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Faro
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777LR Conformal Fuel Tanks For LHR-SYD?

Wed Nov 21, 2007 5:48 pm

A previous thread (http://www.airliners.net/discussions/tech_ops/read.main/209301/) established that wing-to-fuselage fairings are not a practical place to house extra fuel.

For the 777LR, and in order to make it a LHR-SYD reality, how about conformal fuel tanks? These can be installed in the upper fuselage-to-wing junction; any loss in lift on the inbord wing section can be compensated for by extending slightly the wing root leading edge.

Would such a bird fly economically?

Faro
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tdscanuck
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 5:36 am



Quoting Faro (Thread starter):
For the 777LR, and in order to make it a LHR-SYD reality, how about conformal fuel tanks? These can be installed in the upper fuselage-to-wing junction; any loss in lift on the inbord wing section can be compensated for by extending slightly the wing root leading edge.

Would such a bird fly economically?

I doubt it, because such a significant change to the aerodynamics of the aircraft would necessitate a significant (and hence expensive) recertification effort.

In addition, I think you'd find that cargo-hold auxiliary fuel tanks (which the 777-200LR is already certified for) would be a far more economical option. The wing/body fairing is one of the most aerodynamically sensitive spots on the whole aircraft. Adding something there is going to be a very significant aerodynamic and structural effort. Cargo hold aux tanks are, in comparison, a no-brainer.

Tom.
 
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Starlionblue
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 5:47 am

I would think there are better places for conformal fuel tanks than by the wing root. That spot is tough enough aerodynamically. Glom them onto the lower sides of the fuse and there are fewer aerodynamic issues.

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Zkpilot
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 6:48 am

Internal fuel is always a more efficient method for carrying fuel.
The reason why military fighters etc have external tanks is that they significantly increase their range (on a 777 they wouldn't make that much difference) and they are able to be jetisoned if the aircraft needs to quickly lose weight/improve performance (ie F16/F15 etc usually drop them if they are going into a dog-fight situation or supersonic flight).
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A342
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 8:14 am

Fuel volume is NOT the problem, weight is.
Exceptions confirm the rule.
 
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 10:09 am



Quoting Zkpilot (Reply 3):
Internal fuel is always a more efficient method for carrying fuel.
The reason why military fighters etc have external tanks is that they significantly increase their range (on a 777 they wouldn't make that much difference) and they are able to be jetisoned if the aircraft needs to quickly lose weight/improve performance (ie F16/F15 etc usually drop them if they are going into a dog-fight situation or supersonic flight).

The starter meant conformal tanks, not "drop" tanks that hang off the wing. Conformal means "with shape" so they follow the fuselage and "blend", if you will.

Fighters typically can have drop tanks. But there are some where later versions have added conformal tanks. Compare the "classic" F-16:

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... with the new version fitted with conformal tanks:

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Tristarsteve
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 1:08 pm



Quoting A342 (Reply 4):
Fuel volume is NOT the problem, weight is.

two years ago BA operated a standard B777-200 from BRU to MEL non stop on a charter for Tony Blair.
So I would agree. The B777 needs an increase in MTOW, not more fuel tanks.
 
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 4:54 pm

Quoting Starlionblue (Reply 2):
Glom them onto the lower sides of the fuse and there are fewer aerodynamic issues.

But it would be very difficult to show fuel tank integrity in the event of a gear up landing.

Quoting A342 (Reply 4):
Fuel volume is NOT the problem, weight is.



Quoting TristarSteve (Reply 6):
The B777 needs an increase in MTOW, not more fuel tanks.

For SYD-LHR, the 772LR needs a fuel volume increase far more than it needs an MTOW increase. The range for this mission is on the fuel volume limit portion of the payload-range curve, preventing it from being flown with economically useful payloads. An increase in MTOW without a fuel volume increase would not improve payload performance.

Of course if you could increase fuel volume enough, an MTOW increase might be useful for even better mission payload.

Quoting TristarSteve (Reply 6):
two years ago BA operated a standard B777-200 from BRU to MEL non stop on a charter for Tony Blair.

