Cargo doors for dedicated freighters - aft or fwd of the wing

[medviation]

What are some of the advantages/disadvantages of having a main deck cargo door aft or forward of the wing on freighters? I'm sure loading sequences is critical as weight and balance is constantly shifting during the process. Which configuration is faster to load? Also on a structural point of view, which needs more reinforcing? And which one is better in general?

Forward:

http://avherald.com/img/yakutia_b752_vq-bpy_magadan_141206_1.jpg
https://previews.123rf.com/images/prestonia/prestonia1209/prestonia120900041/15103645-Airbus-A330-200F-on-display-at-Singapore-Airshow-February-03-2010-in-Singapore-Stock-Photo.jpg

Aft:

https://i.ytimg.com/vi/wiMRbCyDONA/maxresdefault.jpg
https://abpic.co.uk/pictures/full_size_0349/1523343-large.jpg

[A Squared]

Top, obviously.

https://eamonh.files.wordpress.com/2013/01/hatch-load.jpg

[pattern_is_full]

Ideally - you'd want the door to be between the landing gear, so as to prevent the first pallet put in the door causing the tail (or nose) to flop on the ground.

But there are always complications. In the case of the 777F, putting the door (for a standard container size) ahead of the wing far enough to minimize risk of a loader running into the #1 engine would have put the door into the area where the fuselage is shrinking down to cockpit diameter.

So Boeing put it behind the wing (as close as possible).

The 777F and that Rear Cargo Door | Things With Wings (http://aviationweek.com/blog/777f-and-rear-cargo-door)

On a C-47 taildragger, behind the wing is a no-brainer: 1) away from the props, 2) lots more area, 3) closer to the ground, 4) between the main gear and tail wheel for solid balance.

https://www.army.mil/e2/c/-images/2007/09/09/7423/size0-army.mil-2007-09-14-152855.jpg

On stretched airframes, and especially tail-holers (727/MD-80 variants) - doors ahead of the wings are 1) safely between the gear, 2) in the largest (and often "only") available area, 3) away from the engines.

http://cargofacts.com/wp-content/uploads/2013/06/275-FedEx727100onrampwithcaption1.jpg

That West Air ATPF looks a bit tippy to me, but again - 1) away from props, 2) largest area - plus the forward weight of the engines may be sufficient counterweight, for a careful loadmaster using a calculator. ;)

[stilton]

Interesting breakdown of freighter door positions PIF.


However all Boeing built 747 freighters from the 200 to the 400/400ERF and on to the -8
have had nose loading doors and a rear door behind the wing as standard equipment

[pattern_is_full]

Yeah - you're right - I misread a source.... :( Deleted...

To make up for that - if your "cargo" might just be a passel of skydivers - a door ahead of the engines would be a bluddy BAD idea.

https://cdn.jetphotos.com/full/1/69924_1194717460.jpg

[MarkerInbound]

I'd say we load through the nose only about 10 percent of the time. You can't load tall pallets through the nose so you are giving up a lot of volume, it isolates the cockpit for a longer time and you need ramp space forward of the aircraft. That being said, I've seen a good crew unload from the nose while loading from the side to save turn around time.

[DaveReidUK]

Yes, in fact there's a sequence in the recent ITV documentary series on Heathrow showing a ground crew doing exactly that on a CargoLogicAir 747-400F.

[medviation]

Ideally - you'd want the door to be between the landing gear, so as to prevent the first pallet put in the door causing the tail (or nose) to flop on the ground.

On a forward cargo door freighter you wouldn't position the first pallets at the back right away right? Otherwise you tip the aircraft.

http://www.iasa-intl.com/folders/belfast/Gemini_tipup/GeminiMD11-Dubai.jpg

You would have to constantly be shifting the already loaded pallets as more pallets are being loaded.

Whereas, on on the aft cargo door freighters, the first pallets loaded are positioned straight to the front to secure the CG of the aircraft for the rest of the pallets to be loaded.

Wouldn't an aft cargo door setup save time this way? Or what am I missing?

BTW this question is about landing gear configurations like the 777 or A330 not taildraggers.

[john_tullamarine]

.. hence one uses tail stands while loading/unloading .. takes the worry out of the equation.

[AC560]

I have seen more instances of a misplaced tail stand going into the fuselage then the tail dipping due to CG.

[john_tullamarine]

That's the advantage of discipline and checklists. Flew F27, L188, B727 freighters over a lengthy period .. don't recall ever having a problem with tailstand discipline.

Then again, not enough discipline and the story changes ... as you observe .. not to mention the occasional departure with one still firmly attached ..

[Goldenrivett]

That's the advantage of discipline and checklists.

