedal assembly is translated into hydraulic fluid pressure.

The hydraulic piston responds to the increased pressure by pushing against the piston puck which in turn pushes the rotating disc against the anvil puck, allowing equal braking force friction on both sides of the disc. Special flexible sealing rings keep the puck-to-disc clearance automatically adjusted by returning the hydraulic piston to a neutral position after each braking action.

Disc brakes are so reliable that, normally, visual inspection is required only at 50 hour intervals. One precaution in their use is recommended. The parking brake should be left off and wheel chocks installed if the airplane is to be left unattended. Changes in the ambient temperature can cause the brakes to release or to exert excessive pressure. Metal frame, fabric covered.

Wooden frame, fabric covered. Wooden frame, plywood covered. Two-Spar, Fabric-covered Wing. The main members in a wing are the spars. These are beams, running the length of the wing from wing root to wing tip, which carry most of the load. The spars are intended to stiffen the wing against torsion, or twisting. Some wings are constructed with two or more spars multispar and some with only one main spar monospar.

The latter type of single spar construction is found in certain models of modern airplanes which use a laminar flow airfoil wing design. The ribs run from the leading to the trailing edge. They are cambered to form an airfoil section and their purpose is to give the wing its shape and to provide a framework to which the covering is fastened.

To strengthen the leading edge, nose. These are generally known as false ribs. Compression struts are spaced at regular intervals between the front and rear spars.

They are usually steel tubes and are intended to take compression loads. Further internal bracing is secured by drag and anti-drag wires. These are wires running diagonally from the front to the rear spars, the drag wires taking drag loads and the anti-drag wires anti-drag loads, as their names imply.

External bracing is secured in monoplane types by wing bracing struts which extend out from the fuselage to about the mid-section of the wing. In biplanes, struts are placed between the wings, well out towards the tips. These are braced by incidence wires which run diagonally between the struts, and by flying and landing wires which run diagonally between the struts and the fuselage. The flying wires transmit part of the load to the fuselage in flight and the landing wires support the weight of the wing on the ground.

Some wings are constructed with no external bracing at all. These are known as cantilever wings. Since there is no external support to such a wing, the spars must be made sufficiently strong to carry the load into the fuselage internally with no outside assistance. Transmission of Loads - Internally. The load on a wing comes first on the skin. It is then transmitted to the ribs and from these to the spars and thence carried into the fuselage. In an externally braced wing, part of the load is taken by the bracing struts or the flying or landing wires, as the case may be, and thence transmitted to the fuselage.

These are surfaces, usually of airfoil section, hinged to the trailing edge of the wing towards each wing tip for the purpose of lateral control. Their internal construction is much like that of the wing itself. They are usually hinged to the rear spar.

When fitted, these form a part of the wing structure. Like the ailerons, they are usually hinged to the rear spar. A full description of flaps and their function will be found in the Chapter Theory of Flight. This is a section of the wing nearest the fuselage. On low wing airplanes, it is reinforced to permit the passengers and crew to walk on it. The fittings which attach the wing. Or the separate wing panels, to the fuselage. A small nearly vertical wing like surface usually of airfoil section, attached to the wing tip.

The winglet is incorporated into the design of some modern airplanes. It is usually located rearward above the wing tip and is effective in reducing Induced drag. See Chapter Theory of Flight.

An imaginary straight line joining the leading and trailing edges of the wing. The mean aerodynamic chord MAC is the average chord of the wing. The maximum distance from wing tip to wing tip of an airfoil, wing or stabilizer. Instead of a fixed stabilizer and movable elevators. Some airplanes have a one piece pivoting, horizontal stabilizer that is known as a stabilator.

An airfoil placed at the rear end of the fuselage to balance the airplane and hence provide longitudinal stability. The Tail Section. Surfaces hinged on the trailing edge of the stabilizer to give longitudinal control. A fixed vertical surface placed ahead of the stern post to provide directional stability.

The fin is usually offset from the centre to compensate for the corkscrew motion of the slipstream from the revolving propeller. A movable surface hinged to the fin to give directional control. An adjustable tab either fixed or hinged to a control surface rudder, elevators and ailerons that helps the pilot by eliminating the need to exert excessive pressure on the cockpit flight controls during the various phases of flight.

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A single airfoil section that replaces the combination of stabilizer and elevator. It is attached to the fuselage at a point around which it pivots. A few airplanes of modern design have replaced the familiar tail section with a canard that incorporates a horizontal stabilizer assembly at the front of the airplane. The arrangement, though much more streamlined, is reminiscent of the original Wright airplanes. The airfoils comprising the tail unit assembly are similar to, but of lighter construction, than those of the main structure.

The tail unit is positioned so that it is in the airflow and not blanketed by the main planes or other parts of the structure. Many of the new business airplanes are jet powered as are most of the large transport type airplanes. The gas turbine, or jet, engine can also be used to drive a propeller and, in this configuration, is known as a turboprop engine. Power plants and propellers are discussed in detail in the Chapter Aero Engines. The Cowling The cowling encloses the engine and streamlines the front of the airplane to reduce drag.