I would not characterize Mr. Blair as an economically useful payload.

[Edited 2007-11-22 09:02:13]
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Faro
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 5:08 pm

Thanx everybody for your input on the 777LR.

Now, what if I'm thinking newbuild? I can integrate conformal (or rather, integral overwing-to-fuselage) tankage and optimise my aerodynamics around the wing-fuselage junction from the outset, can't I? And taking fuel away from the wings and into these tanks would give me the added advantage of being able to design thinner, longer, quasi-gliderlike wings with higher aspect ratios. Would this make practical sense?

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mandala499
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 5:53 pm



Quoting Faro (Reply 8):
And taking fuel away from the wings and into these tanks would give me the added advantage of being able to design thinner, longer, quasi-gliderlike wings with higher aspect ratios. Would this make practical sense?

Errr...planes would use up their center tanks before going to wing tanks because they want to bring whatever weight off the body... spread the weight as they say...
Fuel in the hollow wing spaces is supposed to make the wing stronger...

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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Thu Nov 22, 2007 6:27 pm



Quoting OldAeroGuy (Reply 7):
Quoting Starlionblue (Reply 2):
Glom them onto the lower sides of the fuse and there are fewer aerodynamic issues.

But it would be very difficult to show fuel tank integrity in the event of a gear up landing.

Indeed. I wasn't suggesting it was a good idea.

Quoting OldAeroGuy (Reply 7):
Quoting TristarSteve (Reply 6):
two years ago BA operated a standard B777-200 from BRU to MEL non stop on a charter for Tony Blair.

I would not characterize Mr. Blair as an economically useful payload.

 rotfl 

Quoting Faro (Reply 8):
Now, what if I'm thinking newbuild? I can integrate conformal (or rather, integral overwing-to-fuselage) tankage and optimise my aerodynamics around the wing-fuselage junction from the outset, can't I? And taking fuel away from the wings and into these tanks would give me the added advantage of being able to design thinner, longer, quasi-gliderlike wings with higher aspect ratios. Would this make practical sense?

As Mandala499 mentions, fuel in the wings is a good idea since it counteracts upward bending moment. Fuel in the wings allows a lighter wing. Ideally, you want to store less in the fuse and more in the wings.

The practical solution is to make the wings larger for more tankage. See as an example the larger wings on the 345/346 compared to the earlier 342/343.
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Fri Nov 23, 2007 4:21 am



Quoting Starlionblue (Reply 5):
The starter meant conformal tanks, not "drop" tanks that hang off the wing. Conformal means "with shape" so they follow the fuselage and "blend", if you will.

Yes I know what he meant, and they are better allowing them to be used across a wider cross-section of the flight performance envelope... however I was meaning more along the lines that they can be dropped/removed when not needed (less likely with conformal of course as they cost more), but that they also use existing hardstore points where bombs/missiles would normally go. A 772LR has not hardstore points so far as I am aware except where the 2 engines are fitted and they could hardly be called hardstore points lol.
In any case installing an internal tank in the hold is the most practical solution to extra fuel needs.
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Faro
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Sun Nov 25, 2007 1:27 am



Quoting Mandala499 (Reply 9):
Quoting Faro (Reply 8):
And taking fuel away from the wings and into these tanks would give me the added advantage of being able to design thinner, longer, quasi-gliderlike wings with higher aspect ratios. Would this make practical sense?

Errr...planes would use up their center tanks before going to wing tanks because they want to bring whatever weight off the body... spread the weight as they say...
Fuel in the hollow wing spaces is supposed to make the wing stronger...

