Modeling and full-speed range transition strategy for a compound helicopter

Abstract

Compound helicopters are faced with the problem of transition from low-speed helicopter mode to high-speed airplane mode. This study presents a comprehensive flight dynamics model and a full-speed range transition strategy, focusing on Compound Helicopters with Double Propeller Propulsion (CHDPP). In order to consider aerodynamic interactions efficiently, the model integrates classic modeling theories with a simplified imposed rotor wake model and a modified rotor-wing aerodynamic interaction model. The design of the full-speed range transition strategy utilizes a double-layer iterative approach based on the trim method with control redundancy. The inner iteration ensures uniform control surface effectiveness through control surface allocation, while the outer iteration ensures safety and satisfactory handling quality by improving transition paths. We developed a 12 kg CHDPP prototype as the sample CHDPP and carried out a wind tunnel trim experiment for model validation. The results show that the presented model can eliminate correction factors while maintaining sufficient accuracy. The obtained full-speed range transition strategy can ensure safety, cockpit input effectiveness while avoiding abrupt changes and counterintuitive variations in trim characteristics. Furthermore, since the modeling technique is independent of correction factors and the transition strategy design method is not dependent on a specific helicopter configuration in nature, they can be extended to various compound helicopter configurations, eventually providing a robust tool for the development of compound helicopters.