AF 447 Search to resume (part2)
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes
on
0 Posts
Tubby,
Geez, I can see what you mean with all the fuel tanks completely full on an empty aircraft. The total weight would be equal to the maximum TOW, actually, slightly more.
From the Airbus CG chart, I calculate the max operating aft CG limit of 39% @ 205 tons and your 37% estimate pretty much coincides with the BEA projection at the time of the incident.
Thanks for your input on the fuel transfer to and from the trim tanks, I was trying to understand how this might work.
Geez, I can see what you mean with all the fuel tanks completely full on an empty aircraft. The total weight would be equal to the maximum TOW, actually, slightly more.
From the Airbus CG chart, I calculate the max operating aft CG limit of 39% @ 205 tons and your 37% estimate pretty much coincides with the BEA projection at the time of the incident.
Thanks for your input on the fuel transfer to and from the trim tanks, I was trying to understand how this might work.
Join Date: Aug 2009
Location: Germany
Age: 67
Posts: 1,777
Likes: 0
Received 0 Likes
on
0 Posts
Hi,
The BEA is actually under enormous pressures coming from any directions.
Methink it will be a official BEA communication (and information) before the former date announced by the BEA
Google Vertaling
Original press article
Vol AF447 : Il n'y aurait pas eu d'erreur de pilotage | France Soir
The press has a bone to chew on and she is not ready to let go prior to arrival at the spinal
The BEA is actually under enormous pressures coming from any directions.
Methink it will be a official BEA communication (and information) before the former date announced by the BEA
Google Vertaling
Original press article
Vol AF447 : Il n'y aurait pas eu d'erreur de pilotage | France Soir
The press has a bone to chew on and she is not ready to let go prior to arrival at the spinal
Join Date: Jun 2009
Location: Virginia
Posts: 141
Likes: 0
Received 0 Likes
on
0 Posts
Air France-KLM delays a major(1) aircraft purchase till after the Paris Air Show.
Air France repousse l'annonce d'une commande de 100 long-courriers - Le Point
(1) 100 A350 or 787 @ $250M a piece.
May be Airbus will have some eye-to-eye talk with some newspapers...
Air France repousse l'annonce d'une commande de 100 long-courriers - Le Point
(1) 100 A350 or 787 @ $250M a piece.
May be Airbus will have some eye-to-eye talk with some newspapers...
Join Date: Jan 2005
Location: W of 30W
Posts: 1,916
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by HN39
The curious thing is that the threshold did not change to 10° when the speeds became invalid.
Rely on the stall warning that could be triggered in alternate or direct law. It is not affected by unreliable speeds, because it is based on AoA.
I must say this ACA note is terrific. Congratulation to Mister HOUANG. Not much to see with the usual bla bla of a BEA report ...
If I may be permitted to add one more thing about flight simulation...
As good as they are for achieving the objectives they're intended for, the term Full Flight Simulator (FFS) will probably remain a misnomer, regardless of any eventual envelope expansion with regards to the flight data package.
There is one real world factor that is extremely difficult, if not impossible, to generate in an FFS...
FEAR
As good as they are for achieving the objectives they're intended for, the term Full Flight Simulator (FFS) will probably remain a misnomer, regardless of any eventual envelope expansion with regards to the flight data package.
There is one real world factor that is extremely difficult, if not impossible, to generate in an FFS...
FEAR
Join Date: May 2010
Location: USA
Age: 76
Posts: 18
Likes: 0
Received 0 Likes
on
0 Posts
deSitter,
My piloting background is limited to Piper and Cessna, but I have 40+ years in all levels of computer software, hardware, testing, etc. on systems of various sizes. I agree with your take on giving the human the option to shut the computer out of the loop. Our ability to implement complex computer systems surpasses our ability to sufficiently test them or to fully comprehend subtle changes made to software. It is not that people are incompetent, or that excellent tools are not available; it is that we are not perfect, and neither is the software we develop. Minor miscommunications and software glitches brought down an Ariane V, destroyed a Mars lander, forced F-122 fighters to return to base, caused an Airbus to make an unexpected descent, and updated our smart phone clocks incorrectly. I, for one, think there should be a big red "Give Me The Helm" button because there will be more incidents - we just don't know what they will be. I agree, too, with your description of people frozen by unexpected or irrational results - the "deer in the headlights" - especially in times of high stress.
