Design and experimental characterization of modern helicopters rotor brakes

The demands on helicopter rotor brakes are given by laws and airworthiness regulations. The systems are designed and certified according to airworthiness demands such as JAR 27/29 and FAR 27/29. The present paper presents the rotor brake systems of commercial and military helicopters. The rotor brake systems include brake discs made out of steel and brake callipers with two-side-activating pistons. The actuation is performed by independent hydraulic systems. Together with the development of the different helicopter types an evolution of the brake systems took place. An example for this evolution is the indication of the brake control system on a state-of-the art commercial helicopter. Every occurring brake effort between brake disc and brake pads is indicated by the motion of the brake calliper against a micro switch. An example of a brake system which includes a brake disc made out of carbon fiber reinforced carbon material is presented. The disc is mounted with the possibility of sliding in axial direction. The hydraulic actuation is included in the main pressure supply system of the helicopter. Difficulties may occur by inhomogeneous heating of the brake discs. The analysis of the short and long duration tests on test benches and by helicopter flight tests revealed the detailed behavior especially of the thermal spots. The non-uniform heat dissipation caused hot spots and in some cases cracks. With the gained knowledge of the physical behavior, the brake disc was redesigned with success.The goal of the paper is to show the specific demands of helicopter rotor brakes, the designs for different helicopter types as well as the realization of the solutions and system tests.