thepinkmachine
Topic Author
Posts: 386
Joined: Tue Apr 28, 2015 4:43 pm

A350 (alleged) FWD C.G issues

Sun Nov 24, 2019 4:44 pm

On another forum I have read that the 350 is prone to run out of forward c.g. at heavy weights and high fuel loads due to unfavourable fuel vector of the CTR tank - so that loadnig could be problematic, or even payload has to be reduced at times...

Do our resident 350 drivers confirm/deny it?

That would explain alleged payload reductions on long sectors and flying with empty seats, even though payload-range graph looks good. Also, this would explain why FWD cargo compartment was de-activated on the 359ULR... Any truth to it?

Pink (787 pilot and A350 fanboy :) )
"Tell my wife I am trawling Atlantis - and I still have my hands on the wheel…"
 
User avatar
Starlionblue
Posts: 19496
Joined: Fri Feb 27, 2004 9:54 pm

Re: A350 (alleged) FWD C.G issues

Sun Nov 24, 2019 11:15 pm

Never heard such a thing. But then again I don't do the loading.

Payload reduction on very long routes sometimes happens, but this has to do with running out of MTOW, same as any other plane. Strong winds have a big effect on long flights.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
zeke
Posts: 14161
Joined: Thu Dec 14, 2006 1:42 pm

Re: A350 (alleged) FWD C.G issues

Mon Nov 25, 2019 1:24 am

I started reading the thread on purine a week
or two ago where a VS person was saying how hard it is to load the A350 when flying it around empty.

I was thinking to myself therein is the real problem, not having any payload to pay for flying the aircraft.

That person had next to zero experience on type.

Our A350s like the A330s are near the forward limit when empty.

We have two trim sheets on the A350, one for training/ferry with less than 10 POB and the normal one for passenger operations. Reading between the lines VS don’t do this.

Never had a problem loading and I have been up to 280 tonnes on the A359 with passenger cabin full. Likewise been to MTOW on the A350-1000 with a full cabin.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
VSMUT
Posts: 3256
Joined: Mon Aug 08, 2016 11:40 am

Re: A350 (alleged) FWD C.G issues

Mon Nov 25, 2019 3:25 am

zeke wrote:
Our A350s like the A330s are near the forward limit when empty.


Do heavy premium seats contribute to this?
 
thepinkmachine
Topic Author
Posts: 386
Joined: Tue Apr 28, 2015 4:43 pm

Re: A350 (alleged) FWD C.G issues

Mon Nov 25, 2019 7:54 am

Thanks @Zeke and @Starlion blue, myth debunked :thumbsup:

Perhaps it has to do with VS configuration. Having said that, the CTR tank fuel seems to be moving the C.G. forward quite quickly.

Out of curiosity, what would be a typical C.G on a long flight with a full (-ish) pax load?
"Tell my wife I am trawling Atlantis - and I still have my hands on the wheel…"
 
User avatar
Starlionblue
Posts: 19496
Joined: Fri Feb 27, 2004 9:54 pm

Re: A350 (alleged) FWD C.G issues

Mon Nov 25, 2019 8:50 am

thepinkmachine wrote:
Thanks @Zeke and @Starlion blue, myth debunked :thumbsup:

Perhaps it has to do with VS configuration. Having said that, the CTR tank fuel seems to be moving the C.G. forward quite quickly.

Out of curiosity, what would be a typical C.G on a long flight with a full (-ish) pax load?


In the low to mid-30s % MAC is typical. It doesn't vary very much in flight because unlike the A330 there is no fore-aft fuel transfer to control cruise CG.

The centre tank doesn't have a big effect on CoG. Rather short moment arm.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
zeke
Posts: 14161
Joined: Thu Dec 14, 2006 1:42 pm

Re: A350 (alleged) FWD C.G issues

Mon Nov 25, 2019 10:32 am

thepinkmachine wrote:

Perhaps it has to do with VS configuration. Having said that, the CTR tank fuel seems to be moving the C.G. forward quite quickly.

Out of curiosity, what would be a typical C.G on a long flight with a full (-ish) pax load?


That’s what I didn’t understand about that pprune thread, fuel is loaded into the wings first before the centre tank. Loading the fuel into the wings moves the index units back around 240 units and then back to zero units at around 65 tonnes. Only above 65 tonnes it moves forward.

