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Does anyone know why contemporary jet design has departed from
engines embedded in the wings or fuselage? The Comet had some
serious design flaws, but I can't find anything on the engine / wing
design being an inherently bad design.
-- kyle nicholls, August 11, 2003
In addition to the reasons posited by Brad, let me add a few...
Perhaps it is easier to change engine designs if the engine is less a part of the airplane. There are a lot of airframes, both in the piston and jet world, that have gone through a lot of different engine options over the years.
Richard Amster raised the possibility that jet engines need to have a fairly undisturbed stream of air coming in so that part of the turbine isn't "shaded". Maybe sticking the engines out on the wings helps ensure that at all airspeeds and attitudes the engines still get the air that they need.
-- Philip Greenspun, August 16, 2003
Oops, forgot to include a link to the Comet just in case you aren't familiar with the design!
The Royal Air Force (RAF) Museum has a really nice page of Comet info and images.
-- kyle nicholls, August 11, 2003
I suspect that in the late 1940's materials technology did not exist to safely and efficiently mount an engine outside the wing or fuselage as they are today. In many instances when turbine engine maintenance is required it can be a time consuming process. The resulting down time of the aircraft is a huge hit to the profitability of that machine. As a result, engines are often removed from the airframe and another bolted on allowing the aircraft back into service. An engine change on a modern airliner takes only a few hours whereas I think the embedded design would require much more time to access the engine.
A second consideration is that although turbine engines have containment rings at their circumference it is nice to know that if/when they destroy themselves and material exits the nacelle at tremendous speed it will not necessarily rip apart part of the wing too.
Just a couple of thoughts.
-- Bradrick Pretzer, August 12, 2003
Also, might add that the Engineers were possibly looking at the PERFORMANCE problems, mounting the JET ENGINES as close as possible to the CENTER of the JET would greatly reduce induced YAW at the onset of ENGINE FAILURE, therefore much easier to handle the airplane with engine failure as you do not have as much adverse yaw tendencies as opposed to the engines mounted on the Wings. The COMET did not have a super-critical "swept wing" design, found in later JET airplane designs, so I believe this had some bearing on the Engineers plans to construct where the powerplants would live on the airframe. There has been an EXCELLENT documentary in the past on DISCOVERY/WINGS Channel regarding the ill-fated COMET. Of course, its demise was due to lack of knowledge and lack of engineering concerning the PRESSURIZED CABIN especially the ROUND WINDOW designs which were not adequately strengthened to handle the enormous vessel pressures of high altitude flight. The results were catastrophic as it only took time for these airplanes to FAIL at the weakest point of the airframe, the ROUND WINDOW areas in the mid-section of the airframe.
-- MARK CASILLAS, August 18, 2003
Maybe it is something to do with maintenance - when the aircraft is on the ground and the engineers want to have a quick look around it puts the engines closer to them without the need for ladders and platforms. In-wing engines might also give the wing designers a headache trying to stop the engine centerline passing straight through the wing's main spa. There might also be some advantage when the thrust reversers are on, not throwing FOD up around the fuselage or trailing edge flaps - but this would probably be more a reason for having engines away from the fuselage rather than having them low-slung.
-- Steve Harrison, August 20, 2003
Some points: Pod mounted engine configurations do offer maintenace advantages. The 737 was re engined to a high bypass ratio fan from a low bypass engine with no drag penalty. They did have to worry about fod. IIRC the pod config also has some advantages in design for flutter. The pod mount requires a longer landing gear and thus more weight. The Germans tried a over wing pod mount but with, I think, some drag penalty. The design was not sucessful. Every modern design is driven by cost, efficency and very serious adversion to risk so an internal engine configuration would have to offer some very big efficiency advantages. I worked for NASA in a study group that looked at a/c configurations and other tech fixes back in the days of the first engergy crisis. Our previous work was on hypersonic transports. We were wild thinkers back then. Modern dirigibles, oblique winged transports, siteing nuke power plants in space and how to exceed mach 1 without the sonic boom. Fun times and fun people to work with. I wish I could remember the titles of a couple of very good Brit books on a/c configuration design to offer but old age and original sin have cought up with me.
-- michael harper, September 19, 2003
Not an aviaton expert at all (Discovery Wings and too many hours in Microsoft FS4 as a teenager only!), but I think that, while it could be done with a small straight turbo fan, it would be hard to fit a massive high bypass in the same location as the engines in the Comet. Should do some photoshopping on a 777 image to see what it would look like! ;-)
On the other hand, more planes were built after the Comet that didn't have high bypass engines, and still nobody seems to have done it.
I guess it would also be problematic running the main wing spar through the middle of an engine and going around it wouldn't be very strong.
Another reason I would never want it to be done: have you ever been stuck in the window seat in the last row of an MD-80? Not very pleasant at all.
-- Bas Scheffers, October 6, 2003
Flying through turbulence, while being unpleasant for the passengers, is also stressing the wings. To reduce this stress Boeing designed its model 707 with its four jet engines in pods hanging forward of the wings, held in position by fixations that are attached to the wing in a way that it slightly deforms wing camber when flying through turbulence, thus reducing the speed of air flow over the wing temporaely, which has a dampening effect. Boeing got the idea after one of its engineers had visited the Brisol Brabazon plant. Bristol engineers were the first to address the turbulence problem by using the protruding engines of the Brabazon as counterweights to influence wing camber.
-- Herman De Wulf, September 19, 2004
Stumbled across this searching for something else and thought I should shed some light on the issue.
The reason for embedded engines going out of style are manifold. The maintenance issues above play a part and podded engines do help alleviate certain flutter problems, but there are two other main factors:
1) You get long ducts either in or out of the engine. In will mean disturbed air to the engine and a loss of efficiency. Out will mean loss of efficiency due to losses in the tailpipe.
2) In case of uncontained engine failures or engine fires, the wing root is the last place where you want them to happen.
-- John Smith, March 11, 2005