Aerodynamics Man must rise above the Earth -- to the top of the atmosphere and beyond -- for only thus will he fully understand the world in which he lives. — Socrates
Principles of Aerodynamics • Flight involves a balance of 4 forces. • These forces are THRUST, DRAG, LIFT and WEIGHT. • When Thrust and Dragare equal, the airspeed of the aircraft will remain constant in smooth air. • When Lift and Weight are equal, the aircraft will stay at the same altitude.
What is propulsion? • Propulsion means to push forward or drive an object forward. • A propulsion system is a machine that produces thrust to push an object forward. • Thrust is produced through some application of Newton's third lawof action and reaction. • Air pushes on the engine and the engine pushes on the air.
From Newton’s 3rd law, the propeller pushes on the air and the air pushes on the propeller. • Propellers can have from 2 to 6 blades. • The blades are usually long and thin.
Built to push the air • A perpendicular cut through the blade will give an airfoil shape. • The blades are twisted from hub to tip. • The angle of attack of the airfoils at the tip is lower than at the hub
A basic airfoil shape
Engines to turn the propellers • There are 2 types of piston aircraft engines, air-cooled and liquid cooled. • Air-cooled engines are easier to maintain and can withstand more damage. • Liquid cooled engines are more aerodynamic.
Wasp Major Engine • The air cooled R-4360 Wasp Major was developed by Pratt & Whitney in 1942. • This is a 28-cylinder, 4,360 cubic inch engine. • It weighs 3,405 pounds but produces 3,650 horsepower, a ratio of .93 pounds per horsepower.
Convair B-366 Wasp Major engines and 4 jet engines!1948, largest American bomber produced! 230 ft. wingspan
P-47N - WWII - 465 mph
F2G - Super Corsair- 485 mph
Boeing Stratocruiser. This 1950’s airliner also used the wasp major engines. Its cruise speed was about 340 mph.
Lockheed Super Constellation - 1955 - 345 mph
Rolls Royce Merlin engine • The Rolls Royce Merlin engine is the best liquid cooled, piston airplane engine. • A special metal alloy allowed the engine to be very small and still produce 1,700 hp • Any damage to the cooling system, though, and the engine quickly over heats. • This engine powered spitfires, mustangs and a host of other aircraft during WWII.
Supermarine Spitfire - main fighter of Great Britain – late models 445 mph
F-82 Twin Mustangpowered by two Merlin engines, used in Korea in the 1950’s- 465 mph
P-51 Dago Red - Reno Air racer 500+ mph
Turboprop engines • Jet engines can be used to turn the propellers on some aircraft. This propulsion system is called a turboprop. • Its main thrust comes from the propellers, but the propellers are turned by a jet engine. • Propeller-powered aircraft are very efficient for low speed flight. • Increasing drag from the propellers limits these engines to speeds below 600 mph. • Propellers are not used on high speed aircraft.
C-130 Hercules, a turboprop aircraft
P-3 Orion
Turboprop airliners have reasonable speed and excellent fuel economy.
Turbofan jet engines • A turbofan engine is the most modern jet engine. • The core engine is surrounded by a fan in the front and another fan at the rear. • The fan and fan turbine are composed of many blades, • A turbofan gets some of its thrust from the core exhaust and some of its thrust from the rotating fans.
Boeing 747, a turbofan jet aircraft
Airbus 380 - largest commercial passenger jet
C-5 Galaxy - Largest US military transport
Drag • Drag is the aerodynamic force of the air pushing on the moving aircraft.. • Drag is generated by every part of a moving airplane. • If there is no motion, there is no drag. • Drag increases dramatically with increasing speed.
Weight • Weight is the force generated by gravity. • Lift, drag and thrust are mechanical forces. • The gravitational force is a field force; • The source of the force does not have to be in physical contact with the object to generate a pull on the object
Lift • Lift is the force that opposes the weight of an airplane and holds the airplane in the air. • Most of the lift on a normal airplane is generated by the wings. • Lift is a mechanical aerodynamic force produced by the motion of the airplane through the air. • Lift is a result of Newton’s 3rd law and the Bernoulli effect.
Span – the length of a wing • Chord – the width of a wing • Aspect ratio – span/chord • Dihedral angle – angle of wing from plane to wing tip – purpose is stability • Camber – curve of wing • Angle of attack – angle of wing to the oncoming air • Angle of incidence – angle of elevators to oncoming wind.
