The swinging counterweight trebuchet. On internal friction

TL;DR

This paper analyzes energy losses in a swinging counterweight trebuchet caused by internal friction and aerodynamic forces, deriving equations and validating them with experiments, and discusses scaling effects.

Contribution

It introduces a detailed mathematical model including friction and aerodynamic forces in trebuchet dynamics, validated by experiments and discusses implications for scaling to full size.

Findings

Friction and aerodynamic forces significantly affect energy efficiency.

Derived equations match experimental results within acceptable error.

Scaling laws for full-size trebuchets are discussed.

Abstract

Mechanical energy is lost to friction during a shot with a trebuchet. The losses are mainly due to sliding friction at the bearings for the throwing arm and at the hinge for the swinging counterweight, but the aerodynamic force on the sling also contributes. Generalized forces for these sliding and aerodynamic frictions are derived and included in the equations for the internal movement of the engine. The equations are solved by the use of perturbation theory and calculated losses are compared with results from an experimental engine of small dimensions. Scaling to full-size trebuchets is discussed.