Thanks to you all for the exceptional information on this site from obviously very capable professionals. It is a tremendously enlightening and rewarding read for this VFR pilot.
Thanks to you all for the exceptional information on this site from obviously very capable professionals. It is a tremendously enlightening and rewarding read for this VFR pilot.
Join Date: May 2010
Location: MA, USA
Posts: 126
Likes: 0
Received 0 Likes
on
0 Posts
Laser gyros and survival of a CSMU
Sorry to reply late to a couple of topics, but I've been either off the net or very busy the past few days.
--
Ring laser gyros measure changes in angular orientation, and, as previously mentioned by JD-EE, are commonly installed in a "strap-down" configuration (always aligned with the axes of the aircraft or other platform), rather than, as in the older precision inertial nav systems, with the mechanical gyro mounted on a plate having 3- or 4-axis motor drive to keep the gyro erect in an inertial frame, while the aircraft (missile, whatever) rotated around it. That difference is mainly an interesting point, a laser gyro could be installed either way.
Ring laser gyros that have been incorporated into an inertial navigation system (with suitable mathematics), are used, along with accelerometers, to provide the short-term attitude (actually a very long, short-term, since the laser gyros have such low drift), while the accelerometers provide long-term attitude (gravity reference) and accelerations along the axes to integrate into position. (The latter - double integration of accelerations - is where a lot of drift in INS systems comes from, and thus the requirement for some sort of aiding; in a modern aircraft, that aiding would come primarily from GPS and the altimeter).
That is all background for a discussion of tumbling. Tumbling of a mechanical 3-axis gyro (which trys to stay aligned in an inertial frame), occurs when two of the gimbals supporting the gyroscope happen to align, a state known as gimbal-lock, which can physically yank the gyro's spin axis off its original alignment to some other direction. This is bad because it takes a long time, using other aiding, to re-erect the gyro. More sophisticated systems may use 4-axis gimbals, which are steered so that no two ever align.
A strap-down system can suffer a related effect if the mathematical attitude solution involves only the three axes: roll, pitch and yaw. The problem occurs when pitch becomes near vertical and yaw becomes indeterminate. The vehicles that I have worked with are incapable of approaching pitch of +/-90 degrees, and so I cheat and use only roll, pitch and yaw. I'm not sure if, in an INS, this might cause loss of short-term attitude accuracy, or if it will recover a correct indication as soon as the platform leaves the vertical. However, this should never happen, because there is a mathematical construct known as "quaternions" that avoids this problem (don't ask me, I don't know); I suspect that it is a mathematical equivalent to the 4-axis mechanical solution. Hopefully, any aircraft INS is thus designed to avoid mathematical "gimbal-lock".
One more point about laser gyros in INS systems: they allow the system to perform the function of a gyro-compass. After a short alignment period, using the accelerometers and the rotation of the earth, an INS not only knows which way is up (down) but also the direction of true north. The laser gyro INS systems that I am (a little) familiar with acquire true north to an accuracy of a few tenths of a degree within 10 minutes of a cold start, as compared with 6 hours for a mechanical gyro-compass typically used on a ship. This alignment does not drift, even when the platform is in motion.
--
CSMU:
I will begin by confirming that I know nothing about the design of any CSMU in flight recorders, except what I have read on the web. However, I do know a lot about designing electronics for the deep ocean.
Some of the prior discussion, about whether or not to open the recorder, and how water might be detected inside, seems to be "misplaced". It was made clear by BEA at the press conference held the day the recorders arrived in Paris, that the following steps would be performed: open the case, wash the memory board in deionized water, dry the board in a oven, microscopically inspect the board (and, if I recall correctly, repair any obvious damage), and only then try to read the memory.
I do not think that CSMUs are designed the way many posters think, nor the way I would design a typical deep-sea system. Without quoting the dozen or so pages I found (sorry, hurrying), I'm not convinced that a CSMU is actually intended to be water-tight in the sense that a typical pressure housing is sealed and has pressure-proof penetrations for wires. CSMU designs appear to vary considerably between vendors, and are kept as trade secrets or may alternatively be patented.
In the descriptions I have seen, the outer shell, stainless or titanium, is not thick enough (at 1/4 inch) to act, alone, as a pressure housing at 6000 meters depth (20,000 psi, sorry for the mixed metric/English units, I use the MKSA system, but still have not internalized Pascals). It would collapse but for one or both of two mechanisms: either it is designed to leak (not sealed at all) and/or it is internally supported by incompressible materials.
