Phil C6 Posted July 2, 2024 Posted July 2, 2024 Hi, Maybe it's normal FCS logic, I don't know but as it seems strange to me i prefer ask: -1: Under 300kts with full rudder to the right, the plane roll to the right and heading go to the right (till here it seems like other planes) -2: under 300kts if you compensate the rudder roll with stick for keep horizontal wing, the rudder has strangely almost not effect on the heading https://drive.google.com/file/d/1N4LcHiaHvuRKXVJ_NZJO8bTjZTQ0uSTs/view?usp=sharing -3: Over 300kts with full rudder to the right, it roll to the left and heading go to the left https://drive.google.com/file/d/17OZrT4S8xNodglj65UZ4yO-XUyIeDVtH/view?usp=sharing PS: noticed the rudder has much lower effect than F16, F15 and others planes, on F16 is much more violent Best regards F18 rudder effect under 300kts.trk F18 rudder effect over 300kts.trk F16 rudder effect.trk
Ahmed Posted July 2, 2024 Posted July 2, 2024 (edited) The issue here is that the control systems description goes into detail about several subsystems, such as the rudder limiter (that every fast aircraft has), or the mixing of rudder and aileron commands, but leaves a lot of blank areas as it does not specify the exact gains of each of these systems. Thus, any developer has to make educated guesses. There is however a misconception in the DCS community about rudder being a yaw control only. In any conventional aircraft, the rudder will induce roll. The rudder is even the most effective roll control at near-stall AOA. FBW aircraft are traditionally designed to fly like conventional aircraft (that is what every pilot is used to from day 1), so they normally won't just produce an isolated yaw reaction out of a rudder input (see example video of the real F-16 rudder test in the thread above). The only way that an isolated yaw would occur would be by applying opposite roll to stop the yaw from inducing a roll, and this doesn't happen in any DCS module that has ever exhibited this behavior (the old Mirage FM also coming to my mind). In the particular case of the Hornet, it is difficult to gather enough evidence to make a solid case about the rudder FCS implementation. It is, definitely, "odd" in several regimes, compared to conventional handling. Edited July 2, 2024 by Ahmed
DummyCatz Posted July 3, 2024 Posted July 3, 2024 (edited) 7 hours ago, Ahmed said: The issue here is that the control systems description goes into detail about several subsystems, such as the rudder limiter (that every fast aircraft has), or the mixing of rudder and aileron commands, but leaves a lot of blank areas as it does not specify the exact gains of each of these systems. Thus, any developer has to make educated guesses. There is however a misconception in the DCS community about rudder being a yaw control only. In any conventional aircraft, the rudder will induce roll. The rudder is even the most effective roll control at near-stall AOA. FBW aircraft are traditionally designed to fly like conventional aircraft (that is what every pilot is used to from day 1), so they normally won't just produce an isolated yaw reaction out of a rudder input (see example video of the real F-16 rudder test in the thread above). The only way that an isolated yaw would occur would be by applying opposite roll to stop the yaw from inducing a roll, and this doesn't happen in any DCS module that has ever exhibited this behavior (the old Mirage FM also coming to my mind). In the particular case of the Hornet, it is difficult to gather enough evidence to make a solid case about the rudder FCS implementation. It is, definitely, "odd" in several regimes, compared to conventional handling. I'd like to argue that there do exist a complete schematic diagram of the auto flaps up mode and spin mode of FCC OFP v10.1, including all the relevant gain schedules, so no guesses are required and the FCS should be coded as is. What actually require educated guesses are the powered approach mode and FCC OFP v10.7 logic updates. Check NASA TM 107601 Simulation Model of a Twin-Tail, High Performance Airplane for the block diagrams (https://ntrs.nasa.gov/api/citations/19920024293/downloads/19920024293.pdf starting from page 85) If you're wondering, no there's no such logic or interconnect that actively applies opposite roll to stop the yaw from inducing a roll, according to the block diagrams. Edited July 3, 2024 by DummyCatz
Ahmed Posted July 3, 2024 Posted July 3, 2024 (edited) 15 hours ago, DummyCatz said: If you're wondering, no there's no such logic or interconnect that actively applies opposite roll to stop the yaw from inducing a roll, according to the block diagrams. Didn't know about that paper, so that's definitely a great source of info for FCS related issues!. Regarding the quote, then that should be enough proof that yaw should aerodynamically induce roll, as in any other aircraft, and OP would be right (so, no "correct as is"). EDIT: just to see that this has been marked "correct as is" when OP has posted a video where he inputs right rudder and the aircraft ends up turning left makes me lose all faith in the DCS bug reporting process... Edited July 3, 2024 by Ahmed 2
Phil C6 Posted July 4, 2024 Author Posted July 4, 2024 (edited) Hi thx for your answers didn't read the NASA document but maybe FCS have been updated since? Best regards Edited July 5, 2024 by Phil C6
DummyCatz Posted July 8, 2024 Posted July 8, 2024 On 7/5/2024 at 3:01 AM, Phil C6 said: Hi thx for your answers didn't read the NASA document but maybe FCS have been updated since? Best regards There's only a few updates from v10.1 to v10.7, as indicated in the paper https://trace.tennessee.edu/utk_gradthes/2312/ and https://trace.tennessee.edu/utk_gradthes/2372/ So no, it's not related to the FCS. As discussed in the linked thread above, the opposite roll is due to the aerodynamic forces and moments created by the rudder.
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