Rotor config¶
A new RFM_RotorConfig starts empty. The required fields are all 0 and the rotor won't build until you set them, and the log tells you which ones are missing. Fields that have a sensible generic value (tip loss, element count, phase, ground effect and so on) keep it.
Required geometry (group 01)¶
| Field | What it is | UH-1 main | Mi-8 main |
|---|---|---|---|
| Blade Count | 2 | 5 | |
| Radius | Hub centre to blade tip, m | 7.315 | 10.644 |
| Chord | Blade width, m | 0.533 | 0.52 |
| Root Cutout | Where the lifting part of the blade starts, fraction of radius | 0.085 | 0.192 |
| Twist Deg | Total twist from root to tip. Negative means the tip is pitched down (washout). | −10.9 | (uses Blade Stations) |
| Blade Stations | Optional table of chord and twist along the blade. Overrides Chord and Twist. | — | 4 stations |
| Nominal RPM | Rotor speed at 100 % | 324 | 192 |
| Shaft Axis | Thrust direction (Shaft direction and spin) | 0 1 0 |
0 1 0 |
| Shaft Tilt Deg | How far the mast leans forward | 5 | 4.5 |
| Spin Direction | −1 anticlockwise / +1 clockwise, seen from above | −1 | +1 |
Pitch and rigging (group 02)¶
| Field | What it is |
|---|---|
| Collective Min Deg / Max Deg | Blade pitch with the lever all the way down and all the way up, measured at Pitch Reference Fraction of the radius (0.75 by default, the Mi-8 uses 0.7) |
| Cyclic Long Deg / Cyclic Lat Deg | Max cyclic pitch change at full stick |
| Cyclic Long Forward Deg | Optional extra forward travel (0 = same as Cyclic Long Deg). The gearing around centre stays the same, the extra travel only kicks in toward full forward stick. Use it if the aircraft runs out of forward stick before it hits top speed. |
| Phase Deg | Swashplate phase. 90 is right for pretty much every rotor. |
| Cyclic Long Sign / Cyclic Lat Sign | Flip these if a cyclic direction comes out backwards |
If your source gives the collective range at a different spot on the blade (the root, or 0.7R), set Pitch Reference Fraction to that spot instead of converting the numbers yourself.
Cyclic Kinematics on the rotor unit is optional. It swaps the simple cyclic range for real swashplate tilt angles and linkage numbers. The Mi-8 uses it with published swashplate data. Skip it unless you've got that data.
On tail rotors, set Cyclic Long Deg and Cyclic Lat Deg to 0.
Hub type (group 03)¶
| Your hub | Settings |
|---|---|
| Two-blade teetering (Bell 206, UH-1, AH-1) | Teetering on, Rigid Hub Model 0. Set Flap Stop (radians), Precone Deg and Blade Flap Inertia (per blade, estimate it as blade mass × radius² ÷ 3). Only turn on Bell Bar Enabled if the aircraft has a stabiliser bar (the UH-1 does, the Bell 206 doesn't). |
| Fully articulated (Mi-8, UH-60, CH-47, Puma) | Teetering off, Rigid Hub Model 1. Set Hinge Offset (flap hinge, fraction of radius), Lag Hinge Offset, Rigid Flap Up/Down Stop Deg, Rigid Lag Positive/Negative Stop Deg, Pitch Flap Coupling and the blade mass (Blade Mass + Blade Static Moment Kg M, or a Blade Mass Stations table). Turn on Derive Rigid Hinge Inertia From Mass and both Derive … Frequency From Mass switches. Always set a lag damper (Lag Damper Nm Per Rad Sec). Hinged blades with no lead-lag damping can shake the whole aircraft apart (ground or air resonance). If you don't know the value, start from 0.35 × blade flap inertia × lag frequency (per rev) × rotor speed (rad/s). The Mi-8's 8000 is about that, and the authoring check prints this estimate for your rotor. |
| Hingeless / bearingless (Lynx, EC135, BO 105, AS350 Starflex) | There's no dedicated model for these. Treat it as articulated with a bigger equivalent Hinge Offset (around 0.08–0.15). Not flight-tested. |
| Tail rotors | Match the real hub. A two-blade teetering tail (UH-1, Bell 206, AH-1) uses Teetering on. Anything else uses Teetering off with Rigid Hub Model 0 (like the Mi-8's tail). |
What Teetering actually does. On a hub that isn't articulated, Teetering on makes the two blades a seesaw. When one flaps up, the other flaps down, which is how a real two-blade teetering hub works. With Teetering off, every blade shares the same flap angle and they all move together.
So it's not about blade count, pick whatever matches your hub. A seesaw only makes sense with two blades though, so leave it off for anything with 3 or more blades (it's off by default). On tail rotors it barely matters either way, since tail rotor flapping hardly affects the aircraft.
Blade mass doesn't get added to the aircraft's weight. It only describes how the empty mass is spread out in the blades.
Hinge Inertia Relief (articulated hubs, on by default). A real hinged blade spends part of its load moving itself on the flap and lag hinges, and only the rest reaches the hub. With this on, RFM does the same: the hub gets each blade's load minus what went into accelerating the blade about its hinges. The averages don't change, but much less of the blade's per-turn shake reaches the airframe. Leave it on. Each [RFM-ROTOR] line ends with how much it took out.
Aerodynamics (group 04)¶
| Field | What I'd use |
|---|---|
| Elements + Gauss Quadrature | 4 elements with Gauss on (both templates). Tails: 3–4. |
| Use Mach Re Airfoil | On (UH-1). Uses a built-in NACA 0012 table that accounts for Mach number and blade size. |
| Airfoil Decks | Your own lift and drag tables for each blade section. Only use these if you've got real airfoil data. Made-up tables are worse than the built-in section. The Mi-8's tables show the format. |
| Inflow Mode | 2 (UH-1) is a good default for main rotors, 0 for tail rotors |
| Ground Effect | On for main rotors, off for tail rotors |
| Tip Loss, Profile Drag Add, Ground Effect Gain / Floor | Leave them at default, and only tune them against real hover data |
Elastic blade modes (group 05)¶
Optional blade bending and twisting. The Huey uses flap at 4/rev (damping 0.015, 2° tip limit) and torsion at 6.5/rev (damping 0.02, 4° limit, axis at 0.25 chord). Leave these off unless you know your blade's natural frequencies.