747400sp
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Should Boeing Had Kept The 747 Wing At 40 Degrees?

Mon Apr 16, 2007 11:01 am

I read some where that Juan Tripp wanted the 747 wing to be swept at 40 degrees, but Boeing talk him into 37 degrees. It was said, that if Boeing did use the 40 degrees wing, the 747 cruising speed would have been around mach 0.87 to 0.88. With a cruising speed like that, the 747 would have been hard to beat. So do you think Boeing should have kept the 40 degrees wings?
 
cptspeaking
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Mon Apr 16, 2007 11:42 am

Depends...there are pros and cons to everything. Does your source mention why Boeing wanted the 37 degrees? It seems to me that if the pros outweighed the cons, then Boeing wouldn't have made the choice they did. I'm curious myself, I just don't think we've heard the whole story...

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Arniepie
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Tue Apr 17, 2007 12:41 am

Isn't a wing with 40° sweep more unstable specifically on approach (CitationX comes to mind as an example)?
Also you might need a higher Approach and landing speed combined with a higher TO speed which can than lead to reaching max ground speed for the tyres too quickly etc... .

As stated in previous answer probably just a compromise
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Tue Apr 17, 2007 1:12 am

The 40º sweep would have meant more cruise speed, but it would have introduced problems too, as stated, like more weight, etc. I'm afraid fuel consumption would be somewhat higher too, and with the increase of oil prices that happened on the decade of the 70's, I would say it was actually a luck for Boeing to have chosen the 37 degree sweep. The 747 would have been hard to beat, but only speed-wise, which is not the most important part for an airliner.
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FredT
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Tue Apr 17, 2007 1:42 am

Quoting 747400sp (Thread starter):
With a cruising speed like that, the 747 would have been hard to beat.

Instead of the commercial failure it turned out to be?
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474218
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Tue Apr 17, 2007 2:52 am

From what I read about Juan Tripp, he was a business man, not and aeronautical engineer. His input into the 747 was to say he would buy them if Boeing would design and built them.
 
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Tue Apr 17, 2007 5:54 am

The advantages of reduced wing sweep are:
- reduced structure weight
- improved fuel efficiency
- improved runway performance
- improved payload capability at hot and high ops.

The disadvantage is lower maximum cruise speed.

It's a trade off, a compromise. Everything on airliners are compromises.

Reducing the 747 wing sweep is totally in line with the current trend. Airlines don't sell speed any longer. They did that fifty years ago when airliners changed name from DC-4 over DC-6, DC-7 to DC-8. But those days are long time gone.

One decimal point on the cruise Mach number doesn't impress an airline manager these days if it means 100nm reduced range and five dollars extra fuel burn per pax on a long range flight. Plus slightly increased wear on wheels and brakes.

If airlines were selling speed, then the first thing they would do would be to reduce the rediculous check-in queues and demand (and pay for) their major hub airports to reduce the similar security queues. That way they could reduce total travel time to the same level as passengers were used to back in the 70'es and 80'es.

But that won't happen. Travel times seem to continue to increase year by year.
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Tue Apr 17, 2007 6:43 am

Quoting Prebennorholm (Reply 6):
The advantages of reduced wing sweep are:
- reduced structure weight
- improved fuel efficiency
- improved runway performance
- improved payload capability at hot and high ops.

With the supercritical aerofoils like used on the 777 and 380, one does not need as much sweep as on the 744 to avoid a large wave drag increase.
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Blackbird
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Wed Apr 18, 2007 11:28 am

Actually even with the 37.5 degree sweep the 747 is able to do mach 0.88 during a high-speed cruise despite the fact that it often flies slower. The reason lower speeds are selected is to reduce fuel-consumption.

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EssentialPowr
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Wed Apr 18, 2007 12:16 pm

Great point, Zeke.

All things equal, CFD (computational fluid dynamics) has produced consistent Mach .80-.86 range across the spectrum of current airliners, with less wing sweep, which provides advantages mentioned such as increased runway performance, less wing structure/build cost, and bending moments... at about the same Mach #s. The trend, until we have a quantum leap above even the Genx/Trent 1000 motors, is for wing sweep to decrease...
 
