Rotor units¶
A rotor unit is one rotor: its blades, where it sits, what drives it and how the pilot's controls get to it.
| Field | What it is |
|---|---|
| Id | A unique name |
| Role | 1 lift, 2 anti-torque, 3 propulsive (pusher or propeller), 0 generic. It's mostly a label, but it helps RFM pick sensible defaults. |
| Rotor Config | The blade and hub data (Rotor config) |
| Hub Point / Hub Bone | Where the hub is. If both are set, the PointInfo wins. |
| Shaft Axis From Bone | Takes the shaft direction from the hub bone's up axis instead of from the rotor config |
| Drive Mode | 0 = driven by a power group shaft (normal), 1 = free spinning (autogyro), 2 = fixed speed (testing) |
| Power Group Id, Power Output Id | Which group and shaft drive this rotor |
| Control Map | How the pilot's controls get to it (Control maps) |
| Cyclic Kinematics | Optional real swashplate geometry (Pitch and rigging (group 02)) |
| Analytic Wake | This rotor makes downwash that other parts can feel. Off for tail rotors. |
| Wake To Airframe | Its downwash pushes on the fuselage, fin and stabiliser. On for main rotors, off for tail rotors. |
| Shaft Reaction Inertia Kg M2 | See Where does the rotor's spinning mass go? |
| VRS and inflow tuning fields | Leave at 0 (the rotor's built-in defaults) |
Shaft direction and spin: getting anti-torque right¶
This is the one people get backwards the most, so it's worth reading properly.
Shaft Axis (on the rotor config) is the direction the rotor pushes air away from. In other words it's where the thrust points at positive pitch. For a main rotor that's straight up (0 1 0), and Shaft Tilt Deg leans it forward from there.
Spin Direction: −1 is anticlockwise seen from above (American and most European designs), +1 is clockwise (Russian and French designs).
A main rotor twists the fuselage the opposite way to its spin, and the tail rotor has to push the tail to cancel that out:
| Main rotor turns (from above) | Spin Direction | Fuselage wants to turn nose… | Tail rotor has to push tail… | Tail Shaft Axis | Tail control map |
|---|---|---|---|---|---|
| Anticlockwise (UH-1, UH-60, Bell, Sikorsky) | −1 | right | right | 1 0 0 |
Collective From Yaw −0.5, Collective Bias 0.5 |
| Clockwise (Mi-8, Mi-24, Puma, AS350) | +1 | left | left | -1 0 0 |
Collective From Yaw +0.5, Collective Bias 0.5 |
It doesn't matter which side of the boom the tail rotor is on. A canted tail rotor (like the UH-60's) just tilts the axis up a bit, for example 0.94 0.34 0 for about 20°.
RFM counts blade position in each rotor's own turning direction. So a clockwise rotor (Spin Direction +1) on the plain cyclic (no Cyclic Kinematics) needs Cyclic Lat Sign −1, or left stick tilts its disc right. Cyclic Long Sign stays −1 either way. Check it on the ground anyway (step 7 of the test card).
Phase lock. Tandem and intermeshing rotors are kept in step by a synchronising shaft, so their blades never meet. Set Phase Lock Rotor Id on the second rotor to the first rotor's ID and Phase Lock Offset Deg to how far apart the blades sit. RFM keeps the two in that phase (scaled by their nominal RPM ratio), for the visuals, for blade strikes and on other players' screens. If the speeds stop agreeing (a broken drive) the lock lets go, and it takes up again once they match.