my view (for what it's worth, not much probably) is that the X2 shouldnt be referred to as a helicopter by just the use of that one word.
IFMU, the X2 rear rotor AXIS is not perpendicular to the longitudinal one, it's along it thereby eliminating it from the pure helicopter definition.
so, it is a compound helicopter/rotorcraft.
I know its just pedantic but coming from that part of the world G-LYNX originated from it's a matter of some pride here!!
effectively for rotorcraft we have 5 types of vehicle that could hold seperate speed records.
Helicopter; rotor lift, no augmentation - Lynx, UH60 etc
Winged Helo; Rotor and wing lift no augmentation - Mil24, Mil6
Compound helo; rotor lift+ thrust augmentation - X2
Compound winged helo; rotor and wings lift + thrust augmentation - AH56
Tilt rotor - V22, BA609
until of couse someone invents something new.
hypothetical question; how fast would the cuurent fastest coaxial helo go with a pusher prop (say a KA50 with a prop on the back)
DM