The cowling provides cooling of the engine by ducting the cooling air around the engine. On high performance airplanes, adjustable openings called cowl flaps are incorporated into the cowling to control the amount of cooling air circulating around the engine.

Engine Mountings The engine is supported by a structure, usually of steel tubing welded together, called the engine mount, which is made flexible to absorb vibration from the engine and prevent it being transmitted to the fuselage.

This is usually accomplished by engine mount bushings which are made springy in the direction of the engine rotation but rigid otherwise, in order to hold the engine steady fore and aft. Fire Wall Between the main structure and the engine is the fire wall. This is made of a heavy sheet of stainless steel or often a sandwich of asbestos-between two sheets of dural.

Openings for fuel and control lines are made small, with bushings to ensure a snug fit. The fuel tank must be behind the fire wall, whereas the oil tank may be ahead of it - oil being less inflammable than gasoline.

Tank Installations Fuel tanks may be carried in the wings or in the fuselage. The earliest type of main landing gear was a through axle, similar to the wheel and axle. This is now completely obsolete, having been replaced with more sophisticated, shock absorbing landing gear systems.

The landing gear on modern airplanes is either of the fixed gear type or retractable. Fixed Undercarriage On land airplanes, there are two basic classes of fixed gear undercarriage: There are several types of undercarriage in use for the main gear. These are used with both the tail wheel and the tricycle gear configuration. They are split axle, tripod, single spring leaf cantilever and single strut.

The split axle type has the axle bent upwards and split in the centre to enable it to clear obstructions on the ground Fig. This type is used on airplanes such as the Piper PA It is suspended on shock cords wound around a fuselage member which enables the whole assembly to spread when loads come on it.

A strut or tie rod is usually incorporated to brace the structure against side loads. Tripod Landing Gear. Split Axle. The tripod landing gear is illustrated in Fig.

This gear consists of three members hinged so as to form a triangle. Two of these are rigid. The third is an oleo leg, designed to telescope and hence shorten its length when the load comes on the wheel.

On landing, the whole assembly spreads outwards and upwards until springs, rubber discs, or other devices take the weight. The single leaf cantilever spring steel type of main landing gear is used extensively on Cessna airplanes. The gear consists of a single strap of chrome vanadium steel bent to form the shape of the complete undercarriage structure.

It is attached to the fuselage in a cradle bulkhead by bolts. It is capable of storing energy in initial impact, thereby producing quite low load factors. Low maintenance, simplicity and long service life characterize this gear type Fig. On the Cessna Cardinal, a spring steel tubular gear replaces the more familiar single leaf gear described here. The spring steel tubular gear has the same characteristics as the single leaf type.

Single Strut Gear. The single strut type is used on several modern, low wing, fixed gear airplanes such as the Piper Cherokee and the Beech Musketeer. This gear consists of a single leg or strut extending downward from its attachment point on the main spar. The strut usually incorporates a hydraulic cylinder or rubber biscuits for the purpose of absorbing the shock Fig.

Retractable Gear Retractable gears are made to retract or fold up into the wing or fuselage in flight. The mechanical means and methods for accomplishing this are many and varied. The wheel may fold sideways outwards towards the wing or inwards towards the fuselage. The latter is most common on high speed military airplanes when the wing camber is shallow. On some multi-engine airplanes the wheel folds straight back or forward into the nacelle and is left partly projecting in order to protect the belly of the ship in the case of a wheels-up landing.

Some retractable undercarriages are made to turn through 90 degrees as they travel up and so fold into the side of the fuselage. Most retractable undercarriage legs are cantilever, being a single oleo leg, with no external bracing. They are hinged at the top to permit them to fold. The means of retraction may be a hand gear, electric motor, or motor-driven hydraulic pump. Where mechanical means are used, a hand gear is also provided to allow for lowering the gear in an emergency.

Making the undercarriage retractable is a common practice with both the tricycle and tail wheel configuration. In the case of tricycle gear, the nose wheel is also made retractable. In the case of a tail wheel, however, because it is small and causes little drag, it is fixed. Nose Wheel Versus Tail Wheel The practice of placing a steerable third wheel forward of the main gear has found universal acceptance in modern airplane design and is referred to as being a tricycle gear arrangement.

The landing gear arrangement in which the third wheel is rearward of the main gear i. The recent trend to tricycle gear arranger by most manufacturers is this result of certain advantages that this type of landing gear has over the tail wheel arrangement.

These advantages are: Therefore, tricycle geared airplanes can use single runway airports which are becoming more numerous with greater safety in cross wind conditions than can tail wheel airplanes. Tail wheel airplanes have advantages too. The main undercarriage which hits the bumps first is attached to a primary structure and is therefore stronger and more rigid than a nose gear which in the tricycle gear arrangement is the first to hit the bump which is usually fastened to a weaker or nonprimary part of the airframe.

