Definition
Conical metal components used to center and secure a propeller on the tapered or splined shaft of an engine. A front cone fits into the front of the propeller hub and a rear cone seats against the rear of the hub, with the propeller retaining nut drawing both cones together to lock the propeller in precise alignment with the crankshaft.
Plain English
Two cone-shaped metal pieces that sit on either side of a propeller hub and squeeze it tight against the engine shaft, keeping the propeller perfectly centered when the retaining nut is tightened.
Context Anchor
Encountered during propeller installation, removal, and maintenance inspections, especially on aircraft that use a tapered or splined propeller shaft.
Derivation
From the Latin 'conus' meaning a cone shape. The parts are literally cones because the matching tapered surfaces between the cones, the hub, and the shaft are what force the propeller into perfect center alignment as the retaining nut is tightened.
Why Pilots Care
Loose or damaged cones can create vibration, imbalance, or reduced performance.
Analogy
It is like using a tapered plug to center something in a hole before tightening it down. The taper guides the part into the correct position.
Intuition Check
Do not think of propeller cones as part of the propeller blades or as cones of moving air. Here, they are physical metal fittings used to position and secure the propeller on its shaft.
Example Sentence 1
During the propeller installation, the mechanic inspected the front and rear propeller cones for nicks before sliding them onto the shaft.
Example Sentence 2
After landing, the mechanic noticed the propeller cone had come loose and needed re-torquing.