March 26, 201610 yr Ok, I get corrected then.... It's been a long time I last used FSX, and PMDG's 777 but I was convinced the same protections still worked when I disengaged it - my fault, and I'll certainly try to concentrate more on it the next time I test the aircraft. Flying gliders since 1980 Flightsimming since 1992 AMD Ryzen 5600x, 32GB RAM, GPU Nvidia RTX 3060 Ti 8 GB, 1 TB and 500 GB nvme2 SSD drives, HP 27" 60Hz LED monitor @ 1920x1080, T16000, Hotas from old X52 Pro, Saitek Combat Rudder Pro (2010 model)
March 27, 201610 yr Jose, What was it you were expecting to see by turning off the FBW? Boeing FBW doesn't really change the cruise handling characteristics as its a speed trim system, it simply adds protection and provides some additional compensation in Turns and Flap use but it doesn't really change the way the aircraft "Flies". We actually have an extensive explanation of the system in the Introductory section of the manual for the 777. And just so you know, we did model the FBW Disabled mode as well as the protected modes, you just have to know what to look for when one mode changes to another to even be able to tell. In the words of the FCOM the 777 FBW PFCs automatically control pitch to maintain a relatively constant flight path (that's how it compensates for configuration changes, for example). I dont know the details of the control laws, but C*U systems are usually programmed to maintain 1g (vertical) acceleration and bank angle if there is no pilot input. In that case the FBW may well act to stabilise the phugoid more than it would be if FBW was not active (i.e. Direct Law). Vertical acceleration will vary during the phugoid oscillation but it might not be enough to make the system correct for it.
March 28, 201610 yr Ok, I get corrected then.... It's been a long time I last used FSX, and PMDG's 777 but I was convinced the same protections still worked when I disengaged it - my fault, and I'll certainly try to concentrate more on it the next time I test the aircraft. Make sure you understand the FBW control laws, well enough, that you'll know what to look for when you start degrading modes. Rafael Cordoves
March 28, 201610 yr Make sure you understand the FBW control laws, well enough, that you'll know what to look for when you start degrading modes. Thank you, and I think I do understand enough of both C* and C*U law to be able to look for the right effects of degrading modes, and /or how to perform the tests when yet other systems are also not fully functional Flying gliders since 1980 Flightsimming since 1992 AMD Ryzen 5600x, 32GB RAM, GPU Nvidia RTX 3060 Ti 8 GB, 1 TB and 500 GB nvme2 SSD drives, HP 27" 60Hz LED monitor @ 1920x1080, T16000, Hotas from old X52 Pro, Saitek Combat Rudder Pro (2010 model)
March 28, 201610 yr Author Going back to my video, the 777 is FBW and during the oscillation you can glance down at the Multi Function Display and see that the elevator is actually moving. What's the FBW doing here? Another thing I don't understand is that the stabilizer trim changes as well ranging from 3.50 to 5.25, yet the trim speed on the speedtape remains constant at 290. Could anyone clarify this please? Ok, I've done some reading and think I can answer myself now: The pilot's input signal through the yoke/rudder pedals is sent to the ACEs (Actuator Control Electronics) which in turn sends the signal to the PFCs (Primary Flight Computers) for enhancement. The PFCs enhance the signal using other data such as configuration, engine thrust etc. and send the "corrected" signal back to the ACEs which will then send it to the control surfaces. As derived from point 1. the Control Column does not directly control the elevator, instead it generates a pitch signal from the PFC and these will command BOTH the stabilizer AND the elevator to comply with the maneuver. The Pitch Trim switches of the 777 in its Normal Mode control BOTH the stabilizer AND the elevator. As I think we all knew already, the Pitch Trim switches DON'T directly control the stabilizer but instead control the trim reference speed. The PFCs first command the elevator to achieve the desired trim change and then move the stabilizer to "streamline" the elevator, that is, to "align" the stabilizer with the elevator. The PFCs monitor the pilot's inputs (and lets remember that "no" input, is also an input, a neutral input) and the response of the aircraft to said inputs, and adjusts accordingly. In particular, the PFC will minimize airplane response to thrust and configuration changes as well as turbulence. This should explain the behavior observed in the video. I'm still reading on the C*U fly-by-wire logic that's implemented in the 777. On the ground and in Direct Law however, the Pitch Trim switches DO control the stabilizer directly as they would in a conventional aircraft. In Direct Law the PFCs don't work and thus the pilot's input goes directly to the control surfaces through the AECs. I want to test-fly the aircraft in Direct Law (maybe will record a video on that as well). Jaime Beneyto My real life aviation and flight simulation videos [English and Spanish] System: i9 9900k OC 5.0 GHz | RTX 2080 Super | 32GB DDR4 3200MHz | Asus Z390-F
March 28, 201610 yr In Direct Law the PFCs don't work and thus the pilot's input goes directly to the control surfaces through the AECs. I want to test-fly the aircraft in Direct Law (maybe will record a video on that as well). Exactly AlphaFloor, and then please let us know hwat you find, although it may be difficult using only the corresponding EICAS page... and / or external views to try to match ... Thx Flying gliders since 1980 Flightsimming since 1992 AMD Ryzen 5600x, 32GB RAM, GPU Nvidia RTX 3060 Ti 8 GB, 1 TB and 500 GB nvme2 SSD drives, HP 27" 60Hz LED monitor @ 1920x1080, T16000, Hotas from old X52 Pro, Saitek Combat Rudder Pro (2010 model)
March 31, 201610 yr Author Exactly AlphaFloor, and then please let us know hwat you find, although it may be difficult using only the corresponding EICAS page... and / or external views to try to match ... Thx Hello again, I'm posting the link to the thread I opened after having analyzed the 777's FBW a bit deeper. Here's the link: My Analysis of the Boeing 777 FBW System Here's another interesting thread regarding the FBW of the PMDG's 777: PMDG 777 FBW and weird Flight Controls behaviour? I believe the people who followed this thread actively will find these ones interesting as well and will be eager to comment! Jaime Beneyto My real life aviation and flight simulation videos [English and Spanish] System: i9 9900k OC 5.0 GHz | RTX 2080 Super | 32GB DDR4 3200MHz | Asus Z390-F
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