Airbus FBW - some technical q's
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Airbus FBW - some technical q's
Hi folks!
Not being an airbus driver, I was wondering about the FBW system - especially what target values you set with the Sidestick (as that is what I understand you do)
So basically, if you pitch up to, say, 10°, and let the sidestick go, what will it hold?
Will it be those 10° or will it be a 1 G load?
If its pitch, then theoretically, as you speed up, the aircraft will start to climb and if you fly slower, she will descend.
If its G Load, then the aircraft should start a descent if you increase bank angle, correct?
Or is it something completely different?
Regarding the X axis, I guess you simply set the angular acceleration and if you let go at a specific bank angle, it will hold that.
Thanks,
Mark
Not being an airbus driver, I was wondering about the FBW system - especially what target values you set with the Sidestick (as that is what I understand you do)
So basically, if you pitch up to, say, 10°, and let the sidestick go, what will it hold?
Will it be those 10° or will it be a 1 G load?
If its pitch, then theoretically, as you speed up, the aircraft will start to climb and if you fly slower, she will descend.
If its G Load, then the aircraft should start a descent if you increase bank angle, correct?
Or is it something completely different?
Regarding the X axis, I guess you simply set the angular acceleration and if you let go at a specific bank angle, it will hold that.
Thanks,
Mark
Last edited by Ka8 Flyer; 6th Dec 2005 at 09:41.
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Buddy,
Dont get so complicated here.
When stick is neutral it will hold 1G.
Hold the stick back till 10deg is reached; let go and it will hold it.
Bank at any angle (up to 67deg) and you will maintain altitude.
Hope that helps
Dont get so complicated here.
When stick is neutral it will hold 1G.
Hold the stick back till 10deg is reached; let go and it will hold it.
Bank at any angle (up to 67deg) and you will maintain altitude.
Hope that helps
Only half a speed-brake
Ka8, correct.
Pitch 10, release. It will stay at 1 G - keep the pitch.
Roll is roll rate, just as you suggest. For 1 g keeping during accelerated manoeuvres, i never thought of it. It defenitely does not do the silly things you say, perhaps the sidestick 1 g keeping is in fact 0 g change keeping, measured along vertical? It trims automatically for sure, but definitely yo do have to pitch up in turn to keep it level (I doubt in manual it would adjust pitch itself - uncommanded manouevre).
Will it, really? Honest question.
Cheers,
FD.
(the un-real)
Pitch 10, release. It will stay at 1 G - keep the pitch.
Roll is roll rate, just as you suggest. For 1 g keeping during accelerated manoeuvres, i never thought of it. It defenitely does not do the silly things you say, perhaps the sidestick 1 g keeping is in fact 0 g change keeping, measured along vertical? It trims automatically for sure, but definitely yo do have to pitch up in turn to keep it level (I doubt in manual it would adjust pitch itself - uncommanded manouevre).
Bank at any angle (up to 67deg) and you will maintain altitude.
Cheers,
FD.
(the un-real)
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Bank at any angle (up to 67deg) and you will maintain altitude.
Will it, really? Honest question.
If the pilot releases the stick at a bank angle greater than 33°, the bank angle reduces automatically to 33°. Up to 33° the system holds the roll attitude constant when the stick is at neutral.
If the pilot holds full lateral stick deflection, the bank angle will go to 67° and no farther.
But - if the pilot exceeds 33° he will have to make a pitch input, since automatic pitch trim is only active from 0-33°. So you will not maintain altitude if you exceed 33° bank and the pilot does not increase the pitch input on the stick.
Furthermore, and just for some more info: If the bank angle exceeds 45° (while autopilot is active), the autopilot disconnects and the FD bars disappear. The FD bars return when the bank angle decreases to less than 40°.
So long,
DBate
Only half a speed-brake
The entire posting EDITED - DELETED because manufacturer says:
...
In addition, if the bank angle is less than 33 degrees, pitch compensation is
provided...
...
During a normal turn (bank angle less than 33 degrees), in level flight:
· The PF moves the sidestick laterally (the more the sidestick is moved
laterally, the greater the resulting roll rate - e.g. 15 degrees/second at
max deflection).
