Tod From Denmark, joined Aug 2004, 1682 posts, RR: 3 Reply 6, posted (7 years 5 months 1 week 1 day 14 hours ago) and read 2355 times:
Quoting Charliecossie (Reply 5): Can you tell us all which systems are FBW on the 744?
At least throttles, maybe more.
I learned this the hard way a few years ago. Somewhere about STA920, the side of body shear panels have cutouts for control cables and I was going to modify those panels. I spent days looking for the engineering that installed the cables that went through those cutouts with zero results. Eventually I looked at the control stand installation drawings and surprise surprise, just electrical connectors where you would have expected control cables.
Starlionblue From Hong Kong, joined Feb 2004, 15868 posts, RR: 66 Reply 8, posted (7 years 5 months 1 week 1 day 14 hours ago) and read 2335 times:
In the end, aircraft manufacturers will build the plane that customers want. Of course, with many customers, you will have to find a good compromise of their demands.
So:
Boeing customers still want a yoke instead of a sidestick, despite the added weight and more complex construction/maintenance.
If the majority of Boeing customers (by value) changed their minds and wanted a sidestick, I'm pretty sure Boeing would sell them a sidestick.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Tod From Denmark, joined Aug 2004, 1682 posts, RR: 3 Reply 10, posted (7 years 5 months 1 week 1 day 13 hours ago) and read 2297 times:
Quoting HAWK21M (Reply 9): Quoting Tod (Reply 6):
the side of body shear panels have cutouts for control cables and I was going to modify those panels.
Any Pics.
regds
MEL
Former SQ 744, STA955 / RBL125
The oval shaped cutout is provisions for two control cables routed to the engines. Of course the left side is the same. The blank brackets just inboard are for pulley supports.
Speedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0 Reply 11, posted (7 years 5 months 1 week 1 day 7 hours ago) and read 2207 times:
Quoting Tod (Reply 4): Some of the pulley and cable controlled systems on 741 - 743 were converted to FBW on the 744.
Quoting Charliecossie (Reply 5): Can you tell us all which systems are FBW on the 744?
Quoting Tod (Reply 6): At least throttles, maybe more.
I think the miscommunication here is that pretty much every modern airliner has FADEC, or digitally controlled throttles. But a FBW plane is quite different, as it employs computers to move all control surfaces based on inputs from a sidestick or yoke that isn't directly connected to servos or cables.
Quoting Razza74 (Thread starter): Airbus aircraft are all fly by wire, has Boeing taken this philosophy on board with it's range of aircraft, and why no sidestick?
The removal of pulleys and cables would greatly reduce overall weight
Seems like you're equating a traditional yoke in a FBW aircraft with pulleys and cables. If so, well I'm fairly certain there aren't any pulleys or cables in, for example, the FBW 777 or upcoming 787. Starlionblue gives a good explanation why Boeing has opted for a control yoke in its FWB planes above. If you're wondering why existing planes, such as the thoroughly modern 737NG don't have FBW, I've read numerous times on this board that it simply wouldn't have been economical for Boeing to redesign and certify such a substantial upgrade to an already proven design, weight savings or not.
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
Starlionblue From Hong Kong, joined Feb 2004, 15868 posts, RR: 66 Reply 12, posted (7 years 5 months 1 week 1 day 6 hours ago) and read 2179 times:
Quoting Speedracer1407 (Reply 11):
I think the miscommunication here is that pretty much every modern airliner has FADEC, or digitally controlled throttles. But a FBW plane is quite different, as it employs computers to move all control surfaces based on inputs from a sidestick or yoke that isn't directly connected to servos or cables.
The other misconception is about the implementation of FBW. The Airbus control systems that take inputs on the controls and "translate" them into a configuration for the surfaces (as opposed to proportional responses) could easily be achieved with mechanical cables instead of electronic linkages. Thus, FBW with "translation" (as on the 318-321, 330/340, 380, Gripen, Typhoon, Rafale) is quite different from the FBW on the 777 and 787. The difference is not in the cables, it's in the software that takes information from the pilots to the surfaces.
Speedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0 Reply 13, posted (7 years 5 months 1 week 1 day 3 hours ago) and read 2143 times:
Quoting Starlionblue (Reply 12): The Airbus control systems that take inputs on the controls and "translate" them into a configuration for the surfaces (as opposed to proportional responses) could easily be achieved with mechanical cables instead of electronic linkages.
Interesting. But how would a flight control system direct cables and/or hydrolics that "translated" control inputs into unproportional control surface responses without the "intelligence" of computers?
Quoting Starlionblue (Reply 12): Thus, FBW with "translation" (as on the 318-321, 330/340, 380, Gripen, Typhoon, Rafale) is quite different from the FBW on the 777 and 787. The difference is not in the cables, it's in the software that takes information from the pilots to the surfaces.
