newair810
Topic Author
Posts: 1
Joined: Mon May 20, 2019 10:39 pm

Airbus a321 vertical stablizer/ rudder improvements

Fri Oct 04, 2019 4:47 pm

Hi, I have a technical question about airbus planes. I realize the crash of airbus flight 587 has been discussed and I have read the reports from the NTSB. My question is are newer airbuses designed different or is the vertical stabilizer the same basically? Is this unlikely to happen on an Airbus A321.

Here is the accident I am referring to.

https://en.wikipedia.org/wiki/American_ ... Flight_587

Basically my question is has the plane's tail structure changed compared to this plane, which is an a321.

https://www.airfleets.net/ficheapp/plane-a321-6214.htm

I guess basically my question comes about because I have never been on an airbus and I have heard about rudder problems. Just looking for some information from those who are more knowledgeable than me.Thank you.
 
GalaxyFlyer
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Re: Airbus a321 vertical stablizer/ rudder improvements

Fri Oct 04, 2019 7:18 pm

The Airbus has no rudder problems or weaknesses. The AA plane A321, it was an A300-600. After that accident, most AFMs have a warning about inputting rapid, opposing flight controls. I’d guess if similar inputs were applied on any Part 25, there’d be a risk of fin failure

GF
 
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Starlionblue
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Re: Airbus a321 vertical stablizer/ rudder improvements

Sat Oct 05, 2019 7:17 am

To expand on what GalaxyFlyer's post, rudders are not designed to withstand repeated, full, opposing rudder inputs. It is not a certification requirement. Indeed, the AA587 rudder was shown during the investigation to have held up beyond certification requirements before it failed.

Before the accident, both Airbus and Boeing had written to AA about their training, emphasizing that rudder use in such situations was always inappropriate.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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fr8mech
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Re: Airbus a321 vertical stablizer/ rudder improvements

Sat Oct 05, 2019 7:51 am

Just a point of accuracy, the rudder did not fail, one of the vertical stabilizer attachment lugs failed, followed by additional lug failures, which resulted in the vertical stabilizer departing the aircraft.
When seconds count...the police are minutes away.
Unless it's expressly prohibited, it's allowed.
You are not entitled to a public safe space.
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
Max Q
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Re: Airbus a321 vertical stablizer/ rudder improvements

Sat Oct 05, 2019 8:09 pm

I remember reading that AB has modified the flight control software for the rudder on all its FBW transports to protect it and the fin from being overstressed
The best contribution to safety is a competent Pilot.
 
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Starlionblue
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Re: Airbus a321 vertical stablizer/ rudder improvements

Sat Oct 05, 2019 11:19 pm

Max Q wrote:
I remember reading that AB has modified the flight control software for the rudder on all its FBW transports to protect it and the fin from being overstressed


There may have been tweaks, but they are not readily apparent in the manuals. From the FCOM, under Yaw Control, Rudder Travel Limit, "The maximum rudder travel deflection gradually reduces as the speed increases, to avoid high structural loads."

Under Normal Law, "Protections are intended to... Reduce the risk of overcontrolling, or overstressing the aircraft." That being said, the same section includes the phrase, "... these protections are not designed to be structural limit protections (e.g. opposite rudder pedal inputs)."
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
B6JFKH81
Posts: 2125
Joined: Thu Mar 16, 2006 6:35 am

Re: Airbus a321 vertical stablizer/ rudder improvements

Sun Oct 06, 2019 2:07 am

newair810 wrote:
Hi, I have a technical question about airbus planes. I realize the crash of airbus flight 587 has been discussed and I have read the reports from the NTSB. My question is are newer airbuses designed different or is the vertical stabilizer the same basically? Is this unlikely to happen on an Airbus A321.

Here is the accident I am referring to.

https://en.wikipedia.org/wiki/American_ ... Flight_587

Basically my question is has the plane's tail structure changed compared to this plane, which is an a321.

https://www.airfleets.net/ficheapp/plane-a321-6214.htm

I guess basically my question comes about because I have never been on an airbus and I have heard about rudder problems. Just looking for some information from those who are more knowledgeable than me.Thank you.


Out of curiosity, what "rudder problems" have you heard about? I do not recall an A320-series accident for rudder issues in particular. The 737, yes, I remember that, but not the A320-series? As someone in the heavy maintenance field for the A320-series, I haven't seen any reoccurring problems with the rudder or system other than normal stuff.
"If you do not learn from history, you are doomed to repeat it"
 
HugoJunkers
Posts: 18
Joined: Tue Jun 04, 2019 3:23 pm

Re: Airbus a321 vertical stablizer/ rudder improvements

Mon Nov 04, 2019 12:10 am

newair810 wrote:
Hi, I have a technical question about airbus planes. I realize the crash of airbus flight 587 has been discussed and I have read the reports from the NTSB. My question is are newer airbuses designed different or is the vertical stabilizer the same basically? Is this unlikely to happen on an Airbus A321.

