113312 From United States, joined Apr 2005, 416 posts, RR: 1 Reply 3, posted (10 months 2 weeks 1 day 18 hours ago) and read 3678 times:
The reason Boeing and Douglas designed their earliest turbojet planes with engines in pods were:
Get the engines away from the fuel tanks.
Isolate each engine from the other in case of fire or disintegration.
Isolate the engines from the wing structure for above reasons.
Facilitate maintenance and engine change.
Minimize the airflow disturbance on the wing.
I don't think even a small CFM (compared to the GE90) would be feasible, or any other HBP turbofan for that matter. The fan's diameter is just too large. And I'd presume having an engine pod/shroud conformed into the wing would be quite heavier with engines like these than the standard engine mountings used today. Not to mention engine removal for MX would be a pain, but I guess a rail(?) system like many fighters have, where the engines just slide in and out, could be feasible.
Quoting Panais (Reply 2): Yes, something like the Comet.
Considering how tiny those turbojets are, then yeah, they could pull it off. But there are very very few planes that ever had this configuration.
Happiness is just an illusion caused by the temporary absence of reality
Moose135 From United States, joined Oct 2004, 1115 posts, RR: 13 Reply 5, posted (10 months 2 weeks 1 day 18 hours ago) and read 3670 times:
With high-bypass turbofans, this concept isn't very feasible. You would need a *large* intake opening and "tunnel" through the wing, much larger than the Comet shown above, and that wouldn't work very well. Also, it makes the wing structure much more complex, adding weight to allow sufficient strength around the engines. Also, in the event of an engine fire, I think the last place you want the engine is buried in the wing, where the fire could more easily spread to fuel, electrical, hydraulics and other systems.
I have some friends who once worked for Grumman, and we were talking about the E-2 Hawkeye recently. There is a "hole" through the wing spar structure for the engine to pass through, and one of the struggles they had with trying to upgrade the engines was the diameter of the engine - Allison proposed a more powerful engine, but it had a larger diameter turbine, and Grumman wouldn't redesign the wing structure to accommodate the larger opening needed.
KELPkid From United States, joined Nov 2005, 4159 posts, RR: 8 Reply 6, posted (10 months 2 weeks 1 day 16 hours ago) and read 3598 times:
Quoting Panais (Reply 2): I would expect that the engines will be as further away as possible from the cabin.
The reason engines tend to be placed as close to the centerline of the aircraft as possible is to reduce the roll/yaw moment caused by an engine out situation, and keep Vmc (the minimum control airspeed with a single engine inoperative) within reason. If the pilot allows the aircraft's speed to fall below Vmc while climbing with an engine out, the plane will roll over onto it's back
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
SEPilot From United States, joined Dec 2006, 3936 posts, RR: 24 Reply 7, posted (10 months 2 weeks 1 day 15 hours ago) and read 3552 times:
The Comet was designed by engineers still used to piston engines, and buried the engines in the wings because that was similar to the way prop engines were mounted, at least in terms of the location of thrust vectors. But as 113312 points out, Boeing and Douglas found that there were decided advantages to pod mounting (Boeing actually developed the pod design for the B-47, and found that it had almost no aerodynamic penalty, as well as the functional advantages described.) Once turbofan engines came on the scene with their larger diameters, the structural problems of burying them have made any thought of burying them in the wing a total non-starter. This has also led to the death of tri-jet, as the larger the engine the more problems encountered in trying to mount one in the tail. Remember that the more complicated a structure, the heavier it will be, and having to go around a large engine greatly complicates any structure.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
474218 From United States, joined Oct 2005, 3745 posts, RR: 1 Reply 8, posted (10 months 2 weeks 1 day 14 hours ago) and read 3490 times:
Quoting KELPkid (Reply 6): The reason engines tend to be placed as close to the centerline of the aircraft as possible is to reduce the roll/yaw moment caused by an engine out situation, and keep Vmc (the minimum control airspeed with a single engine inoperative) within reason. If the pilot allows the aircraft's speed to fall below Vmc while climbing with an engine out, the plane will roll over onto it's back
If you have an effective rudder system the engines can be place further outboard on the wings, providing the paying passenger with a quieter flight. A perfect example is the DC-10 and the L-1011.
