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39 votes
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Why was the DC-9-80/MD-80 so successful despite being obsolete almost from birth?

It's simple. Cheap (development costs amortized decades before) and reliable. They made money for airlines. Or, you know, they wouldn't have bought them. There's more to operating costs than fuel ...
John K's user avatar
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31 votes
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Why do airliners have "pressure bulkheads"?

What part aft of the bulkhead would leak pressure? That's a partial misunderstanding of what a bulkhead is there for. You could build the aft cone section to keep the pressure, but it would be a ...
Federico's user avatar
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16 votes
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Why does the DC-9-80/MD-80 have this cusp in its fuselage?

It's not a stress concentrator; it's just the opposite. What you're missing is that the floor itself at the pinched part forms a tension bridge that allows a more or less 'ovalized' circle while ...
John K's user avatar
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16 votes
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What is this hole on the tail of an MD-88?

That is the ram air intake for the air conditioning packs.
Mike Sowsun's user avatar
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15 votes

Why do airliners have "pressure bulkheads"?

You can think of an airliner (or any other pressurized airplane, or a submarine) as a pressurized container with control surfaces and a nosecone stuck to it. Rather like a submarine, an airliner has ...
Rostol's user avatar
  • 249
10 votes
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Why does the MD-87 have strakes on its engines?

They are indeed strakes which serve to reduce flow separation on the lower rear engine fairing by creating a vortex which will mix the outer, faster flow with the slowed down boundary layer on the ...
Peter Kämpf's user avatar
9 votes

Why was the DC-9-80/MD-80 so successful despite being obsolete almost from birth?

First, the airframe and systems were well-engineered and had few flaws and good aerodynamic qualities. Second, the cost to re-engine it with higher bypass ratio engines would have been high, and as ...
niels nielsen's user avatar
9 votes
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Did the DC-9 ever use RATO in revenue service?

The JATO/RATO retrofits were used only by Overseas National (later National Airways) when operating out of hot/high airfields for military contracts. They were never used as passenger flights, but you ...
Ron Beyer's user avatar
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7 votes
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What prevents DC-9 series aircraft from being reengined with more-efficient engines?

A re-engine program can be pretty expensive. This can make sense on military aircraft that take much longer to accumulate hours and cycles, or even cargo aircraft like the DC-8 in a similar position. ...
fooot's user avatar
  • 73.4k
6 votes

MD81: Why are there so many lights on the fuselage?

I think they are reflection from some light posts in the background environment (green line above the blue "horizon" light), and the reflection of the wingtip position light.
GHB's user avatar
  • 1,406
6 votes
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What is the round thing on the tip of an MD-90 wing?

This is a logo light. The MD90 as originally delivered to Delta didn't have these. This is the wingtip light arrangement on an airplane without the logo light.
Sports Racer's user avatar
  • 2,648
6 votes

Why does the DC-9-80/MD-80 have this cusp in its fuselage?

To add to John's answer, why did they do it? To make more room in the passenger area. It is important to remember that, opposite a submarine, pressure is higher on the inside of the aircraft in ...
Robert DiGiovanni's user avatar
5 votes

Why was the DC-9-80/MD-80 so successful despite being obsolete almost from birth?

The MD80 was not obsolete at the time of its first flight and the decade thereafter. The market situation for 150 pax aeroplanes around 1980: Boeing B727-200: first flight 1967. Three JT8D-7/9/11 ...
Koyovis's user avatar
  • 61.8k
5 votes

Why does the DC-9-80/MD-80 have this cusp in its fuselage?

This is called the "double bubble". The 737 has a similar but less pronounced design. Both aircraft had a primary requirement to seat a specific number of passengers in each row: 5 in the DC-9 and ...
bscottid's user avatar
4 votes

MD81: Why are there so many lights on the fuselage?

I'd say they're reflections. You can see the reflection of a building or something like it on the fuselage, and if you look close enough, you can see the poles of the 2 first lights. Also most of them ...
Sami's user avatar
  • 2,164
4 votes

Why do airliners have "pressure bulkheads"?

Pressure bulkheads are the primary structure members which combined with a fuselage or cabin provide a sealed pressure vessel and carry the fwd and aft pressure loads when the cabin is pressurized - ...
Romeo_4808N's user avatar
  • 73.8k
4 votes

Where can I find information on the DC-9's turn radius in flight?

No different from any other jet. Use this turn radius calculator http://www.csgnetwork.com/aircraftturninfocalc.html
John K's user avatar
  • 132k
4 votes

Why was the DC-9-80/MD-80 so successful despite being obsolete almost from birth?

There's also benefit to parts commonality between aircraft, where if all of the DC-9 variants that an airline was flying were using JT8D engines, then that's one less airframe difference to be ...
Milwrdfan's user avatar
  • 1,789
3 votes

Why does the DC-9-80/MD-80 have this cusp in its fuselage?

The answer is soap bubbles: They are filled with slightly higher pressure air, and when they're attached to each other, they have a planar "reinforcement-like" part between them. (see the picture) ...
Nyos's user avatar
  • 131
2 votes

Why do airliners have "pressure bulkheads"?

A dome is one of the most resilient and versatile shapes in engineering. It is the ideal shape to resist internal cabin pressure. When you blow a balloon it fills out into a sphere too. So the ...
kamran's user avatar
  • 995
2 votes

What is the round thing on the tip of an MD-90 wing?

It looks like a recognition/logo light or aft white position light. An MD-88 has a combination aft white position light and white strobe light assembly that is installed in the trailing edge of each ...
STWilson's user avatar
  • 1,746
2 votes

Why was the DC-9-80/MD-80 so successful despite being obsolete almost from birth?

Regarding the aspect of obsolence: in contemporary personal land transport, the Otto engine is, by pretty much all means, obsolete. There are very few cases in which the Otto engine outperforms an all-...
Jpe61's user avatar
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