The next layer inward is typically thermal insulation. One reference identifies this as "silica" which is a mineral and is possibly packed densely enough to support the shell, but I wonder how good its insulation properties would be if it were packed that hard.
The next layer is the thermal mass (works in conjunction with the insulation to limit the temperature inside. In some designs, this is identified as paraffin, with the phase change providing the primary heat absorption. This opens the possibility that the paraffin is also used as a water block.
The description of the Honeywell data recorder, which has been previously linked in this forum, mentions that their CSMU "uses modular "dry-block" materials for both the insulating liner and thermal mass, there is no need to deal with the sticky thermal gels or special insulating fluids." This implies to me that it is common to protect the memory boards from water with gel or fluid, rather than using an enormous increase in weight to make the CSMU a traditional pressure vessel. It is also possible that I am wrong about that, and the gels/fluids are secondary protection; in which case, the outer shell must be water tight and adequately supported internally.
It is possible that the boards are conformal coated with something that will resist water for a long time. I am speculating about that; I did not find that mentioned in any reference.
Note well that it is not necessary to protect the memory chips from pressure, only (possibly) from water. Epoxy encapsulated integrated circuits (the most common and inexpensive packaging) do not have voids, and so there is no space to implode, which would subsequently damage the die (circuit) inside. [There are some special devices, such as solid-state accelerometers and pressure sensors, that require a void space to operate, and thus they are not pressure tolerant, beyond the strength of the case.]
While we normally deploy complex electronics in pressure cases, we have also designed and tested numerous "pressure-tolerant" circuits that operate in an oil filled space that is equalized to ambient pressure. Appropriately packaged semiconductors; ceramic, mica, and some solid tantalum capacitors; most resistors; carefully characterized inductors (core materials can change properties with pressure); ordinary wire and connectors; and many other components; all work fine at pressures of 20,000 psi and even greater.
--
Ring laser gyros measure changes in angular orientation, and, as previously mentioned by JD-EE, are commonly installed in a "strap-down" configuration (always aligned with the axes of the aircraft or other platform), rather than, as in the older precision inertial nav systems, with the mechanical gyro mounted on a plate having 3- or 4-axis motor drive to keep the gyro erect in an inertial frame, while the aircraft (missile, whatever) rotated around it. That difference is mainly an interesting point, a laser gyro could be installed either way.
Ring laser gyros that have been incorporated into an inertial navigation system (with suitable mathematics), are used, along with accelerometers, to provide the short-term attitude (actually a very long, short-term
, since the laser gyros have such low drift), while the accelerometers provide long-term attitude (gravity reference) and accelerations along the axes to integrate into position. (The latter - double integration of accelerations - is where a lot of drift in INS systems comes from, and thus the requirement for some sort of aiding; in a modern aircraft, that aiding would come primarily from GPS and the altimeter).That is all background for a discussion of tumbling. Tumbling of a mechanical 3-axis gyro (which trys to stay aligned in an inertial frame), occurs when two of the gimbals supporting the gyroscope happen to align, a state known as gimbal-lock, which can physically yank the gyro's spin axis off its original alignment to some other direction. This is bad because it takes a long time, using other aiding, to re-erect the gyro. More sophisticated systems may use 4-axis gimbals, which are steered so that no two ever align.
A strap-down system can suffer a related effect if the mathematical attitude solution involves only the three axes: roll, pitch and yaw. The problem occurs when pitch becomes near vertical and yaw becomes indeterminate. The vehicles that I have worked with are incapable of approaching pitch of +/-90 degrees, and so I cheat and use only roll, pitch and yaw. I'm not sure if, in an INS, this might cause loss of short-term attitude accuracy, or if it will recover a correct indication as soon as the platform leaves the vertical. However, this should never happen, because there is a mathematical construct known as "quaternions" that avoids this problem (don't ask me, I don't know
); I suspect that it is a mathematical equivalent to the 4-axis mechanical solution. Hopefully, any aircraft INS is thus designed to avoid mathematical "gimbal-lock".One more point about laser gyros in INS systems: they allow the system to perform the function of a gyro-compass. After a short alignment period, using the accelerometers and the rotation of the earth, an INS not only knows which way is up (down) but also the direction of true north. The laser gyro INS systems that I am (a little) familiar with acquire true north to an accuracy of a few tenths of a degree within 10 minutes of a cold start, as compared with 6 hours for a mechanical gyro-compass typically used on a ship. This alignment does not drift, even when the platform is in motion.
