Aircraft propeller blades are subject to damage from foreign objects such as sand, rain, hail, and birds etc. Propeller blades that are mounted towards the rear of an aircraft are particularly susceptible to foreign object damage. Runway debris, such as sand, runway markers, stones, ice, water, slush and segments of tire tread etc., may be kicked up into a plane of rotation of the blades. Collision between the foreign objects and the propeller blades may require the removal of the damaged blades from the propeller for repair.
Typically, propeller blades are mounted to a hub of a propeller by means of a pitch retention member. The member is rotatable within the hub to allow the pitch of the propeller blade mounted therein to be set as required. A spinner may enclose the hub and the member.
To replace a damaged blade, the spinner and/or the blade retention member and/or the hub may have to be disassembled. Because of the complexity of the disassembly (and subsequent reassembly), blade changes are time consuming, expensive and subject to error. The problem is multiplied by propellers which have a plurality of blades. Some counter-rotating prop-fan propellers may have as many as 18 blades.
In counter-rotation prop-fans, each blade is rather heavily loaded absorbing as much as 1000 horsepower of engine torque and developing as much as 1,500 pounds of engine thrust. Heavily loaded propeller blades are subject to high vibratory loads and stresses. Moreover because prop-fan blades are swept, they are subject to instability at high speed.