MD-90 From United States, joined Jan 2000, 7402 posts, RR: 18 Reply 9, posted (10 months 2 weeks 1 day 9 hours ago) and read 3389 times:
Quoting SEPilot (Reply 7): (Boeing actually developed the pod design for the B-47, and found that it had almost no aerodynamic penalty, as well as the functional advantages described.)
Well, credit does need to be given to the Germans. I believe they were the ones to discover that mounting engines in pods was the best way to go and Boeing got their hands on some of that data after WWII ended.
Starlionblue From Greenland, joined Feb 2004, 13570 posts, RR: 68 Reply 10, posted (10 months 2 weeks 1 day 8 hours ago) and read 3361 times:
Quoting 113312 (Reply 3): Get the engines away from the fuel tanks.
Isolate each engine from the other in case of fire or disintegration.
Isolate the engines from the wing structure for above reasons.
Facilitate maintenance and engine change.
Minimize the airflow disturbance on the wing.
AFAIK yet another reason is that engines slung forward alleviate wing twist. The wing tends to twist "back" and the weight of the engines counteracts the tendency.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
If you have an effective rudder system the engines can be place further outboard on the wings, providing the paying passenger with a quieter flight. A perfect example is the DC-10 and the L-1011.
Well, the DC-10 and and L-1011 were also trijets, not twins, which meant that losing a wing engine wasn't as big of a deal as losing one engine in a twin. The tail engine is also providing thrust, so the roll tendency isn't as great as it would be in, say, a 777-200LR [where you know that, should you lose an engine on takeoff, the other engine will be instantly cranked up to an insane 115,000 lbs. of thrust!]
I did get a few opportunties to fly on DC10-10s, thanks to AA, who used to use them on intra-Texas routes I remember it being a really cool experience, but I don't remember "quiet" being part of that experience (and come to think of it, I don't think "quiet" really descibed any McDonnell Douglas product particularly well ). The first plane that I recall really being blown away by how quiet it was was the 767...
I never did get to try the DC-10's competition, the L-1011, much as I wanted to... (and a crying shame that is! )
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
Tdscanuck From Canada, joined Jan 2006, 5639 posts, RR: 56 Reply 12, posted (10 months 2 weeks 1 day 6 hours ago) and read 3313 times:
Quoting Panais (Thread starter): Not hanging from the wing but being part of the wing. This will greatly reduce drag and therefore, make the plane faster and more fuel efficient.
I think it's pretty unlikely to reduce drag. Although the wetted area will go down, the weight is almost guaranteed to go up because now you need to carry wing bending loads around the engine (check out the banjo fitting on a DC-10 to see how ugly that can get). Also, with a modern high-bypass turbofan, the engine diameter is so large relative to wing thickness (especially if you stick it far outboard) that you've basically added two more fuselages (from the aerodynamic point of view). Wing-fuselage aerodynamics is among the toughest to optimize and it causes a bunch of problems...putting the engines in the wings makes this three times as bad.
If you can truly bury the engine in the fuselage, like fighters and UAV's do, then you can ditch most of these problems. However, for obvious reasons, you can't do that on a commercial jet.
Dw747400 From United States, joined Aug 2001, 975 posts, RR: 1 Reply 15, posted (10 months 2 weeks 1 day 3 hours ago) and read 3249 times:
Quoting KELPkid (Reply 11):
Well, the DC-10 and and L-1011 were also trijets, not twins, which meant that losing a wing engine wasn't as big of a deal as losing one engine in a twin.
Moving the engines outboard also provides structural benefits. Even in a twin, engineers will tend to move the engines outboard to maximize wing bending relief--they are just more restrained than in three and four engined jets.
If you talk to an engineer who worked on the L1011, they will point out that the wing engines are further outboard, providing a more efficient wing structure when compared to the DC-10. The -10, with its tail mounted engine, has less rudder area, and thus less rudder authority, than the L1011 with its buried engine. Some Lockheed guys are REALLY proud of this!