A tail wheel will easily absorb bumps that may be severe enough to damage a nose gear. On most modern airplanes, regardless of whether they have a fixed or retractable undercarriage, the nose wheel and the tail wheel are steerable by the pilots controls. Shock Absorbers The purpose of the shock absorber is to prevent landing shock damage to the fuselage or body of the airplane. Pilots may accidentally impose heavy stresses due to faulty landings.

If these stresses were not properly absorbed by the landing gear, they could easily cause failure in the airplane structure. Shock absorbers generally are divided into four classes: Low Pressure Tyres: On some types of light airplanes these are the sole means provided for absorbing shocks. The principal difficulty with tires and some of the other shock absorbing devices is that they do not dissipate the shock but store it and kick the airplane back into the air after a rough landing.

When the airplane hits the ground the momentum must be absorbed in the undercarriage. To absorb this energy on springs or rubber alone would result in the aircraft being bounced into the air again. On practically all modern airplanes, the energy produced on landing is dissipated by forcing oil an incompressible fluid from one side of a piston to the other through a small orifice. The displacement of the oil is thus delayed, cushioning the shock of landing for the reason that the bulk of the energy is absorbed in forcing the oil through the restricted orifice.

The simple oleo Fig. On landing, these will telescope, and the oil will be displaced from the lower to the upper, but is delayed in doing so by the restricted orifice. Since the oil, once displaced, will not return until the airplane again leaves the ground, the oleo leg serves only to absorb the shock of landing.

Further shocks experienced while taxiing or taking off are handled by devices such as the spring shown in Fig. Two types of rubber shock absorbers are in use, usually in conjunction with the oleo, to cushion further shocks after landing. These take the form of rubber discs or doughnuts, and shock cord, which is an elastic cord wound around two moving members.

Spring Steel: The spring steel type of landing gear, as described above, is in itself a shock absorber capable of storing energy. Brakes The advantage of the use of brakes on airplanes is two-fold: They provide quick deceleration, or pull-up, after landing. For heavy and high speed airplanes that land with faster initial, or hotter, speeds, such quick deceleration is important, especially when landing on short runways.

Differential or individually operated brakes, ensure better control after landing, to prevent ground loops, etc. They also provide better manoeuvrability on the ground. On some models of airplanes, steering while taxiing is accomplished only by the use of the brakes. They are needed to perform short radius turns. Due to the much higher landing speeds of modern airplanes, brakes have to be powerful, reliable and capable of dissipating heat very rapidly. Nearly all airplanes use disc brakes operated by hydraulic pressure, sandwiching a rotating disc between two brake linings called pucks.

These pucks are located in a fixed cast unit, grooved to permit the disc to float freely. Attachment of the disc is attained by splitting tie periphery into the wheel hub.

This floating action allows the disc to move laterally during braking and permits the use of one moving puck. The fixed puck is called the anvil; the moving one is called the piston puck. Pressure applied against the brakes that usually are part of the rudder pedal assembly is translated into hydraulic fluid pressure.

The hydraulic piston responds to the increased pressure by pushing against the piston puck which in turn pushes the rotating disc against the anvil puck, allowing equal braking force friction on both sides of the disc. Special flexible sealing rings keep the puck-to-disc clearance automatically adjusted by returning the hydraulic piston to a neutral position after each braking action.

Disc brakes are so reliable that, normally, visual inspection is required only at 50 hour intervals. One precaution in their use is recommended. The parking brake should be left off and wheel chocks installed if the airplane is to be left unattended. Changes in the ambient temperature can cause the brakes to release or to exert excessive pressure.

A further problem can occur in airplanes that are flown infrequently e. Since the discs are made of steel, they are subject to corrosion and rust, especially if exposed to unusual amounts of moisture, salt or industrial pollution. In an airplane that is used daily, the corrosion and rust are rubbed off by repeated use. The prime element of the braking system is the hydraulic fluid.

It transmits pressure and energy, lubricates the moving parts of the system and aids in cooling the working parts. It is important to check carefully the Owners Manual to find out exactly what kind of brake fluid to use. Mixing different fluids negates the effectiveness of the hydraulic system.

Some brake fluids can break down the rubber rings of incompatible systems. Brake fluid must be kept scrupulously free of contamination by dirt which can render the system effectively inoperative. In some airplanes, the brakes are operated by pneumatic air pressure. A pressure bag is incorporated on the inside of the brake assembly. Air pressure admitted to this pressure bag causes it to expand, forcing the brake shoes to move radially outward against the surface of the brake drum.

They move in opposite directions to each other and are controlled by movement of the control wheel or stick. Torque Tube Aileron Control Three types of control systems are traditionally used to operate the ailerons. When stick control is used, any of these systems may be employed.

With wheel control, cables and pulleys are generally used, although in some cases, push and pull rods may be utilized.