Much has been made, recently, of Airbus's FBW philosophy, what with hard limits and all. Several Airbus pilots have contributed, but I can't seem to recall reading posts from any 777 pilots on this forum. I'd love to hear from pilots and/or engineers who are familiar with the day in /out operation of Boeing's FBW philosophy, and how flying such a plane is different from flying either a modern Airbus or a non-FBW boeing.
O
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
Tristarsteve From Sweden, joined Nov 2005, 3689 posts, RR: 34 Reply 14, posted (7 years 5 months 1 week 1 day ago) and read 2127 times:
Quoting Charliecossie (Reply 5): Can you tell us all which systems are FBW on the 744?
The reason you havent got a reply yet is no-one can remember, and we all need to look in the book. From memory (I am at home)
The B744 has FBW throttles and flaps.
The A320 has steel cable controlled rudder.
The B777 control columns are connected to sensors and actuators. If the A/P is flying the aircraft the actuators move the control columns and throttles. The B777 has a couple of cable controlled spoilers.
As engineers we work on many different aircraft. I work on B777 B744 B757 B767 A319/20. All have varying degrees of FBW. Even the B757/B767 have FBW spoilers. The B767 has FBW throttles.
HiFi From Brazil, joined Apr 2005, 192 posts, RR: 0 Reply 16, posted (7 years 5 months 1 week 20 hours ago) and read 2080 times:
Quoting Speedracer1407 (Reply 11): If you're wondering why existing planes, such as the thoroughly modern 737NG don't have FBW, I've read numerous times on this board that it simply wouldn't have been economical for Boeing to redesign and certify such a substantial upgrade to an already proven design, weight savings or not.
Another reason is that the weight issue for aircraft the size of a 737 is questionnable... a FBW control system means a LOT of wire...
As to "direct control" versus "translated inputs", a FBW aircraft can have both, with a yoke or with a sidestick.
FBW only means that there aren't any mechanical linkages (cables, pulleys, rods, ...) and that the control device (yoke/column or sidestick) is monitored by position sensors that send the position information through wires to the actuators for them to respond accordingly. It does not assume that a computer applies control laws. The system can be analog or digital. Digital is easier if you want to put a computer in the loop enhancing or modulating pilot commands.
When a computer is in the loop, it gives the pilot the opportunity of commanding the aircraft by inputing an attitude, instead of a surface deflection. When pulling on the sidestick or column, the aircraft interprets it as "give me a 5º positive pitch" and commands the surfaces in order to achieve and maintain a 5º pitch attitude. When directly controlling the surfaces, by pulling on the column or sidestick, the pilot will command the elevators proportionally and the resulting pitch angle will depend on aircraft speed and AOA. The pilot will have to trim the aircraft in order to maintain the 5º pitch attitude.
FBW also gives you the choice of using force feedback or not, whether you use a yoke or a sidestick.
I don't know the 777 and 787 well enough to say if their s/w "translates" pilot inputs, but I believe it does. Do we have any 777 pilots here? When pulling on the column, do you command pitch or elevator deflection? The huge difference between Airbus and Boeing philosophies is envelope protection (BOTH use envelope protection), but that's a whole different discussion!
Starlionblue From Hong Kong, joined Feb 2004, 15868 posts, RR: 66 Reply 18, posted (7 years 5 months 1 week 20 hours ago) and read 2069 times:
Quoting Speedracer1407 (Reply 13): Quoting Starlionblue (Reply 12):
The Airbus control systems that take inputs on the controls and "translate" them into a configuration for the surfaces (as opposed to proportional responses) could easily be achieved with mechanical cables instead of electronic linkages.
Interesting. But how would a flight control system direct cables and/or hydrolics that "translated" control inputs into unproportional control surface responses without the "intelligence" of computers?
You would still need computers. They would be driving servos that drove mechanical cables that drove surfaces.
Quoting HiFi (Reply 16): As to "direct control" versus "translated inputs", a FBW aircraft can have both, with a yoke or with a sidestick.
Indeed, and if a FBW Airbus reverts down from normal law do direct law yo upretty much get "direct control", that is proportional.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Klaus From Germany, joined Jul 2001, 20845 posts, RR: 55 Reply 19, posted (7 years 2 months 3 weeks 2 days 19 hours ago) and read 1814 times:
Quoting HiFi (Reply 16): Another reason is that the weight issue for aircraft the size of a 737 is questionnable... a FBW control system means a LOT of wire...