Alessandro From , joined Dec 1969, posts, RR: Reply 16, posted (10 months 2 weeks 1 day 2 hours ago) and read 3226 times:
Quoting MD-90 (Reply 9): Well, credit does need to be given to the Germans. I believe they were the ones to discover that mounting engines in pods was the best way to go and Boeing got their hands on some of that data after WWII ended.
Even better, Boeing got hold of German designers whom contributed a lot to the B707.
It seem a bit old fashion, Tu-104 and Tu-124 also had this design.
DocLightning From United States, joined Nov 2005, 7122 posts, RR: 44 Reply 17, posted (10 months 2 weeks 1 day 1 hour ago) and read 3202 times:
Quoting 113312 (Reply 3): The reason Boeing and Douglas designed their earliest turbojet planes with engines in pods were:
Get the engines away from the fuel tanks.
Isolate each engine from the other in case of fire or disintegration.
Isolate the engines from the wing structure for above reasons.
Facilitate maintenance and engine change.
Minimize the airflow disturbance on the wing.
And Area Rule. Putting engines out in front decreases the sudden cross-section change of the wing area.
Alessandro From , joined Dec 1969, posts, RR: Reply 18, posted (10 months 2 weeks 1 day ago) and read 3195 times:
Yes, many advantages of the current design, one of the few advantages I can see is less risk for FOD with things from the ground sucked into the engine when it´s higher up.
Jambrain From United Kingdom, joined Sep 2008, 130 posts, RR: 0 Reply 20, posted (10 months 2 weeks 15 hours ago) and read 3028 times:
Some of the blended wing designs have engines at least partially in wing e.g. http://www.aoe.vt.edu/research/groups/bwb/
To get the airflow to achieve high propulsive efficiency (it is more efficient to accelerate a large mass of air less) you would need a set of fans driven by gears otherwise the fan diameter would be too large.
SEPilot From United States, joined Dec 2006, 3936 posts, RR: 24 Reply 21, posted (10 months 2 weeks 15 hours ago) and read 3008 times:
Quoting HAWK21M (Reply 19):
If true.Structurally that would a huge load outboard.
That is actually an advantage; the more you can distribute the load over the wingspan the easier it is on the wing spars.
Quoting Alessandro (Reply 16):
Quoting MD-90 (Reply 9):
Well, credit does need to be given to the Germans. I believe they were the ones to discover that mounting engines in pods was the best way to go and Boeing got their hands on some of that data after WWII ended.
Even better, Boeing got hold of German designers whom contributed a lot to the B707.
It seem a bit old fashion, Tu-104 and Tu-124 also had this design.
What is your authority on this? I have read "The Road to the 707" by William Cook, who was one of the engineers on the project; he says nothing about any German engineers. And the Boeing design was quite different from the German design; the Germans had the engine tight against the wing (like the 732, which might have been influenced by the Germans) but the B-47 was suspended away from and in front of the wing, which was done to provide sufficient airflow between the engine and under the wing to avoid an increase in drag. This is something the Germans had not done. The idea of sweeping the wing was gotten from the Germans, as well as a lot of the jet engine technology, but I never heard that the podded engine ever was.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Scooter01 From Norway, joined Nov 2006, 845 posts, RR: 10 Reply 22, posted (10 months 2 weeks 10 hours ago) and read 2936 times:
Quoting SEPilot (Reply 21): Quoting MD-90 (Reply 9):
Well, credit does need to be given to the Germans. I believe they were the ones to discover that mounting engines in pods was the best way to go and Boeing got their hands on some of that data after WWII ended.
Even better, Boeing got hold of German designers whom contributed a lot to the B707.
It seem a bit old fashion, Tu-104 and Tu-124 also had this design.
What is your authority on this? I have read "The Road to the 707" by William Cook, who was one of the engineers on the project; he says nothing about any German engineers. And the Boeing design was quite different from the German design; the Germans had the engine tight against the wing (like the 732, which might have been influenced by the Germans) but the B-47 was suspended away from and in front of the wing, which was done to provide sufficient airflow between the engine and under the wing to avoid an increase in drag. This is something the Germans had not done. The idea of sweeping the wing was gotten from the Germans, as well as a lot of the jet engine technology, but I never heard that the podded engine ever was.
