Definition
A spring made from a coiled strip of pre-stressed flat metal that exerts a nearly constant pulling force throughout its full range of extension, rather than the increasing force produced by a conventional coil spring.
Plain English
A flat metal strip rolled into a coil that pulls with the same strength no matter how far you pull it out.
Context Anchor
Seen in aircraft maintenance and component descriptions where a part must be pulled, returned, or held with a steady force over a range of movement.
Derivation
The name describes the behaviour: the spring delivers a force that stays constant. A normal spring follows Hooke's law — the more you stretch it, the harder it pulls back. A constant-force spring is built so that force does not change as it extends.
Why Pilots Care
In instruments and mechanisms, a constant pulling force keeps movement smooth and predictable. If the force changed with position, readings or actions would not be linear, leading to inaccuracy or uneven operation.
Analogy
Think of a tape measure that retracts. The little metal tape pulls back with about the same gentle tug whether you've pulled out six inches or six feet. That steady pull is a constant-force spring at work.
Intuition Check
Constant-force does not mean the spring does not move. It means the spring is designed to pull with nearly the same force while it moves.
Example Sentence 1
The instrument used a constant-force spring to keep the indicator pointer's return movement smooth across its full range.
Example Sentence 2
Constant-force springs are used in certain instrument mechanisms to maintain steady pointer pressure without variation.