PPL Principles of Flight PDF

PRINCIPLES OF FLIGHT (PPL) Aircraft – any weight-carrying device designed to be supported by the air I. Varieties of aircraft Categories: (1) Airplane – engine-driven, fixed wing, heavier than air aircraft supported in flight by aerodynamic lift produced when air flows over its wings Cla...

PRINCIPLES OF FLIGHT (PPL) Aircraft – any weight-carrying device designed to be supported by the air I. Varieties of aircraft Categories: (1) Airplane – engine-driven, fixed wing, heavier than air aircraft supported in flight by aerodynamic lift produced when air flows over its wings Class: a. Single engine land c. Single engine sea (Type: Cessna 152, etc.) b. Multi-engine land d. Multi-engine sea (2) Rotorcraft (helicopter, gyroplane) (3) Glider (4) Lighter-than-air (airship, hot air balloon) (5) Powered lift (also called ‘tilt-rotor’) Categories of aircraft according to intended use (for aircraft certification): 1. Normal – common to most small airplanes, includes trainer aircraft 2. Utility – same as normal, but can withstand heavier stress 3. Acrobatic – fewest operation limitations 4. Commuter – carry passengers but limited to 19 seats and 19,000lbs or less 5. Transport – airlines 6. Restricted – special purpose aircraft (e.g. spray planes, water bombers) 7. Limited – military aircraft which are allowed to be used for limited purposes in civilian aviation 8. Provisional – newly designed aircraft which have not met all the requirements for initial certification 9. Experimental – amateur home-built or racing aircraft as well as research and development aircraft used to test new design concepts II. Major airplane components (1) Fuselage – houses the cabin and/or cockpit which contain seats for the occupants and controls for the airplanes. Also provides room for cargo and other attachment points for others major airplane components Types of construction: 1. Truss – visible struts and wire braced wings 2. Monocoque – uses skin to support almost all imposed loads FOR TRAINING PURPOSES ONLY  3. Semi-monocoque – uses a substructure riveted to the airplane’s skin to maintain the shape of the airframe and increase its strength (2) Wings – produce lift for the airplane’s flight; contoured to take advantage of lift generation Types of wing location: Types according to number of sets: a. High wing a. Mono-plane b. Mid wing b. Bi-plane c. Low wing c. Tri-plane  Ailerons – extend from the mid-point of each wing outward to the tip; move in opposite direction (one goes up, one goes down)  Flaps – extend from the wing root to the mid-point (3) Empennage (tail) – consists of:  Vertical stabilizer (“fin”) - Rudder: used to yaw the airplane’s nose to the left or right  Horizontal stabilizer - Elevator: used to pitch the airplane’s nose up or down - Stabilator: one-piece horizontal stabilizer pivoting up and down *Trim devices (trim tab [elevator, rudder, aileron]; anti-servo tab): used to lessen or relieve the control resistance or pressure (4) Landing gear/Undercarriage – absorbs landing loads and supports the airplane on the ground Types: a. Conventional – has a rear-mounted or tail wheel (also called “tailwheel” or “tail draggers”) b. Tricycle – has a nosewheel Classifications: a. Fixed gear b. Retractable Brakes – typical training planes use disc brakes located on the main wheels; activated by applying pressure on the top of the rudder pedals *Differential braking – used to steer the plane while on the ground at slow speeds FOR TRAINING PURPOSES ONLY (5) Powerplant a. Engine – provides power to turn the propeller accessories, provide electrical power, create vacuum source, etc. b. Firewall – located between the engine compartment and cockpit; protects the occupants and serves as a mounting point for the engine c. Cowling – streamlines the nose of the airplane, protects and covers, helps cool the engine d. Propeller – mounted on the front of the engine, translates rotating force from the engine to forward acting force called thrust III. Aerodynamics Aerodynamics – the study of forces and the resulting motion of objects through the air. (Any aircraft or object moving through the air depends on the laws of aerodynamics.) Physical properties of air: 1. Air has weight and can be weighed. 2. Air exerts pressure. 