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 Drag are 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 law of 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

• 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.

Ground Effect

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.