fly by wire

[Guest robertv]

Dear all,More and more aircraft use fly-by-wire. Basicly this means the computer is doing the flying and the pilot by for example a joystick tells the computer how to adjust the flightpath. Fly-by-wire however, atleast for the aircraft (Falcon 7x biz-jet) i am working on, also means some hard limits to for example pitch, angle-of-attack and g-limits. The aircraft also reacts in a different way; if the joystick is in the center the aircrafts computers automaticly maintain the current bank and pitch. So for example it would maintain a 3 degrees nose up and 10 degrees bank without touching the controls. Then when you push the joystick left and let the bank go to 15 degrees and bring the stick back to neutral; the plane keeps 15 degrees bank and 3 degrees up. Now the big question is ofcourse; how on earth would i achieve something like that in FS? Are there any aircraft already that have this? Probably this would have to be build into the panel, or could i put some of the hard limits into the aircraft mdl.In short the things i am looking for:attitude limit; a hard limit which disallows pitch attitudes below say 30 and above say 25 degrees. (Bank on this particular aircraft is not limited, for example on the airbusses it is)g-limit;a hard limit which disallows g-forces larger then 3G (basicly this would have to be something that overwrites full stick back but limits the elevator and trim to such a setting that 3G or less is maintained)angle-of-attack limit;a hard limit which disallows an angle of attack larger then say 9 degrees (of course intended to prevent stalling). The high angle of attack is to be prevented by pitching down (not by full engine thrust like on the Airbusses)keep current pitch and bank;The sidestick is only intended for changing the pitch and bank of the aircraft; when in neutral the pitch and bank should stay right as they are; only when an input is given the pitch or bank will change, however it will be automaticly kept again when the stick goes back to neutral. A little addition is that the bank should go back to 0 when it is say -2 or +2 degrees.Any help or thoughts or hints on how to do these things would be greatly appreciated!Kind regards,Robert Versluys

[dragonflightdesign 98]

Hi RobertI did something similar regarding hard limits on aircraft attitude back in FS2000 days. It was for a Beechcraft 1900 EFIS desktop training simulator (I'm still under NDA about who for) and I built in the limits by constantly checking the aircraft attitude, then overriding the user input when they were exceeded. In one or two cases I had to smooth out the override because the aircraft tended to bounce violently as it fought two conflicting inputs when the pilot input was only just greater than the hard limit. My current project also demands that I override user-demanded inputs under certain circumstances so yes, that can be done and it isn't too difficult. Very many FS aircraft exhibit this type of override e.g. if you get a total failure of the hydraulic system, prevents flaps/slats/gear/rudder from working.Regarding the joystick input: I can think of a theoretical way of doing it but implementation may be a problem. Ignoring the hard limits discussed above, you will need to constantly check aircraft attitude and joystick input (requests for aileron, elevator etc) and store the two. When the joystick requests a lesser input than the maximum input currently stored, the lesser input must be overridden by the greater one. When the joystick passes through the neutral position for that control input, you will need to override the opposite input by applying the requested input as a negative effect to the currently held input on the original axis (did that make sense?). At eighteen ticks a second you should be able to take complete command of the aircraft attitude based on user demand quite smoothly.Mind you, the code should be quite interesting!!-Dai

[spokes2112 179]

Robert, Dai is the man for the ideas on this - I just have a comment. PMDG on their 737NG series got the Hold/Pitch on center working, in the Boeings it's called CWS with 2 modes, CWS-P & CWS-B. ( Control Wheel Steering Bank/Pitch ) Their job was probably a little tougher as they had to separate the active CWS single axis from the autopilot while keeping the inactive CWS mode from interfering from the autopilot Lateral/Pitch mode. I tried working with this back in FS2002 so excuse me if I donot have the exact info. But below is what I tried. For CWS pitch IIRC could work like this - IF CWS-P MODE ON and WHEEL PITCH CENTERED Then Find what AP lateral mode selected, store it. Turn ON (>K:AP_ATT_HOLD_ON) & Turn Off (>K:AP_WING_LEVELER_OFF) and restore AP lateral mode stored before if necessary. ( When ATT hold is turned on LEVEL is automatically turned on too :-( )For CWS bank / Bank Limiting - I found this and used it for bank limiting. Keep in mind it has to run in the background as it uses AP_HEADING to make work. So all heading bugs, logic, windows must use their own variable. I found when using the stock 737 autopilot that the bank in degrees would equall quite closely ( not exact ) the difference between commanded heading and current heading normalized. EX. commanded 0*, current 15* would give a 15* left bank. The .air file would need to be adjusted so a max bank available is entered. (30* for me). So if I required a 5* Right bank ( by limiter or CWS-B ) AP_HEADING would be engaged AP_Heading would be 5 + Current aircraft heading normalized.These where just observations when doing a project that fizzled, maybe it can help?Roman

[Guest phlerp]

A fly by wire system is best made with SimConnect. There are functions for overriding input from the user so you wouldn't have any conflicting input.

[Rocky 128]

A full fly-by-wire system is implemented in the Wilco/FeelThere Airbus Series.It maintains pitch and bank (in fact, it maintains load factor, not pitch), it provides bank angle protection (67

[badderjet 181]

but I am not a specialist.

Ha ha Eric, I think you've really come a long way as far as gauges are concerned! Keep up the great work! :(

I am happy that you work on a Dassault bizjet, it is really missing in our Flight Sim world.

OMG, I can only second that. The Falcons belong to the nicest planes that I know, especially the 7X. :( It's got one top of the line flight deck, outstanding performance, and is simply one helluva plane! :( Can't wait to see you progress on your project. All the best for it! :(Etienne