Here is the accident I am referring to.

https://en.wikipedia.org/wiki/American_ ... Flight_587

Basically my question is has the plane's tail structure changed compared to this plane, which is an a321.

https://www.airfleets.net/ficheapp/plane-a321-6214.htm

I guess basically my question comes about because I have never been on an airbus and I have heard about rudder problems. Just looking for some information from those who are more knowledgeable than me.Thank you.


The A320 series of aircraft have a very advanced flight control system that protects the aircraft not only from stalls but minimum flying speed, dive angle, climb angle and roll angle (when in normal law) but also harsh accelerations in pitch, roll and yaw. For instance when a A320 pilots pulls back on his side stick he is demanding a certain pitch rate from the FBW system and this is measured by gyros and accelerometers. Its the same for yaw (rudder inputs). Its very useful, for instance when the A320 rotates on take-off the FBW system controls the pitch rate and rotation angle so that no tail strike is suffered. Some of Airbuses Maximum Take Off Weight increases were achieved by increasing rotation rate and rotation angle so that the aircraft can get of the ground quicker.

The problem with old "steel wire" aircraft is that when the speed doubles "Q" the aircrafts control surfaces become 4 times more powerful for the same deflection and it is easy to over stress the aircraft. Limiting the over stress was achieved by giving the pilot artificial feel so that he flies by the amount of force rather than deflection.

In the A320 FBW system the ADIRU knows the aircrafts speed and air pressure and reduce the control surface deflection as speed increases so that the aircraft always rolls, pitches, yaws at about the same rate and furthermore the rate is adjusted to complete precision because the FBW takes into account the gyros and accelerometers. For this reason the A320 is unlikely to ever damage itself from excess pilot inputs. Should several sensors of the aircraft fail the aircraft will revert from normal law to alternate law which still limits deflection and should that fail there is direct law in which the control deflect as per the side stick and rudder peddles. There is a further 4th law called mechanical law where stabiliser trim and rudder are controlled by mechanical backup.

See
http://www.airbusdriver.net/airbus_fltlaws.htm
 
1989worstyear
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Joined: Sun Dec 04, 2016 6:53 pm

Re: Airbus a321 vertical stablizer/ rudder improvements

Mon Nov 04, 2019 12:17 am

HugoJunkers wrote:
newair810 wrote:
Hi, I have a technical question about airbus planes. I realize the crash of airbus flight 587 has been discussed and I have read the reports from the NTSB. My question is are newer airbuses designed different or is the vertical stabilizer the same basically? Is this unlikely to happen on an Airbus A321.

Here is the accident I am referring to.

https://en.wikipedia.org/wiki/American_ ... Flight_587

Basically my question is has the plane's tail structure changed compared to this plane, which is an a321.

https://www.airfleets.net/ficheapp/plane-a321-6214.htm

I guess basically my question comes about because I have never been on an airbus and I have heard about rudder problems. Just looking for some information from those who are more knowledgeable than me.Thank you.


The A320 series of aircraft have a very advanced flight control system that protects the aircraft not only from stalls but minimum flying speed, dive angle, climb angle and roll angle (when in normal law) but also harsh accelerations in pitch, roll and yaw. For instance when a A320 pilots pulls back on his side stick he is demanding a certain pitch rate from the FBW system and this is measured by gyros and accelerometers. Its the same for yaw (rudder inputs). Its very useful, for instance when the A320 rotates on take-off the FBW system controls the pitch rate and rotation angle so that no tail strike is suffered. Some of Airbuses Maximum Take Off Weight increases were achieved by increasing rotation rate and rotation angle so that the aircraft can get of the ground quicker.

The problem with old "steel wire" aircraft is that when the speed doubles "Q" the aircrafts control surfaces become 4 times more powerful for the same deflection and it is easy to over stress the aircraft. Limiting the over stress was achieved by giving the pilot artificial feel so that he flies by the amount of force rather than deflection.

In the A320 FBW system the ADIRU knows the aircrafts speed and air pressure and reduce the control surface deflection as speed increases so that the aircraft always rolls, pitches, yaws at about the same rate and furthermore the rate is adjusted to complete precision because the FBW takes into account the gyros and accelerometers. For this reason the A320 is unlikely to ever damage itself from excess pilot inputs. Should several sensors of the aircraft fail the aircraft will revert from normal law to alternate law which still limits deflection and should that fail there is direct law in which the control deflect as per the side stick and rudder peddles. There is a further 4th law called mechanical law where stabiliser trim and rudder are controlled by mechanical backup.

See
http://www.airbusdriver.net/airbus_fltlaws.htm


I think calling a 32 year old system "advanced" is not the best choice of words, but otherwise spot on.
Stuck at age 15 thanks to the certification date of the A320-200 and my parents' decision to postpone having a kid by 3 years. At least there's Dignitas...
 
