Section 6.7 / 6.8

Springs & Bearings

Spring types and spring rate; plain and rolling-element bearings, load types, fit and failure modes.

Notes

Free

Main ideas

Springs store and release energy and apply a controlled force. Types: helical compression and tension (extension), torsion, leaf, spiral and Belleville (disc) springs for high load in a small deflection. Materials include spring steel and phosphor bronze (non-magnetic, corrosion-resistant).
Spring rate (stiffness) is the force needed per unit of deflection, F = k·x (Hooke's law) — a 'stiffer' spring has a higher rate k. Springs fail by fatigue, permanent 'set' (loss of free length) and corrosion.
Bearings reduce friction between moving parts. Plain (journal/bush) bearings slide — white metal, bronze or PTFE; rolling-element bearings use balls or rollers on inner and outer races with a cage separating them.
Ball bearings mainly take radial load (plus a little thrust); roller bearings take higher radial loads; TAPER-roller bearings carry combined radial AND axial (thrust) loads; dedicated thrust bearings take pure axial load.
Bearing care: correct fit (interference on the rotating race), set pre-load/end-float, keep them clean and lubricated. Failure modes include contamination, spalling and brinelling (indentation of the races from shock or static overload).
⚠ Exam trap: a taper-roller bearing takes combined radial and thrust load, whereas a plain ball bearing is essentially radial. Spring rate is force ÷ deflection — do not confuse a stiff (high-rate) spring with a strong one.

Key formulas

Solved examples

A wheel hub must support both the aircraft's weight (radial) and the side loads of cornering/turning (axial). Which bearing type suits it and why?
Taper-roller bearings, usually fitted in opposed pairs. Their conical rollers and races react radial load and axial (thrust) load at the same time, and the pair can be pre-loaded to set the correct end-float — ideal for a wheel that carries weight and side loads together.

Mind map

Free

Quiz

Pro

This quiz is part of Engineer

Upgrade to unlock every quiz, mock exam and advanced simulation across all modules. Notes and mind maps stay free.