HELICOPTER

PROPELLER - converts the power delivered by an engine into propulsive thrust. also known as AIRSCREW

PROPELLER HUB – the central portion of the propeller that is fitted to the propeller shaft, securing the blades by their roots.

BLADE – One arm of a propeller butt to the tip. Propellers usually have two or more blades.

BLADE SHANK – thick, rounded portion of the blade near the hub of the propeller; designed to give strength to the blade.

BLADE TIP – portion of a propeller blade that is furthest from the hub.

LEADING EDGE – the forward or "cutting edge" of the blade that leads in the direction the propeller is turning.

TRAILING EDGE – the rear edge

BLADE BACK – the curved or cambered side of a propeller blade.

BLADE FACE – the flat side of a propeller blade.

CHORDLINE – an imaginary line drawn through the blade from the leading edge to the trailing edge.

BLADE ANGLE OR BLADE PITCH – angle between the blade chord line and the plane of rotation.

ANGLE OF ATTACK – angle between the blade chord and the relative airflow.

HELIX ANGLE – angle between the plane of rotation and the relative airflow.

PLANE OF ROTATION – an imaginary plane perpendicular to the shaft. It is the plane that contains the circle in which the blades rotate.

RELATIVE WIND – the air that strikes and pass over the airfoil as the airfoil is driven through the air

BLADE CUFFS – an airfoil-shaped attachment made of thin sheets of metal, plastic, or composite material. Blade cuffs mount on the blade shanks and are primarily used to increase the flow of cooling air to the engine naceles

BLADE STATIONS – these are reference lines, usualy designed as measurements, made from the hub. These lines are numbered and locate positions on the propeller blade. They are usualy designated at 6-inch intervals.

BLADE BUTT / BLADE BASE / ROOT – the end of the blade that fits in the propeller hub.

PITCH DISTRIBUTION / TWIST – the gradual twist in the propeller blade from shank to tip

PROPELLER BLADE ANATOMY

·       TIP SECTION – High airspeeds at the tips require a thin airfoil profile to minimize drag

·       MID SECTION – the bulk of the thrust is produced by the middle section of the propeller blade. The airfoil profile and twist in this area are optimized for aerodynamic performance

·       ROOT SECTION – a thicker airfoil section provides the necessary blade strength and also gives a profile which stals at a higher angle of attack.

Rotational Velocity = 2πr x RPM

PROPELLER THEORY - When the propeller rotates through the air, a low-pressure area is created at the back of the blade; much like the wing's curvature creates a low-pressure area above the wing. This low-pressure area, combined with the constant, or high-pressure area at the face of the blade allow a propeller to produce thrust

FACTORS AFFECTING THRUST PRODUCED:

·       Angle of attack of the propeller blades

·       Rotational Speed (RPM)

·       Airfoil Shape

Stationary: With no forward velocity, the relative wind is directly opposite the movement of a propeller blade. In this condition, a propeller's angle of attack is the same as its blade angle.

Forward Motion: When the aircraft begins moving forward, the relative wind direction shifts because, in addition to rotating, the propeller now has forward motion. The result is that the relative wind is much closer to the angle of attack. In this case, the angle of attack will always be less than the blade angle

Constant forward velocity but increased propeller's rotational speed: the propeller's trailing edge moves a greater distance for the same amount of forward movement. As propeller speed increases, the relative wind strikes the propeller blade at a greater angle and the angle of attack increases

FINE PITCH - Shallow/low blade angle, Shorter distance travelled in one revolution, Allows the engine to spin easily and operate at a high speed (rpm). Take-off and landing

COARSE PITCH - High blade angle Longer distance travelled in one revolution Limit the speed at which the engine can operate. Cruise

GEOMETRIC PITCH – the theoretical distance a propeller should advance in one revolution with no slippage.

EFFECTIVE PITCH – the distance it actualy advances in one revolution. It accounts for propeller slippage in the air

PROPELLER SLIP – the difference between the geometric pitch of the propeller and its effective pitch. High slip indicates inefficiency

PROPELLER DIAMETER & NUMBER OF BLADES - depend on the power the propeller is required to absorb, the take-off thrust it is required to produce, and the noise limits which have to be met

DROP - DIRECTION, ROTATION, ORIENTATION, POSITION

PROPELLER MOUNTING

·       TRACTOR - front of an engine and pul an aircraft through air

·       PUSHER - aft end of an engine and push an airplane through air

·       PUSH-PULL PROPELLER

COUNTER-ROTATING PROPELLER - propeller on one wing turn in the opposite direction to the one on the other wing. Balance propeller torque effects

CONTRA-ROTATING PROPELLER - two propellers rotate in opposite directions around the same axis.