Typically as SB we are around 29-30% MAC at high weights. The takeoff band at 280 tonnes is between 26.8% and 28.2%. At 275 tonnes it’s at 26% to 33%.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
UAL916
Posts: 13
Joined: Thu Apr 17, 2008 11:53 pm

Re: A350 (alleged) FWD C.G issues

Wed Nov 27, 2019 10:57 pm

Very much so. Light loads, premium heavy forward cabins, and longhaul flights do not mix well. Seems to be more apparent on the A359 having offloaded many pallets of freight and cargo ULDs in my experience. Often times we cannot make use off all payload available, nor cargo volume since we hit the FWD CG limits.
 
User avatar
zeke
Posts: 14161
Joined: Thu Dec 14, 2006 1:42 pm

Re: A350 (alleged) FWD C.G issues

Thu Nov 28, 2019 6:14 am

UAL916 wrote:
Very much so. Light loads, premium heavy forward cabins, and longhaul flights do not mix well. Seems to be more apparent on the A359 having offloaded many pallets of freight and cargo ULDs in my experience. Often times we cannot make use off all payload available, nor cargo volume since we hit the FWD CG limits.


Absolute garbage post.

On the -900 if you only have load in the forward zone of the cabin (rest of the aircraft empty which is unheard of), that is -200 index units. If you fill up holds 3&4, and have hold 5 half full moves the CG 1050 index units aft (24 tonnes of cargo). 850 index units (1050-200) is equivalent to 18 tonnes on hold 2. That’s 42 tonnes of cargo (18+24), 4 tonnes of passengers, and whatever catering is being carried, around 51 tonnes total payload. You can carry that out to around 6000nm.

On the -1000 just fill up the forward cabin, rest of the aircraft empty that’s -300 index units. Throw 32.5 tonnes in holds 3,4&5, that’s around 1700 index units. Put 20.4 tonnes in hold 2 that’s -975, which leaves around another 5 tonnes in hold 1. That’s around 58 tonnes of cargo, 5 tonnes of passengers, and catering, around 68 tonnes of total payload.

These are both extreme cases with no economy passengers carried at all (which is not the way to run an airline, it posts to another bigger issue), carry even a small number of economy passengers and you can load even more.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
UAL916
Posts: 13
Joined: Thu Apr 17, 2008 11:53 pm

Re: A350 (alleged) FWD C.G issues

Thu Nov 28, 2019 5:01 pm

zeke wrote:
UAL916 wrote:
Very much so. Light loads, premium heavy forward cabins, and longhaul flights do not mix well. Seems to be more apparent on the A359 having offloaded many pallets of freight and cargo ULDs in my experience. Often times we cannot make use off all payload available, nor cargo volume since we hit the FWD CG limits.


Absolute garbage post.

On the -900 if you only have load in the forward zone of the cabin (rest of the aircraft empty which is unheard of), that is -200 index units. If you fill up holds 3&4, and have hold 5 half full moves the CG 1050 index units aft (24 tonnes of cargo). 850 index units (1050-200) is equivalent to 18 tonnes on hold 2. That’s 42 tonnes of cargo (18+24), 4 tonnes of passengers, and whatever catering is being carried, around 51 tonnes total payload. You can carry that out to around 6000nm.

On the -1000 just fill up the forward cabin, rest of the aircraft empty that’s -300 index units. Throw 32.5 tonnes in holds 3,4&5, that’s around 1700 index units. Put 20.4 tonnes in hold 2 that’s -975, which leaves around another 5 tonnes in hold 1. That’s around 58 tonnes of cargo, 5 tonnes of passengers, and catering, around 68 tonnes of total payload.

These are both extreme cases with no economy passengers carried at all (which is not the way to run an airline, it posts to another bigger issue), carry even a small number of economy passengers and you can load even more.