In larger transport airplanes, the control systems are usually operated by a system of cables and pulleys aided by hydraulic systems. The new generation of transport airplanes have incorporated computerized control systems which allow operation of the aircraft controls ailerons and also elevators and rudder with electronic signalling.

The controls are activated by electronic signals sent through wires from computers in the cockpit. When the control wheel is rotated to the right or the control stick moved to the right , the left aileron moves down and the right aileron moves up. The lifting capability of the left wing is therefore increased at the same time as the lifting capability of the right wing is decreased.

The left wing lifts and the right wing descends and the airplane rolls to the right. The airplane will continue to roll to the right, steepening the angle of bank, until the controls are neutralized establishing a particular angle of bank. When the control wheel is rotated to the left, the left aileron moves up and the right one moves down and the airplane rolls to the left. The movable horizontal tail surface may be either elevators or stabilators. The elevators or stabilators are operated by: These systems are connected to the pilots control column.

The elevators are hinged to the trailing edge of the horizontal stabilizer and are controlled by forward or aft movements of the control wheel.

They move together. When the control wheel is pushed forward, the elevators move down, increasing the lifting capability of the tail. The tail rises and the nose of the airplane moves down.

When the control wheel is pulled back, the elevators move up, the lift on the tail is decreased, the tail moves down and the nose of the airplane rises. Push and Pull Rod Elevator Control. The stabilator is a one piece, horizontal tail surface that pivots up and down. It operates on the same principle as the elevators, moving up or down, changing its angle of attack and hence its lifting capabilities as the pilot pulls back or pushes forward on the control wheel. The rudder is attached to the trailing edge of the vertical stabilizer, or fin, and is connected to the rudder pedals by a cable system.

Pressure applied to the left rudder pedal displaces the rudder to the left into the airstream, increasing the pressure on the left side of the tail and forcing the tail to move to the right. The nose of the airplane moves to the left. Pressure applied to the right rudder pedal moves the nose of the airplane to the right. The rudder is used with the ailerons to achieve co-ordinated turns. Cable Rudder Control. TRIM SYSTEMS Several types of trim devices are incorporated into the control system to help the pilot by eliminating the need to exert excessive pressure on the cockpit flight controls during the various phases of flight.

Trim Tabs Trim tabs are adjustable devices located at the trailing edge of control surfaces such as elevators, rudders or ailerons.

Their function is to permit the pilot to fly the airplane in a desired attitude, under various load and airspeed conditions, without the need to apply constant pressure in any particular direction on the flight controls. A trim tab is, in effect, a control surface hinged to another control surface. It is designed to move above or below the chord line of the control surface to which it is attached and thereby create an aerodynamic force that assists the pilot in holding the control in the desired position.

The trim tab, for example, is deflected downward in order to hold the control surface up. See Fig. Elevator Trim Tab. The trim tab is operated from the cockpit by its own control which is located to be within easy reach of the pilot.

A tab position indicator is incorporated in the control mechanism to show the nose up or nose down position of the tab setting. The mechanism that operates the trim tab is usually a system of wires and pulleys. The trim tab is not the only device for affecting trim. Some trimming devices incorporate an adjustable spring tension as a means to exert pressure on the control surface to maintain the trimmed position.

These are known as bungees. Some form of inflight adjustable trim control is incorporated into the pitching plane of even the smallest airplane. Trim controls are also used on aileron controls, especially on multi-engine airplanes, and on rudder controls. On airplanes, in which in-flight adjustable trim is incorporated only on the elevator controls, ground adjustable trim tabs are often attached to ailerons or rudder.

These have the effect of helping to correct any slight tendency of the airplane to roll or yaw as the result of less than perfect rigging. Anti-servo tabs serve as trimming devices on stabilators. Servo tabs are a device found most often on larger airplanes.

They are connected directly to the control column. As in the case of the elevator, if the pilot moves the control column back, the servo tab is deflected downward.

Air pressure on the tab deflects the elevator control upward to achieve a nose up attitude. The control column controls the servo tab, the elevator is free floating and moves in accordance with the tab deflection. Adjustable Stabilizer On some airplanes, longitudinal trim is achieved by adjusting the angle at which the stabilizer is attached to the fuselage.

The leading edge of the stabilizer is moved up or down by means of a screw jack device that is controlled by a wheel or crank in the cabin. To effect a nose down attitude of the airplane, the leading edge of the stabilizer is rotated up, giving the stabilizer a higher angle of attack.

The stabilizer, like trim tabs, can be set in any position between full up and full down. The adjustable stabilizer has the advantage of producing less drag than the conventional trim tab.

Adjustable Stabilizer. Movable Tail On some airplanes, the entire empennage is hinged to pivot either forward or aft. A nose down attitude is achieved by rotating the tail aft. A nose up attitude results from rotating the tail forward. Movable Tail. Low carbon steels are tough, ductile and readily weldable but are incapable of being surface hardened except by case hardening.

