Question: Stab Trim setting - Airbus
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Joined: Jan 2022
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From: Miami
Question: Stab Trim setting - Airbus
Just asking the audience what is the better practice
On dispatch paperwork, Company provides both TO CG%, and Stab Trim (N/U or N/D x.x)
are folks:
1. setting CG on the trim wheel (inner scale, somewhat harder to see)
2. Stab Trim on the trim wheel, or alternatively,
3. setting stab trim using the trim wheel but references the electronic lower screen display when flight controls page is up.
#3 seems better in a dark cockpit and allows both crews to better see it, in my opinion
Thank you
On dispatch paperwork, Company provides both TO CG%, and Stab Trim (N/U or N/D x.x)
are folks:
1. setting CG on the trim wheel (inner scale, somewhat harder to see)
2. Stab Trim on the trim wheel, or alternatively,
3. setting stab trim using the trim wheel but references the electronic lower screen display when flight controls page is up.
#3 seems better in a dark cockpit and allows both crews to better see it, in my opinion
Thank you
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Joined: Oct 2016
Posts: 170
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From: Winterthur
Just asking the audience what is the better practice
On dispatch paperwork, Company provides both TO CG%, and Stab Trim (N/U or N/D x.x)
are folks:
1. setting CG on the trim wheel (inner scale, somewhat harder to see)
2. Stab Trim on the trim wheel, or alternatively,
3. setting stab trim using the trim wheel but references the electronic lower screen display when flight controls page is up.
#3 seems better in a dark cockpit and allows both crews to better see it, in my opinion
Thank you
On dispatch paperwork, Company provides both TO CG%, and Stab Trim (N/U or N/D x.x)
are folks:
1. setting CG on the trim wheel (inner scale, somewhat harder to see)
2. Stab Trim on the trim wheel, or alternatively,
3. setting stab trim using the trim wheel but references the electronic lower screen display when flight controls page is up.
#3 seems better in a dark cockpit and allows both crews to better see it, in my opinion
Thank you
Joined: Jun 2007
Posts: 3,443
Likes: 39
From: Wanderlust
Just asking the audience what is the better practice
On dispatch paperwork, Company provides both TO CG%, and Stab Trim (N/U or N/D x.x)
are folks:
1. setting CG on the trim wheel (inner scale, somewhat harder to see)
2. Stab Trim on the trim wheel, or alternatively,
3. setting stab trim using the trim wheel but references the electronic lower screen display when flight controls page is up.
#3 seems better in a dark cockpit and allows both crews to better see it, in my opinion
Thank you
On dispatch paperwork, Company provides both TO CG%, and Stab Trim (N/U or N/D x.x)
are folks:
1. setting CG on the trim wheel (inner scale, somewhat harder to see)
2. Stab Trim on the trim wheel, or alternatively,
3. setting stab trim using the trim wheel but references the electronic lower screen display when flight controls page is up.
#3 seems better in a dark cockpit and allows both crews to better see it, in my opinion
Thank you
Last edited by vilas; 15th May 2023 at 13:12.
Joined: Sep 2002
Posts: 2,188
Likes: 6
From: La Belle Province
For specific values of "safe". ;-)
The mistrimmed takeoff tests for certification generally consider the stab at one end of the band and the aircraft (weight, CG, etc) corresponding to the other end. So if no additional failures or unusual circumstances arise, you are indeed "safe".
If "something else" does happen, though, being fully (or partly) mistrimmed could result in a degraded ability to cope with that event.
The mistrimmed takeoff tests for certification generally consider the stab at one end of the band and the aircraft (weight, CG, etc) corresponding to the other end. So if no additional failures or unusual circumstances arise, you are indeed "safe".
If "something else" does happen, though, being fully (or partly) mistrimmed could result in a degraded ability to cope with that event.
Joined: Jun 2007
Posts: 3,443
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From: Wanderlust
Spoiler
6th Feb 2015, 06:20vilas my SOP has always shown to select the fuel prediction page to set the CG after engine start. the trim units on the back of the QRH were deleted with an advisory circular informing that this procedure was unnecessary for this airplane and only to be used on the company A300's
Joined: May 2004
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From: Ziltoidia... indeed'd.
PITCH TRIM handwheel................................................... ...........................................................S ET
Set takeoff CG on pitch trim handwheel.
Same thing here, in my SOP, in the after start flow, the stab trimm should be set following the CG for take off, which should be compared using the TO CG from the loadsheet and the GW CG displayed in the FUEL PRED page. In reality everybody keeps using the DN or UP figures from the load sheet because it is more straight forward, but it has already happened to me taking off using DN instead of UP of viceversa. It had almost NIL effect during rotation because the value of the trim itself was quite close to zero, but I can imagine it being somewhat of an issue with hight values.
