Blackbird
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Jets Of The Eighties (Speed Or Fuel Consumption?)

Fri Dec 22, 2006 7:53 am

I noticed how many airplanes built in the eighties, the 767, the 757, the A-320, and such (technically the MD-80 was a derivitive of the DC-9, so I'm not listing it) were designed to fly at a slower Mach 0.80 or Mach 0.82

Did the aircraft designers choose the speed for efficiency, or did the airlines specifically ask for a slower aircraft hoping to save fuel?

Andrea
 
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Fri Dec 22, 2006 8:19 am

Through my research, I found that the 757 and 767, based on the 727-300/727XX/7N7/7X7 projects, were conceived right after the explosion in fuel costs in 1973. I also found this, which will answer your question (at least for the Boeing aircraft):

Quote:
Unlike the 727, which was designed for high performance in the 1960s, the 7N7 was aimed specifically at the economy minded short-haul routes where speed was less vital. Boeing calculated that climb consumed 60 percent of the fuel that the 7N7 would use on a 500-nautical-mile trip. It was therefore expected to spend almost as much time climbing and descending as cruising. As a result, the wing was optimized for a Mach 0.8 cruise, substantially less than the 727's Mach 0.9 top speed (147)

Norris, Guy. Boeing. MBI Publishing Company. Osceola: 1998
 
KELPkid
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Fri Dec 22, 2006 8:26 am

The fallout from the two oil cricises of the 1970's (1973 and 1979-and I remember the gas lines in '79  Wink ) had caught up with us by the eighties, and I think that's the reason that many airliner designs that began in the late 1970's and saw the light of day in the 1980's (e.g. 757/767) emphasized fuel effeciency. I also remember my first 767 flight, and thinking what a quiet plane it was compared to the 727's/DC-9's/737-200's  Smile
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Blackbird
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Fri Dec 22, 2006 12:00 pm

So if there was a plane that could do Mach 0.85 with the desired fuel efficiency, it would have been accepted by the airlines?

Andrea K
 
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zeke
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Fri Dec 22, 2006 11:27 pm

Quoting Blackbird (Reply 3):
So if there was a plane that could do Mach 0.85 with the desired fuel efficiency, it would have been accepted by the airlines?

The Convair 990 entered service in 1961, it cruised at M0.91, sadly it used too much fuel.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 12:14 am

Quoting Zeke (Reply 4):
The Convair 990 entered service in 1961, it cruised at M0.91, sadly it used too much fuel.

Wasn't that more a conesquence of Convair's choice of engines, though? The GE J79 wasn't exactly the most effecient engine around...  Wink
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Blackbird
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 5:18 am

So, the airlines would have accepted a Mach .85 plane if it was just as efficient as the 757/767/A-320?

Blackbird
 
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 6:30 am

Quoting Blackbird (Reply 6):
So, the airlines would have accepted a Mach .85 plane if it was just as efficient as the 757/767/A-320?

Sure. They would have accepted a Mach .95 plane. Even a Mach 1.2 plane if it had had the same fuel burn, the same noise footprint, the same maintenance cost etc....
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Blackbird
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 6:53 am

Of course....

They didn't know HOW to build a mach 0.85 airliner that could meet the fuel-burn requirements back then. I don't know if extensive wing/body blending, supercritical foils, and a 30-degree sweep even would have done the trick.

Andrea K
 
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 7:05 am

Quoting Blackbird (Reply 8):
Of course....

They didn't know HOW to build a mach 0.85 airliner that could meet the fuel-burn requirements back then. I don't know if extensive wing/body blending, supercritical foils, and a 30-degree sweep even would have done the trick.

Andrea K

Would that even do the trick today? Visions of unsold Sonic Cruisers flying past my head...  spin 
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Blackbird
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 8:18 am

I'm actually not entirely sure!

People knew about supercritical airfoils back then, but I'm not sure if they really had the technical know-how to make one extremely efficient. And it's not just the aerodynamics, it's the engine too! (although jet engines are affected by aerodynamic laws, I meant that even with a spectacularly advanced aircraft design, if you powered it by a crappy engine, it wouldn't work all that well.)

Andrea K
 
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 6:30 pm

Airliners used to be all about speed, romance, luxury and a whiff of danger. If you flew somewhere, you were important, on an important mission or stinking rich. Adjusted for inflation, a hop across the pond in a flying boat cost about as much in 1940 as a rocket ride in the Concorde in the modern era.

Somewhere along the way, airliners switched to hauling beef instead of passengers. Shorts, flip-flops and sleeveless T-shirts became the favored dress. Your seat mate turned into your 5-abreast row mate and he might just be stinking, rather than stinking rich.

Speed has become unimportant versus the ability to loft paying tonnage over vast distances. It is worse than sardines-in-a-can; it is more like rats-in-a-trap.

I expect that Greyhound will, someday, become an airline.
 
Blackbird
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RE: Jets Of The Eighties (Speed Or Fuel Consumption?)

Sat Dec 23, 2006 7:52 pm

Actually, how effective were 1975-85's supercritical airfoil designs? I'm actually curious

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