Mild steels can be hardened, are strong but less ductile, less weldable. Used for fuselages and control surfaces. High carbon steels exhibit increased strength and hardness but at the sacrifice of ductility and weldability. Alloy steels, such as chrome moly, are very strong and resistant to impact and vibration. Used in the fabrication of fuselages. Alloy steels containing nickel called stainless steel are very corrosion resistant.

Used for stressed skin structures, particularly in seaplane construction. An aluminium wrought alloy containing copper and magnesium. Has a very high tensile strength and fatigue endurance. Susceptible to corrosion but can be treated by anodizing. Used for ribs, tanks, bulkheads, propeller blades, fittings, etc. The aluminium protects the dural and prevents corrosion. Very corrosion resistant. Used in seaplane construction.

Needs no anodizing. An alloy in which magnesium forms the principal constituent. Combines tensile strength with light weight one-third lighter than aluminium.

Used extensively in aircraft engine construction. Very corrodible in sea water, and should always be anodized. A metal honeycomb pattern between sheets of metal Fig. For cabin floor, door surfaces, etc.. Honeycomb Sandwich Construction. In supersonic airplanes, its ability to dissipate high temperatures makes it particularly suitable for wing skin structures.

Fibreglass cloth and epoxy resin molded over a foam form constitute the airplane structure. Composites have the advantage of weighing much less than aluminium and other conventional materials, while possessing great strength that is derived from their hidden fibres.

A graphite-composite material is also being used in some new airplanes. Wood is still used in airplane construction for structural members. Plywood is used as a covering, giving a very smooth finish. Some airplanes are all wood; others are partly wood.

Airplanes whose fuselage structures are made of steel tubing may be covered with cotton, linen or synthetic fabric. The fabric is drawn taut either by the use of aircraft dope cotton or linen or by shrinking with a hot iron synthetics such as dacron. Fabric is also used as the covering of wings whose spars and ribs are either all wood or all metal or a combination of both.

The attack may take place over an entire metal surface or it may be penetrating in nature, forming deep pits. There are a number of different types of corrosion. This is produced by atmospheric conditions due to the moisture in the air. The effect is worse in the vicinity of salt water. The action consists of the dissolving of the surface by oxidation. Such oxidation is easy to detect. It may be removed and the surface treated with some preventative so further damage will not occur.

This type is more serious. It is caused by chemical or electrolytic action between the alloys in the metal itself. It may not become visible until considerable damage has been done. Surface protection aids very little in the prevention of this type of corrosion. The affected parts must be removed and replaced. Dissimilar Metals. When metals of different chemical properties are in contact in the presence of moisture, the metal most easily oxidized will be subject to corrosion. Stress Corrosion.

When a metal part is overstressed over a long period of time under corrosive conditions, stress corrosion may result. Parts that are susceptible to stress corrosion are over tightened nuts in plumbing fittings, parts joined by taper pins that are overtorqued, fittings with pressed in bearings.

Stress corrosion is not easy to detect until cracks begin to appear. Corrosion fatigue is a type of stress corrosion that occurs where cyclic stresses are applied to a part or assembly. These stresses produce pores or cracks in the surface coating which allow moisture to penetrate. Fretting Corrosion occurs when there is a slight movement between close fitting metal parts.

The movement destroys any protective film on the metal surface and also produces fine particles of metal and oxide that tend to absorb and retain moisture. A number of surface treatments have been developed to reduce or eliminate corrosion. Aluminium alloys are usually anodized, a process that provides a protective film.

Steel parts are protected by cadmium plating, chrome plating or by phosphate processes that protect the surface from oxidation. A pressure of your hand on the surface of, say, a small empty box is a stress. If the small box is crushed, it is said to be strained. A wire stretched is another example of strain.

There are five distinct types of stress: Airplane wings are subjected to compression stresses. Bracing wires in airplanes are usually in tension. A screwdriver is subjected to severe torsional stress when forcing a screw into hardwood. Landing gear must be made to withstand torsional stresses. The blades of scissors exert a shear stress on a piece of paper, which is sheared as a result. BENDING, as the name implies, means the bending of a long member due to a load or weight being imposed on it, Aircraft spars, or beams, must resist severe bending stresses.

An airplane structure in flight is subjected to many stresses due to the varying loads that may be imposed. The designers problem is to try to anticipate the possible stresses that the structure will have to endure, and to build it sufficiently strong to withstand these. This problem is complicated by the fact that an airplane structure must be light as well as strong.

Strength and lightness are essential in the structure of an airplane. Another factor almost as essential as strength is rigidity. Excessive deflection or bending under a load may lead to a loss of control with serious consequences. Lack of rigidity may also lead to flutter.

This is a rolling or weaving motion which arises when a deflection of a part of the structure causes the air forces on it to change in synchronism with its natural period of vibration. Flutter is most likely to occur in wings and control surfaces and may lead to structural failure.