Thanks for the friendly reply. Given the conditions you listed its quite apparent it would in the FWD CG range. However, in the real world the loading is far from the variables you gave. Consider this: A359 uplifts 85+ tons of fuel for the flight, the route yield's a fair amount of premium passengers booking the J cabin full or nearly full. Throw in a 50% loaded Y cabin. Very rarely do we use the max payload available for the AFT hold, as we often volume out with baggage containers alone or with a 1-2T pallet thrown into the mix. Lastly bulk compartments at some airlines are not utilized to even half full, the A350 has an already smaller bulk compartment, and with airlines putting ever more pressure on baggage delivery goals bags are encouraged to be sorted and instead put in the appropriate containers. With the conditions I listed we often times see the CG go past the FWD limit or creep up to just short of it with not much margin.

Cargo varies day-to-day not every flight calls for 3-4T pallets which can help bring the CG in range. Certain routes can see 8-10 (1-2 Ton Pallets) which require more volume than payload. There isn't enough CG left on the table to bring it AFT with the above conditions. We have no options left and will call for the offload of a pallet or two since the CG is to far forward often times with only 1 pallet in the FWD compartment and the rest empty.

Now is this something we see on daily basis? No. However, it is far more common than you would think with Y class loads being low during the off season of travel. Operational days where there is very few cargo booked onto flights, requires moving around passengers in the Y cabin to the rearmost seats for takeoff, and no further bookings/ upgrades accepted for premium cabins.
 
User avatar
zeke
Posts: 14161
Joined: Thu Dec 14, 2006 1:42 pm

Re: A350 (alleged) FWD C.G issues

Thu Nov 28, 2019 5:18 pm

Still your claims are baseless.

With 85 tonnes of fuel the index moves forward around -220 index units (it’s zero at around 65 tonnes). To counter that all you need is 30 passengers in economy.

Deciding not to load the aircraft correctly by putting light baggage containers in the aft hold is hardly an issue with the aircraft. You can put them in hold 1 and the heavy cargo in the back.

We use bulk cargo all the time, again something your airline has chosen not to use, rather than a problem with the aircraft.

When’I get a chance I will do a trim sheet for yours 85tonne fuel, full premium, and half Y and show how it can easily be loaded to max load.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
UAL916
Posts: 13
Joined: Thu Apr 17, 2008 11:53 pm

Re: A350 (alleged) FWD C.G issues

Thu Nov 28, 2019 7:00 pm

zeke wrote:
Still your claims are baseless.

With 85 tonnes of fuel the index moves forward around -220 index units (it’s zero at around 65 tonnes). To counter that all you need is 30 passengers in economy.

Deciding not to load the aircraft correctly by putting light baggage containers in the aft hold is hardly an issue with the aircraft. You can put them in hold 1 and the heavy cargo in the back.

We use bulk cargo all the time, again something your airline has chosen not to use, rather than a problem with the aircraft.

When’I get a chance I will do a trim sheet for yours 85tonne fuel, full premium, and half Y and show how it can easily be loaded to max load.


I would love to post load-sheets however I cannot for obvious reasons. Notice I said 85 PLUS tons of fuel. 85 is merely the base fuel plug in some numbers well above 85T and you can see what it does to the CG. It would not be loading the aircraft incorrectly the difference is negligible two baggage containers can often times weigh around 1-1.5T side by side combined, which is not to far off from a pallet ranging from 1-2T. When possible placing the heavier quantity in the AFT is always performed but with near equivalent weights there is not much room for moving the CG back.

Factor in also that, J class pax often times do not check-in large amounts of luggage. Combine that with a 50% or less loaded Y cabin, there simply aren't enough baggage containers at times, and a operational day with light cargo bookings leaves the AFT hold not at maximum capacity and the FWD hold going empty. Its not uncommon to get creative at times and purposely put in large quantities of baggage/cargo in the bulk to shift that CG back AFT up against the FWD limit.

Again it seems to be only an issue at light loads in Y, heavy loads in Premium cabins, and high fuel uplift. When the Y cabin is booked to 70% or higher the CG is well within range with the pax weight, galley weight, and added luggage weight.
 
User avatar
zeke
Posts: 14161
Joined: Thu Dec 14, 2006 1:42 pm

Re: A350 (alleged) FWD C.G issues

Fri Nov 29, 2019 7:33 pm

UAL916 wrote:
Notice I said 85 PLUS tons of fuel. 85 is merely the base fuel plug in some numbers well above 85T and you can see what it does to the CG. It would not be loading the aircraft incorrectly the difference is negligible two baggage containers can often times weigh around 1-1.5T side by side combined, which is not to far off from a pallet ranging from 1-2T. When possible placing the heavier quantity in the AFT is always performed but with near equivalent weights there is not much room for moving the CG back.