· Not necessary to make a pitch correction
· Not necessary to use the rudder.
...
Tea, coldrex, thermometer, socks...
FD
(the un-real)
...
In addition, if the bank angle is less than 33 degrees, pitch compensation is
provided...
...
During a normal turn (bank angle less than 33 degrees), in level flight:
· The PF moves the sidestick laterally (the more the sidestick is moved
laterally, the greater the resulting roll rate - e.g. 15 degrees/second at
max deflection).
· Not necessary to make a pitch correction
· Not necessary to use the rudder.
...
Tea, coldrex, thermometer, socks...
FD
(the un-real)
Last edited by FlightDetent; 6th Dec 2005 at 13:50.
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Thread Starter
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So is it vertical acceleration that is kept constant (ie vertical speed)?
If you are in level flight and you let go of the sidestick and then pull back the thrust levers, will the aircraft start to pitch up to maintain altitude?
If you are in level flight and you let go of the sidestick and then pull back the thrust levers, will the aircraft start to pitch up to maintain altitude?
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Stick free the A320 series aircraft will essentially maintain 1G. However the auto-trimming may not be able to totally compensate for all pitching moments.
Since the FBW system is maintaining a 1G load rather than holding a specific pitch attitude, the Airbus has a number of interesting handling traits. If you happen to be hand flying in turbulent conditions, you will see the aircraft pitch up and down slightly as the FBW system attempts to maintain 1G in the vertical gusts. Some pilots, new to the Airbus, have mistaken this characteristic as an uncommanded pitch changes and made an unnecessary entry on the aircraft maintenance logbook.
When in a turn up to 33 degrees of bank, the FBW system will maintain the appropriate G load for the bank angle (i.e. 1.14G for a 30 degree bank). This minimizes the need for any pitch inputs during normal turns.
Another fascinating characteristic of the A320 series is due to the high resolution of the vertical accelerometers. When cruising at higher altitudes, the local force of gravity is slightly less than 1G. Since the FBW system is sensitive enough to discern this difference, the aircraft will slowly pitch up, in order to maintain 1G. The greater the altitude, the more pronounced the pitch rate. Even at FL390, this characteristic, while slightly annoying is easily controlled.
While I don’t have any experience on the A330/340, I have been told its FBW system is more sophisticated. On the A330/340, the system takes the aircraft altitude into account, and will reduce the stick free G load so the aircraft will not exhibit the minor pitch up tendency of the A320 series. Unfortunately, I don’t have any documentation regarding the A330. Possibly some of the pilots who fly the A330/340 could comment.
Best regards,
The Kid
Since the FBW system is maintaining a 1G load rather than holding a specific pitch attitude, the Airbus has a number of interesting handling traits. If you happen to be hand flying in turbulent conditions, you will see the aircraft pitch up and down slightly as the FBW system attempts to maintain 1G in the vertical gusts. Some pilots, new to the Airbus, have mistaken this characteristic as an uncommanded pitch changes and made an unnecessary entry on the aircraft maintenance logbook.
When in a turn up to 33 degrees of bank, the FBW system will maintain the appropriate G load for the bank angle (i.e. 1.14G for a 30 degree bank). This minimizes the need for any pitch inputs during normal turns.
Another fascinating characteristic of the A320 series is due to the high resolution of the vertical accelerometers. When cruising at higher altitudes, the local force of gravity is slightly less than 1G. Since the FBW system is sensitive enough to discern this difference, the aircraft will slowly pitch up, in order to maintain 1G. The greater the altitude, the more pronounced the pitch rate. Even at FL390, this characteristic, while slightly annoying is easily controlled.
While I don’t have any experience on the A330/340, I have been told its FBW system is more sophisticated. On the A330/340, the system takes the aircraft altitude into account, and will reduce the stick free G load so the aircraft will not exhibit the minor pitch up tendency of the A320 series. Unfortunately, I don’t have any documentation regarding the A330. Possibly some of the pilots who fly the A330/340 could comment.
Best regards,
The Kid
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Ka8 Flyer,
Answer to your question.
If you are flying level and you retard the thrust levers to idle,
the FBW system will maintain level flight. Once a minimum safety speed is reached, the autothrust will advance the thrust to prevent the plane from stalling.
I am facinated by the FBW system everytime i fly it. I am new to the Bus and i love it.
Something else that you might like to know:
In a single engine failure, the FBW will keep wings level regardless of thrust settings.
If you lived in Australia I'd take you on a simulator. An experience you can't miss.
Answer to your question.
If you are flying level and you retard the thrust levers to idle,
the FBW system will maintain level flight. Once a minimum safety speed is reached, the autothrust will advance the thrust to prevent the plane from stalling.
I am facinated by the FBW system everytime i fly it. I am new to the Bus and i love it.
Something else that you might like to know:
In a single engine failure, the FBW will keep wings level regardless of thrust settings.
If you lived in Australia I'd take you on a simulator. An experience you can't miss.
Some off the cuff thoughts:
I don't have the FCOMs handy, but I think engine inop the aircraft will roll to 7deg AOB max without aileron input in normal law. Regardless of thrust setting? Hmm, if speed greater than the applicable Vmca then yes.
The ATT vs G discussion is interesting, but generally not relevent as flight/environmental conditions are normally more dynamic so corrections [ S/S inputs] are inevitable. As expected, the big engined [ie non CFM] aircraft appear more affected by thrust changes.
The turbulence response is a factor, one reason why Airbus suggest "global" sidestick inputs.
Can't say that I've thought it prudent to play with the sidestick at high altitude [330/340] but A/P disconnect does not appear to produce any pitch up tendency.
Overall, Airbus FBW is generally a delight to fly. The Pilot just needs to remember that the aircraft still obeys the physical laws of Aerodynamics and Gravity should he get it wrong!
I don't have the FCOMs handy, but I think engine inop the aircraft will roll to 7deg AOB max without aileron input in normal law. Regardless of thrust setting? Hmm, if speed greater than the applicable Vmca then yes.
The ATT vs G discussion is interesting, but generally not relevent as flight/environmental conditions are normally more dynamic so corrections [ S/S inputs] are inevitable. As expected, the big engined [ie non CFM] aircraft appear more affected by thrust changes.
The turbulence response is a factor, one reason why Airbus suggest "global" sidestick inputs.
Can't say that I've thought it prudent to play with the sidestick at high altitude [330/340] but A/P disconnect does not appear to produce any pitch up tendency.
Overall, Airbus FBW is generally a delight to fly. The Pilot just needs to remember that the aircraft still obeys the physical laws of Aerodynamics and Gravity should he get it wrong!
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KA8 Flyer - I don't think Bantios' explanation is quite correct. In level flight if you close the thrust levers the airspeed will reduce to a minimum level then the autoflight system will trim the aircraft nose down to descend so as to maintain that speed. Left untouched the aircraft will descend into the ground at that speed. If you attempt to intervene by pulling the stick back you will reduce the airspeed further into the alpha-protection range, then the engines will go to full power to prevent the stall.
Its been a while!! just wondered how its done in a 'bus (AP failure/FMGC failure/Emer Elec..... just a few scenarios that could lead to manual flight!!
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Originally Posted by bantios
Buddy,
Dont get so complicated here.
When stick is neutral it will hold 1G.
Hold the stick back till 10deg is reached; let go and it will hold it.
Bank at any angle (up to 67deg) and you will maintain altitude.
Hope that helps
Dont get so complicated here.
When stick is neutral it will hold 1G.
Hold the stick back till 10deg is reached; let go and it will hold it.
Bank at any angle (up to 67deg) and you will maintain altitude.
Hope that helps
Airbus apparently use C* control laws with g-load for pitch response correct?. If the aircraft is climbing (autopilot/climb schedule computers off) at a velocity vector angle of 15 degrees, in order to maintain 15 degrees of pitch, i.e zero pitch rate, the aircraft must fly with a g-load less than 1, (In theory if the plane was flying straight up at 90 degrees to hold this angle 0g is necessary).
So is Airbus using G-command or pitch rate command, where neutral stick equates to zero pitch rate.
Thanks
Obi