Presentation on Optical Computing MADE BY: Divyansh Dhakre ME.-A, III YEAR

Contents

PURPOSE OF PROPELLER Thrust is generated by the propulsion system of the aircraft Propeller is one of the propulsion system It pulls (or pushes) the aircraft forward through the air

PROPELLER MATERIAL Composite and plastic propellers Aluminum propellers Stainless steel propellers Fibreglass-reinforced Nylon Fibreglass Carbon Fibre

TYPES OF AIRCRAFT PROPELLERS Fixed pitch Wooden Propellers Metal Propellers Ground adjustable pitch Two-position Controllable pitch Constant speed Full Feathering Reversing

PROPELLER FUNCTION The propeller consist of two or more blades connected together by a hub. The hub serves to attach the blades to the engine shaft. The blades are made in the shape of an airfoil like wing of an aircraft.

DESCRIPTION OF PROPELLERS A propeller generates an aerodynamic force. The propeller is rotated by the engine and this creates thrust and moves the aircraft forward. Diameter is the width of the circle described by the rotating blades.

DESCRIPTION OF PROPELLERS Leading Edge of the airfoil is the cutting edge that slices into the air. As the leading edge cuts the air, air flows over the blade face and the camber side.

DESCRIPTION OF PROPELLERS Blade Face is the surface of the propeller blade that corresponds to the lower surface of an airfoil or flat side.

DESCRIPTION OF PROPELLERS Blade Back / Thrust Face is the curved surface of the airfoil. Blade Shank (Root) is the section of the blade nearest the hub. Blade Tip is the outer end of the blade farthest from the hub.

DESCRIPTION OF PROPELLERS Plane of Rotation is an imaginary plane perpendicular to the shaft. Blade Angle is formed between the face of an element and the plane of rotation. Blade Element are the airfoil sections joined side by side to form the blade airfoil.

DESCRIPTION OF PROPELLERS Relative Wind is the air that strikes and pass over the airfoil as the airfoil is driven through the air. Angle of Attack is the angle between the chord of the element and the relative wind. Blade Path is the path of the direction in which the blade element moves.

DESCRIPTION OF PROPELLERS Pitch refers to the distance a spiral threaded object moves forward in one revolution. Geometric Pitch is the theoretical distance a propeller would advance in one revolution. Effective Pitch is the actual distance a propeller advances in one revolution in the air.

DESCRIPTION OF PROPELLERS Rake is the measurement of the angle of the tilt of the blade's tip toward or away from the gear case. The angle is measured on a line extending from the center of the hub through the center of one blade.

PROPELLER PERFORMANCE Under normal conditions the propeller is able to convert 85% of the brake horse power from the engine into thrust. Thus propeller efficiency is the ratio between thrust horsepower and brake horsepower. Power = Force x Distance / Time (rate of doing work) Propeller efficiency Thrust x TAS / Brake Horse Power

PROPELLER EFFICIENCY A propeller's efficiency  is determined by:

CALCULATING TIP SPEED The formula VTIP = π d n, where π is a constant (3.14159), d is diameter in meters, n is angular velocity (RPM) in revolutions per minute, VTIP then results in meters/minute For example: a propeller of 72" diameter (1m83) with a RPM of 2600 gives a tip speed of: π * 1,83 * 2600 = 14947,7 meters/minute or 896,9 km/h.

FORCES ACTING ON A PROPELLER Five forces act on the blades of an aircraft propeller in motion: Thrust bending force- thrust loads on the blades act to bend them forward. Centrifugal twisting force- acts to twist the blades to a low or fine pitch angle. Aerodynamic twisting force- the blade is twisted towards a coarse pitch position. Centrifugal force- the force felt by the blades acting to pull them away from the hub when turning. Torque bending force- propeller blades bend away from the direction of rotation.

