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Author Topic: 707-320Badv vs 707-320C  (Read 1191 times)

Offline swiftus27

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707-320Badv vs 707-320C
« on: October 31, 2011, 11:58:30 AM »
Same Engines (Pratt & Whitney JT3D-3 )
Same Fuel Burn  (okay, 11,900 vs 11,910)
Same Pax  (180 max 210)
Same Max Range (4,390 vs 4,410)
Same MTOW (151,500)
Only 60m min runway difference

Explain to me why the max payload of the C is 34,000kg and the B is 21,400???  Shouldn't something above be different as well?

Offline Lurkmat

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Re: 707-320Badv vs 707-320C
« Reply #1 on: October 31, 2011, 02:32:01 PM »
Cargo space maybe?


Offline swiftus27

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Re: 707-320Badv vs 707-320C
« Reply #2 on: October 31, 2011, 02:47:21 PM »
But wouldn't that cargo make the plane consume more fuel?

Offline Meicci

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Re: 707-320Badv vs 707-320C
« Reply #3 on: October 31, 2011, 03:02:16 PM »
Maybe it would have lower fuel usage, but because of the increased cargo space it is same with the older one.. Just guessing.

Offline TK1244

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Re: 707-320Badv vs 707-320C
« Reply #4 on: October 31, 2011, 05:57:36 PM »
Explain to me why the max payload of the C is 34,000kg and the B is 21,400???  Shouldn't something above be different as well?
Because of the different undercarriage used by 320B and 320C. From 1965 all/most 320B's had the same undercarriage as the C, allowing the B to carry max payload of 34,000kg ;)
TK Regional

Offline swiftus27

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Re: 707-320Badv vs 707-320C
« Reply #5 on: October 31, 2011, 06:47:09 PM »
Thanks TK, but still... wouldn't another variable be different if it has to move 12,600 kg more!?

Offline alexgv1

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Re: 707-320Badv vs 707-320C
« Reply #6 on: October 31, 2011, 06:56:44 PM »
Thanks TK, but still... wouldn't another variable be different if it has to move 12,600 kg more!?

Maybe it was certified to that MTOW but it could never actually reach that because of the payload limitations on the undercarriage??
CEO of South Where Airlines (SWA|WH)

Offline TK1244

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Re: 707-320Badv vs 707-320C
« Reply #7 on: November 01, 2011, 09:13:36 AM »
Thanks TK, but still... wouldn't another variable be different if it has to move 12,600 kg more!?
Maybe it was certified to that MTOW but it could never actually reach that because of the payload limitations on the undercarriage??
Your welcome,
What I can remember is that the B actually was able to carry more payload, but due to the certification specifications, I was only certified for 21,400kg due to the undercarriage. The change allowed the aircraft to lift off the same amount as the C.
There are several aircraft which had the same problem, some solved the problem by adding a center main gear, like the A340.
TK Regional

Offline bdnascar3

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Re: 707-320Badv vs 707-320C
« Reply #8 on: November 02, 2011, 11:49:18 AM »
Also remember that this was still new technology, so the regulators took a very conserveative approach. MTOW could have changed on paper only with the 'new' model after regulators were convinced that it was safe.

Wizard

  • Former member
Re: 707-320Badv vs 707-320C
« Reply #9 on: November 02, 2011, 07:01:46 PM »
I found this:

707-320B Adv
Yes, Adv for "Advanced" like a 727-200Advanced.
This is a -320B with all the changes the -320C has, internal and external (loss of ventral fin, 3rd LE segment inboard, etc). Early (1st year) -320BAdv's still had the old-style nose gear doors, but most have the later rectangular ones. No cargo-door (duh), no hat-rack door. But otherwise identical to a -320C.

source: http://www.airlinercafe.com/page.php?id=72

Offline swiftus27

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Re: 707-320Badv vs 707-320C
« Reply #10 on: November 02, 2011, 08:30:49 PM »
I found this:

707-320B Adv
Yes, Adv for "Advanced" like a 727-200Advanced.
This is a -320B with all the changes the -320C has, internal and external (loss of ventral fin, 3rd LE segment inboard, etc). Early (1st year) -320BAdv's still had the old-style nose gear doors, but most have the later rectangular ones. No cargo-door (duh), no hat-rack door. But otherwise identical to a -320C.

source: http://www.airlinercafe.com/page.php?id=72

all I am asking:

If everything else is the same, how could this 707 be allowed to have such a higher MTOW.   It appears to burn no more fuel.  It isn't using more advanced engines.  All other stats on the compare aircraft page are almost exactly the same.

The doors don't make the difference in the stats here.  It's not like people/baggage weigh more or less because the door is shaped slightly differently.  Americans aren't THAT fat in the 1960s (I kid, I kid).   

Offline alexgv1

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Re: 707-320Badv vs 707-320C
« Reply #11 on: November 02, 2011, 10:34:44 PM »
As someone said previously it could be just what is down on paper for the MTOW rather than a practical issue.
CEO of South Where Airlines (SWA|WH)

Offline swiftus27

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Re: 707-320Badv vs 707-320C
« Reply #12 on: November 02, 2011, 11:29:55 PM »
As someone said previously it could be just what is down on paper for the MTOW rather than a practical issue.

I didn't dispute that.  Some are taking it too far in another direction. 


flightsimer

  • Former member
Re: 707-320Badv vs 707-320C
« Reply #13 on: November 03, 2011, 04:14:09 AM »
Gotta know how the aircraft were supposed to be used to understand it. The -320C was developed with cargo operations in mind. All the C was, was a 320B fitted with a cargo door and a new floor.

While the C did feature new landing gear bogeies that supported a higher MTOW, this higher MTOW wasnt directly caused by the new gear. To support the cargo operations, a new cargo floor was needed. This new floor was stregthened to support a heavier payload and this is directly where the increase in payload comes from.

Now payload is everything in the plane that is being carried (pax, baggage, cargo, etc). Because of the floor area restraints of carrying passengers, the C model will have the same payload weight as a B when carrying passengers in the same configuration. However, if the C were to be carrying all cargo, it will indeed lift more weight because of the fact that cargo is volume limited , not area.

So if you look at the payload range charts, you would see that at 34,000kg, the -320C will only go ~3000nm, while the 21,000kg -320B will go over 4000nm.

Fuel flow is going to be the same because its the same exact engines. the -320B and C both have the same engines and same fuel tanks. Because of this, you are trading off fuel for payload and that is why with an increase of 13,000kg's of cargo, the -320C goes 1000nm less than the -320B.  


This is the same reason why there has been no 777-200/200ER/200LR's converted into freighters yet. Boeing designed the 777 with a composite floor. When the 777-200F was designed, they replaced the composite floor beams with steel beams to support the weight of the cargo. Any converted 777's will be payload restricted simply because the floor wont be able to support the same weights the -200F does. However, structurally, the 777 airframe itself can support the same weights(relatively speaking) as the new factory built -200F's.

edit: while i say 320B or B model above, i am refering to the -320B Adv. I didnt feel like having to Adv every time i said it...

 

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