[dingaling]

Helicopters glide or 'autorotate' tolerably well after engine or driveshaft failure, at least enough to land controllably.

In the R22 two-seater the best glide ratio is about 4:1 ( 4ft horizontal for 1ft drop ) and those at my local airfield practice autorotation to landing all day long.

Apparently the worst helicopters for autorotation are those with Kamov's superimposed coaxial rotor system, which struggle to reach 2:1 for some aerodynamic reason I don't know.