To prevent flutter, the wing and tail structures must be made stiff against both bending and twisting. The narrow margin of safety permitted by weight limitations in airplanes makes it necessary that every member must bear its proper share of the load in every condition of flight.

To attain uniform and adequate structural safety, it is essential to calculate what load each part may be called upon to carry. Such a determination of loads is called a stress analysis. This is a complicated mathematical process, and is distinctly a job for only the trained engineer. The load imposed on the wings depends on the type of flight.

The wings must support not only the weight of the airplane but also additional loads imposed during manoeuvres. The definition of wing loading may be slightly modified for particular applications, for example, with reference to ultra-light airplanes. See Ultra-Lights in Chapter Airmanship. The weight of an airplane standing on the ground or its weight due to gravity alone is commonly referred to as a dead load. The additional loading imposed is called a live load. The load factor is the ratio of the actual load acting on the wings to the gross weight of the airplane.

In other words, it is the ratio of the live load to the dead load. When an airplane is in level flight, the lift of the wings is exactly equal to the weight of the airplane. The load factor is then said to be 1. In most manoeuvres, such as a change in attitude, a banked turn, a pull out or any manoeuvre causing acceleration, centrifugal force enters the picture and brings about a change in the load factor.

In a 60 degree bank, the load factor goes up to 2. In a hard landing, the total load acting upward on the wheels may be as much as three times the weight of the airplane. The landing load factor in this case would be 3.

A load factor of 3 is often expressed as In this case, the letter refers to gravity. Hence, 3g means a load on the wings equal to three times the weight of the airplane due to gravity alone. There are, of course, maximum limits to which an aircraft is designed. These are usually referred to as limit load factors. The fact that it is sometimes possible to exceed these limits is evidence of the safety factor that is incorporated in all aircraft designs.

Nevertheless, the limit load factor should not be exceeded intentionally because of the possibility of causing permanent set or distortion of the structure. The flight manoeuvres which impose high load factors are: These should be executed with due consideration on the pilots part of the stresses which the particular airplane he is flying is designed to withstand.

Airplanes which fly at several times their stalling speed are subject to excessive g loads in some circumstances. In an airplane that is flying at twice its stall speed, if the angle of attack is abruptly increased to obtain maximum lift, a load factor of 4 will be produced; at three times the stall speed, 9g would result; at four times the stall speed, 16g would result. Weight also can result in high load factors.

If an airplane is heavily loaded, the allowable load factors will be reduced accordingly and the pilot is likely to damage the structure in manoeuvres that would normally be quite safe.

Therefore when doing aerobatics always be sure that the airplane is lightly loaded. In flying a heavily loaded airplane, a pilot should not trust his senses in determining the actual load on the wings.

Because the heavy airplane is steady even in rough air, the pilot may get the false impression that the air turbulence is not excessive. However, the wings sense the actual load and may be about at their breaking point.

On the other hand, a pilot flying an airplane that is lightly loaded may experience a good deal of buffeting and personal discomfort in rough air. Because of this, he may feel that the load factor is excessive whereas the wings which sense the actual load are not being over stressed. In any degree of turbulence, it is important to reduce the airspeed to prevent damage to the airplane structure.

See Gust Load below. Gust Load. Gusts are rapid and irregular fluctuations of varying intensity in the upward and downward movement of air currents. An airplane in a rising or descending current of air is not affected. When, however, the speed or direction of the air current changes abruptly such as when flying at high speed through successive up-and-down gusts , load changes are imposed on the airplane structure.

When an airplane flies out of a down-gust and immediately into an up-gust, for example, the effect on the wings is to suddenly increase the angle of attack.

From the Ground Up, 29th Edition

The lift is then in excess of the weight, and the airplane accelerates in an upward direction, just as it would if the pilot suddenly pulled back on the controls. If the total lift were to exceed the total weight by a factor of 2, the airplane would experience a 2g acceleration.

This is known as a gust load. Gusts, therefore, can impose very high load factors on the airplane. In fact, since gust loads can be sufficiently severe to be dangerous, it is wise to avoid, if at all possible, extremely rough air. The faster the airplane is going, the more stress to which it is subjected when a vertical gust is encountered. For this reason, when flying in rough air conditions, it is safer to slow the airplane to a speed somewhat below the normal smooth air cruising speed.

On encountering any degree of turbulence, the airspeed should be reduced to the recommended manoeuvring speed. Airplane manufacturers always specify in the Aircraft Owners Manual a recommended manoeuvring speed VA for each model of airplane. This is the maximum speed at which full deflection of the controls can be made without exceeding the design limit load factor and damaging the airplane primary structure.

The airplane designer determines the manoeuvring speed by a formula that multiplies the flaps-up, power-off stall speed at gross weight by the square root of the design limit load factor of the airplane.

Most general aviation, normal category airplanes are certificated to withstand 3. The manoeuvring speed works out to be 1. This airspeed guarantees that the airplane will stall at the limit load factor. However, this manoeuvring speed is not always the best speed at which to penetrate turbulence. In the first place, an airplane flying into turbulence is flying with power.