Only half a speed-brake
Joined: Apr 2003
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From: Commuting not home
Thank you.
I assumed a (non-existent) MOD to display % on the PERF T. O. p.g. in lieu of stab trim units.
Always has been a big fan of ditching the NU/ND +/- altogether, although being forced to the complete opposite corner by present SOP.
Unfortunately what's explained is a complete nono here as the TO pg has TO CG units whereas FUEL has the present calculated CG. The difference being the moment effect of taxi fuel used........... Yes. I know. But 'more busy, more safe', captain.
Enjoy your rules, best wishes.
I assumed a (non-existent) MOD to display % on the PERF T. O. p.g. in lieu of stab trim units.
Always has been a big fan of ditching the NU/ND +/- altogether, although being forced to the complete opposite corner by present SOP.
Unfortunately what's explained is a complete nono here as the TO pg has TO CG units whereas FUEL has the present calculated CG. The difference being the moment effect of taxi fuel used........... Yes. I know. But 'more busy, more safe', captain.
Enjoy your rules, best wishes.
Joined: Sep 2002
Posts: 2,188
Likes: 6
From: La Belle Province
An alternative to using the actual +/- physical stab position - which does have a risk of the +/- confusion, or even the "-" sign being dropped from the display, leading to an apparent positive value - is to use a stab "index" rather than values in degrees, with the index chosen such that it is only positive.
In the CRJs, for example, the stab physical travel is +2 to -13 degrees, but the "stab units" value is defined as "2 - stab angle" which results in a value of "0" corresponding to "-2 degrees" and "+15" corresponding to "-13 degrees"; even on the Challenger 600 series, where the range was "0 to -8 degrees" and then "0 to -9 degrees", the "units" concept was used, simply to avoid presenting a negative number with a perceived fear of dropping the minus sign even then. (This may well be a superseded concern, rooted in older display technology)
In the CRJs, for example, the stab physical travel is +2 to -13 degrees, but the "stab units" value is defined as "2 - stab angle" which results in a value of "0" corresponding to "-2 degrees" and "+15" corresponding to "-13 degrees"; even on the Challenger 600 series, where the range was "0 to -8 degrees" and then "0 to -9 degrees", the "units" concept was used, simply to avoid presenting a negative number with a perceived fear of dropping the minus sign even then. (This may well be a superseded concern, rooted in older display technology)
Joined: May 2004
Posts: 496
Likes: 19
From: Ziltoidia... indeed'd.
An alternative to using the actual +/- physical stab position - which does have a risk of the +/- confusion, or even the "-" sign being dropped from the display, leading to an apparent positive value - is to use a stab "index" rather than values in degrees, with the index chosen such that it is only positive.
In the CRJs, for example, the stab physical travel is +2 to -13 degrees, but the "stab units" value is defined as "2 - stab angle" which results in a value of "0" corresponding to "-2 degrees" and "+15" corresponding to "-13 degrees"; even on the Challenger 600 series, where the range was "0 to -8 degrees" and then "0 to -9 degrees", the "units" concept was used, simply to avoid presenting a negative number with a perceived fear of dropping the minus sign even then. (This may well be a superseded concern, rooted in older display technology)
In the CRJs, for example, the stab physical travel is +2 to -13 degrees, but the "stab units" value is defined as "2 - stab angle" which results in a value of "0" corresponding to "-2 degrees" and "+15" corresponding to "-13 degrees"; even on the Challenger 600 series, where the range was "0 to -8 degrees" and then "0 to -9 degrees", the "units" concept was used, simply to avoid presenting a negative number with a perceived fear of dropping the minus sign even then. (This may well be a superseded concern, rooted in older display technology)
Joined: Nov 2006
Posts: 367
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From: Tropics
Thank you.
I assumed a (non-existent) MOD to display % on the PERF T. O. p.g. in lieu of stab trim units.
Always has been a big fan of ditching the NU/ND +/- altogether, although being forced to the complete opposite corner by present SOP.
Unfortunately what's explained is a complete nono here as the TO pg has TO CG units whereas FUEL has the present calculated CG. The difference being the moment effect of taxi fuel used........... Yes. I know. But 'more busy, more safe', captain.
Enjoy your rules, best wishes.
I assumed a (non-existent) MOD to display % on the PERF T. O. p.g. in lieu of stab trim units.
Always has been a big fan of ditching the NU/ND +/- altogether, although being forced to the complete opposite corner by present SOP.
Unfortunately what's explained is a complete nono here as the TO pg has TO CG units whereas FUEL has the present calculated CG. The difference being the moment effect of taxi fuel used........... Yes. I know. But 'more busy, more safe', captain.
Enjoy your rules, best wishes.
