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B-777F Question  
User currently offlineTheGov From United States of America, joined Apr 2003, 414 posts, RR: 3
Posted (1 year 9 months 5 days 6 hours ago) and read 4034 times:

I have a design question about the B-777F. Until the introduction of the 777F, all Boeing freighters with the exception of the 747F, had their main deck cargo door ahead of the wing. Why, then, did Boeing place the main deck cargo door on the 777F aft of the wing? I always assumed the reason it was aft of the wing on the 747F was because of the nose door option on the 747F but cannot come to a logical conclusion as to why the change on the 777F.
Thanks


Always a pallbearer, never a corpse.
14 replies: All unread, jump to last
 
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3477 posts, RR: 67
Reply 1, posted (1 year 9 months 5 days 5 hours ago) and read 3937 times:

Putting the door ahead of the wing risks interference between the cargo loader and the engine inlet, given the short 777F forebody. This concern goes away with the cargo door aft of the wing and there is adequate space between cargo door and wing. Having the wing trailing higher than the inlet lip also helps.

Besides, loading cargo from aft to forward instead of forward to aft, lessens the chance the airplane will be a tail sitter.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineViscount724 From Switzerland, joined Oct 2006, 24906 posts, RR: 22
Reply 2, posted (1 year 9 months 4 days 10 hours ago) and read 3336 times:

Quoting TheGov (Thread starter):
Until the introduction of the 777F, all Boeing freighters with the exception of the 747F, had their main deck cargo door ahead of the wing.

The MD-11C combi (not the pure freighter) had the main deck cargo door behind the wing. Only 5 of that model were built, all for Alitalia.


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User currently offlinebikerthai From United States of America, joined Apr 2010, 2072 posts, RR: 4
Reply 3, posted (1 year 9 months 3 days 18 hours ago) and read 3012 times:

Note that all the aft door examples are larger airplanes. Can you fit an aft door to properly fit on a 767-200?

bt



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlineStitch From United States of America, joined Jul 2005, 30636 posts, RR: 84
Reply 4, posted (1 year 9 months 3 days 18 hours ago) and read 3000 times:
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Quoting bikerthai (Reply 3):
Can you fit an aft door to properly fit on a 767-200?

It appears all the 767-200 passenger to freighter conversions have the main deck cargo door forward. The KC-46A will also have a forward door.

I expect this is the case for the 767-300P2F, as well, since new-build 767-300Fs have the door forward.

[Edited 2012-10-31 06:50:57]

User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2543 posts, RR: 24
Reply 5, posted (1 year 9 months 3 days 14 hours ago) and read 2911 times:

Quoting OldAeroGuy (Reply 1):

Putting the door ahead of the wing risks interference between the cargo loader and the engine inlet, given the short 777F forebody. This concern goes away with the cargo door aft of the wing and there is adequate space between cargo door and wing.

Manoeuvring the cargo loader around the wing trailing edge and avoiding the flap fairings must also be part of the equation for designers, especially for an aircraft with aft engines which have a correspondingly shorter rear fuselage.

Like the 777F, the A300 has a relatively short forward fuselage but the cargo conversions have the door forward of the wing.

Quoting OldAeroGuy (Reply 1):
Besides, loading cargo from aft to forward instead of forward to aft, lessens the chance the airplane will be a tail sitter.

All other things being equal this risk would determine the door placement I imagine.

Quoting Viscount724 (Reply 2):
The MD-11C combi (not the pure freighter) had the main deck cargo door behind the wing. Only 5 of that model were built, all for Alitalia.

Combis need to have the door aft if the pax are seated in the forward section. That's probably why the 747 has its side cargo door aft too, because IIRC that started life as a door for the Combi version.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlinebikerthai From United States of America, joined Apr 2010, 2072 posts, RR: 4
Reply 6, posted (1 year 9 months 3 days 13 hours ago) and read 2875 times:

The other design consideration when putting in an aft main cargo door aft is the location of the main landing gear bay and the aft lower cargo door. You need to space them far enough away to avoid stress flow from the major fuselage cut-outs from influencing each other.

Structural wise, with an aft door, wouldn't you weaken the fuselage from reacting load between the tail and the wing?
It would be easier to strengthen that aft door cut-out if the design was built in from the start.

Quoting OldAeroGuy (Reply 1):
Besides, loading cargo from aft to forward instead of forward to aft, lessens the chance the airplane will be a tail sitter.

You can turn that around . . . considering with an aft door you have no choice but put the first pallet in aft of the MLG.
With a forward door, you can at least get a few pallets in before you put that aft pallet in place.  



bt



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlineak907 From United States of America, joined Mar 2012, 42 posts, RR: 0
Reply 7, posted (1 year 9 months 3 days 9 hours ago) and read 2797 times:

Having the door aft of the wing has pros and cons when it comes to loading and unloading. On the pro side, when unloading, pallets come off and make the plane nose heavier, until pallets are moved back to be unloaded again. Repeating this the plane will become nose heavier throughout the unloading. When loading, pallets move into the plane, making it tail heavy, until pallets are moved forward, when it becomes nose heavy again. The con is, for example the 747F that has the capability to move all maindeck pallets forward of the door at once, the plane will become very tail heavy very fast.

