Definition
A calibrated spring inside an engine governor that applies an adjustable downward force on the flyweights. The pilot's propeller control changes the compression of this spring, which sets the RPM the governor will try to maintain. When centrifugal force from the spinning flyweights equals the spring's force, the governor is on-speed and holds the selected RPM.
Plain English
The spring inside a propeller governor that the pilot effectively tightens or loosens with the prop control to tell the engine what RPM to hold.
Context Anchor
Seen in constant-speed propeller systems, propeller governor descriptions, and some engine or fuel-control governor discussions.
Derivation
Called a 'speeder' spring because its compression sets the speed (RPM) the governor will hold. Tightening it commands a higher speed; loosening it commands a lower speed.
Why Pilots Care
A properly functioning speeder spring prevents engine overspeed or underspeed, protecting the engine and maintaining efficient propeller performance across different flight conditions.
Analogy
Think of it like the tension knob on a cruise control. The knob doesn't move the car directly -- it just tells the system what speed to hold. The speeder spring does the same job for engine RPM.
Intuition Check
Do not read “speeder” as a part that simply makes the engine go faster. The speeder spring sets the speed the governor tries to maintain; the governor then adjusts the system to match that setting.
Example Sentence 1
When the pilot pushed the propeller control forward, the speeder spring compressed further, commanding a higher governed RPM.
Example Sentence 2
During preflight checks the mechanic inspected the speeder spring for proper tension and signs of wear.