747400sp
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Wed Apr 18, 2007 1:07 pm

Quoting Zeke (Reply 7):
With the supercritical aerofoils like used on the 777 and 380, one does not need as much sweep as on the 744 to avoid a large wave drag increase.

Is the 747-8 going to have it's wing sweep less that earlier model of 747?
 
SCAT15F
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Wed Apr 18, 2007 2:12 pm

Quoting 747400sp (Reply 10):
Is the 747-8 going to have it's wing sweep less that earlier model of 747?

The 748 wing is going to be the same 37.5 degree sweep as far as I know (the wing will be re-lofted to make it supercritical but the planform will be the same)
 
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Wed Apr 18, 2007 10:45 pm

Quoting Blackbird (Reply 8):
Actually even with the 37.5 degree sweep the 747 is able to do mach 0.88 during a high-speed cruise

VC-25As routinely cruise at mach 0.90, so form a purely aerodynamic standpoint the wing isn't the limiting factor. As you said, the fuel consumption is the major issue.
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Max Q
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 2:31 am

Actually, Trippe wanted a sweep of 40 Degrees for the 747 and Boeing wanted 35, they compromised exactly in the middle at 37.5 degrees !
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Blackbird
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 3:46 am

To Dw747400,

Technically the 747 can fly safely up to Mach 0.92 (barber pole), of course fuel consumption would be rather high. The 747-SP occasionally did this, but it was a lighter design with nearly the same thrust so it wasn't as fuel thirsty.


Max Q, that is actually correct.

You have to keep in mind, PanAm had engineers of their own on staff for consulting should they need a new airplane from what I remember. And for a Mach 0.88 cruise, they felt a 40-degree sweep would be necessary to get the job done. Boeing wanted a 35-degree sweep because it would enable a greater span for the same area (aspect ratio), better low-speed performance, lighter structural weight, less extreme dutch-roll tendencies. So they compromised at 37.5 degrees sweepback.

As an interesting note... the DC-8 selected a 30-degree sweepback even though they knew 35-degrees would get them superior performance for high-speed according to their estimates, but because they wanted low-speed handling traits that would be closer to the DC-7's, particularly at high-flap settings for approach, I'm not sure if dutch roll was a factor, although a 30-degree sweepback would almost certainly have a lower-dutch roll tendency than a 35-degree wing. Ultimately they managed to get a airfoil-design that would achieve virtually the same high-speed performance of the 35-degree sweep, and provide the same performance of a 30-degree wing at low-speed, and probably the dutch roll characteristics of a 30-degree sweepback. Luckily they managed to get the best of both worlds. When Douglas scaled up it's design to meet Juan Trippe's desire for a 6-abreast plane, the tail was swept back 35-degrees to reduce drag, and wing area was increased substantially to hold the longer, wider fuselage, although the wing-sweep stayed about the same. The DC-8 was capable of virtually the same cruise speeds as the 707.


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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 3:55 am

Quoting Dw747400 (Reply 12):
VC-25As routinely cruise at mach 0.90, so form a purely aerodynamic standpoint the wing isn't the limiting factor. As you said, the fuel consumption is the major issue.

When I flew on the last AC 744 flight FRA-YYZ in 2004, I remember the Captain telling me that occasionally they flew mach 0.91 when late on an inbound flight. They figured that the additional costs of trying to find new flights/hotels and what not for those inconvenienced outweighed the extra fuel costs. On a side note we were 1h30 mins late leaving FRA and arrived a few minutes early in YYZ, after talking to the pilot her was cruising around for a good majority of the flight in the .88-.90 range. One down side however he explained that the air was actually supersonic over parts of the wing, leaving a slightly rougher ride.
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N231YE
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 4:00 am

Many good points and information here. However, don't forget that in the 1960s, speed was everything, so it made sense to design the 747 wing for high speed operations.

But then October 1973 came around, and things began to change...
 
EssentialPowr
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 5:10 am

Quoting N231YE (Reply 16):
However, don't forget that in the 1960s, speed was everything, so it made sense to design the 747 wing for high speed operations.

The point being that CFD allows contemporary designs to have the same speeds with less sweep...
 
