Rear Engines...

[n757st]

The reason why no "new" aircraft are configured like an MD88 is because it is less efficient - particularly with new technology which alows pylon design to be optimized.

The reason Douglas and early jet makers used aft engines was to keep the wing clean. The British VC10 had the first supercritical wing - which just could not be done as well with engines disturbing the flow. Airflow around pylons was not completely understood, especially transonic flow. There are still advantages to a clean wing and new designs like the GV, Global Express and Citation X make the most of their efficient wings.

However, as the airplane scales up you have several problems:

First, aircraft with tail mounted engines typically get nose heavy with every pound of weight. The LEMAC is back there with the weight of the engines. Empty the opposite is true and I've heard some business jets can't go out with two pilots and full fuel due to aft CG limitations. Since airplanes are more efficient with an aft CG, having an airplane get more efficient at higher weights is a good thing.

Second, by suspending the weight of the engine mid span some of the stress can be removed from the wing spar & spar box. One "advantage" the DC-10/MD-11 had on the L1011 was that its' engines were mounted further out mid span and the forces were better distributed. The L1011 had all kinds of work arounds and still had spar problems. Many operators actually had to replace the rear spars in mid life.

Third, the lighter load on the fuselage allows for thinner - less heavy skins.

Fourth, the entire fuselage, keel, and systems weight of an all up aircraft can be reduced with everything located in the middle. Fewer fuel lines, bleed air lines, wires and what not make for a lighter airplane.

With new technology allowing engineers to whip up computational fluid dynamics models in almost real time on a PC wing mounted engines are starting to make sense in jet about every application. Look at the new Honda Jet, or an E170 - really elegant engineering solutions to get the most our of the least thrust and fuel burn.

I remember reading that another reason douglas went with that design was easier off loading of cargo, no special equipment was needed as bads could be loaded at ground level.

 

[IAHERJ]

Not to mentioned one of my favorite maneuvers, the POWERBACK!! Just saw AA do one here in Austin a few days ago.

Actually CAL used to powerback the 737-100/200 series years ago. It was a noisy experience.

IAHERJ

 

[CopilotDoug]

I remember reading that another reason douglas went with that design was easier off loading of cargo, no special equipment was needed as bads could be loaded at ground level.

Yeah, Douglas designed the DC-9s to be pretty self sufficient. No airstairs required either.

 

[aa73]

Not to mentioned one of my favorite maneuvers, the POWERBACK!! Just saw AA do one here in Austin a few days ago.

IAHERJ

IAH,

Strange, we quit doing powerbacks two years ago. Maybe the tug was broken? Anyways, yes, the powerback definitely puts hair on your chest. 73

 

[PhatAJ2008]

Why stop the powerbacks?