A plane with the door forward of the wing, everything is reversed. the plane will become tail heavy during unloading unless steps are taken to move a certain number of pallets forward to equalize the CG. During loading, pallets are not moved to their final location when loaded, instead, they are temporarily positioned forward of the CG until more pallets are loaded. Then they can be moved to their final position.

Personally, I prefer planes with their cargo door aft of the wing, and my experience is with 744F, 748F, 762F, 777F, and MD11F. Interestingly, the cargo door on the 747-8F is closer to the wing than the 747-400F, even though its longer.


User currently offlineViscount724 From Switzerland, joined Oct 2006, 24906 posts, RR: 22
Reply 8, posted (1 year 9 months 3 days 9 hours ago) and read 2797 times:

Quoting Jetlagged (Reply 5):
Quoting Viscount724 (Reply 2):
The MD-11C combi (not the pure freighter) had the main deck cargo door behind the wing. Only 5 of that model were built, all for Alitalia.

Combis need to have the door aft if the pax are seated in the forward section. That's probably why the 747 has its side cargo door aft too, because IIRC that started life as a door for the Combi version.

DC-10 combis had the cargo compartment and main deck cargo door at the front, as on 707 and DC-8 combis. I recall a couple of Sabena DC-10 combi flights where the passenger cabin started behind the 2nd door. I doubt there was enough room behind the DC-10 wing for a cargo door and related ground equipment.


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User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (1 year 9 months 2 days 14 hours ago) and read 2582 times:

Quoting bikerthai (Reply 6):
Structural wise, with an aft door, wouldn't you weaken the fuselage from reacting load between the tail and the wing?

For other load reasons, the door is considerably stouter than the fuselage. All the cargo doors I've seen are load-carrying when closed (the 777F has a giant visible shear roller on the bottom edge for this reason) so, I suspect, the fuselage with the door closed is actually stronger than without the door there at all.


Tom.


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3477 posts, RR: 67
Reply 10, posted (1 year 9 months 2 days 10 hours ago) and read 2516 times:

Quoting bikerthai (Reply 6):
Quoting OldAeroGuy (Reply 1):Besides, loading cargo from aft to forward instead of forward to aft, lessens the chance the airplane will be a tail sitter.
You can turn that around . . . considering with an aft door you have no choice but put the first pallet in aft of the MLG.
With a forward door, you can at least get a few pallets in before you put that aft pallet in place.

But one pallet aft of the gear at the cargo door location is not enough to make the airplane tip.

After that pallet is moved forward, there is less chance for any subsequent pallet to tip the airplane.

Quoting Jetlagged (Reply 5):
Quoting OldAeroGuy (Reply 1):
Putting the door ahead of the wing risks interference between the cargo loader and the engine inlet, given the short 777F forebody. This concern goes away with the cargo door aft of the wing and there is adequate space between cargo door and wing.
Manoeuvring the cargo loader around the wing trailing edge and avoiding the flap fairings must also be part of the equation for designers, especially for an aircraft with aft engines which have a correspondingly shorter rear fuselage.

But the flap are retracted during cargo loading and the wing trailing edge is much higher than the engine inlet.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlinefuelfool From United States of America, joined Feb 2011, 138 posts, RR: 0
Reply 11, posted (1 year 9 months 2 days 8 hours ago) and read 2450 times:

Quoting Jetlagged (Reply 5):
Like the 777F, the A300 has a relatively short forward fuselage but the cargo conversions have the door forward of the wing.

The A310 is a nightmare. The MD is a pain, but the aft lower is horrible.



I love the smell of jet fuel in the morning...Smells like victory!
User currently offlineElpinDAB From United States of America, joined Apr 2005, 468 posts, RR: 4
Reply 12, posted (1 year 9 months 2 days 1 hour ago) and read 2356 times:

Quoting tdscanuck (Reply 9):
(the 777F has a giant visible shear roller on the bottom edge for this reason

I suspect this is here to support the weight of the door. The cargo door must weigh alot, being an add-on to an already structurally sound wall...To cut-out and then add on would add weight and structural necessity.

Basically, I think the roller would do nothing except neutralize any negative results.


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2543 posts, RR: 24
Reply 13, posted (1 year 9 months 1 day 13 hours ago) and read 2266 times:

Quoting OldAeroGuy (Reply 10):
But the flap are retracted during cargo loading and the wing trailing edge is much higher than the engine inlet.

I'm not sure what height has to do with this, at full elevation the loader will be above the level of both the engine inlet and wing trailing edge at full elevation, so clearance is required for either position. I didn't say the flaps would be extended but even when retracted the fairings project behind the trailing edge.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (1 year 9 months 1 day 7 hours ago) and read 2161 times:

Quoting ElpinDAB (Reply 12):

Quoting tdscanuck (Reply 9):
(the 777F has a giant visible shear roller on the bottom edge for this reason

I suspect this is here to support the weight of the door.

You're thinking of a different set of rollers. The shear roller is oriented such that it's literally incapable of supporting the weight of the door. It can only react fore/aft loads.

Tom.


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