--
CSMU:
I will begin by confirming that I know nothing about the design of any CSMU in flight recorders, except what I have read on the web. However, I do know a lot about designing electronics for the deep ocean.
Some of the prior discussion, about whether or not to open the recorder, and how water might be detected inside, seems to be "misplaced". It was made clear by BEA at the press conference held the day the recorders arrived in Paris, that the following steps would be performed: open the case, wash the memory board in deionized water, dry the board in a oven, microscopically inspect the board (and, if I recall correctly, repair any obvious damage), and only then try to read the memory.
I do not think that CSMUs are designed the way many posters think, nor the way I would design a typical deep-sea system. Without quoting the dozen or so pages I found (sorry, hurrying), I'm not convinced that a CSMU is actually intended to be water-tight in the sense that a typical pressure housing is sealed and has pressure-proof penetrations for wires. CSMU designs appear to vary considerably between vendors, and are kept as trade secrets or may alternatively be patented.
In the descriptions I have seen, the outer shell, stainless or titanium, is not thick enough (at 1/4 inch) to act, alone, as a pressure housing at 6000 meters depth (20,000 psi, sorry for the mixed metric/English units, I use the MKSA system, but still have not internalized Pascals
). It would collapse but for one or both of two mechanisms: either it is designed to leak (not sealed at all) and/or it is internally supported by incompressible materials. The next layer inward is typically thermal insulation. One reference identifies this as "silica" which is a mineral and is possibly packed densely enough to support the shell, but I wonder how good its insulation properties would be if it were packed that hard.
The next layer is the thermal mass (works in conjunction with the insulation to limit the temperature inside. In some designs, this is identified as paraffin, with the phase change providing the primary heat absorption. This opens the possibility that the paraffin is also used as a water block.
The description of the Honeywell data recorder, which has been previously linked in this forum, mentions that their CSMU "uses modular "dry-block" materials for both the insulating liner and thermal mass, there is no need to deal with the sticky thermal gels or special insulating fluids." This implies to me that it is common to protect the memory boards from water with gel or fluid, rather than using an enormous increase in weight to make the CSMU a traditional pressure vessel. It is also possible that I am wrong about that, and the gels/fluids are secondary protection; in which case, the outer shell must be water tight and adequately supported internally.
It is possible that the boards are conformal coated with something that will resist water for a long time. I am speculating about that; I did not find that mentioned in any reference.
Note well that it is not necessary to protect the memory chips from pressure, only (possibly) from water. Epoxy encapsulated integrated circuits (the most common and inexpensive packaging) do not have voids, and so there is no space to implode, which would subsequently damage the die (circuit) inside. [There are some special devices, such as solid-state accelerometers and pressure sensors, that require a void space to operate, and thus they are not pressure tolerant, beyond the strength of the case.]
While we normally deploy complex electronics in pressure cases, we have also designed and tested numerous "pressure-tolerant" circuits that operate in an oil filled space that is equalized to ambient pressure. Appropriately packaged semiconductors; ceramic, mica, and some solid tantalum capacitors; most resistors; carefully characterized inductors (core materials can change properties with pressure); ordinary wire and connectors; and many other components; all work fine at pressures of 20,000 psi and even greater.
Last edited by auv-ee; 20th May 2011 at 17:50.
Join Date: Aug 2007
Location: London, New York, Paris, Moscow.
Posts: 3,632
Likes: 0
Received 0 Likes
on
0 Posts
Air France-KLM delays a major(1) aircraft purchase till after the Paris Air Show.
Air France repousse l'annonce d'une commande de 100 long-courriers - Le Point
(1) 100 A350 or 787 @ $250M a piece.
May be Airbus will have some eye-to-eye talk with some newspapers...
Air France repousse l'annonce d'une commande de 100 long-courriers - Le Point
(1) 100 A350 or 787 @ $250M a piece.
May be Airbus will have some eye-to-eye talk with some newspapers...