SilverComet
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 5:21 am

How hard would it be to have a swing wing design on an airliner?
 
N231YE
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 6:21 am

Quoting EssentialPowr (Reply 17):
The point being that CFD allows contemporary designs to have the same speeds with less sweep...

My apologies...did not realize that. I was thinking that newer airliners have less sweep at a cost of less speed (efficiency matters more than speed, contrary to the 1960s).

I think I remember reading the 777 is actually one of the fastest, if not the fastest civilian aircraft today, thanks to a well-engineered wing...if that is true, then I see the connection: CFD would allow the 777 to be extremely cost efficient, one of the 777 program's driving forces, yet also have a high speed.
 
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 7:13 am

Quoting N231YE (Reply 19):
I think I remember reading the 777 is actually one of the fastest, if not the fastest civilian aircraft today, thanks to a well-engineered wing...if that is true, then I see the connection: CFD would allow the 777 to be extremely cost efficient, one of the 777 program's driving forces, yet also have a high speed.

The Queen of the Skies - 747 still holds that title, but the 777 is very close and uses less fuel at the same time. On a long flight 12hours+ (eg LAX-MEL, LAX-AKL etc) the difference can add up to a small but substantial amount of time.
My understanding of the 748I is that it will infact be M0.01 slower than the 744... anyone else out there know about/care to comment about this?  Smile
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 9:45 am

Quoting Zkpilot (Reply 20):
The Queen of the Skies - 747 still holds that title, but the 777 is very close and uses less fuel at the same time. On a long flight 12hours+ (eg LAX-MEL, LAX-AKL etc) the difference can add up to a small but substantial amount of time.
My understanding of the 748I is that it will infact be M0.01 slower than the 744... anyone else out there know about/care to comment about this?

I thought the 747-8 will actually be Mach 0.01 faster than the 744.
 
Blackbird
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 11:05 am

You know Mach 0.01 is only about 6.6 miles an hour @ 35,000 feet. It's not a major difference unless you're flying over an obsecene distance.

Andrea Kent
 
747400sp
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 1:02 pm

Quoting ZBBYLW (Reply 15):
One down side however he explained that the air was actually supersonic over parts of the wing, leaving a slightly rougher ride.

My father was told, that during alot of there military charter flight, Flying Tiger would fly there 747s at full speed and they were pretty bumply ride.
 
EssentialPowr
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 1:07 pm

Quoting N231YE (Reply 19):
...if that is true, then I see the connection: CFD would allow the 777 to be extremely cost efficient, one of the 777 program's driving forces, yet also have a high speed.

That is exactly right. The 777 is almost as fast as the 747 with less wing sweep, but has the aforementioned benefits of a "straighter" wing as well...
 
BAE146QT
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 4:43 pm

Quoting SilverComet:
]How hard would it be to have a swing wing design on an airliner?

I doubt it would be impossible, (though imagine rotating engine pylons!!!), but think about the problems that a swing-wing* is designed to solve.

Compromising on the (fixed) sweep of a wing solves many of the same problems but is far less complex and, more importantly, weighs less.

Incidentally, I read somewhere that although the 2707 was originally designed to have a swing wing, they dropped the idea, (before they dropped the project entirely) when they realised that the wingbox would occupy half of the fuselage.


*I'm assuming you mean a variable-geometry wing with perhaps 10 degrees of movement, rather than something like the F-14, whose flight regime is somewhat more varied than an airliner.
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speedracer1407
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 6:10 pm

Quoting SilverComet (Reply 18):
How hard would it be to have a swing wing design on an airliner?

To add to BA3-146QT's response, consider the fact that everything on a modern airliner is optimised for greatest efficiency within fairly narrow range of cruising speed. By increasing that cruising speed with variable geometry wings, many of the aerodynamic components such as control surfaces and engine nacells would have to be heavily research and developed for optimization at high subsonic speed. This, combined with the obvious weight and complexity costs, makes VG wings on commercial airliners impossibly expensive, at least in today's economy.