3. Air has temperature. (A) Four forces in flight a. Lift - Upward force created by the airflow as it passes over and under the wing. It supports the airplane in flight. b. Weight – opposes lift and is caused by the downward pull of gravity. c. Thrust - forward force which propels the airplane through the air. d. Drag – backward or retarding force which limits the speed of the airplane. *Opposing forces are equal in steady-state level flight. (B) Newton’s laws of motion 1st Law – a body at rest tends to remain at rest; and a body in motion tends to remain in motion at the same speed and direction unless an outside force acts upon it. 2nd Law – A body will accelerate with acceleration proportional to the force and inversely proportional to the mass. 3rd Law – For every action there is an equal and opposite reaction. (C) Bernoulli’s Principle – as the velocity of a fluid increases, its internal pressure decreases FOR TRAINING PURPOSES ONLY (D) Airfoils Airfoil – any surface (such as wings) which provides aerodynamic force when it interacts with a stream of moving air  Leading edge – part of the airfoil meeting the wind first  Trailing edge – part of the airflow from the upper surface rejoins the airflow from the lower surface  Camber – characteristic curve of the airfoil’s upper and lower surfaces  Chord line – an imaginary straight line drawn through the airfoil from the leading edge to the trailing edge  Relative wind – airflow which is parallel to and opposite the flight path of the airplane  Angle of attack – the angle between the chord line of the airfoil and the direction of the relative wind *Critical angle of attack – angle at which a stall occurs (E) Wing design factors - Wing design is based on the anticipated use of the airplane, cost, and other factors. a. Camber - characteristic curve of the airfoil’s upper and lower curve b. Wing planform – refers to the shape of the airplane’s wings when viewed from above or below (Elliptical, Rectangular, Tapered, Sweptback) c. Aspect ratio – relationship between length and width of a wing; in general, the higher the aspect ratio, the higher the lifting efficiency of the wing Aspect ratio = Span / Average chord d. Wing area – total surface of the wings e. Angle of incidence – refers to the angle between the wing chord line and a line parallel to the longitudinal axis of the airplane f. Washout or twist – a built-in twist that causes a lower angle of attack at the wingtips compared with near the wing root g. High-lift devices – designed to increase efficiency of airfoils at low speeds (the most common high-lift device is the trailing-edge flaps) Types of trailing-edge flaps:  Plain: attached to the wing by a hinge FOR TRAINING PURPOSES ONLY   Split: hinged only to the lower portion of the wing  Slotted: similar to plain but helps prevent airflow separation  Fowler: attached to the wing by a track and roller system; when extended it moves rearward as well as down Lift-to-drag ratio In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or vehicle, divided by the aerodynamic drag it creates by moving through the air. A higher or more favorable L/D ratio is typically one of the major goals in aircraft design; since a particular aircraft's required lift is set by its weight, delivering that lift with lower drag leads directly to better fuel economy in aircraft, climb performance, and glide ratio. Types of drag: 1. Induced drag – generated by the airflow circulation around the wings as it create lift; increases with flight at slow airspeed as the angle of attack increases. 2. Parasite drag – caused by an aircraft surface which deflects or interferes with the smooth airflow around the airplane a. Form drag – results from turbulent wake caused by the separation of airflow from the surface of a structure b. Skin friction drag – caused by roughness of the airplane’s surface c. Interference drag – occurs when varied currents of air over an airplane meet and interact 3. Total drag – sum of parasite and induced drag *Ground effect – occurs close to the ground where the earth’s surface restricts the downward deflection of the airstream from the wing, decreasing induced drag (most prominent within a height of one wingspan above the surface). (F) Three axes a. Longitudinal (Roll) – controlled by the ailerons b. Lateral (Pitch) – controlled by the elevator c. Vertical (Yaw) – controlled by the rudder *The common reference point for the three axes is the airplane’s center of gravity (CG), which is the theoretical point where the entire weight of the airplane is considered to be concentrated. FOR TRAINING PURPOSES ONLY (G) Aircraft stability Stability – characteristic of an airplane in flight that causes it to return to a condition of equilibrium, or steady flight, after it is disrupted 2 major categories: (1) Static stability – initial tendency that an object displays after its equilibrium is disrupted a. Positive static stability: tendency to