Join Date: Aug 2009
Location: Germany
Age: 67
Posts: 1,777
Likes: 0
Received 0 Likes
on
0 Posts
Hi,
Le Figaro belong to Dassault
Dassault Group - Wikipedia, the free encyclopedia
Dassault is a big shares older of Airbus (Airbus is part of EADS)
EADS Global Website - En
Is it LE FIGARO belongs to Airbus
Dassault Group - Wikipedia, the free encyclopedia
Dassault is a big shares older of Airbus (Airbus is part of EADS)
EADS Global Website - En
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes
on
0 Posts
glad rag,
How so? A customer with a potential $25B order paints himself into a corner?
AF/KLM paints themselves even further into "coffin corner" IF this is to be believed.
Join Date: Feb 2011
Location: Australia
Age: 63
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
Gratuitous Swipe not appreciated
Whilst desitter has previously outed himself as a sceptic of the FBW model of modern aviation, I believe he poses a reasonable question that is undeserving of the gratuitous swipe levelled at him by machaca.
It appears that desitter’s question is framed as a statement (with the possibly offensive “on top of the curve” and “up to snuff with modernity” assertions). Nonetheless, it is a question in my reading, which is: why are so many of the pilots on this forum so vehement in their defense of the FBW computer-controlled flight model?
I, too, would like a reasoned answer to this question. What do the pilots know that the non-pilots do not know/understand.
I am not a sceptic of FBW as desitter appears to be, but, as a designer of computer systems and with three decades experience in the computer/electronics industry designing/testing non-life-dependant systems and a WAIS score of 135, I believe I could understand your explanations should you care to share them.
As SLF, I’d like to know that if/when the computer throws up its metaphorical hands, the pilot in command has the training/experience/skills to take control of the aircraft and fly it in what has often been referred to in this forum as “stick-and-rudder” mode.
I’m interested to know what are the preconditions for such an eventuality (that is, the need for stick-and-rudder flight)? What are the minimum systems/displays required for the pilot to achieve control of the aircraft once the computer has relinquished it to the pilot?
Footnote:
It is a frightening proposition to me – and I suspect many others - that a computer (programmed by a team of experts in the fields of aviation, software, electronics and control systems) with multiple redundancies inherent in its design can get to a point where its received data from all its sources “does not compute” and at that point it relinquishes control to two people trained only* as pilots; at which point they are expected to do something with the beast that the computer(s) could not – that is, bring it back under control.
*NB: I have the utmost respect for pilots and their training and I am confident to fly again in the future.
My point is, there are just two of them and they are in a pressure-cooker situation. The team of designers and programmers have between them a breadth of knowledge and expertise that the pilots could never hope to emulate in the midst of a crisis.
It appears that desitter’s question is framed as a statement (with the possibly offensive “on top of the curve” and “up to snuff with modernity” assertions). Nonetheless, it is a question in my reading, which is: why are so many of the pilots on this forum so vehement in their defense of the FBW computer-controlled flight model?
I, too, would like a reasoned answer to this question. What do the pilots know that the non-pilots do not know/understand.
I am not a sceptic of FBW as desitter appears to be, but, as a designer of computer systems and with three decades experience in the computer/electronics industry designing/testing non-life-dependant systems and a WAIS score of 135, I believe I could understand your explanations should you care to share them.
As SLF, I’d like to know that if/when the computer throws up its metaphorical hands, the pilot in command has the training/experience/skills to take control of the aircraft and fly it in what has often been referred to in this forum as “stick-and-rudder” mode.
I’m interested to know what are the preconditions for such an eventuality (that is, the need for stick-and-rudder flight)? What are the minimum systems/displays required for the pilot to achieve control of the aircraft once the computer has relinquished it to the pilot?
Footnote:
It is a frightening proposition to me – and I suspect many others - that a computer (programmed by a team of experts in the fields of aviation, software, electronics and control systems) with multiple redundancies inherent in its design can get to a point where its received data from all its sources “does not compute” and at that point it relinquishes control to two people trained only* as pilots; at which point they are expected to do something with the beast that the computer(s) could not – that is, bring it back under control.
*NB: I have the utmost respect for pilots and their training and I am confident to fly again in the future.
My point is, there are just two of them and they are in a pressure-cooker situation. The team of designers and programmers have between them a breadth of knowledge and expertise that the pilots could never hope to emulate in the midst of a crisis.
Last edited by andianjul; 20th May 2011 at 02:08. Reason: Oops, a bit failed in the cut and paste.
