@ Frank:
To fly a looping properly the aircraft needs speed. A fixed wing aircraft gets speed from its propulsion system, i.e. the propeller or the jet engine.
A helicopter does not have such kind of propulsion to create forward thrust but gets forward speed by tilting the rotor disk forward and therefore pushes the thrust of the rotor backward. Doing so the helicopter can stay in the air AND fly forward using only ONE propulsion, whilst the fixed wing stays in the air by using lift force of the wing AND thrust.
You see that to fly a looping properly with a helicopter one component is badly missing. Ether enough thrust or enough lift. And as you stated correctly a helicopter will more likely do a flip backward than a proper looping.
To the Lynx: have you ever seen this particular Lynx which hold the speed record? It is heavily modified! Try to find it on the internet, it’s worth a look. Helicopters are limited in speed due to the phenomena/problem of advancing and retreating blades during forward flight. So now there is math involved: the blade moving forward adds its tip speed, resulting from the rotational speed of the rotor, and the speed of the forward flight. Roughly we will gain around 950 km/h at the blade-tip. So what, you will say? Here comes an other famous Austrian into play: Ernst Mach. At this speed of the blade tip we will soon have Mach-speed. No good! Due to a huge amount of aerodynamic problems at this point of speed (Mach) this is the reason for a natural speed limiter of helicopters in general.
On the speed record Lynx engineers have tuned all systems to squeezed out some extra knots to hit the record.