The power-on stall speed of an airplane is significantly less than its power-off stall speed. In the second place, turbulence is a form of wind shear which causes airspeed fluctuations. Rapid airspeed fluctuations of 5 to 15 knots in light turbulence and up to 25 knots in severe turbulence can be expected. Consequently, the best airspeed at which to penetrate turbulence should be at least 10 knots below the published manoeuvring speed to compensate for the stall delaying effects of power and the effect of wind shear.

A further consideration is the fact that the published manoeuvring speed is valid only when the airplane is at gross weight.

Because stall speed decreases as weight decreases and because the manoeuvring speed is a function of stall speed, a lightly loaded airplane should be flown at a slower airspeed in turbulence than one that is more heavily loaded.

The lightly loaded airplane is accelerated more easily by gusts. All of these factors demonstrate that the safest airspeed at which to penetrate turbulence is one that is somewhat less than the published manoeuvring speed and, depending on the all-up weight, would range between 1. This speed is below VA but well above the stall. While it is important to worry about subjecting the airplane to excessive structural loads when flying in turbulence, it is also essential to maintain control of the airplane at all times while in flight.

Having adequate control to recover from the lateral and directional upsets that are the result of excessive turbulence requires flying at an airspeed at which the control surfaces are effective. The airspeed at which to fly in turbulence is therefore a compromise between structural and controllability margins. The accepted procedure for flight in turbulence is to keep the wings level; maintain a normal pitch attitude and move the controls smoothly and slowly to recover from attitude displacement.

Do not try to maintain altitude. Vertical air. Do try to maintain attitude and airspeed. It is quite possible in turbulent conditions for the airplane to stall. In most instances, the wings stall and recover before the pilot even realizes what has happened.

Safety is unlikely to be jeopardized unless the airplane has undesirable stall characteristics or is flying near to the ground as during the approach to landing when a stall can result in an accident. In these instances, a higher airspeed nearer to the published manoeuvring speed to allow for a greater margin above stall is preferable. These facts relating to loads are of critical importance and should be understood and intelligently applied so that you never impose loads on any airplane that you might be flying in excess of the limit load for which it was designed.

All maintenance, repairs, new installations, modifications, etc. A record of both flight time and air time and particulars of every flight is kept in a suitable Aircraft Journey Log. Air time is defined as the period of time commencing when the airplane leaves the supporting surface and terminating when it touches the supporting surface at the next point of landing. Flight time is defined as the total time from the moment an airplane first moves under its own power for the purpose of taking off until the moment it comes to rest at the end of the flight.

Flight time is the time pilots should record in their log books. Air time and flight time should be recorded to the nearest 5 minutes e.

In certain cases, log book information may be recorded in a computer data bank, rather than in a hard copy log book. Although the Air Regulations do not require it, it is a recommended practice to keep log books for an ultra-light airplane as well, so that there is a record of maintenance, repairs, modifications, etc.

Theory of Flight Why learn about Theory of Flight? The pilot today has a large variety of airplanes from which to choose. Some of these airplanes may fly at less than knots top speed while others are capable of speeds well into the hundreds of knots. Some are single seaters carrying only the pilot, while others, even in the single engine light airplane classification, may carry 10 or more passengers.

Some airplanes have laminar flow airfoil sections; others have airfoils of conventional design.

Every one of these airplanes has different flight characteristics. If a pilot has a good grasp of the fundamentals of flight, he will understand what to expect of each different airplane that he may have the opportunity to fly.

He will understand how best to handle each airplane as a result of his knowledge of the theory of design. He will comprehend the various loads to which an airplane of a particular design may be exposed while flying under abnormal or adverse conditions of flight. Not only to get the best performance but also to ensure the safety of each flight, an understanding of Theory of Flight is essential. The study of theory of flight and aerodynamics can be a lifetime proposition. New theories are forever being put forward.

Some questions have answers that are difficult to find. Others perhaps do not yet have adequate answers. The information that comprises this chapter can only be considered an introduction to a substantial but fascinating study. These are thrust, drag, lift and weight. The force exerted by the engine and its propeller s which pushes air backward with the object of causing a reaction, or thrust, in the forward direction.

The resistance to forward motion directly opposed to thrust. The force upward which sustains the airplane in flight. The downward force due to gravity, directly opposed to lift. When thrust and drag are equal and opposite, the airplane is said to be in a state of equilibrium.

That is to say, it will continue to move forward at the same uniform rate of speed. Equilibrium refers to steady motion and not to a state of rest. If either of these forces becomes greater than the force opposing it, the state of equilibrium will be lost. If thrust is greater than drag, the airplane will accelerate or gain speed. If drag is greater than thrust, the airplane will decelerate or lose speed.

Similarly, when lift and weight are equal and opposite, the airplane will be in equilibrium. If lift, however, is greater than weight, the airplane will climb.

