Study of the Direct Turbine Driven Rotor system in various flight conditions

Abstract

Currently, a mechanical transmission by a spool driving the rotor is implemented in helicopters. This system is heavy and costly. Antoine Hubert, the founder of the Belgian company Sagita based in Wandre, has invented a system that does not need mechanical transmission. Indeed, this mechanical part is replaced by a turbine which drives directly two contra-rotating rotors, where blades are attached. The purpose of this work is to prove the viability of this system. Two aircraft uses this TDR system : the Sherpa helicopter, and the S-75 Drone. The Sherpa project began few years ago, and was the first aircraft built with this technology. The current project is the S-75 Drone, for which two versions are studied : the first one with two blades per rotor is its prototype version which was tested during this work. The second configuration has three blades per rotor. It is the one considered for a future commercialization. These aircraft and the TDR system are introduced in the first part of this work. The viability of this system is studied in two main parts. First of all, the cycle is studied at the nominal point, and the desired performances are compared with the one obtained during this study. The power delivered by the cycle will be compared by the one which is necessary for each flight condition. The determination of the pressure ratio of the fan is one of the objective of this part. The off-design conditions are then introduced in the second part of this work. Atmospheric pressure, temperature and altitude are the main variables. Their implications on the TDR cycle will be shown, as well as the potential limitations they introduce. The three aircraft are studied, and a comparison between the performances of the two versions of the S-75 Drone will be done. A comparison with a classical two-spool turboshaft will then conclude this study.