I bet this ground crew wish they had used that and some SA.
(6 slides)
https://www.slideshare.net/guestcad801/plane-funat-china-airlines

[john_tullamarine]

.. oh, dear.

[parabellum]

You can't load tall pallets through the nose

Is that true of the dedicated -400F, built as such or just the ones that have been converted from the pax -400? I should know, having flown the dedicated -400F but it was a long time ago! I seem to remember there is a problem with pallet height, at the forward end, on the converted aircraft.

[SMT Member]

No converted -400 (or -200 or -300) have had the nose-door installed - that's only ever been an option on the production freighters.

As for height/width restrictions, the NCD offers a height of around 254cm, whereas the SCD has a height of 310. The NCD is also quite a bit narrower, at a minimum of 264cm vs 341 for the SCD. There's also height restriction all the way from the nose to behind the 'bump, with a max of 243cm vs 300cm in the remainder of the main-deck. Since the 'bump' on a converted -400 is quite a bit longer than on a production freighter, there are an additional 2 positions affected by the restriction.

[MarkerInbound]

Boeing didn't raise the cockpit on the factory freighters so both factory freighter and BCFs have a lower main deck ceiling towards the front. The upper deck is shorter on the factory freighters so more of the main deck can hold tall pallets/cans.

[john_tullamarine]

You can't load tall pallets through the nose so you are giving up a lot of volume

Then again, loading was a bit of a doddle on the Queen of the Skies (https://www.google.com.au/search?q=IPEC+Argosy+freighter&start=10&sa=N&tbm=isch&imgil=8NB_tljxrKp6PM%253A%253BRTq7TGnTfAHqpM%253Bhttp%25253A %25252F%25252Fwww.aussieairliners.org%25252Fargosy%25252Fvh-bba%25252F1920.027.html&source=iu&pf=m&fir=8NB_tljxrKp6PM%253A%252CRTq7TGnTfAHqpM%252C_&usg=__hHPZOk0_4kiM-Gd_7Hwcp9X3OxE%3D&biw=1366&bih=628&ved=0ahUKEwjYnMf-iZLUAhULe7wKHUx6D9k4ChDKNwgr&ei=6n0qWdj_F4v28QXM9L3IDQ#imgrc=8NB_tljxrKp6PM:).

(... exits, quietly, stage left ....)

[BluSdUp]

Not a good idea at all i suppose , for cost and structural reasons.

We can in the SLF ops do a much quicker turn with front and rear offloading and boarding onto apron. And lift-on wheelchairs front and back AND 20 minutes of fueling .
With airbridge, no way.
Is turnaround time as important with freight ops? It looks to me that a lot of large freighters are sitting idle.
We have from 06:00 until 24:00 to do our business, mostly.

Anyway , I am sure the loaders would find new way of tipping the Canoe!

One in front side, one behind wing, two loaders, incoming rear offload. New stuff, stuff it in front. Sounds simple, cant be.

I shall stick with SLF.
Happy Loading ( And Takeoff, Landing is the easy and fun part)

[vmandr]

@ OP

And which one is better in general?

maybe... the one that:
- has 2 crew ops
- burns least
- lifts more
- flies further

:)

[barit1]

Can there be any question?

https://s-media-cache-ak0.pinimg.com/originals/c5/a1/37/c5a13760db9e0000f462971c8b182a41.jpg

[CE-HAM]

I may have misunderstood this, but in the concept phase of the A320 P2F they decided to put the cargo door behind the wing, because the added structural weight of the door mechanism was beneficial for the angle of attack in cruise. Usually, the tail must be aerodynamically pushed down a little. This was then done by the added weight in the back - not the front.

[DaveReidUK]

Usually, the tail must be aerodynamically pushed down a little. This was then done by the added weight in the back - not the front.

If it was as easy as that, why didn't they build the A320 with the wing a bit further forward from the outset ?

[CE-HAM]

It's not easy. Moving wings or control surfaces forward and aft has many more consequences than moving "dead weight" as a door mechanism. For pax ops, the wing was/is in its optimum position. Now Airbus wanted to add some weight (the door) and it was better to put it aft of the wings and not forward. Thus the aircraft can be trimmed less nose-heavy and drag is reduced. In case of the B737 freighter the decision was different which proves that there are many factors more factors going into these decisions than I know of.

[Ex Cargo Clown]

Easy on a 74F, unload the rear MD and load Cpt 1&2 LD. Helped being able to put Q6 pallets through the nose as well.

[DaveReidUK]

It's not easy. Moving wings or control surfaces forward and aft has many more consequences than moving "dead weight" as a door mechanism. For pax ops, the wing was/is in its optimum position. Now Airbus wanted to add some weight (the door) and it was better to put it aft of the wings and not forward. Thus the aircraft can be trimmed less nose-heavy and drag is reduced.