Flow2706
Posts: 196
Joined: Sat Jan 28, 2017 7:20 pm

Re: Airbus a321 vertical stablizer/ rudder improvements

Mon Nov 04, 2019 11:49 am

HugoJunkers wrote:
The A320 series of aircraft have a very advanced flight control system that protects the aircraft not only from stalls but minimum flying speed, dive angle, climb angle and roll angle (when in normal law) but also harsh accelerations in pitch, roll and yaw. For instance when a A320 pilots pulls back on his side stick he is demanding a certain pitch rate from the FBW system and this is measured by gyros and accelerometers. Its the same for yaw (rudder inputs). Its very useful, for instance when the A320 rotates on take-off the FBW system controls the pitch rate and rotation angle so that no tail strike is suffered. Some of Airbuses Maximum Take Off Weight increases were achieved by increasing rotation rate and rotation angle so that the aircraft can get of the ground quicker.

At least the A320CEO series rotates in ground law, which is essentially direct law, so during rotation elevator deflection is directly proportional to sidestick deflection, the normal law 'blends in' shortly after rotation. There are no protections provided during rotation. However, I heard that the A320NEO is different in this respect and also some of the other Airbus types may have a specific flight control law during rotation.
 
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Starlionblue
Posts: 19495
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Re: Airbus a321 vertical stablizer/ rudder improvements

Mon Nov 04, 2019 3:04 pm

HugoJunkers wrote:
newair810 wrote:
Hi, I have a technical question about airbus planes. I realize the crash of airbus flight 587 has been discussed and I have read the reports from the NTSB. My question is are newer airbuses designed different or is the vertical stabilizer the same basically? Is this unlikely to happen on an Airbus A321.

Here is the accident I am referring to.

https://en.wikipedia.org/wiki/American_ ... Flight_587

Basically my question is has the plane's tail structure changed compared to this plane, which is an a321.

https://www.airfleets.net/ficheapp/plane-a321-6214.htm

I guess basically my question comes about because I have never been on an airbus and I have heard about rudder problems. Just looking for some information from those who are more knowledgeable than me.Thank you.


The A320 series of aircraft have a very advanced flight control system that protects the aircraft not only from stalls but minimum flying speed, dive angle, climb angle and roll angle (when in normal law) but also harsh accelerations in pitch, roll and yaw. For instance when a A320 pilots pulls back on his side stick he is demanding a certain pitch rate from the FBW system and this is measured by gyros and accelerometers. Its the same for yaw (rudder inputs). Its very useful, for instance when the A320 rotates on take-off the FBW system controls the pitch rate and rotation angle so that no tail strike is suffered. Some of Airbuses Maximum Take Off Weight increases were achieved by increasing rotation rate and rotation angle so that the aircraft can get of the ground quicker.

The problem with old "steel wire" aircraft is that when the speed doubles "Q" the aircrafts control surfaces become 4 times more powerful for the same deflection and it is easy to over stress the aircraft. Limiting the over stress was achieved by giving the pilot artificial feel so that he flies by the amount of force rather than deflection.

In the A320 FBW system the ADIRU knows the aircrafts speed and air pressure and reduce the control surface deflection as speed increases so that the aircraft always rolls, pitches, yaws at about the same rate and furthermore the rate is adjusted to complete precision because the FBW takes into account the gyros and accelerometers. For this reason the A320 is unlikely to ever damage itself from excess pilot inputs. Should several sensors of the aircraft fail the aircraft will revert from normal law to alternate law which still limits deflection and should that fail there is direct law in which the control deflect as per the side stick and rudder peddles. There is a further 4th law called mechanical law where stabiliser trim and rudder are controlled by mechanical backup.

See
http://www.airbusdriver.net/airbus_fltlaws.htm


Quite a few of the statements in this post are inaccurate.

- In normal law, fore and aft stick deflection gives a proportional load factor demand, not a pitch rate.
- In normal law, side stick deflection gives a proportional roll rate.
- Rudder input gives a yaw command. However, there is no proportional yaw rate logic, so to speak. Rudder deflection is handled by the yaw damping system, and you shouldn't be touching the pedals except on takeoff, landing and engine out.
- As Flow2706 says, during rotation pitch is in ground mode, with elevator deflection proportional to stick input. This is direct pitch law, with full authority. The rotation rate is thus controlled by the pilot, not by the flight control computers. Flight mode is blended in as the aircraft becomes airborne.
- AFAIK there have been no MTOW weight increases by changing rotation rate and angle. I don't see how rotation rate could change the MTOW. Rotation rate target is around 3 degrees per second. Pitch target for rotation is the same on various weight variants of the A330 (15 degrees) and on variants of the A350 (12.5 degrees).
- The only "feel" in an Airbus is the spring in the sidestick. Obviously the resistance in the spring does not change with speed. The protection is in the flight control system, not in a force feedback mechanism ("artificial feel") giving more resistance at higher speeds.
- Alternate law still maintains maneuver protection, but other protections such as pitch angle are lost.
- It isn't "mechanical law". It is called "mechanical backup".
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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