Typical propeller blade positions from feather position through the reverse position. Normal sequence of blade  travel is feather, high pitch, low pitch, locks/ground idle, reverse pitch, and then back following the same path.  Fixed turboprop engines are shut down on the locks to prevent load on the engine during restart. Reverse Locks Flight idle Ground idle Power Feather −2 to −8° 1 to 2° 10 to 12° 0° 20 to 35° 85 to 90° Figure 7-3.  Propeller range positions.  Pitch is not the same as blade angle, but because pitch is  largely determined by blade angle, the two terms are often  used interchangeably. An increase or decrease in one is usually  associated with an increase or decrease in the other. Propeller  slip is the difference between the geometric pitch of the  propeller and its effective pitch.  [Figure 7-4]  Geometric pitch  is the distance a propeller should advance in one revolution  with no slippage; effective pitch is the distance it actually  advances. Thus, geometric or theoretical pitch is based on  no slippage. Actual, or effective, pitch recognizes propeller  slippage in the air. The relationship can be shown as: Geometric pitch – Effective pitch = slip Geometric pitch is usually expressed in pitch inches and  calculated by using the following formula: GP = 2  ×  π R  ×  tangent of blade angle at 75 percent station R = Radius at the 75 percent blade station  π = 3.14 Although blade angle and propeller pitch are closely related,  blade angle is the angle between the face or chord of a  blade section and the plane in which the propeller rotates.  [Figure 7-5]  Blade angle, usually measured in degrees, is  the angle between the chordline of the blade and the plane of  rotation. The chordline of the propeller blade is determined  in about the same manner as the chordline of an airfoil. In  fact, a propeller blade can be considered as being composed  of an infinite number of thin blade elements, each of which  is a miniature airfoil section whose chord is the width of the  propeller blade at that section. Because most propellers have  a flat blade face, the chord line is often drawn along the face  of the propeller blade. Slip Effective pitch Geometric pitch Angle of relative wind Chord line Thrust Forward velocity Rotational velocity b l a d e a n g l e P i t c h o r o f a t c k A n g l e Relative wind Figure 7-5.  Propeller aerodynamic factors.  Figure 7-4.  Effective pitch and geometric pitch.  7-3 The typical propeller blade can be described as a twisted  airfoil of irregular planform. Two views of a propeller blade  are shown in  Figure 7-6 . For purposes of analysis, a blade can  be divided into segments that are located by station numbers  in inches from the center of the blade hub. The cross-sections  of each 6-inch blade segment are shown as airfoils in the  right side of  Figure 7-6 . Also identified in  Figure 7-6  are the  blade shank and the blade butt. The blade shank is the thick,  rounded portion of the propeller blade near the hub and is  designed to give strength to the blade. The blade butt, also  called the blade base or root, is the end of the blade that fits  in the propeller hub. The blade tip is that part of the propeller  blade farthest from the hub, generally defined  as the last 6  inches of the blade.