return to its original attitude after its displacement b. Negative static stability: tendency to move farther away from the original attitude c. Neutral static stability: tendency to remain in its displaced attitude (2) Dynamic stability – describes the time required for an airplane to respond to its static stability following a displacement from a condition of equilibrium a. Positive dynamic stability: tendency to return to the original attitude directly, or through a series of decreasing oscillation b. Negative dynamic stability: oscillations increasing in magnitude as time progresses c. Neutral dynamic stability: attempts to return to its original state of equilibrium, but the oscillations neither increase nor decrease in magnitude as time passes Longitudinal stability – involves the pitching motion or the tendency of the airplane about its lateral axis Lateral stability – stability about an airplane’s longitudinal axis 4 common design features: (1) Dihedral – upward angle of the wings (2) Keel effect – steadying influence exerted by the side area of the fuselage and vertical stabilizer (3) Sweepback – wings are angled backward from wing root to tips (4) Weight distribution Directional stability – stability about an airplane’s vertical axis (the vertical tail is the primary contributor) (8) Turns - The horizontal component of lift causes an airplane to turn. *Centripetal force – directed inward, acts toward the center of rotation *Centrifugal force – acts outward, from the center of rotation FOR TRAINING PURPOSES ONLY  *Adverse yaw effect – outside wing produces more drag than the inside wing; causes a yawing tendency towards the outside turn (9) Turning tendencies a. Torque – the clockwise action of a spinning propeller causes a torque reaction which tends to rotate the airplane counterclockwise, about its longitudinal axis *Newton’s 3rd law of motion: “for every action there is an equal and opposite reaction” *Torque effect is greatest in a single engine airplane during a low airspeed, high power flight condition. b. Gyroscopic precession – the resultant reaction when a force is applied to the rim of a rotating disc. The reaction to a force applied to a gyro acts in the direction of rotation and approximately 90 degrees ahead of the point where force is applied c. Asymmetrical thrust (“P” factor) – results from the descending propeller blade on the right producing more thrust that the ascending blade on the left d. Spiraling slipstream – as the slipstream produced by the propeller rotation wraps around the fuselage, it strikes the left side of the vertical fin causing the tail of the airplane to move to the right, and the nose to yaw left about its vertical axis (10) Stalls and spins Stall – Loss of lift caused by exceeding the critical angle of attack and destroying the smooth flow of air over an airfoil. ( An airplane always stalls when the critical angle of attack is exceeded, regardless of airspeed, flight attitude, or weight.) Types of stall: 1. Accelerated stall – caused by abrupt or excessive control movement 2. Secondary stall – caused by attempting to hasten the completion of a stall recovery 3. Crossed control stall – cross control of aileron and rudder with excessive backpressure. Classification of stall: 1. Power-off 2. Power-on Stall recognition: 1. Reduction in control effectiveness FOR TRAINING PURPOSES ONLY  2. Loss of RPM (for fixed wing props; for power on stalls) 3. Reduction in sound of airflow 4. Buffeting, uncontrollable pitching or vibrations 5. Sinking feeling Stall recovery – decrease the angle of attack Coefficient of lift is a way to measure lift as it relates to angle of attack. Factors affecting stall speed: a. Weight e. Load factor b. Flaps f. Frost, snow, ice c. Angle of bank g. Turbulence d. Center of gravity *Load factor – ratio of the load supported by the airplane’s wings to the actual weight of the aircraft and its contents *Limit load factor – number of “G’s” an aircraft can sustain on a continuing basis without permanent structural damage. Spin – an aggravated stall which results in the airplane descending in a helical or corkscrew path; uncoordinated maneuver with wings unequally stalled Phases of a spin: 1. Incipient spin 2. Fully developed spin 3. Spin recovery Spin recovery: 1. Move throttle to idle 2. Neutralize ailerons 3. Determine direction of rotation (may use Turn Coordinator) 4. Apply full opposite rudder 5. Apply elevator forward to neutral position 6. As rotation stops, neutralize rudders 7. Gradually apply aft elevator to return to level flight, then add power FOR TRAINING PURPOSES ONLY