Definition
A force that produces twisting in a structure or component. In an aircraft, torsional forces try to rotate one part of a structure relative to another about its long axis, creating shear stress across the cross-section.
Plain English
A twisting force. It tries to turn one end of something one way while the other end stays put or turns the other way.
Context Anchor
Seen in aircraft structures, engine and propeller discussions, and maintenance descriptions of parts that can be twisted by operating loads.
Derivation
From the Latin 'torquere,' meaning 'to twist.' The same root gives us 'torque.' Knowing this makes torsional force easy to remember: it is the force that produces twist.
Why Pilots Care
Unchecked torsional forces in rotating engine components can cause fatigue cracks and eventual failure.
Analogy
Think of wringing out a wet towel. Your two hands apply a torsional force, twisting the towel about its length.
Intuition Check
Do not think of torsional force as a straight push or pull. If the force is trying to twist a part around its length, it is torsional.
Example Sentence 1
The propeller produces a torsional force on the crankshaft as it drives the aircraft forward.
Example Sentence 2
Mechanics check the propeller shaft for twisting damage after a sudden stoppage that applied extreme torsional force.