Frusheen Posted October 18, 2016 Posted October 18, 2016 BUG TEMPLATE: Description: Helicopter rotor head does not change rpm when decelerating from fast forward flight with fully lowered collective and aft cyclic. DCS Version: 2.0 Steam: No Map: NTTR SP/MP: SP Reproducible: Yes Step to Reproduce: perform a rapid deceleration while maintaining altitude by lowering collective and applying a large amount of aft cyclic. Screenshot/Video available: can be provided on request Track Available: No Mission File: No Controllers: In signature OS: Windows 10 CPU etc: in signature Mods: No Any Additional Information: This does seem to be implemented when the rotor head is not being driven i.e in autorotation. __________________________________________________Win 10 64bit | i7 7700k delid @ 5.1gHz | 32Gb 3466mhz TridentZ memory | Asus ROG Apex motherboard | Asus ROG Strix 1080Ti overclocked Komodosim Cyclic | C-tek anti torque pedals and collective | Warthog stick and throttle | Oculus Rift CV1 | KW-908 Jetseat | Buttkicker with Simshaker for Aviators RiftFlyer VR G-Seat project: http://forums.eagle.ru/showthread.php?p=2733051#post2733051
Mt5_Roie Posted October 18, 2016 Posted October 18, 2016 Rotor speed is actually a factor of DCS engine, not the module itself. Once the rotors are spinning, no matter which heli module you fly, the motion will all be the same. BUG TEMPLATE: Description: Helicopter rotor head does not change rpm when decelerating from fast forward flight with fully lowered collective and aft cyclic. DCS Version: 2.0 Steam: No Map: NTTR SP/MP: SP Reproducible: Yes Step to Reproduce: perform a rapid deceleration while maintaining altitude by lowering collective and applying a large amount of aft cyclic. Screenshot/Video available: can be provided on request Track Available: No Mission File: No Controllers: In signature OS: Windows 10 CPU etc: in signature Mods: No Any Additional Information: This does seem to be implemented when the rotor head is not being driven i.e in autorotation. 1 Coder - Oculus Rift Guy - Court Jester
Frusheen Posted October 18, 2016 Author Posted October 18, 2016 I don't follow you Roie. The rotor rpm needle can over speed on both the Huey and mi8 by performing the same maneuver from fast forward flight. There is also an audio change associated with it. The gazelle rotor rpm can over speed when in autorotation but not in powered flight. This is not correct behavior. __________________________________________________Win 10 64bit | i7 7700k delid @ 5.1gHz | 32Gb 3466mhz TridentZ memory | Asus ROG Apex motherboard | Asus ROG Strix 1080Ti overclocked Komodosim Cyclic | C-tek anti torque pedals and collective | Warthog stick and throttle | Oculus Rift CV1 | KW-908 Jetseat | Buttkicker with Simshaker for Aviators RiftFlyer VR G-Seat project: http://forums.eagle.ru/showthread.php?p=2733051#post2733051
Mt5_Roie Posted October 18, 2016 Posted October 18, 2016 Ahh...I though you were talking about the actual rotation speed of the rotors. Once a helicopter is up to speed, the speed it rotates is actually set by DCS. Just because something can be done on the Huey and MI-8 doesn't mean it can be done on the Gazelle. Remember the Gazelle is a different helicopter after all. For instance, the Huey has a throttle you can adjust (I think the MI-8 has one too, but haven't flown it in a while) - but the Gazelle doesn't. So it's not really a fair comparison saying the Gazelle should be able to do something just because the other helicopters can do it. But since your not talking about the actual visible rotation speeds of the blades, I'll add this to the test queue this week and will move it along. I don't follow you Roie. The rotor rpm needle can over speed on both the Huey and mi8 by performing the same maneuver from fast forward flight. There is also an audio change associated with it. The gazelle rotor rpm can over speed when in autorotation but not in powered flight. This is not correct behavior. Coder - Oculus Rift Guy - Court Jester
gospadin Posted October 18, 2016 Posted October 18, 2016 I think his point is that as you lower collective, rotor braking forces will decrease as blade AoA decreases, causing it to speed up if torque from the engine isn't also instantly decreased. Even with lightweight blades, I'd expect a slight lag if you alter collective too quickly. Edit: I do not possess any SA342 maintenance documentation, so I don't know what the expected behavior of their engine/rotor governing system would be, or if it even has one. My liveries, mods, and missions for DCS:World M-2000C English Cockpit | Extra Beacons Mod | Nav Kneeboard | Community A-4E