Agreed but the primary objective of desiging an efficient wing is to increase lift whilst reducing drag. If one can do that with longer, thinner wings which carry a little less fuel but are reinforced near the root in order to accomodate wing-to-fuselage faired fuel tanks, it's a design trade-off that may well be worth taking, no?
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Sun Nov 25, 2007 3:00 am



Quoting Zkpilot (Reply 11):
however I was meaning more along the lines that they can be dropped/removed when not needed (less likely with conformal of course as they cost more)

I'm pretty sure that conformal fuel tanks -- on the F-16 and F-15, at least -- cannot be dropped in the air. They must be removed on the ground.
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Sun Nov 25, 2007 8:06 am



Quoting Faro (Reply 12):
Agreed but the primary objective of desiging an efficient wing is to increase lift whilst reducing drag. If one can do that with longer, thinner wings which carry a little less fuel but are reinforced near the root in order to accomodate wing-to-fuselage faired fuel tanks, it's a design trade-off that may well be worth taking, no?

It may but longer thinner wings are better suited for lower speeds than jet airliners'.

Quoting Lemmy (Reply 13):
I'm pretty sure that conformal fuel tanks -- on the F-16 and F-15, at least -- cannot be dropped in the air. They must be removed on the ground.

Indeed.
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XT6Wagon
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Mon Nov 26, 2007 6:55 am



Quoting OldAeroGuy (Reply 7):
For SYD-LHR, the 772LR needs a fuel volume increase far more than it needs an MTOW increase. The range for this mission is on the fuel volume limit portion of the payload-range curve, preventing it from being flown with economically useful payloads. An increase in MTOW without a fuel volume increase would not improve payload performance.

Isn't that the 0 internal fuel tank curve though?

Regardless, it remains that unless you got more payload, its not going to be worth the extra plane type or extra fuel burn for any of the airlines currently flying that route with one stop.

That said, the 777-200LR with the GEnX'd engines, and other improvements that Boeing develops and rolls into the production model every few years could very well tip that balance. Its one of those routes that a tiny change in efficiency can make huge changes in the bottom line. Every pound of fuel you don't have to burn due to a small change is less cost and more payload. On a flight that long.... you have alot of hours and alot of miles to make tiny changes into dramatic ones.
 
tdscanuck
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Tue Nov 27, 2007 1:32 am



Quoting Faro (Reply 12):
Agreed but the primary objective of desiging an efficient wing is to increase lift whilst reducing drag. If one can do that with longer, thinner wings which carry a little less fuel but are reinforced near the root in order to accomodate wing-to-fuselage faired fuel tanks, it's a design trade-off that may well be worth taking, no?

It's theoretically possible but, in practice, it seems to be the case that the additional weight of the reinforcement doesn't buy its way onto the aircraft through increased performance. I have a very hard time picturing a circumstance where a conformal tank would come out ahead of a slightly thickened airfoil.

Tom.
 
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Tue Nov 27, 2007 5:58 am



Quoting XT6Wagon (Reply 15):
Isn't that the 0 internal fuel tank curve though?

The 772LR is fuel volume limited for the SYD - LHR mission ESAD with the three optional aux. tanks as well as with no aux. tanks. It's less limited with three aux. tanks of course, but still limited below an economically viable payload.

When Boeing was pitching a 772LR to Qantas for this mission, an additional three aux. tanks (six total) were proposed.
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XT6Wagon
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Tue Nov 27, 2007 10:29 am



Quoting OldAeroGuy (Reply 17):
The 772LR is fuel volume limited for the SYD - LHR mission ESAD with the three optional aux. tanks as well as with no aux. tanks. It's less limited with three aux. tanks of course, but still limited below an economically viable payload.

Good to know, still I bet that reduced fuel burn will make the 777-200LR turn the corner on these routes. Or not depending on GE and Boeings ability to reduce the fuel burn. Lower OEW or higher MTOW I doubt would be as productive, though possibly far more valuable to some of the other members of the 777LR family like the Freighter.
 
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RE: 777LR Conformal Fuel Tanks For LHR-SYD?

Wed Nov 28, 2007 6:04 am

To heck with conformal tanks, I want to see a 777 with tip tanks! That would nicely reduce the bending moment on the wings too. And probably do a nice secondary job as tip fences.

Note: although this suggestion should be considered tongue firmly in cheek, it's not all that farfetched. Consider the many fighters and biz-jets that used tip tanks, not to mention the B-52 (so those aren't quite on the tip, but close enough), some Canberras and the B-45.

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