Articulated rotor blades

[Aviator168]

Can articulated rotor blades be fix pitch? In other words, no collective.

 

[XXavier]

Can articulated rotor blades be fix pitch? In other words, no collective.

Rotors with individually articulated blades use to have a swashplate (or a spider) giving collective and cyclic control. There are rare exceptions, like a British helicopter of the late 40s, the 'Fairey Gyrodyne', that had no collective, controlling the rotor lift with a pitch-lag coupling, so that pitch changed with the RRPMs. And most classic autogyros (like the C30) had fully articulated rotors, but lacked collective control of the blades' pitch.

 

[Jean Claude]

Hinged three-bladed rotor like C30 avoids the drag vibrations but unfortunately not "ground resonance".
Hinged two-bladed rotor restore drag vibrations, now transformed into cyclic differences in individual centrifugal forces, and keeps the serious downside of ground resonance

 

[WaspAir]

Can articulated rotor blades be fix pitch? In other words, no collective.

The McCulloch J-2 and the Air & Space 18A have what amounts to a two-position collective (flat for spin-up and a fixed position for flight). The J-2 has a stiff spring on the spin-up lever to resist accidental change to the pitch once airborne. On the 18A, there is a weight-on-wheels switch that prevents airborne engagment of the servo used to reduce pitch (although some 18As have a collective trim STC that is used to bump up rpm to delay onset of retreating blade stall when at low weight and high speed). Both aircraft are functionally fixed collective from take-off to landing, with a change only possible on the ground when prepping to depart.

 

[XXavier]

The McCulloch J-2 and the Air & Space 18A have what amounts to a two-position collective (flat for spin-up and a fixed position for flight). The J-2 has a stiff spring on the spin-up lever to resist accidental change to the pitch once airborne. On the 18A, there is a weight-on-wheels switch that prevents airborne engagment of the servo used to reduce pitch (although some 18As have a collective trim STC that is used to bump up rpm to delay onset of retreating blade stall when at low weight and high speed). Both aircraft are functionally fixed collective from take-off to landing, with a change only possible on the ground when prepping to depart.

Thanks to the post below this line, I'am now able to understand it...