Fly-By-Wire

Hi, I'm new. Just a 14-year-old Air Force hopeful, wondering about the F-16's fly-by-wire system. I thought the FBW system completely eliminates the need for a rudder pedals. Does the F-22, F-35, and F-15 have these, too? Please explain.

The rudder pedals don't have any physical linkage to the aircraft's rudder, but moving them back and forth might make the rudder (and perhaps other control surfaces) on the aircraft move. The fly-by-wire control system decides which ones and how much, if at all. If you didn't have rudder pedals, what control input device would you use to yaw the aircraft? If an aircraft has an ability to yaw (as opposed to pitch or roll), then you want to give the pilot some way (within limits) to tell the aircraft, "Hey, yaw right/left!"

Does the F-35 have fly-by-wire? Can the computers of an F-16 or F-22 go down and still be flyable? Like, if you take out the F-15 computers it's still flyable.

Vtugimora wrote:Does the F-35 have fly-by-wire? Can the computers of an F-16 or F-22 go down and still be flyable? Like, if you take out the F-15 computers it's still flyable.

The F-16 is quad redundant, and can loose 2 branches before degradation can be noticed. Basically the DFLCC (flight control computer) can cope with failures, and still have full authority over the flight controls. Total flight control failure is possible, but highly un-likely. Your more likely to shell your pump or loose your engine than you are to loose all authority for your flight controls. It's a really good system.

The F-22 is similar in concept, but very different in design...i'll keep it at that.

The rudder is controlled just like the rest of the aircraft...with transducers. The rudder works off a fully wired system just like the rest of the jet.

Flight controls, hmmmm where do we start? A TOTAL flight control failure is virtually impossible. Like said before, it is quad redundant and can still function with just one branch. Inputs from the stick (pitch and roll) are split into 4 signals by force sensing transducers in the stick assembly. These signals are sent to the FLCC and compared with signals from the ECA (on analog FLCS) consisting of AOA, airspeed, mach number. The ECA gets these air data signals from the PSA which gets total and static pressures 1 and 2 (PT1,2 and PS1,2) from the pitot static probe and AOA 1 and 2 from the AOA probes. Impact pressure (Qc) is derived from subtracting static pressure (Ps) from total pressure (Pt) and is representative of airspeed. Mach # can then be calculated by deviding inpact pressure (Qc) by total pressure (Pt). A third source of total and static pressure is needed and supplied by the air data probe to the CADC. All of these signals and used to schedule FLCS surfaces along with sitck and rudder imputs from the pilot. The third source of AOA (collected by air data probe) is corrected by signals collected by the AOS (angle of sideslip) ports and the differential pressure sensor. If at least two of the air data signals of the same type (Pt or Ps) are missing, the ECA will go into STANDBY GAINS which is a preset value programmed into the ECA so that FLCS surfaces can still be scheduled. I think the values are 600knts at sea level with the gear up and 250knts at sea level with the gear down(On DFLCC jets there is no ECA and this is all done inside the DFLCC). Not to mention FLCS power. On out jets there are 5 sources of FLCS power that are also quad redundant meaning you have 20 potential sources of FLCS power. Plus two hydraulic systems. So to get a COMPLETE FLCS failure you would have to lose all 20 sources of FLCS power, both hydraulic systems, all 4 branches of FLCS, and all air data imputs. So as you can see, pretty much impossible unless the jet is seriously shot up in combat. I'll stop writing for now and I'm sure there is something that I missed or mis-styped so if there is any erroneous data in my novel feel free to correct me.

Vtugimora wrote:Does the F-35 have fly-by-wire? Can the computers of an F-16 or F-22 go down and still be flyable? Like, if you take out the F-15 computers it's still flyable.

Yes, the F-35 is fly-by-wire.
And no, in the (extremely unlikely) case that the FLCS should completely go 'down', the F-16 (and F-22 and F-35) is not flyable. First, the pilot would have no way to move the control surfaces. Secondly, even if he could he would not be able to maintain control of the aircraft. All three aircraft are naturally unstable (for most of their flight envelopes) and the pilot would not be able to compensate quickly or precisely enough to maintain control. Hence, the crucial need for very high reliability and system redundancy.

There are so many redundancies and safe guards built into the FLCS of the 16 that there has NEVER been a crash linked to a complete FLCS fail and never will be. If this was to happen you would see every 16 world wide grounded and lockhead engineers running around like chickens with their heads cutt off. Just not going to happen and this is 70's technology. I'm sure the 35 and 22 will have the same kind of safety record as far as FLCS goes when they reach the end of their service life.

The only way to land with a "complete" flight control systems failure is via "the nylon let down system". It's the very last back up we have in the "Viper"..!!

Well technically we could glide in in a TOTAL flight control failure. But that all depends on airspeed and alitude. But that is for civi planes. The F-16 is a bit of a wonder for me. If I remember right when 927 when down at Nellis I heard a pilot say if he cut off the fuel supply and basically turned off the jet at approach to the runway he could have made it. But I see too many variables for that such as fuel load and config which he had a centerline, two wing tanks, and two travel pods. Any pilots know the dash 1 procedures for total flight control system failure. Besides saying goodbye to the aircraft?

You can only fly the jet if the FLCS is working otherwise as Raptor Claw mentioned the jet itself is designed as a very "unstable" jet thus giving you extreme maneuverability. But you have to have the flight control system operating either normally (even though you can fly it in a degraded mode), or the EPU can run the flight control system. But if you completely lose the flight controls then you're up the proverbial river and in need of the "NLS" Nylon Letdown System...!! Parachute that is...!!

The best reason to still have rudder pedals is for nose wheel steering (NWS) and braking. FBW does nothing for that, only way to stop is the pedals. I don't see that going away anytime soon.

YOU ARE NEVER GOING TO LOSE TOTAL FLIGHT CONTROLS DUE TO A FAULT IN THE FLCS SYSTEM ITS SELF!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I don't know how much more I can emphasize that. If you lose all power to the jet, of course, you will have total lose of FLCS. But you will never have a total FLCS failure attributed to the system its self. There are just way to many safe gaurds and fail safes built in. You only need one source of power (main gen, stby gen, epu gen, FLCS PMG, and aircraft batt) which are all quad redundant, one hyrdaulic system, one FLCS branch working.......blah blah blah....IT HAS NEVER HAPPENED AND IT NEVER WILL!!!! I dought if there is any procedures in the -1 for this. If this were to happen you better put your head back and pull the D-ring cause you're GOING to crash.

WOW! Okay, you don't have to yell, I get it ><

The question was simply whether an F-16 could "fly" if the FBW flight control system failed [in its entirety]. The question was not whether this would be likely to happen. It was a good theoretical question with a definite theoretical answer. The answer, as others have already stated, is no. No, the pilot has no way to control the F-16 if the FBW flight control system goes down. And since the aircraft relies on this flight control system to keep from going out of control, total loss of the flight control system would lead to total loss of control rather quickly. Even if this has 0.0001% chance of happening, we can still give this 14 year-old high school student a straight answer instead of a bunch of convoluted technospeak. The young man knows enough to know that the F-15 can still fly without its flight control computers. It can fly with only the hydromechanical flight controls, albeit not as well. It can also fly with only electrical signals if the hydromechanical system fails. In normal operation the hydromechanical flight controls are augmented by a "fly-by-wire" control system. They work together for optimal flight control, but either system can control jet by itself. Some people here need to learn how to answer a (good) theoretical question with the proper theoretical answer.

Thanks Raptor One.

Although I appreciate the info, about the probability of that happening.

Thanks again.

Now I just need to decide on what I want to fly.....hm....