Question regarding -400M (Combi)

[andrej]

With eminent end of life for KLM's B744 fleet and increased cargo fleet utilization, several interest threads appeared on airliners.net forums.

Few questions came up, that left me wondering as well. Given how well versed many of you are with B744s, I thought that I would ask here:

 

Is it possible to fly a combi with main deck pallets while the passenger cabin is empty without the center of gravity going out of limits? Since the cargo section is between doors 4 and 5, I'd imagine that would be very tail heavy. I know that there are ballast tanks, but is it sufficient to cover the "heavy" tail?
Is it correct, that initially, -400Ms came with a moveable wall? But then regulation came that it must have benn fixed in place? Am I mistaken this with something else?
Is the OEW still roughly 180 Tons? Besides strengthened floors, what other major modifications are there vs. -400?

Thanks for your answers!
Cheers,

[Hardy Heinlin]

As for the center of gravity: The combi can get tail heavy indeed, even when pax are in the cabin. This can be balanced by keeping a certain amount of fuel in the center tank (which is slightly forward of the center of pressure). For this reason the FMC PERF INIT page provides the BALLAST FUEL alert function for combis.


Regards,

|-|ardy

[andrej]

Thanks for your response Hardy. Yes, ballast fuel seems like the most logical response. Whilst typing my question, I was not aware that it can be up to ~45 tons. That would most likely be able to cover extreme situation (i.e. loading the cargo area on main deck). I have to say that I always liked -400M for its ability. It's like a Swiss army knife (to a certain point).

I looked at some available information and it seems that  that OEW and MZFW for -400M is higher vs. -400 (~2-5 tons), and it can carry anywhere from 7 - 16 tons more cargo (pax + freight). Would this be sound assumption or am I misreading data? 

It looks like every plane has unique weights (and this goes for all version). I was not aware that customer options and decisions could have such an impact on weights. It would be nice, if Boeing could provide such detailed information. Maybe one day.

Cheers

[DougSnow]

I was looking in the KLM 747 FCOM and for them, Ballast Fuel wasn't authorized for any 747, Pax or Combi.  I dont have a KLM 747 Weight/Balance Manual.

Both Boeing and Airbus provide a 2 volume weight and balance manual for each aircraft, Volume I (speaking of Boeings) are all of the standards for a given model - fuel distribution, and all the balance data for a given model (e.g., B747-400 with PW4056 at UAL). Volume II comes with each individual tail number and is the tailored empty weight report for each aircraft.

[Jeroen Hoppenbrouwers]

... and even when we install 6 pounds worth of equipment and wiring, we have to issue an amendment to adjust both weight and balance.

[michelvsr]

Hello,
In my airline, use of ballast fuel was not forbidden but not really recommanded because of two main problems :

-   Ballast fuel must be included in ZFW, in other words, ZFW + Ballast fuel < MZFW, condition which reduce strongly the possible effect
-   On aircraft with scavenge jet pumps, transfert of fuel from center tank towards main tank 2 and 3 begins when M2 or M3 < 27 tons without any possible control... This automatic transfert will reduce the ballast fuel quantity and this reduction is very difficult to evaluate...

Cheers.

[andrej]

I was looking in the KLM 747 FCOM and for them, Ballast Fuel wasn't authorized for any 747, Pax or Combi.  I dont have a KLM 747 Weight/Balance Manual.

Thanks Doug! Interesting information. This would suggest that KLM either limited its main freight deck utilization or there was no need to counter-balance the weight? Or is there other reason?

Seems like Volume II is much more valuable for all. Would it be destroyed once the plane is scrapped? I would be interested in getting such manual. I wonder if it is even possible.

... and even when we install 6 pounds worth of equipment and wiring, we have to issue an amendment to adjust both weight and balance.

That means that Volume 2 must have pages and pages of amendments. Interesting. Would this also include any addition to its skin (for example plates)?

-   On aircraft with scavenge jet pumps, transfert of fuel from center tank towards main tank 2 and 3 begins when M2 or M3 < 27 tons without any possible control... This automatic transfert will reduce the ballast fuel quantity and this reduction is very difficult to evaluate...

Thanks for this information, Michel. Seems like it was/is more limiting than I have expected.

Cheers,

[Jeroen Hoppenbrouwers]

Would this also include any addition to its skin (for example plates)?

Yes. When we install the Iridium antenna, which is like a shoe sole, we need to drill holes in the crown skin. This is a weak spot, so even for a one-inch round hole and four 1/4 inch bolt holes, we need to provide at least a doubler plate, and sometimes even a tripler, all riveted. Plus gasket etc. Then we typically install a tray against the crown from the inside and all this dead metal counts.


Hoppie

[JRBarrett]

Would this also include any addition to its skin (for example plates)?

Yes. When we install the Iridium antenna, which is like a shoe sole, we need to drill holes in the crown skin. This is a weak spot, so even for a one-inch round hole and four 1/4 inch bolt holes, we need to provide at least a doubler plate, and sometimes even a tripler, all riveted. Plus gasket etc. Then we typically install a tray against the crown from the inside and all this dead metal counts.


Hoppie

Along with a detailed structural analysis of the modification by a certified D.E.R. (At least for the initial installation if part of an STC). Sometimes the paperwork for these sort of projects weighs as much as the installed equipment!

[Jeroen Hoppenbrouwers]

It weighs more.

Our full equipment and tray is 4.5 pounds plus a few pounds wiring.

The paper stack for the 737 STC is two feet of USA Letter size paper. Ok it's a PMA, not a TSO. Everything is included.

Hoppie