69

I believe there this could be traced back to the so-called downwash angle of the air coming off the wing. Looking at the picture below (and put on some imaginary engines on the back like the DC9/MD80), it becomes clear that by mounting it upwards by a few degrees would make it meet the airstream at the streamline angle: You would want to that streamline ...


39

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 burn, and in any case, fuel prices in the mid 90s were cheaper than at any time since the 20s in constant dollars. Fuel was so cheap that Air Canada was ...


31

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 much heavier solution. The shape of the final aft section is not well suited to resist pressurization stresses: the best shape is a sphere; the cylinder (with ...


30

The vertical stabilizer is on the centerline. The line you see is not the centerline, it's the overlap of the aluminum sheets that form the circular fuselage. (Source) (Source) Non-aviation example of what I mean by overlap and centerline. On the other hand, propeller aircraft may employ different methods to counter the left turning tendencies. Tail ...


19

When the FLAP/SLAT handle is in the 0° to 13° range, the slats are in the mid-sealed position. The slats will be in the extended position whenever the FLAP/SLAT is in the 15° to 40° range. The range between 13° and 15° is the DO NOT USE range.[1] Given the above and the analogue nature of the input (dial-a-flap), between 13 and 15° the slats are very likely ...


16

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 still maintaining tension loading on the skins and frames as if it was a pure circle. If I had a rubber balloon filled with air and was able to run a string ...


16

That is the ram air intake for the air conditioning packs.


15

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 a floor with seats, a nose to make it aerodynamic, wings for lift, and a tail section for control (yes, I know I am way oversimplifying it, and that's the whole ...


10

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 lower rear part of the fairing. You will notice that the nacelle is mounted at an angle of 3 degrees to the fuselage: This is to position the intake and nacelle in ...


10

In most aircraft, the standby magnetic compass is mounted well above the main instrument panel, usually above the central window post, in order to reduce interference. In the three piece window of the MD-80 (without a central window post), this is not possible, resulting in the different location for compass. All the Douglas jet aircraft has this type of ...


9

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 could say that these were "revenue" flights as they were done for monetary compensation. I can't find any history on ALM980, only that it was registered as ...


9

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 such needed to be included in the cost-benefit analysis and balanced against the costs of operating the plane as-is with its original engines. The expected ...


9

Based on this diagram—found in this Boeing MD-80 series document—we can estimate the average lateral center of gravity along the buttock line for each passenger seat: Using the seating diagram that you provided in your question, I estimated the average center of weight along the buttock line for A, C, D, E, and F to be -50, -30, +10, +31, and +51 ...


9

The "D" seat is very near the aircraft centerline, and thus the roll axis. Since roll moment is the distance from the roll axis times weight, if the distance is small, the roll moment is very small. What roll moment is created can easily be canceled by a little bit of aileron trim if needed. The water tank on MD-80s is also placed on the LH side of the ...


8

Considering that the slide was not deployed, it is definitely unsuccessful. The MD-80 series (also the DC-9 and boeing 717) had tail cone assemblies which could be jettisioned in case of an emergency. When operated, the tailcone is expected to swing to the left of the fuselage due to to its own weight because of the way it was rigged. The jettison cone is ...


7

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. But the newest aircraft in the MD-80 series are going on 20 years at this point. They just don't have enough life left to justify that kind of expense. Most of ...


6

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.


6

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.


5

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 flight, rather than lower. So structural design favors a cross brace to hold it together. A submarine would be strongest if it were perfectly spherical. Also, ...


5

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 its successors, 6 in the 737. Seat-bottoms are the widest parts of the seat, so they made the fuselage the widest there. But continuing arc downward from there ...


5

On the fuselage, only 3 per side (discounting the red anti-collision which is above/below): Ground flood aka runway turnoff lights. Leading edge for inspecting the wing and for higher visibility on ground to other vehicles. Nacelle. (airliners.net) And here they are from an MD-80 flight manual:


5

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 engines. MD-80: first flight 1979. Two JT8D-200 engines. The first generation of JT8D had a bypass ratio of 0.7, the JT8D-200 engines had an increased bypass ...


4

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 are at or near the windows' corners. There aren't any housings or mounts to lights on those spots.


4

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 concerned about when it comes to maintenance and parts supplies.


4

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 - think of them kind of like the end caps on a cylindrical air storage tanks on an air compressor. As for the aft stairs on a DC-9 or a 727, the stairs are aft of ...


4

No different from any other jet. Use this turn radius calculator http://www.csgnetwork.com/aircraftturninfocalc.html


4

Your linked Google Images search leads to examples such as this: Source: amazon.com The manufacturer being Mechanical (the company's name). A little dive into the patents reveals this invention: Source: Google Patents US3145281A Also by Mechanical, for, you guessed it, a Multipole circuit breaker with trip devices located in the housing of a single pole. ...


4

Historical yet pertinent note: Concorde was the first plane to have electronic anti-skid, which means the DC-9 (also electronic) had the system installed after entry into service. The relevant patent for this answer is: Anti-skid control system for aircraft. The nose gear ground shift is part of the anti-skid system (see below; click to view). ...


4

Indeed the MD-90 elevator is different. It's hydraulically powered with manual reversion capability. Whereas the MD-80 is tab-controlled with nose-down hydraulic assist in extreme angles of attack (for stall recovery). The 2001 MD-90 bulletin (MD-90-01-02) could have been precautionary against the tab-controlled manual reversion when parked in gust ...


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