Lift balancing on the Gyrhino

WaspAir

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Cannot agree with this. How do you explain that in an articulated rotor system, during pre-rotation when rpm is low, the blades do not flap down.
They don't flap up, either. In prerotation at low rpm the blades are not yet flying (essentially stalled with inadequate airspeed) and they're not flapping at all, neither up nor down. Airspeed (with pitch) is what makes everything happen.

When you get significant rpm going in prerotation, you have darn little dysmmetry because you're sitting still (only the prevailing wind to make any difference in airspeed) for the spin-up with no pitch.

Most articulated systems use symmetrical airfoils held at essentially zero collective pitch, so they make very little lift during spin-up. Add some pitch, you get some lift, and the blades cone up. Move forward in that condition and you need flapping for compensation of the airspeed difference across the disc.
 
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XXavier

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The reference 'Autogyros' given by JC in post #20 is a highly interesting and instructive book, available free in the internet. Here's the link:
 

WaspAir

Supreme Allied Gyro CFI
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Aviator168, on re-reading your posts I wonder if maybe we are using terms differently. In case it might help to get us on the same page, here's how I would describe what's going on in an articulated rotor. If it isn't helpful, no worries.

First, coning and flapping are very separate things. Coning is a response to producing lift along a blade that is only attached at one end. It is a bit like the wingtips on a B-52 bomber that droop when the airplane is on the ground yet reach way up under the lifting loads at speed. Despite the name, it's not truly a geometric straight-sided cone shape, which would mean all the flexing happened at the root and the blade remained perfectly straight, but instead has some slight curvature. The span-wise lift distribution and the blade structure will influence how much shape change you get and where. The role of centripetal/centrifugal reactions here is to add rigidity to the disc, resisting coning. Coning is quite symmetrical in normal straight and level flight because the rotational speed around the disc is pretty constant, with only a very slight slight lead/lag variation (per conservation of angular momentum) and the overall lift of the disc is balanced. Watching a helicopter at lift off, you can see the coning take shape as the pilot "pulls pitch" to add collective and the blades respond to the applied lifting load.

Flapping results from the blade seeing different airspeed at different places as it progresses on its path around the disc during forward flight. It is self-regulating in normal flight conditions, with a rising on the advancing side and a dropping on the retreating side, conventionally enabled by a hinge at the root, and is independent for each blade, without any linkages between them (they are merely attached to the same hub). Without pilot intervention, there is just enough upward flapping speed on the advancing side and just enough downward flapping speed on the retreating side that the change in angle of attack from side to side compensates for the airspeed difference the blade encounters. (Note that it is the upward/downward speed, not the position, that makes the difference in angle of attack.) The blade flies its way through this process as the airspeed it sees varies around the disc. Ground adjustable trim tabs and/or the pitch control links are adjusted so that each blade will fly the very same track with respect to the airframe and vibration is avoided.
 
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