FIXED PITCH PROPELLERS - provide maximum efficiency for the forwarding motion of a plane

·       Climb Propeller – lower blade angle best performance at takeoff and climb; high RPM

·       Cruise Propeller – slightly higher blade angle efficient at cruising speed and at high flight altitude; lower RPM

·       Standard Propeller – al-around performance under normal conditions

·       Test Club Propeller – used to test and break in reciprocating engines

VARIABLE PITCH / ADJUSTABLE PROPELLERS

·       GROUND-ADJUSTABLE PROPELLER

·       CONTROLLABLE PROPELLERS

·       CONSTANT-SPEED PROPELLERS

o   FEATHERING PROPELLERS - to reduce propeller drag to a minimum under one or more engine failure conditions. 90°

o   REVERSE PITCH PROPELLERS - propeller blades can be rotated to a negative angle to produce reverse thrust

PROPELLER CONSTRUCTION MATERIAL

·       WOOD PROPELLERS - Hardwoods such as birch and maple possess the flexibility and strength. absorb engine vibration. laminated together with waterproof resin glue = propeller blank

·       STEEL PROPELLERS - hollow steel sheets, foam material to absorb vibration

·       ALUMINUM ALLOY PROPELLERS - less maintenance, better engine cooling airflow

·       COMPOSITE PROPELLERS

MODULE 2

Fixed-Wing: Lift, Drag

Propeller: Thrust, Torque

PROPELLER TWIST - By "twisting" the blade, you get a relatively uniform angle of attack across the entire propeller blade

FORCES ACTING ON A PROPELLER IN FLIGHT

·       THRUST - force that move the aircraft through the air.

·       CENTRIFUGAL FORCE - causes the greatest stress, most significant force. tries to pul the blades out of the hub

·       TORQUE BENDING FORCE - occur as air resistance opposes the rotational motion of the propeller blades. tends to bend the blades opposite the direction of rotation

·       THRUST BENDING FORCE - attempts to bend the propeller blades forward at the tips

·       AERODYNAMIC TWISTING FORCE -results from the fact that, when a propeller blade produces thrust, most of the thrust produced is exerted ahead of the blade's axis of rotation. tends to increase a propeller's blade angle.

·       CENTRIFUGAL TWISTING FORCE - opposes aerodynamic twisting force in that it attempts to decrease a propeller's blade angle.

STRESSES ACTING ON A PROPELLER IN FLIGHT

·       BENDING STRESSES induced by the thrust forces. tend to bend the blades forward

·       TENSILE STRESSES caused by centrifugal force which tends to throw the blades out of the hub

·       TORSIONAL STRESSES due to the forces which tend to twist the blades toward a lower blade angle.

BLADE VIBRATION – buffeting and vibration. The most critical vibrational stress location is around six inches from the tips of the blade.

·       if the propeller hub appears to swing in a slight orbit, the vibration is usualy caused by the propeller.

·       If the propeller hub does not appear to rotate in an orbit, the difficulty is probably caused by engine vibration

·       The critical range is indicated on the tachometer by a RED ARC

BLADE TRACKING - the process of determining the positions of the tips of the propeller blades relative to each other

An out-of-track propeller causes airframe and engine vibration and tension, which may cause premature failure of the propeller

STATIC IMBALANCE - occurs when the center of gravity (CG) of the propeller does not coincide with the axis of rotation

DYNAMIC IMBALANCE results when the CG of similar propeller elements, such as blades or counterweights, does not folow in the same plane of rotation

AERODYNAMIC IMBALANCE results when the thrust (or pul) of the blades is unequal. This can be largely eliminated by checking blade contour and blade angle setting.

TURNING TENDENCIES

·       TORQUE REACTION - Newton's 3rd Law of Motion

·       CORKSCREW EFFECT/ SPIRALING SLIPSTREAM - yawing tendency due to slipstream. powerful sideward force on the vertical tail surface of the aircraft

·       GYROSCOPIC PRECESSION

o   Precession is the resultant action, or deflection, of a spinning rotor when deflecting a force applied to it’s rim

·       ASYMMETRIC LOADING / P-FACTOR

·       when the downward moving propeller blade takes a bigger "bite" of air than the upward moving blade while an aircraft is flying with a high AOA. Asymmetric thrust causes planes to turn left.

·       With a higher AOA, the downward sweeping blade creates much more thrust (or lift), making your airplane want to yaw to the left

MODULE 3

14 CFR: Part 35

14 CFR: PART 35 – AIRWORTHINESS STANDARDS: PROPELLERS

·       SUBPART A – GENERAL

·       SUBPART B - DESIGN AND CONSTRUCTION

·       SUBPART C - TESTS AND INSPECTIONS

14 CFR: PART 25 (SECTION 25.925) – PROPELLER CLEARANCE

·       Tricycle Landing Gear: at least 7 inches

·       Taildragger: at least 9 inches

·       Water: at least 18 inches

·       At least one inch of radial clearance between the blade tips and the airplane structure

·       At least one-half inch of longitudinal clearance between the propeller blades or cuffs and stationary parts of the airplane

Momentum Theory

The Rankine-Froude momentum theory, also known as the actuator disk theory, is used to explain how a propeller or a rotor (like those on ships or helicopters) generates thrust by pushing fluid, such as water or air, backwards.

Blade Element Theory

This theory breaks down a blade into many smal elements and analyzes the forces on each element separately to understand the overal performance of the blade.