Since Army aircraft are operated under combat conditions, they might exceed these design limits. Therefore, maintenance personnel must check constantly for failures and for signs of approaching failure in aircraft structural units. Compression is resistance to being pushed together or crushed. Compression is produced by two forces pushing toward each other in the same straight line. The landing struts of an aircraft are under compression after landing.
Torsion is resistance to twisting.
A torsional force is produced when an engine turns a crankshaft. Torque is the force that produces torsion. Tension is resistance to being pulled apart or stretched. Tension is produced by two forces pulling in opposite directions along the same straight line. Pilots put the cables of a control system under tension when they operate the controls.