Not necessarily. At least the A380 (and probably the 787) has a modified ethernet networking system, which uses packetized information flow. A single cable can accomodate multiple signal flows simultaneously, and intelligent routers can automatically circumvent faulty cables if required. This way you can both save weight and increase redundancy and safety at the same time.
DfwRevolution From , joined Dec 1969, posts, RR: Reply 20, posted (7 years 2 months 3 weeks 2 days 17 hours ago) and read 1799 times:
Quoting Klaus (Reply 19): Not necessarily. At least the A380 (and probably the 787) has a modified ethernet networking system, which uses packetized information flow. This way you can both save weight and increase redundancy and safety at the same time.
In the case of the 737NG, it really doesn't matter. The 737NG is lighter than its respective A320 counterparts, so there was little reason for Boeing to shell out millions of dollars when there is little value to be gained.
It doesn't always make sense to implement technology just for the sake of technology.
Jetlagged From United Kingdom, joined Jan 2005, 2452 posts, RR: 17 Reply 21, posted (7 years 2 months 2 weeks 6 days 16 hours ago) and read 1633 times:
Quoting Klaus (Reply 19): At least the A380 (and probably the 787) has a modified ethernet networking system, which uses packetized information flow. A single cable can accomodate multiple signal flows simultaneously, and intelligent routers can automatically circumvent faulty cables if required.
ARINC 429 buses have carried multiplexed digital flight control signals, in the form of digital words with a label and direction indicator (SDI) for many years (in one direction and without intelligent routing of course). The 777 introduced ARINC 629 which allows bi-directional databuses.
An ARINC 429 word is not really a packet in ethernet terms but it is a self contained packet of information (including data, status, label number, SDI, parity, etc) which only the addressed equipment will read, other equipment on the bus ignores it.
The wires used are shielded twisted pairs, very light compared to control cables. Early analogue FBW (e.g. Concorde) did require heavier gauge wires but data could still be mechanicaly multiplexed.
I think the main reason Boeing didn't put FBW on the 737NG was that the aircraft would have had to be re-certified at great cost, for no real gain. FBW technology is only any benefit if applied from original design.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
CCA From Hong Kong, joined Oct 2002, 707 posts, RR: 14 Reply 23, posted (7 years 2 months 2 weeks 6 days 16 hours ago) and read 1614 times:
777 FBW
The actuator control electronics (ACEs) receive input signals from all pilot controls. In the normal mode during manual flight, the ACEs receive pilot control inputs and send these signals to the three Primary Flight Computers (PFCs). The PFCs verify these signals and information from other airplane systems in order to compute control surface commands. These commands are then sent back to the ACEs. The ACEs send enhanced signals to the flight control surface actuators.
Flight Envelope Protection
The flight envelope protection system reduces the possibility of inadvertently exceeding the airplane's flight envelope. The flight envelope protection system provides crew awareness of envelope margins through tactile, aural, and visual cues. The protection functions do not reduce pilot control authority.
Normal Mode Pitch Control
In the normal mode, airplane pitch control characteristics are like conventional airplanes, with improved handling qualities. Unlike conventional airplanes, the control column does not directly position the elevator in flight. The control column commands the PFCs to generate a pitch maneuver. The PFCs automatically position the elevator and the stabilizer to generate the commanded maneuver. The PFCs constantly monitor airplane response to pilot commands and reposition the elevator and stabilizer to carry out these commands. Airplane pitch responses to thrust changes, gear configuration changes, and turbulence are automatically minimized by PFC control surface commands.
The PFCs also provide compensation for flap and speedbrake configuration changes, and turns up to 30° of bank. The PFCs automatically control pitch to maintain a relatively constant flight path. This eliminates the need for the pilot to make control column inputs to compensate for these factors. For turns up to 30° of bank, the pilot does not need to add additional column back pressure to maintain altitude. For turns of more than 30° of bank, the pilot does need to add column back pressure. As airspeed changes, the PFCs provide conventional pitch control characteristics by requiring the pilot to make control column inputs or trim changes to maintain a constant flight path.
Elevator Variable Feel
The PFCs calculate feel commands based on airspeed. In general, control column forces increase:
• as airspeed increases for a given column displacement, or
• as column displacement increases.
Klaus From Germany, joined Jul 2001, 20845 posts, RR: 55 Reply 24, posted (7 years 2 months 1 week 2 days 17 hours ago) and read 1438 times:
Quoting Jetlagged (Reply 21): An ARINC 429 word is not really a packet in ethernet terms but it is a self contained packet of information (including data, status, label number, SDI, parity, etc) which only the addressed equipment will read, other equipment on the bus ignores it.
That is pretty much exactly how every serial bus communication works, including ethernet...
25 Gr8Circle: ALL Airbus aircraft are not FBW...the older A300 and 310 were not....it started with the A320....
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