Factor in also that, J class pax often times do not check-in large amounts of luggage. Combine that with a 50% or less loaded Y cabin, there simply aren't enough baggage containers at times, and a operational day with light cargo bookings leaves the AFT hold not at maximum capacity and the FWD hold going empty. Its not uncommon to get creative at times and purposely put in large quantities of baggage/cargo in the bulk to shift that CG back AFT up against the FWD limit.

Again it seems to be only an issue at light loads in Y, heavy loads in Premium cabins, and high fuel uplift. When the Y cabin is booked to 70% or higher the CG is well within range with the pax weight, galley weight, and added luggage weight.


So what I did was a generic trim sheet for a basic airframe at 130 tonnes at the forward CG limit at 775 IU. I put in 4900 kg of catering, 1215 kg of crew.

Cargo/bags loaded 2525 kg in hold 1, 18504 kg in hold 2, 9532 kg in hold 3, 13878 kg in hold 4, hold 5 (bulk) left empty. Front of the aircraft I loaded with 100%, 64 pax, in the back just 110 (51% load). Added 85500 kg of fuel (85000 at takeoff). That gives me a TOW of 280,000 kg with the CG within limits.

So the aircraft is carrying 55829 kg of revenue payload (41383 kg of cargo/bags and 14446 kg (174 pax)) around 14 hrs of flight time depending on what the company fuel policy says, and landing very close to MLW.

Now you are saying the issue is worse when more than 85000 kg is loaded. In my example above I have loaded it to MTOW, so if you load more fuel, payload has to come off to remain below MTOW. So I put another 10,000 kg of fuel onboard at takeoff, and also have to remove 10,000 kg of cargo.

As hold 1 & 2 are infront of the fuel tanks any forward shift of fuel by loading more into the center tank has a smaller moment arm than the removal of cargo from the forward hold. So I increased the load in hold 1 to 5000 kg, and decreased the load in hold 2 to 6029 kg, now with a cargo baggage load of 31383 kg, and MTOW at 280000 kg within limits.

The fact that I had to move load from hold 2 to hold 1 as more fuel is loaded means the issue does not get worse as more fuel is loaded, it gets better as the moment arm to the centre tank is smaller than the moment arm to hold 2, I had to move more load from hold 2 to hold 1 to get it in the envelope.

This is done for the 280 tonne MTOW aircraft which has a narrower CG band above 275 tonne.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
N212R
Posts: 222
Joined: Wed Dec 14, 2016 5:18 pm

Re: A350 (alleged) FWD C.G issues

Sun Dec 01, 2019 5:06 am

zeke wrote:
Absolute garbage post.


And yet I somehow find his first-hand explanation more believable than your back-handed, haughty dismissal.

Go figure...
 
User avatar
zeke
Posts: 14161
Joined: Thu Dec 14, 2006 1:42 pm

Re: A350 (alleged) FWD C.G issues

Sun Dec 01, 2019 5:40 am

N212R wrote:
zeke wrote:
Absolute garbage post.


And yet I somehow find his first-hand explanation more believable than your back-handed, haughty dismissal.

Go figure...


Don’t understand what you mean.

I have regularly operated the A350-900&1000 and have done so now for around 3.5 years. I would have to be in the top 5% of people with the most experience on type worldwide. Our fleet I understand has the highest daily utilisation worldwide.

I have regularly flown the type over long sectors with high fuel loads.

Never have I had these claimed CG issues. Normally we always have at takeoff CG around 29-30% which is nearer the aft limit.

And then we get a person saying they are having CG issues when they have stated heavy loads in the forward cabin and light loads in the aft cargo hold (which even a PPL holder would not do).

Instead of recognition that their actual issue is they way they choose to load the aircraft, not the aircraft itself.

And I have clearly debunked their claim about adding fuel moves the CG forward. In order to load the additional fuel payload needs to be removed from forward hold as the aircraft would be at MTOW which moves the CG aft as the moment arm to the forward hold is larger than the moment arm to the centre tank.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News

Who is online

Users browsing this forum: No registered users and 15 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos