Once the takeoff is established and the aircraft reaches 60 kt., rotor collective pitch was reduced to a fixed setting of 5 deg. Acceleration and deceleration is then performed with the TCL beep button while flight direction is controlled through the cyclic stick. Feet come completely off the pedals since the aircraft is computer trimmed through propeller pitch. Essentially, the aircraft is flying in airplane mode, with the cyclic being the control yoke and TCL toggle switch being the throttle.
When we were clear of the controlled area, Jammayrac pushed the TLC forward and put us in a 3,000 ft./min. climb at 118 kt. at 20% torque, climbing to 7,000 ft. The X3 literally pushes you back in the seat as though it is a corporate jet on climb-out. Performance limits for climbs are up to 5,500 ft./min. with a climb slope of 40 deg.
As mentioned, the dissymmetry in blade speeds causes increasing vibration. Traditionally these are controlled through use of either passive dampeners or active devices that sense and counter the vibration frequencies. No anti-vibration systems are installed on the X3 and test pilots who have flown the aircraft at speeds in excess of 232 kt. say that neither vibration nor stability appear to be a problem, and that the aircraft can be flown hands-off without either anti-vibration or stability-augmentation systems installed.
It is still too early to determine whether such systems will be needed in a production aircraft, but Eurocopter says the X3 “has validated the H3 concept beyond expectations, [and] even at 232 kt. is behaving like a flying carpet without autopilot or stabilization systems, and can be flown hands-off.” We took the X3 up to 220 kt., where I found the aircraft can indeed be flown hands-off with good stability, but with a noticeable amount of vibration.
As for stability, I was able to put the aircraft into a series of turns increasing to 60 deg. of bank, with feet off the pedals and collective lever down, maintaining both altitude and airspeed—more or less. In unfamiliar helicopters I tend to lose a couple hundred feet of altitude while losing or gaining 10-20 kt. in sharp turns, but in the X3 the loss or gain was about half that, or less. Turn-speed limitations are 45 deg. at 220 kt. and 60 deg. at 210 kt.
The aircraft does have a four-axis autopilot, taken from the EC155. At one point while I had the aircraft in straight and level flight, Jammayrac turned off the autopilot. The cyclic got just “squirrelly” enough to notice it, but not so much that it would present a problem.
Returning to the airfield, Jammayrac set us up for a standard arrival, maintaining level flight during the entire approach—which was just a bit disconcerting since on conventional helicopters the view changes as the nose is pulled up to reduce speed. Speed was adjusted with the TCL beep button until about 50 kt. At that point, the aircraft transitions back to helicopter mode, where speed is controlled with the cyclic and altitude with the collective.
Eurocopter is not predicting when a next-generation hybrid helicopter will roll off the production line, although executives acknowledge that “usually a period of 10 years is necessary before an aircraft of this type can be introduced on the market.” But the company also says X3 technology may be integrated into “certain products” in the Eurocopter family by the end of the decade.