A320 Load factor protection

[calypso]

Does any one know where does the load factor value comes from for the load factor protection. Is it a IRS feed or a predictive computation from the FAC based on other parameters ?. The FCOM does not say.

[LEVEL600]

Load factor is sensed by four accelerometers, which are mounted behind side panels in forward cargo compartment.

[calypso]

It rings a bell, thanks. Do you know how are they powered and what the logic is in case of failures? also would you have a FCOM reference.

[LEVEL600]

Power supply is provided thru "respective" computer : ACCLRM #1 from ELAC 1,ACCLRM #2 from SEC 1, ACCLRM #3 from ELAC 2, ACCLRM #4 from SEC 2. Single accelerometer fault causes only class 2 maintenace message, F/CTL will be displayed as STATUS for pilots. Btw. if ELAC 1, SEC 1 or 2 is deactivated as per MEL, due to power supply you lose one accelerometer too. If more than one acclrm. fails, aircraft switch to ALTERNATE or DIRECT law. FCOM probably does not cover description so deep. Just schematic in DSC 27-10-20 shows accelerometers input to ELACs. I am sorry, whole logic is not really so simple as I was able describe here from my memory.

[Microburst2002]

LEVEL 600 you know your stuff!

I have a question:

The load factor limit is based on the maximum loads, which are calculated for MTOW. So if the MTOW is 77 tons and in clean config the g limit is 2.5 gs, the maximum load is 77x2.5 tons right?

So if you are in approach to destination after a ferry flight and your GW is only 45 tons, you can only pull 2.5, with is much less load (45x2.5 tons).

So this "full authority" that Airbus boasts about in case of a GPWS is not so full, I guess, because if in that approach you would survive with a 77x2.5 ton pull up to avoid a mountain, but not with a 45x2.5 ton one… Well, someone could go to the lawyers and sue Airbus for a lot of millions

[Fursty Ferret]

Doesn't work like that. Load factor is effectively a force proportional to the weight. Just because the wings don't fall off doesn't mean you can exceed 2.5G on the rest of the structure (think cargo hold flooring etc).


Not sure what you're trying to prove re GPWS performance but you're completely wrong. Nominally the light and heavy aircraft will achieve the same acceleration in the pitch axis but the flight path change in the lighter aircraft will be faster.

[henra]

So if you are in approach to destination after a ferry flight and your GW is only 45 tons, you can only pull 2.5, with is much less load (45x2.5 tons).


And rightfully so. Fuel taken from the wing tanks won't help unloading the structure.
Only fuel taken from the Center tank would theoretically allow you to pull a little bit higher g without overloading the Center wing structure.
Still, even in that case the objections by @Fursty Ferret are valid.
Anyway if 2,6g instead of 2,5g would have saved the day I would consider that really, really unlucky. I don't remember a single case in aviation history where such a difference in allowable g would have made a difference....

[CONF iture]

Maybe in Perpignan pulling some extra G could have saved the day ...

[henra]

Maybe in Perpignan pulling some extra G could have saved the day ...

You can only pull as much g as the wings will carry. If too slow like in Perpignan, load factor protection won't make a difference.
More altitude and thus more Speed at the time of recovery would have made a difference.

[CONF iture]

180 to over 240kt is not little speed ...

[Microburst2002]

Fursty Ferret wrote:
Doesn't work like that. Load factor is effectively a force proportional to the weight. Just because the wings don't fall off doesn't mean you can exceed 2.5G on the rest of the structure (think cargo hold flooring etc).


Not sure what you're trying to prove re GPWS performance but you're completely wrong. Nominally the light and heavy aircraft will achieve the same acceleration in the pitch axis but the flight path change in the lighter aircraft will be faster.

Wow, Fursty, Where is your netiquette?

Actually, the limit load of an airplane is not measured in Gs, but in force (kilos or newtons or whatever). Then, certification requires that the airplane has to be able to withstand a given load factor at the certified MTOW. However, at less weights you need more Gs to have that same limit load.

[Clandestino]

Maybe in Perpignan pulling some extra G could have saved the day ...How many Gs one needs to pull up from 50° nose down at 1200 ft doin' 180kt. Say, what is A320 Vs1g in clean config at 53.7t?

Actually, the limit load of an airplane is not measured in Gs, but in force (kilos or newtons or whatever).Ever seen any real AOM/FCOM?

[CONF iture]

How many Gs one needs to pull up from 50° nose down at 1200 ft doin' 180kt. Say, what is A320 Vs1g in clean config at 53.7t?
As long as the slightest chance does exist to bring back the airplane to scrap it afterwards, anytime. Much better than scrapping it still brand new on the spot with all on board ...

[Microburst2002]

Clandestino, 2.5 g is a limitation you see in the FCOMs, but the limit load is just that: a load. If you don't exceed it you don't have any structural concerns.

At MTOW, you will reach that limit load if you pull 2.5 g. At lower weights you don't reach it with 2.5 g. It takes more g. that is why I say that in a GPWS scenario, you might require any extra g load available due to your weight being low.