If weight is greater than lift, the airplane will sink. Let us first consider the force of lift. LIFT If you consider the definitions cited by air authorities, a boy flying a kite could be construed to be a pilot in charge of an airplane!

Ponder the idea a moment and it may not appear quite as absurd as it seems at first glance. A kite is an inclined plane, the weight of which is supported in the air by the reaction of the wind flowing against it. If we substitute for the string, which holds the kite against the wind, the engine and propeller of an airplane, which move the wings forward against the airflow, we will see that the analogy of the kite is not without some validity.

The wings of an airplane are so designed that when moved through the air horizontally, the force exerted on them produces a reaction as nearly vertical as possible. It is this reaction that lifts the weight of the airplane.

Airfoils An airfoil, or airfoil section, may be defined as any surface designed to obtain a reaction from the air through which it moves, that is, to obtain lift. It has been found that the most suitable shape for producing lift is a curved or cambered shape. The camber of an airfoil is the curvature of the upper and lower surfaces. Usually the upper surface has a greater camber than the lower. An Airfoil Section. How Is Lift Created What, then, causes this lift, you may ask.

Air flowing around an airfoil is subject to the Laws of Motion discovered by Isaac Newton. Air, being a gaseous fluid, possesses inertia and, therefore, according to Newton's First Law, when in motion tends to remain in motion. The introduction of an airfoil into the streamlined airflow alters the uniform flow of air. Newton's Second Law states that a force must be applied to alter the state of uniform motion of a body.

The airfoil is the force that acts on the body in this case, the air to produce a change of direction. The applications of such forces cause an equal and opposite reaction Newtons - Third Law called, in this case, lift. As the air passes over the wing towards the trailing edge, the air flows not only rearward but downward as well.

This flow is called downwash. At the same time, the airflow passing under the wing is deflected downward by the bottom surface of the wing. Think of a water ski or surfboard planning over the water. In exerting a downward force upon the air, the wing receives an upward counter force.

Remember Newton's Third Law - for every action there is an opposite and equal reaction. Therefore, the more air deflected downward, the more lift is created. Air is heavy; its weight exerts a pressure of The reaction produced by the downwash is therefore significant.

Airflow over an Airfoil. The phenomenon defined by Bernoulli's Principle also has an effect in the production of lift by the wing moving though the air. Scientist Daniel Bernoulli discovered that the total energy in any system remains constant.

In other words, if one element of an energy system is increased, another decreases to counter balance it. Take the example of water flowing through a venturi tube. Being incompressible, the water must speed up to pass through the constricted space of the venturi. The moving water has energy in the form of both pressure and speed. Within the venturi tube, pressure is sacrificed decreased to accelerate the speed of the flow.

Pressure Distribution over an Airfoil. Air is a fluid, just like water, and can be assumed incompressible insofar as speed aerodynamics is concerned. As such, it acts exactly the same way as water in a venturi tube. Picture the curved upper surface of a wing as the bottom half of a venturi tube.

The upper half of this imaginary tube is the undisturbed airflow above the wing. Air flowing over the wing's upper surface accelerates as it passes through the constricted area just as it does in the venturi tube.

The result is a decrease in pressure on the upper surface of the wing that results in the phenomenon known as lift. Relative Airflow Relative airflow is a term used to describe the direction of the airflow with respect to the wing. In other texts, it is sometimes called relative wind. It a wing is moving forward and downward, the relative airflow is upward and backward. If the wing is moving forward horizontally, the relative airflow moves backward horizontally.

The flight path and the relative airflow are, therefore, always parallel but travel in opposite directions. Relative airflow is created by the motion of the airplane through the air creates relative airflow.

It is also created by the motion of air past a stationary body or also creates it or by a combination of both. Therefore, on a take-off roll, an airplane is subject to the relative airflow created by its motion along the ground and also by the. In flight, however, only the motion of the airplane produces a relative airflow. The direction and speed of the wind have no effect on relative airflow.

Angle of Attack and Centre of Pressure The angle at which the airfoil meets the relative airflow is called the angle of attack See Fig. The envelopes indicated in Fig. These exist only in close proximity to the surfaces. They represent the comparative distribution of pressure as determined by pressure plotting. In Fig. As the angle of attack is increased, the changes in pressure over the upper and lower surfaces and the amount of downwash, i. Beyond this angle, they decrease Fig.

If we consider all the distributed pressure to be equivalent to a single force, this force will act through a straight line. The point where this line cuts the chord of an airfoil is called the centre of pressure. Thus, it will be seen that as the angle of attack of an airfoil is increased up to the point of stall, the centre of pressure will move forward.

Beyond this point, it will move back. The movement of the centre of pressure causes an airplane to be unstable. Angle of Attack.They are usually hinged to the rear spar. S And the drag by: It therefore includes the fuselage, wings, tail assembly and undercarriage.

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Truss Type Fuselage. Theory of Flight Why learn about Theory of Flight?

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