Join Date: Jan 2008
Location: Herts, UK
Posts: 748
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by deSitter
CogSim - that's exactly right, and it's the point I'm trying to make. It's not enough to just be able to turn off the FMC - there has to be a designed-in envelope of stability that is familiar to crew and instantly available, and that will stimulate their natural instincts, not present them with puzzlers that eat into their situational awareness.
Join Date: Jun 2010
Location: SBA
Age: 56
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
Basic flight controls, a functioning attitude indicator, some running engines and their associated power displays, and an altimeter or equivalent are enough to get you out of trouble in cruise.
What are the minimum systems/displays required for the pilot to achieve control of the aircraft once the computer has relinquished it to the pilot?
"When did you stop beating your wife?"
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by deSitter
If computers are going to fly airplanes, then they must do so under complete command of the crew, and in a sudden control emergency, it is senseless to lack an instant "GIMME" switch, that turns the airplane into a very big stick-and-rudder platform.
b) even so, the captain do select his course, speed, flight level, etc., the computers do not. He is in full charge of the flight.
c) both autopilot and autothrust can maintain a safe flight, only if certain flight parameters are not exceeded.
d) at any time, the captain may decide to take over and revert to manual flight.
e) in manual flight, flight envelope protections do not "fly" the aircraft, neither do drive your car an ABS instead of you; if you still have some flight envelope protection working, then, there is no more reason to turn them off than to disconnect your ABS if you were on the edge of losing control of your car; once control is lost, you may kill yourself, but an ABS can also save you if you need to use your brakes more efficiently.
Originally Posted by deSitter
I have no doubt that in the end, we'll find out that the crew lost precious time trying to figure out what to do with the FMC
Originally Posted by deSitter
or even as someone suggested earlier, put the AP back in charge when that was sure to lead to disaster.
b) nonetheless, this end result would not be due to computers choice but to captain action; if captain think that airspeed is reliable when it is not, who is to blame?
c) can't you see the paradoxe: if one had to "fight" (like you said) with such computer, why would he give the computer its full control back in a hurry without even trying to fly his aircraft?
Originally Posted by deSitter
I have no idea why some professional aviators are so adamant, to the point of irrationality, in their defense of flight computers.
Originally Posted by deSitter
Perhaps it is the human need to feel "on top of the curve" and "up to snuff" with modernity. No one is arguing that FMCs are not a great idea for normal flight - but when it becomes an end in itself, something has gone off the rails.
Join Date: Aug 2009
Location: Germany
Age: 67
Posts: 1,777
Likes: 0
Received 0 Likes
on
0 Posts
Hi,
And of course a speed indicator.
Seem's the AF447 had one .. but unfortunately the speed show was not the real one ......
That's complicated somewhat the "get you of the trouble in cruise"
Basic flight controls, a functioning attitude indicator, some running engines and their associated power displays, and an altimeter or equivalent are enough to get you out of trouble in cruise.
Seem's the AF447 had one .. but unfortunately the speed show was not the real one ......
That's complicated somewhat the "get you of the trouble in cruise"
Thread Starter
Defense of FBW
Salute!
First thing I want to make clear - if anyone here has flown a fully fly-by-wire plane with zero mechanical backup before 1979, then speak up. Even the Airbus has a mechanical linkage with the stabilizer ( slow, but still mechanical). The jet I flew, as with the Space Shuttle had ZERO mechanical connections or hydraulic connections between the pilot and the control surfaces. It was all electric, with computers in the way.
That being said, if anyone questions my trust in FBW, then look at the pic I posted of a wounded jet that I landed after a few harrowing minutes. The FBW system saved me from punching out, and I doubt any normal jet would have given me the opportunity to continue flying and then land the damned thing.
++++++++++++++++++++++++++++++++++
All must realize that the FBW system I flew and the ones other vehicles have flown with since then do not simply convert pressure or control movement to direct movement of all the control surfaces. None!
Most have limits as to control surface movement rates and those rates are adjusted for dynamic pressure, mach, etc. So a ten pound pull might move the elevator a few degrees at 0.78 M, but move the same elevator 10 or 15 degrees when approaching the field with gear down.
Some systems place a premium upon AoA, and this too is varied according to the plane's configuration for landing or cruising or fighting.
The gee limits are the easiest to program and fly with.