Such designs are often born out of necessity, so perhaps if the developed world's runways were far too short to accomidate heavy long-range aircraft, we might see unique designs such as VG jets that can take off and land on short runways, and then cruise at high speed for long distances.
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SilverComet
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu Apr 19, 2007 11:36 pm

Quoting BAe146QT (Reply 25):
I doubt it would be impossible, (though imagine rotating engine pylons!!!),

Yes I can easily imagine the complexity and weight penalty involved in rotating engine pylons for wing mounted engines. But I was thinking more along the lines of tail-mounted engines, with a wing sweep that ranged from (more or less) perpendcular to the fuselage for low speed flight to a significant amount of sweep for cruise. This would allow a lower approach/takeoff speed and hence higher weights on limiting runways and longer range cruises.

As I understand it, maximum cruise speed is limited by the critical Mach number. Having the wing sweep futher back when required would push that limit further back would it not? As far as drag is concerned, as long as we remain in the high subsonics, and given the wings are sweeping further back, it would not be that much of a penalty right? (Correct me if im wrong)

Quoting Speedracer1407 (Reply 26):
By increasing that cruising speed with variable geometry wings, many of the aerodynamic components such as control surfaces and engine nacells would have to be heavily research and developed for optimization at high subsonic speed.

Hmm i would think that as long as you don't go supersonic anywhere on the aircraft, the aerodynamics wouldn't change that much and only a reasonable amout of research would be required for optimization. I understand that due to the curvature of the fuselage and nacelles, you end up with varying 'local' airspeeds at different areas along the surface, but my understading is that this is most significant on the upper surface of the wing. Once you have solved that issue, the rest should be ok.

Quoting BAe146QT (Reply 25):
they dropped the idea, (before they dropped the project entirely) when they realised that the wingbox would occupy half of the fuselage.

That's exactly what i wanted to know. I am not familiar with the complexities of swing wing design. Didn't think it would take up that much space.

Thanks for your input, BAe146QT and Speedracer1407  Smile.
 
legoguy
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 20, 2007 12:13 am

Out of interest, what are the wing sweep of the following aircraft...

Boeing 757 / 757 / 747

and the Airbus A330 / (A345 + A346)

I know Airbus prefers the less swept wings.
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SCAT15F
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 20, 2007 12:21 am

Doesn't the MD-11/DC-10 have a really sharp sweepback? almost the same (if not the same) as the 747?
 
Blackbird
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 20, 2007 2:03 am

At Mach 0.88 the 747 has supersonic flow over parts of the wing? Or is that above Mach 0.88?

Regarding the MD-11 and DC-10, they have 35-degree sweepbacks

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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 20, 2007 3:38 am

Quoting SilverComet (Reply 27):
I am not familiar with the complexities of swing wing design. Didn't think it would take up that much space.

Huge weight and space penalties. Even military designers abandoned the concept years ago due to this. Wing technology which negated the need for variable sweep came along.
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SEPilot
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 20, 2007 8:35 am

Quoting Blackbird (Reply 14):
The DC-8 was capable of virtually the same cruise speeds as the 707.

I was under the impression that the high-speed aerodynamics of the DC-8 were never as good as the 707, which is why Juan Trippe never ordered another one after the initial 25.

Quoting SilverComet (Reply 18):
How hard would it be to have a swing wing design on an airliner?

As a machine design engineer, one of the maxims I live by is that it takes a lot of thought to make things simple. The idea of trying to make a swing wing airliner is one of those that gives me an instant headache. As others have pointed out, an airliner is designed to basically fly at one speed, and just has to be able to slow down enough to be able to land safely. It is so much simpler to do that with flaps and slats than it would be with a swing wing that it does not even rate discussing. The problem is that a swing wing would not do away with the disadvantages of more sweep in terms of structural strength and dutch roll characteristics, but would add immense problems in terms of weight, complexity (read maintenance), space, and reliability. How would you like to be a passenger in a swing wing jet and have the wings fail to swing back to low angle for landing? The military have a procedure for that; it's called ejection. Not practical for an airliner.
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EssentialPowr
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 20, 2007 1:38 pm

Quoting Blackbird (Reply 30):
At Mach 0.88 the 747 has supersonic flow over parts of the wing? Or is that above Mach 0.88?

What you are referring to is called "supercriticality" and it is common on contemporary jet wing designs for some local flow to be supersonic even at mach numbers as low as .78 or so...