Frusheen Posted October 18, 2016 Author Posted October 18, 2016 (edited) Thanks. I compared to the other helicopters due to you stating it was not possible to model in dcs. The type of governor employed is not the issue. When a helicopters rotor is presented at high angle to the oncoming air flow with low pitch on the rotor blades they rotate more quickly (this is because the rotor head is free to rotate from the gearbox and is what allows autorotation). It has nothing to do with the other dcs helicopters. It is basic helicopter aerodynamics and it does not appear to be modeled. The engine governor is working to control the rotor rpm it can't overcome this phenomenon as the rotor head is free to rotate. Unless the Gazelle has some kind of active rotor brake in flight other than the rotor brake in the cockpit then performing the maneuver should cause a rapid increase in headspeed and a drop in engine rpm as the governor tries to compensate. At the moment the rpm needles don't even flinch. Thanks for passing it up the line so it can be addressed along with some of the other flight model issues. Edited October 18, 2016 by Frusheen __________________________________________________Win 10 64bit | i7 7700k delid @ 5.1gHz | 32Gb 3466mhz TridentZ memory | Asus ROG Apex motherboard | Asus ROG Strix 1080Ti overclocked Komodosim Cyclic | C-tek anti torque pedals and collective | Warthog stick and throttle | Oculus Rift CV1 | KW-908 Jetseat | Buttkicker with Simshaker for Aviators RiftFlyer VR G-Seat project: http://forums.eagle.ru/showthread.php?p=2733051#post2733051
Goggles Posted November 4, 2016 Posted November 4, 2016 (edited) I was doing some autorotations: With increasing airspeed (after initial pitch down), the rotor RPM is supposed to increase. In the model, it decreases to the point of unflyability. The converse is also the issue: When slowing down, the rotor RPM increases when it should decrease. Rotor RPM should also be affected by G Loading: pulling G's increases the weight on the rotor, thereby increasing RPM. In an autorotation at constant airspeed (120 km/hr), Rotor RPM should increase in a turn as G loads increase. In the model, RPM stays the same. Indeed, in a real helicopter, you may have to pull on collective a little bit in order to prevent over speeding the rotor RPM in a turn. G loading is not modeled in the simulation. The only reason the model increases the rotor RPM in the flare in the autorotation is because the model incorrectly increases rotor RPM because of speed decrease. RPM should increase more dramatically because of G loading in the flare, and should counteract the natural slowing of the rotor because of the decreasing airspeed. That's the basic problem with not getting an increase in rotor RPM during a flare in the model. Rotor dynamics are not correct. Edited November 4, 2016 by Goggles
Goggles Posted November 4, 2016 Posted November 4, 2016 Thanks. I compared to the other helicopters due to you stating it was not possible to model in dcs. The type of governor employed is not the issue. When a helicopters rotor is presented at high angle to the oncoming air flow with low pitch on the rotor blades they rotate more quickly (this is because the rotor head is free to rotate from the gearbox and is what allows autorotation). It has nothing to do with the other dcs helicopters. It is basic helicopter aerodynamics and it does not appear to be modeled. The engine governor is working to control the rotor rpm it can't overcome this phenomenon as the rotor head is free to rotate. Unless the Gazelle has some kind of active rotor brake in flight other than the rotor brake in the cockpit then performing the maneuver should cause a rapid increase in headspeed and a drop in engine rpm as the governor tries to compensate. At the moment the rpm needles don't even flinch. Thanks for passing it up the line so it can be addressed along with some of the other flight model issues. "performing the maneuver should cause a rapid increase in headspeed and a drop in engine rpm as the governor tries to compensate. At the moment the rpm needles don't even flinch. " You would split the needles, but you would not see the engine RPM drop in this situation, because the governor keeps the engine RPM steady (the engine is single spool: the turbine is on the same shaft as the compressor; it does not have a free power turbine). Only the rotor RPM would increase. The freewheeling unit uncouples the rotor from the engine drive when torque goes negative. That also permits autorotation.
Goggles Posted November 4, 2016 Posted November 4, 2016 Ahh...I though you were talking about the actual rotation speed of the rotors. Once a helicopter is up to speed, the speed it rotates is actually set by DCS. Just because something can be done on the Huey and MI-8 doesn't mean it can be done on the Gazelle. Remember the Gazelle is a different helicopter after all. For instance, the Huey has a throttle you can adjust (I think the MI-8 has one too, but haven't flown it in a while) - but the Gazelle doesn't. So it's not really a fair comparison saying the Gazelle should be able to do something just because the other helicopters can do it. But since your not talking about the actual visible rotation speeds of the blades, I'll add this to the test queue this week and will move it along. You adjust the throttle in the Huey in case the governor fails and you need to switch it to emergency. Then it flies like a helicopter with no governor, like many piston helicopters. But it is very challenging and a run-on landing is suggested. Otherwise, the twist grip throttle on the collective is rotated full open, and the governor keeps the RPM's at the proper rate. Same with the MI-8. But the issue has nothing to do with the throttle or governor.
Recommended Posts