RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 1 PROPELLERS Aim: To understand the principles and considerations in a propeller producing thrust. Application: All stages of flight where the engine is running Definitions: Blade - an aerofoil which converts engine power into thrust. Blade Angle - the angle between the blade chordline and the plane of rotation. Blade Back - the cambered side of the blade. Blade Face - the flat side of the blade. Helix Angle - the angle between the resultant velocity of the blade and the plane of rotation. Angle of Attack - the angle between the chordline of the blade and the relative airflow. Torque - resistance to motion in the plane of rotation. Engine Torque - Torque Produced by the engine, force that turns the propeller Propeller Torque - Caused by drag of the propeller blades, opposes propeller rotation Principles: - The combination of the forward velocity and rotational velocity creates a helical motion of the propeller through the air. Brief 25 RMIT Flight Training Propellers RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 2 - The tip travels fastest due to greater distance travelled in same time. Root travels slowest. Therefore varying lift (thrust) forces. - To even out forces, blade is twisted to compensate. Blade angle at hub needs to be much greater than blade angle at tip. - Geometric pitch is how far the propeller would theoretically advance in one revolution. - Effective pitch is how far the propeller actually advances in one revolution. - The difference between geometric and effective pitch is called slip. Considerations: Propeller Damage - usually occurs first on leading edge, cause it hits the air first. - avoid high power settings on loose surfaces like gravel. Propeller Fatigue - most likely to occur on blade face. Brief 25 RMIT Flight Training Propellers RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 3 Efficiency - fixed-pitch propellers are most efficient at only one airspeed and RPM combination. The C172 is fitted with a cruise prop. Airmanship: - Always perform thorough pre-flight inspections on the propeller. - Handle the engine smoothly. - Low power settings on ground to avoid damage. Brief 25 RMIT Flight Training Propellers作者: haoyu405 时间: 2010-9-23 10:30:29