I've heard that they actually overspeed the rotor system relative to it's
normal autorotative rpm. The added inertia is what gets them airborne but
it's
then critical to get some forward speed going so it can establish an
autorotative state when the rotor system slows back down to normal rpms.


I've got some time in the Air & Space 18A and it uses this method for a jump
takeoff. I'd have to dig out the books, but it seems that the rotor is
oversped about 100 RPM. When the jump is commenced rotor RPM decays
immediately though.



I've also heard that they actually over pitch the rotor blades to make the
jump
and that has to be let back down to a setting that will allow the rotor
blades
to establish an autorotative state as the aircraft accelerates forward. This
part really makes me wonder. It sounds like it would be pretty critical to
get
it right. Can confirm whether this is true or not?

As far as the 18A goes, this is not the case. When the jump is began in the
18A the hydraulic pressure holding the blades at flat pitch is released
allowing them to pitch. Once pitch is introduced the rotors remain at that
pitch until the flight is ended. There is no mechanism for varying the pitch
in flight. Other aircraft may vary.





Stephen Austin
Austin Ag Aviation
Charleston, Missouri