@FlyingRaccoon
Been tinkering a LOT with the new multirotor Helicopter FM - however, I’m yet to find a decent balance between the tandem-specific variables…
Aircraft is CH47D, tandem helicopter with two “main” rotors. I’ve been able to get a decent yaw with both rotors banking in opposite directions (pedal_on_bank)
However, I’m yet to find a combination of cycl_y_on_cycl_y and cycl_y_on_collective that works consistently and correctly. Have tried different combination of values, and the results are consistently giving me pitch+yaw rotations (NOT accurate). Eg. Pitch up and the aircraft will also yaw clockwise. Pitch down and aircraft yaws CCW.
Note that removing both of these lines from CFG results in a more accurate handling of the aircraft, though far from perfect.
Any clarification or guidance you can provide as to how to avoid the yaw reactions when using cycl_y_on_cycl_y and cycl_y_on_collective on this sort of tandem rotor configs?
Hello @vantech
Can you elaborate a bit on what you consider is not accurate?
I checked with our core sim engineers and induced yaw is to be expected.
They would need more details to be able to help.
Regards,
Sylvain
May be a little difficult to explain in words, but I’ll give it a shot:
- Setup is two tandem “main” rotors. Front rotor is located at 19,0,13 and back rotor at -19,0,17. Note that one of the rotors is more elevated than the other, and both are at the same distance from the center of the aircraft.

- Both rotors are configured with
pedal_on_bank = 0.1 (enough for this heli config since the distance between rotors generate enough torque)
cycl_y_on_collective = 0.3 (enough for this setup IMO)
cycl_y_on_cycl_y = 0.3 (enough for this setup IMO)
No entries for pedal_on_cycl_x, pedal_on_collective.
Now, the problem I’m having is that any pitch up/down has a violent yaw response - Upon further investigation, I understand now that it has to do with the additional torque the rotor with increasing collective applies to the system. As such this sort of tandem rotor configs will not benefit from cycl_y_on_collective, and that would be set to zero (we do not want any sort of yaw reactions upon pitch)
However, I’m now having another issue - the helicopter has a strong roll tendency to the left. Both rotors have cyclic_bank_centre set to zero, but upon take off the aircraft will strongly roll to the left, requiring a significant amount of cyclic input. As if there was some sort of dyssymetry of lift, which on this sort of rotor configs is cancelled out by the other rotor.
Finally, another issue that I’m having is that the aircraft has a tendency to pitch aggressively upon increasing airspeed, to the point where it is difficult to control. It is perfectly stable and controllable in pitch upon takeoff, but shortly after gaining some speed the aircraft begins pitching up, for which I have to respond applying down rotor trim. When speed is near 100kts, no amount of down trim or cyclic is enough to keep the aircraft from pitching, and at some point it ends up flipping over itself.
Is this behavior consistent with what’s shown in the Sim Forces debug?
That’s something we need to improve documentation on obviously.
The orange disk shows the forces applied on the blades while the blue disk shows the resulting force on the helicopter.
If your helicopter has a tendency to roll to the left, this must be visible on the bank angle of the blue disks.
Upon reviewing the information you provided, our engineers suspected an incorrect phase lag that would impact both bank and pitch.
This is something you can adjust with blade_flap_rigidity and blade_flap_inertia.
The Engines aircraft debug also provides useful numerical information in that regard.
I hope this helps.
Regards,
Sylvain