With all of the above in mind, I have tried to show that flying about with a cosmic computer-assisted flight control system is not fool proof. With virtually no limits compared to the Airbus, we quickly found a way to beat the computers and wind up in a deep stall. It was a combo of aero and aft center of gravity. We couldn't get out unless we could turn off the computer control of our elevator. Only the elevator. This is prolly not a great idea for the Airbus, but who knows?
PLZ revisit the F-16 'Semper Viper" articles I have posted.
My problem with the Airbus fly-by-wire implementation is two-fold: 1) Too damned many reversion sequences and autopilot connections with the flight control computers with their laws and sub-laws and sub-sub-laws....., then 2) Flying with aft c.g. that most planes would not be certified for.
In the Viper we had to live with a possibility of getting into a deep stall and then using the manual pitch override to "rock" outta the thing. Heh heh, I am sure the PAX would like that ride in the 'bus. Until we got a bigger horizontal tail we balanced fuel forward until coming back home. This did not completely preclude a deep stall, but it significantly reduced the probability, as well as helping to get outta one quickly.
I do not recommend a "direct" control of the elevator in the Airbus for several reasons, so we have to live with what we can control tomorrow, and then maybe re-visit the reversion sequences and control rates, limits, etc.
No reason to fly with an extreme aft c.g. when there is the possibility of prolonged turbulence. I am talking about a CB and not clear air turbulence that exists for 20 or 30 seconds.
much more to discuss, but just back from TDY and have to think more.
First thing I want to make clear - if anyone here has flown a fully fly-by-wire plane with zero mechanical backup before 1979, then speak up. Even the Airbus has a mechanical linkage with the stabilizer ( slow, but still mechanical). The jet I flew, as with the Space Shuttle had ZERO mechanical connections or hydraulic connections between the pilot and the control surfaces. It was all electric, with computers in the way.
That being said, if anyone questions my trust in FBW, then look at the pic I posted of a wounded jet that I landed after a few harrowing minutes. The FBW system saved me from punching out, and I doubt any normal jet would have given me the opportunity to continue flying and then land the damned thing.
++++++++++++++++++++++++++++++++++
All must realize that the FBW system I flew and the ones other vehicles have flown with since then do not simply convert pressure or control movement to direct movement of all the control surfaces. None!
Most have limits as to control surface movement rates and those rates are adjusted for dynamic pressure, mach, etc. So a ten pound pull might move the elevator a few degrees at 0.78 M, but move the same elevator 10 or 15 degrees when approaching the field with gear down.
Some systems place a premium upon AoA, and this too is varied according to the plane's configuration for landing or cruising or fighting.
The gee limits are the easiest to program and fly with.
With all of the above in mind, I have tried to show that flying about with a cosmic computer-assisted flight control system is not fool proof. With virtually no limits compared to the Airbus, we quickly found a way to beat the computers and wind up in a deep stall. It was a combo of aero and aft center of gravity. We couldn't get out unless we could turn off the computer control of our elevator. Only the elevator. This is prolly not a great idea for the Airbus, but who knows?
PLZ revisit the F-16 'Semper Viper" articles I have posted.
My problem with the Airbus fly-by-wire implementation is two-fold: 1) Too damned many reversion sequences and autopilot connections with the flight control computers with their laws and sub-laws and sub-sub-laws....., then 2) Flying with aft c.g. that most planes would not be certified for.
In the Viper we had to live with a possibility of getting into a deep stall and then using the manual pitch override to "rock" outta the thing. Heh heh, I am sure the PAX would like that ride in the 'bus. Until we got a bigger horizontal tail we balanced fuel forward until coming back home. This did not completely preclude a deep stall, but it significantly reduced the probability, as well as helping to get outta one quickly.
I do not recommend a "direct" control of the elevator in the Airbus for several reasons, so we have to live with what we can control tomorrow, and then maybe re-visit the reversion sequences and control rates, limits, etc.
No reason to fly with an extreme aft c.g. when there is the possibility of prolonged turbulence. I am talking about a CB and not clear air turbulence that exists for 20 or 30 seconds.
much more to discuss, but just back from TDY and have to think more.
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Khashoggi
You don't need a speed indicator to keep out of trouble in cruise. Pitch, power, altitude, and attitude.
Originally Posted by gums
2) Flying with aft c.g. that most planes would not be certified for.
Beside, there is few differences between combat aircraft flight envelope and airliners ones, as far as pure "flying abilities" are concerned.
Last edited by Jetdriver; 20th May 2011 at 08:22.