Wings and Newton’s 3rd law • According to Newton’s 3rd law, the wings push on the air and the air pushes on the wings. • For an aircraft wing, both the upper and lower surfaces contribute to the flow turning. • All kites with strings use primarily Newton’s 3rd law to fly.
Wings and the Bernoulli effect • The Bernoulli effect states that faster moving air has less pressure. • The curved upper surface of a wing forces the air above the wing to go a longer distance to meet the air passing along the bottom of the wing. • Since the two air streams meet at the same time the air passing over the top of the wing must go faster. • In going faster this air has less pressure and the greater pressure of the air below the wing pushes the wing up.
Factors affecting lift - Any body moving through the air can create lift if it turns the flow of air. • There are many factors that affect the turning of the flow of air. • Wing shape, thickness and wing area have a large effect on lift. • The ratio of the wing span to the wing area also affects the amount of lift generated by a wing. • The angle of attack, or the angle of the wing to the wind affects lift.
Controlling Roll • The roll axis lies along the aircraft centerline. • The rolling motion is caused by the ailerons. • The ailerons work in pairs, the lift on one wing increases as the lift on the opposite wing decreases. • The forces are not equal, so, there is a net twist, or torque about the center of gravity. • The aircraft rotates about the roll axis. • The pilot can use this ability to bank the aircraft which helps the airplane to turn.
Controlling Pitch • Pitch is an up or down movement of the nose. • The pitching motion is caused by the elevator of this aircraft. • There are usually two elevators on each side of the vertical stabilizer. • The elevators work in pairs; • With downward deflection, lift increases in the upward direction. • With upward deflection, lift increases in the downward direction. • The pilot can use this ability to make the airplane loop. • Many aircraft loop naturally, the deflection can be used to trim or balance the aircraft to prevent a loop.
Controlling Yaw • Yaw is a side to side movement of the nose of an aircraft. • The yawing motion is caused by the deflection of the rudder of an aircraft. • The change in side force created by deflecting the rudder generates a torque about the center of gravity which causes the airplane to rotate. • The pilot uses this ability to keep the nose of the aircraft pointed in the direction of travel
Attitude • The Attitude of an aircraft is it's relationship to the ground. • When in a level attitude, the centerline of the aircraft is parallel to the earth's surface. • When the nose of the aircraft is above the horizon, this is called a nose high attitude. • If the nose is below the horizon, the aircraft is in a nose low attitude.
Center of Gravity • The weight of the airplane, pilot, passengers, fuel and baggage is distributed throughout the aircraft. • The total weight can be considered as being concentrated at one given point, shown as the Center of Gravity. • If the plane were suspended by a rope attached at the center of gravity ( referred to as the CG) it would be in balance. • The Center of Gravity (CG) is affected by the way an aircraft is loaded. • Every aircraft has a maximum forward and rearward CG position at which the aircraft is designed to operate..
Gliders • A glider is a special kind of aircraft that has no engine. • In order for a glider to fly, it must generate lift to oppose its weight. • To generate lift, a glider must move through the air. • But the motion of a glider through the air also generates drag. • With the drag unopposed, a glider quickly slows down until it can no longer generate enough lift to oppose the weight. • All airplanes with no power are gliders!!
Glider forces continued • A glider trades altitude for velocity. • It trades the potential energy difference from a higher altitude to a lower altitude to produce kinetic energy, which means velocity. • Gliders are always descending relative to the air in which they are flying. • If the pilot can locate a pocket of air that is rising faster than the glider is descending, the glider can actually gain altitude, increasing its potential energy
Ground Effect • This phenomenon is often observed when an airplane is landing. • Pilots often describe a feeling of "floating" or "riding on a cushion of air”. • There is no "cushion of air.” • What happens is that the ground partially blocks the trailing vortices and decreases the amount of downwash generated by the wing. • This reduction in downwash increases the effective angle of attack of the wing so that it creates more lift and less drag than it would otherwise.
Stalls • As a wing increases its angle of attack, airflow can no longer flow smoothly over the wing. • Eddies or burbles will form, causing the wing to approach its stall speed. • When a wing finally stalls, it will no longer produce lift and aircraft will drop towards the ground. • With sufficient altitude, stall recovery can be obtained by decreasing the angle of attack. • The thinner the wing the smaller the angle before stall.