Now you've lost me completely, I'm afraid.

If we agree that the 4,500 A320s built to date had their wing correctly positioned(!), then adding the additional weight of a cargo door either forward or aft of the wing would require compensating changes in the weight distribution on the other side of the wing in order to maintain the CofG in an acceptable range relative to MAC.

That's no different to what happened, for example, when they stretched the A320 into the A321 by inserting fuselage plugs both forward and aft of the wing - in fact the forward plug is around 50% longer than the aft one.

So it's hard to see how there would be any specific aerodynamic advantages resulting from putting an A320 cargo door aft, rather than forward of the wing.

[Lancelot de boyles]

If it's anything at all like a B737 freighter, the forward cargo door plus a bulkhead tends to bias to a forward CG in a vast majority of loads. Very forward, in some cases.
Flown empty, or with light loads, or with a container load each with similar masses, a ballast container aft is required to achieve an in trim configuration.
With a cargo net instead of a bulkhead, the forward CG is alleviated.
Add the longer fuselage of a -400, and you start to encounter greater considerations of fuselage bending (Banana).

[Rwy in Sight]

Just a question some one with very limited experience on cargo ops. How do you secure ballast in short notice? I have read once in PPRuNe that sometime in the past bricks were used for ballast but I don't remember how they were procured.

[FlyingStone]

Airbus had the "advantage" of not considering A319F when positioning the doors, as they only planned A320 and A321 conversions.

I don't think it's possible to put the cargo door aft of the wing on the 737-300, let alone -200 where everything started.

[Owain Glyndwr]

When I googled A320 P2F I found the following extract from "Air Cargo World":

>The technical challenge for EFW was resolving the issue of where to put the cargo door without aggravating the A320’s forward centre of gravity issue.

Aircraft stability involves balancing a number of factors including the centre of gravity (CG) and centre of pressure.

EFW’s head of aircraft conversion sales, Andreas Mayer, spoke to ACW and says: “We had the problem of a design decision to put a cargo door in the back, the A320 has a forward centre of gravity issue and putting structural reinforcement in the rear we would have cured that problem, but we created new problems by putting in a door at the rear because the structure was very weak at that area and we had to reinforce to a much greater extent and we were required to do a full fatigue test. Then we realised the aircraft is going into an unstable state, flutter, and it created…new technical challenges.”<

>Mayer explains: “We now have the door in the front. Our cargo door location is at two different locations for the A320 and A321, so we do not have the door in the same position.

“On the A321 it is further back due to the forward CG issue. We are trying to put the door as far back as possible without reducing loading clearance for the engine nacelle.”<

Does anyone know what the forward CG issue was/is? The text suggests it may be specific to a freighter version

[dixi188]

Maybe there is a lot more galley and toilet weight at the rear on a pax A320 that causes the fwd. C of G issue when it is removed.

[Owain Glyndwr]

Yes, I understand that removing the furnishings could move the empty CG forward, but why would that be a problem?

[barit1]

Pardon my dandruff while I scratch my head.

Seems to me the job of the cargo dispatcher is to plan the pallet etc. loading to optimize CG for the loaded aircraft. Given a random selection of heavy vs light pallets, he's got some pretty powerful levers to pull. And a loadmaster-type computer package to do 80-90% of the work.

I realize that a positioning flight gives him fewer tools - so be it. But what am I missing? :confused:

[Vessbot]

Now you've lost me completely, I'm afraid.

If we agree that the 4,500 A320s built to date had their wing correctly positioned(!),


That's not a necessarily true assumption... at least in the sense that there are no CG problems. Such problems are common.

For example, the CRJ 200 at full or nearly full loads is often outside the forward limit, requiring the movement of passengers backwards. If it's totally full so that no one can move, then you have to add ballast. Now if a 190 pounds jumpseater wants to get on, he's really a 400+ pound weight addition.

So it's hard to see how there would be any specific aerodynamic advantages resulting from putting an A320 cargo door aft, rather than forward of the wing.

Do you see it now? If you're more commonly bumping against one end of the allowable range, and you're about to add weight, naturally it's better to add it closer to the other end.

[DaveReidUK]

On converted, stretched bizjets, I can believe.

But on a clean-sheet airliner design? Did Airbus really get it that wrong?

[Vessbot]

Well I'm talking about the general case, I can't speak specifically to the Airbus. It could very well be perfect. And you're right that the CRJ isn't the best example, for the reason you said. But it shouldn't take too much imagination to consider that even a clean sheet design could fix the wing in place at a stage where it would take too much re-engineering to move it, and subsequently something else happens that moves the CG.

[Ex Cargo Clown]

Don't know if there any loadies/drivers on here but doesn't the MD11F have some serious ground CoG issues: