“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:
- As airplanes grew larger and faster, "hinge moments" (forces required to deflect control surfaces) increased rapidly, making manual control difficult for pilots.
- Anton Flettner's invention, the Flettner tab, provided a solution by using a small auxiliary surface to leverage air pressure, significantly reducing the pilot's effort to move large control surfaces.
- Flettner's design evolved into various types: trim tabs (to set neutral positions), servo tabs (to reduce control forces), and anti-servo tabs (to intentionally increase control forces), which are crucial for the stability and feel of aerodynamically balanced "all-flying tails" or stabilators.
Key takeaways sponsored by Aviator Pro | Start Your Training ->
See a mistake? Contact us.
