Helicopter Hybridisation - the Key for Drastic Reductions of Fuel Burn and Emissions

With the objective to secure the future of the helicopter in times of strongly growing fuel prices, a hybrid drive system is proposed, consisting of Diesel engines, generators and electric engines, replacing turbines, gear boxes and the tail rotor drive train. Instead, the electric-engines will drive the main and tail rotor and will thereby allow new degrees of freedom in design and operation. These are high variations of rotor speed (for the tail rotor down to zero), tilting of the main and tail rotor and an installation of the Diesel engines below the cabin floor, favourable for the centre of gravity position and passenger crash safety. The reduced rotor speed saves fuel and diminishes exterior noise. The hybridisation has become attractive by the appearance of advanced high torque, low weight electric motors, high power density batteries and new efficient Diesel engines. The advantages of such systems become visible mainly for missions with moderate TOW or over long distances, since here the beneficial effects of rpm reduction and lower fuel burn dominate. Reliability, failure safety and certifiability can be enabled by multiple redundancy of all relevant drive system components by segmentation or multiplication. For Life Cycle and Direct Operation Costs, the hybrid drive shows superior values if it succeeds to keep the inherent added system weight low. For the concept of the all electric helicopter, the hybrid system may be a welcome development as intermediate step.