“Hinge moment” is the technical name for the force required to deflect a control surface. In small, relatively slow airplanes, hinge moments are not very large; pilots move the controls with ease. But as control surfaces get larger and speeds get higher, hinge moments grow rapidly. They increase with the chord length of the control surface, with the square of speed and with the cube of the linear dimensions. Thus, if you double the speed, the hinge moments grow four times greater; if you double the size of an airplane, keeping all of its proportions unchanged, they become eight times greater. If you double both size and speed, hinge moments increase by a factor of 32.
Hinge Moments Explained
Key Takeaways:
- "Hinge moments," the force required to deflect aircraft control surfaces, increase significantly with aircraft size and speed, posing a challenge for manual control.
- Anton Flettner's ingenious invention of tabs allowed pilots to manually control large aircraft by using a small auxiliary surface to leverage air pressure and move main control surfaces with less effort.
- Tabs evolved into various forms, including trim tabs (for setting neutral position), servo tabs (for reducing control forces), and anti-servo tabs (which increase forces to provide control feel and stability for "all-flying tails" or stabilators).
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