Quoting Starlionblue (Reply 31):
Quoting SilverComet (Reply 27):
I am not familiar with the complexities of swing wing design. Didn't think it would take up that much space.


Huge weight and space penalties. Even military designers abandoned the concept years ago due to this. Wing technology which negated the need for variable sweep came along.

Not really. "Cost" is relative; witness the F14, F11 1 and B1. Since Supersonic a/c have nver worked very well in the domestic market, a swing wing airliner was never given much consideration although if politics (noise police) allowed it to proliferate, and if a supersonic a/c was ever going to be able to use 8000' or less runways, then a swing wing concept may very well have come to fruition.
 
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Sat Apr 21, 2007 12:09 am

Quoting EssentialPowr (Reply 33):

Not really. "Cost" is relative; witness the F14, F11 1 and B1.

Of course in some cases the cost and complexity is justified. But a new F-14 (F/A-18 and F-35 for example) does not have a swing wing.

Quoting EssentialPowr (Reply 33):
Since Supersonic a/c have nver worked very well in the domestic market, a swing wing airliner was never given much consideration although if politics (noise police) allowed it to proliferate, and if a supersonic a/c was ever going to be able to use 8000' or less runways, then a swing wing concept may very well have come to fruition.

Agreed. It's all about cost AND benefit.
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EssentialPowr
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 27, 2007 6:34 am

Quoting Starlionblue (Reply 34):
Of course in some cases the cost and complexity is justified. But a new F-14 (F/A-18 and F-35 for example) does not have a swing wing.

And neither do those a/c have the range/MGTOW/top speed combination of the F14, to include the -18E/F.
In fact, one of the many gripes about the F18 A/B/C/D was its short legs and the lack of landing weight. Either fuel good ordnance had to be dumped in a lot of cases...not a good combination. In order to get an a/c with the F14s weight and top speed on and off a carrier, swing wings were a necessity and probably still are for an a/c of equal capability.
 
Blackbird
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri Apr 27, 2007 10:58 am

Actually, I said "virtually the same" not "the same" regarding the DC-8's speed. I think the DC-8's problems weren't because it was slightly slower, it was because it's range came dramatically short of the planned target.

To my knowledge, the DC-8 has better landing performance, and about the same takeoff performance as the 707 (although the DC-8 might have a lower AoA due to the slots, and larger flap area)

Andrea Kent
 
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SEPilot
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Fri May 04, 2007 9:33 am

Quoting Blackbird (Reply 36):
Actually, I said "virtually the same" not "the same" regarding the DC-8's speed. I think the DC-8's problems weren't because it was slightly slower, it was because it's range came dramatically short of the planned target.

It was my understanding (much of which comes from "The Road to the 707" written by one of the engineers involved) that because of the fact that Boeing at this time had their own high-speed wind tunnel while Douglas had to rent time on the NACA tunnel plus Boeing's experience with the B-47 and B-52 that the 707 had much more air tunnel development than Douglas was able to manage which accounted for the difference in high-speed high-altitude performance; one penalty of which was range.
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Blackbird
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Sat May 05, 2007 5:58 am

I did not know that Douglas did not have a high-subsonic/transonic tunnel of it's own.

Andrea Kent
 
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RE: Should Boeing Had Kept The 747 Wing At 40 Degrees?

Thu May 10, 2007 1:26 am

Quoting Blackbird (Reply 38):
I did not know that Douglas did not have a high-subsonic/transonic tunnel of it's own.

They didn't in the 50's; they had to rent time in the NACA tunnel. I don't know if they built one later; I doubt it due to the financial uncertainties that dogged them for the rest of their existence. I also don't know if McDonnell had one either. Boeing built theirs during the war in a spectacular bit of foresight; they were rolling in money from building B-17's and B-29's, and had an inkling that the postwar period would be a time of major advances in aeronautics, and suspected that they would have trouble allocating the resources for it then. They committed to building a transonic wind tunnel before they were really aware of the possibilities of jet engines; they probably knew of Whittle's developments but nobody had any idea of what it would lead to. They had a very difficult time with wartime priorities getting it done, but they did, and it paid off hansomely down the road.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler

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