Airbus Helicopters X3 Flight Tests: Overview Of X3 Flight Test Phase And Perspectives For The Racer Fast Rotorcraft Airbus Demonstrator

Dominique Fournier, Airbus Helicopters, France

Abstract

Airbus Helicopters X3, an hybrid helicopter technology demonstrator, was initiated in late 2007 and had flown from 2010 to 2013. The concept is based on an economics equation. For a vertical takeoff and landing aircraft, speed can result in a decrease of the mission cost if the gain of productivity is not impaired by an unacceptable increase of the Life Cycle Cost. X3 is a rotorcraft of gyrodyne type, defined and built in a very limited time an budget to evaluate if a standard Airbus H155 rotor can fly at a speed above 220kt, and to acquire as much data as possible. Initially planned to fly around 50 hours, it has achieved 156 flight hours during several flight test campaigns. X3 does take one of its sources in compound helicopters projects developed during the three decades following World War II. Some are well known (the Rotodyne) some are less known (the Gazelle SA349Z).

The first flight of X3 on September 6, 2010, was an incredible and intense achievement, with particular technical facts (as usual during first flight) around the temperature of one of the lateral gear box and vibrations of the structure. The tuning of the lift sharing between the wing and the rotor is a key factor to achieve performance objectives. This tuning shall take into account performance, of course, but also dynamic loads and rotor mast bending moment; and shall found the appropriate compromise between contradictory constraints.

Another very interesting flight test phase deals with the rolling takeoff. Rolling takeoff on helicopters is performed when there is a need to fly at a gross weight such that power margin in hover (standard helicopter takeoff technic) is not sufficient, for example in hot and high conditions. This could be quite a tricky maneuver on helicopters while on X3 it was very easy to perform and was associated with very interesting performance, takeoff distance being in the range of 70m at 5 tons.

In the frame of the European CleanSky2 program, Airbus has launched a second generation demonstrator based on X3 architecture. While X3 was a pure technology demonstrator (not optimized at all in terms of empty weight), Racer (RApid Cost Efficient Rotorcraft) will focus on mission capacity demonstration. While keeping the global architecture principles of X3, some major improvements have been made to achieve empty weight, safety, noise and performance objectives. One example of this optimization is the box wing concept and associated lateral rotors integration.