Aerodynamics – What Makes Airplanes FlyDoylestown Pilots AssociationBoy Scouts Aviation Day 10/13/2012 Maj William J. Doyle, Jr. Civil Air Patrol, New Jersey Wing, Assistant StanEval Officer Check Pilot / Instructor-Pilot CFI A&I, AGI, IGI, CFAI, FAAST Rep
Aerodynamics Lesson Plan • What is an Airplane and What Makes It Fly • The Airplane • Flight Controls • Axes of Rotation • Forces Acting on the Airplane in Flight • Dynamics of the Airplane in Flight • Ground Effect • How Airplanes Turn • Torque (Left-Turning Tendency) • Airplane Stability • Stalls and Spins
How Do the Flight Controls Work? • Push the stick (or yoke) forward and the houses get bigger. • Pull the stick (or yoke) back and the houses get smaller. • Hold the stick (or yoke) back too long and the houses get really small then they get bigger again. (You just did a loop.)
Airplane Components - Fuselage • Open truss • clearly visible struts and wire braces • Stressed skins • monocoque • skin supports all loads • semi-monocoque • sub-structure riveted to skin to maintain shape and increase strength
Airplane Components - Wings • Monoplane • single set of wings • Biplane • two sets of wings • Ailerons • move in opposite directions for turns • controls roll (or bank) • controlled by yoke or stick • right pressure turns right • left pressure turns left • Flaps • extend downward to increase lifting force for landings and sometimes takeoffs • controlled by flap handle or switch • pre-selected positions or variable positions
Airplane Components - Empennage • Vertical Stabilizer and Horizontal Stabilizer • help steady airplane for straight flight • Rudder controls yaw • controlled by floor pedals • right pressure moves nose to right • left pressure moves nose to left • Elevator (stabilator on Cherokee) controls pitch • controlled by yoke or stick • forward pressure lowers nose • back pressure raises nose • Trim Tab helps hold pitch attitude • controlled by trim wheel • move wheel forward for nose down trim • move wheel back for nose up trim
Airplane Components - Landing Gear • Gear Types • Fixed Gear • Retractable Gear • Tricycle Gear • Conventional Gear (tail dragger) • Landing Gear Struts • Spring steel struts • bungee cord struts • oleo struts • shock disks • Brakes • Disc brakes • Differential braking
Airplane Components - Powerplant • Engine • provides power to turn propeller • distinguishes airplane from glider • Firewall • separates cockpit from engine • mounting point for engine • Propeller • translates engine rotational force into forward-acting force called thrust
Wing Planforms Aspect Ratio = Wing Span ÷ Average Chord
What Makes an Airplane Fly? • For an airplane to takeoff, thrust must overcome drag and lift must overcome gravity (sometimes called weight) • So is there relevancy here to what you study in school? • Applicable Subject in School = Science • High School Course = Physics (study the chapter on Bernoulli’s Law)
What Makes an Airplane Fly? • The laws of physics apply to everything. • They apply to F-16 fighters and to the USAF Thunderbirds.
What Makes an Airplane Fly? • The laws of physics apply to everything. • They apply to ultra lights.
What Makes an Airplane Fly? • The laws of physics apply to everything. • They even applied to the Wright Brothers in the Wright Flyer at Kitty Hawk, NC.
Four Forces of Flight Vector Vector Vector Vector
Four Forces of Flight • Lift • upward force from airflow over and under wing • Weight • downward force of gravity • Thrust • forward force propelling airplane through air • Drag • rearward force retarding force limiting speed
Newton’s Laws of Force and Motion • Newton’s First Law • A body at rest tends to remain at rest, and a body in motion tends to remain moving at the same speed and in the same direction. • Newton’s Second Law • When a body is acted upon by a constant force, its resulting acceleration is inversely proportional to the mass of the body and is directly proportional to the applied force. • Newton’s Third Law • For every action there is an equal and opposite reaction.
Bernoulli’s Principle Bernoulli’s Principle • Explains how the pressure of a moving fluid (liquid or gas) varies with its speed of motion. • States that as the velocity of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases. • Explains what happens to air passing over the curved top of the airplane wing.
Components of an Airfoil • Airfoil: a structure designed to obtain reaction upon its surface from the air through which it moves or that moves past such a structure. • Camber: curvatures of the upper and lower surfaces of the airfoil. The camber of the upper surface is more pronounced than that of the lower surface, which is usually somewhat flat. • Chord Line: a straight line drawn through the profile connecting the extremities of the leading and trailing edges. • Mean Camber Line:reference line drawn from the leading edge to the trailing edge, equidistant at all points from the upper and lower surfaces. • Leading Edge faces forward in flight and is rounded. • Trailing Edge faces aft in flight and is narrow and tapered.
Angle of Attack and Wing Stalls Air circulation around an airfoil occurs when the front stagnation point is below the leading edge and the aft stagnation point is beyond the trailing edge.
Effect of Wingtip Twist Wingtip Wing Root
Effect of Stall Strip Wingtip Wing Root
Types of Drag • Parasite Drag • Caused by any aircraft surface which deflects or interferes with smooth airflow around airplane • Form drag • results from turbulent wake caused by the separation of airflow from the surface of the structure • Interference drag • occurs when varied currents of air over an airplane meet and interact • Skin friction drag • caused by roughness of the airplane’s surfaces • Induced Drag • Generated by the airflow circulation around the wing as it creates lift
Ground Effect • Result of earth’s surface altering the airflow patterns around the airplane. • Occurs within one wingspan above the ground. • When in ground effect • Induced drag decreases and excess speed in the flare may cause floating. • Airplane may become airborne before it reaches its recommended takeoff speed.
Longitudinal Stability and Balance • Longitudinal Stability • Pitching motion or tendency of airplane to move about its lateral axis. • Determined by the location of the center of gravity in relation to the center of pressure. • Center of Pressure • Point along wing chord where lift is considered to be concentrated. • Sometimes called the center of lift. • Center of Gravity • Determined by the distribution of weight, either by design or by the pilot. • Can affect longitudinal stability.