Heli Rotor Articulation (Very Techinical)

[scotg 204]

Hi all, I'm trying to figure out helicopter rotorheads. I was looking at the fully articulated rotors on the Pawnee, and watching their behavior in motion. Fully Articulated means they have flap, pitch and lag pivot movements, but the game really only seems to deal with the articulation if it's visible in-game. Having a look at the code and seeing what it actually does can be a little hard to follow; there's a LOT going on now. First, the droop of the blades is gradually straightened out as the rotor shaft turns faster and faster. Second, as the blades straighten, the flap of the blade is raised; this is not so graceful and looks similar to a strong gust of wind suddenly inverting an umbrella into a bowl. Incidentally, it appears in the model.cfg that each blade pitch axis is defined, although I do not notice a change in-game. On a real chopper it would look like if you hold your arm out the side of your body, hand flat and horizontal, and then rotate your forearm 90 degrees to where your hand is vertical. The super detailed AH-64D Apache mod by Nodunit and Franze actually does this. Though the Pawnee appears to be rigged the same way, I can't see the result. Blade pitch isn't all that important, at the moment, so getting back to the topic... Third, in addition to the blade straightening and flap raise of the blades, they can be angled depending on the direction the pilot stick (cyclic) is moved. This is where it gets tricky, because in-game the blade flap is initiated by the cyclic controls (leaning forward, back, left, or right). On the Pawnee an individual blade also adjusts its flap angle up or down depending on its progress in the 360 rotation of the hub and is independent of the other blades' flap angles. Look at the image of the rotation path as I applied a left cyclic lean:

The hub stays in place while the blades individually tilt. It looks excellent and mimics the behavior of an articulated hub quite well. Now that we've established all that, however, the challenge I am facing is how to do this with a semi-rigid rotorhead system, as seen on the Hueys and Robbies. On the semi-rigid system there are usually just two blades that are rigidly connected. When one blade is "flapped" upwards, the other is "flapped" down; for this reason it is also sometimes called a teetering rotorhead. A picture of this would depict the entire blade assembly to be in a straight line no matter what the angle (except for blade flexing/drooping). In a real semi-rigid heli, the blades are rigidly attached to one another but still have pitch and sometimes even lag pivots (like folding blades but less range of motion); hence, it is called semi-rigid. Now that I see it in action, the lack of it has become a sore thumb on all the non-updated choppers. If it's a noticeable effect enough to use with the Hummingbird/Pawnee and the Mohawk, then it would be even more noticeable on my semi-rigid heli, but how do we set up the skeletal hierarchy?