Has everyone suddenly forgotten how to build airplanes?
Only half a speed-brake
Last edited by FlightDetent; 17th Sep 2019 at 09:22. Reason: Addressed now
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There is a pitching moment attenuation issue, not a CoG one. To avoid manifestation of the problem a CoG restriction was put in place, until the flight controls are sorted out.
I assume this was due to a problem with the initial design.
I am still a bit baffled by this one. Few questions
- the 320 and 321, obviously related, are fairly different airframes. Can they both be impacted by the same issue ?
- is this LH specific (due to their cabin seating) ? If not all operators ? oops...
- is this just a matter of "tuning" the FBW software or something more fundamental ?
- am I correct im my understanding that this was "discovered" in simulation ?
CoG limit applies to all operators, however not all operators find the limit to be limiting, if you know what I mean. I know of one operator that checked their historical load data and found they’d never loaded aft of the new limit, not that they’ve had the neo for long.
The 320 issue is not the same as the 321. The 321 will be fixed with ELAC L103. The 320 problem was discovered by computer simulation and requires a very specific set of circumstances. The 321 problem was discovered in flight testing.
The 320 issue is not the same as the 321. The 321 will be fixed with ELAC L103. The 320 problem was discovered by computer simulation and requires a very specific set of circumstances. The 321 problem was discovered in flight testing.
Only half a speed-brake
atakacs
For the A320 specifically
Reference Airbus Operational Telex 999.0059/19
- In case of unfavourable aft CG position behind the newly outlined limits
- when not in clean configuration
- while the aircraft is decelerating i.e. from a certain max flaps speed down to minimum reasonable speed ("Vls") -10 kts
- then, if in close sequence TOGA thrust is applied and full back stick is pulled
A computer simulation executed as a part of further FCS development efforts revealed that an excessive pitch attitude might result. It was never encountered in service or during a flight test.
-----
The pitch can still be controlled with normal sidestick input, just by releasing the full aft grip.
Yet that excessive pitch is not supposed to happen under normal control of the FCS system. There should be a "hard stop" where the elevators are manipulated (behind pilot's back) in such a manner so that the nose would stop raising - even with full back stick being pulled.
A speculation on my part is that the "over-ruling" of the pilots full up input and the pitch-up moment of the underslung thrust is too soft in the "wobbly CoG area" (see Aihkio above). Thus in the future versions the FCS will be allowed to flex more muscle.
It is not a stability nor controllability issue of the airframe aerodynamical configuration. E.g. with abnormal hydraulic the A/C can still be flown properly through the G/A manoeuvre with only one elevator or frozen horizontal stabiliser - in the full original CoG range.
That's the cart and horse.
----
If the airline's specific configuration is very tail heavy when empty, loading upfront might be a challenge. That being said, in the common tkof range 60t+ I really do not remember seeing TO CG above 35 all that often. Allegedly LH needs to take action.
What can you do in case you had to?
- Load bags to front, or even carry ballast there
- Play with the pottable water tank load (tiny little)
- Put your half-load pantry into the front galley
- If fuel is less than 8t (around-ish), transfer the outer wing tanks into inners
- Carry ballast fuel in the centre tank (the issue looks more critical at low weights and this would work nicely)
But none of those are, ehm, "operation personnel proof". The solution no to sell the last few seats is rather charming if it does the trick,
- the seats are easily blocked in the DCS systems
- you can put pressure on the OEM due to lost revenue
- with a good pricing system, you never really sell full 100% seats (though I believe LH to be super-efficient)
For the A320 specifically
Reference Airbus Operational Telex 999.0059/19
- In case of unfavourable aft CG position behind the newly outlined limits
- when not in clean configuration
- while the aircraft is decelerating i.e. from a certain max flaps speed down to minimum reasonable speed ("Vls") -10 kts
- then, if in close sequence TOGA thrust is applied and full back stick is pulled
A computer simulation executed as a part of further FCS development efforts revealed that an excessive pitch attitude might result. It was never encountered in service or during a flight test.
-----
The pitch can still be controlled with normal sidestick input, just by releasing the full aft grip.
Yet that excessive pitch is not supposed to happen under normal control of the FCS system. There should be a "hard stop" where the elevators are manipulated (behind pilot's back) in such a manner so that the nose would stop raising - even with full back stick being pulled.
A speculation on my part is that the "over-ruling" of the pilots full up input and the pitch-up moment of the underslung thrust is too soft in the "wobbly CoG area" (see Aihkio above). Thus in the future versions the FCS will be allowed to flex more muscle.
It is not a stability nor controllability issue of the airframe aerodynamical configuration. E.g. with abnormal hydraulic the A/C can still be flown properly through the G/A manoeuvre with only one elevator or frozen horizontal stabiliser - in the full original CoG range.
That's the cart and horse.
----
If the airline's specific configuration is very tail heavy when empty, loading upfront might be a challenge. That being said, in the common tkof range 60t+ I really do not remember seeing TO CG above 35 all that often. Allegedly LH needs to take action.
What can you do in case you had to?
- Load bags to front, or even carry ballast there
- Play with the pottable water tank load (tiny little)
- Put your half-load pantry into the front galley
- If fuel is less than 8t (around-ish), transfer the outer wing tanks into inners
- Carry ballast fuel in the centre tank (the issue looks more critical at low weights and this would work nicely)
But none of those are, ehm, "operation personnel proof". The solution no to sell the last few seats is rather charming if it does the trick,
- the seats are easily blocked in the DCS systems
- you can put pressure on the OEM due to lost revenue
- with a good pricing system, you never really sell full 100% seats (though I believe LH to be super-efficient)
Last edited by FlightDetent; 18th Sep 2019 at 00:13.
Only half a speed-brake
The red/green lines are the new limits, cca 4 points of % more forward than the original. A common operational rule is that additional 2 points % padding is applied due to uncertainties between reality and the paperwork.
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And therein lies the problem.
As the systems have improved, the point at which they fail keeps getting deeper and deeper into the areas that make the aircraft unnecessarily hard to fly. At some point, as they keep progressing, the 'system' will hand over a larger and larger bag of **** each time.
Airbus has had the effect of weakening pilot skills because they've automated a lot of the day to day stuff...but at the same time, when it all goes tits-up, you'll need those very same weakened skills.
Just a thought.....
As the systems have improved, the point at which they fail keeps getting deeper and deeper into the areas that make the aircraft unnecessarily hard to fly. At some point, as they keep progressing, the 'system' will hand over a larger and larger bag of **** each time.
Airbus has had the effect of weakening pilot skills because they've automated a lot of the day to day stuff...but at the same time, when it all goes tits-up, you'll need those very same weakened skills.
Just a thought.....