STRESS ACTING ON A PROPELLER The stress acting on a propeller in flight are: Bending stress tend to bend the blade forward as the airplane is moved through the air by the propeller. Tensile stress caused by centrifugal force. Torsion stress produced in rotating propeller blades by two twisting moments.

PROPELLER AERODYNAMICS The airplane propeller consists of two or more blades and a central hub to which the blades are attached. The propeller blades are like airfoils and produce forces. The power needed to rotate the propeller blades is furnished by the engine. An airplane moving through the air creates a drag force opposing its forward motion. If an airplane is to fly, there must be a force applied to it that is equal to the drag, but acting forward. This force is called “thrust.”

PROPELLER AERODYNAMICS One surface of the blade is cambered or curved, the other surface is flat like the bottom surface of a wing. The chord line is an imaginary line drawn through the blade from its leading edge to its trailing edge. Airfoil sections of propeller blade

PROPELLER AERODYNAMICS Blade angle measured at a specific point along the length of the blade. Pitch is not the same as blade angle, but because pitch is largely determined by blade angle, the two terms are often used interchangeably. Propeller blade angle

PROPELLER AERODYNAMICS Each section of a propeller blade moves downward and forward. The angle at which this air strikes the propeller blade is its angle of attack. Air deflection produced by this angle causes the dynamic pressure at the engine side of the propeller blade to be greater than atmospheric, thus creating thrust. The shape of the blade also creates thrust, because it is cambered like the airfoil shape of a wing.

PROPELLER AERODYNAMICS As the air flows past the propeller, the pressure on one side is less than that on the other. As in a wing, this produces a reaction force in the direction of the lesser pressure. In the case of a wing, the airflow over the wing has less pressure, and the force (lift) is upward. In the case of the propeller, which is mounted in a vertical instead of a horizontal plane, the area of decreased pressure is in front of the propeller, and the force (thrust) is in a forward direction. Aerodynamically, then, thrust is the result of the propeller shape and the angle of attack of the blade.

PROPELLER AERODYNAMICS Propeller efficiency varies from 50 to 87 percent, depending on how much the propeller “slips”. Propeller slip is the difference between the geometric pitch of the propeller and its effective pitch. Propeller slippage

TORQUE AND P FACTOR To the pilot, “torque” (the left turning tendency of the airplane) is made up of four elements These four elements are: Torque Reaction from Engine and Propeller Corkscrewing Effect of the Slipstream Gyroscopic Action of the Propeller Asymmetric Loading of the Propeller (P-Factor)

ELEMENTS PRODUCING TORQUE Torque Reaction from engine and propeller as the internal engine parts and propeller are revolving in one direction, an equal force is trying to rotate the airplane in the opposite direction. Torque reaction

ELEMENTS PRODUCING TORQUE Corkscrewing Effect of the Slipstream The high-speed rotation of an airplane propeller gives a corkscrew or spiraling rotation to the slipstream. Corkscrewing slipstream

ELEMENTS PRODUCING TORQUE Gyroscopic Action of the Propeller gyroscopic action occurs when a force is applied to any point on the rim of the propeller’s plane of rotation; the resultant force will still be 90° from the point of application in the direction of rotation. Gyroscopic precession

ELEMENTS PRODUCING TORQUE Asymmetric Loading of the Propeller (P Factor) It is caused by the resultant velocity, which is generated by the combination of the velocity of the propeller blade in its plane of rotation and the velocity of the air passing horizontally through the propeller “disc. Asymmetrical loading of propeller (P-factor)

ELEMENTS PRODUCING TORQUE Each of these four elements of torque effects vary in values with changes in flight situations. In one phase of flight, one of these elements may be more prominent than another; whereas, in another phase of flight, another element may be more prominent.

BIBLIOGRAPHY http://en.wikipedia.org/wiki/Propeller_(aircraft) http://www.thaitechnics.com/propeller/prop_intro.html http://www.airfieldmodels.com/information_source/model_aircraft_engines/propellers.htm

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