I believe MD-90 is onto something there. As we know, some of the German engineers went to the Soviet Union, where Bruno Baade was in the design-team that developed the Alexeev 150 bomber: http://www.aviastar.org/air/russia/alekseev_150.php
Not that any of these aircraft became any successes, they had other problems that plagued them, but one can clearly see where the podded engines and the bicycle type undercarriage came from.
Bsergonomics From United Kingdom, joined Jan 2002, 462 posts, RR: 0 Reply 23, posted (10 months 2 weeks 10 hours ago) and read 2926 times:
The wing-bending argument is irrelevant in the current age of material sciences. However, as Boeing found out (by accident) very early on, if you mount the engines further outboard and under the wing (the former is the important bit rather than the latter), it prevents wing flutter at higher Mach numbers.
So, (ignoring for the moment the arguments about risk assessments, maintenence, fuel capacity, etc.) if you want to mount an engine inside the wing, the big pay-off will be if you mount it in the middle of the wing, rather than close to the fuselage.
The Comet was a world-leader that was killed by its windows, not by the airframe, nor by the engines. However, there is a good lesson to be learned from the Comet - don't mount your engines next to each other. If one lets go, it's liable to take the other one with it.
Enjoy!
The definition of a 'Pessimist': an Optimist with experience...
Alessandro From , joined Dec 1969, posts, RR: Reply 24, posted (10 months 2 weeks 9 hours ago) and read 2913 times:
Quoting SEPilot (Reply 21): What is your authority on this? I have read "The Road to the 707" by William Cook, who was one of the engineers on the project; he says nothing about any German engineers. And the Boeing design was quite different from the German design; the Germans had the engine tight against the wing (like the 732, which might have been influenced by the Germans) but the B-47 was suspended away from and in front of the wing, which was done to provide sufficient airflow between the engine and under the wing to avoid an increase in drag. This is something the Germans had not done. The idea of sweeping the wing was gotten from the Germans, as well as a lot of the jet engine technology, but I never heard that the podded engine ever was.
OldAeroGuy From United States, joined Dec 2004, 2818 posts, RR: 61 Reply 25, posted (10 months 2 weeks 9 hours ago) and read 2912 times:
Quoting Bsergonomics (Reply 23): The Comet was a world-leader that was killed by its windows, not by the airframe, nor by the engines.
In the end though, the Comet configuration was a dead end design. What commercial airplane uses it today?
The B-47 configuration lives on in every Airbus and Boeing commercial transport in production today (except for the bicycle landing gear and the tandem flight deck).
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
Dw747400 From United States, joined Aug 2001, 975 posts, RR: 1 Reply 26, posted (10 months 2 weeks 9 hours ago) and read 3093 times:
Quoting Bsergonomics (Reply 23): The wing-bending argument is irrelevant in the current age of material sciences.
I'm not an expert on materials, but I don't see how the basic rule that reducing loads allows a smaller, lighter structure changing. It may shift on the priority list, but placement of engines, fuel, etc. along the wings should still be important in minimizing the structural weight--no matter what the spars are made of. If I'm missing something, please explain in more detail!
Quoting Bsergonomics (Reply 23): However, there is a good lesson to be learned from the Comet - don't mount your engines next to each other. If one lets go, it's liable to take the other one with it.
Also a lesson sadly taught by the Concorde.
Quoting Scooter01 (Reply 22): About engines buried in the wings, I cannot help thinking about the Avro Canada Jetliner:
Thanks for that link... very interesting aircraft I knew nothing about other than the name. Anyone notice the specs say this old bird had a near 1 to 1 thrust to weight ratio? 4x14,400 lbs with a Max Takeoff Weight of 65,000!
OldAeroGuy From United States, joined Dec 2004, 2818 posts, RR: 61 Reply 27, posted (10 months 2 weeks 9 hours ago) and read 3084 times:
Quoting Dw747400 (Reply 26): Anyone notice the specs say this old bird had a near 1 to 1 thrust to weight ratio? 4x14,400 lbs with a Max Takeoff Weight of 65,000!
I believe that 14,400 lb is total thrust rather than thrust per engine.
Dw747400 From United States, joined Aug 2001, 975 posts, RR: 1 Reply 28, posted (10 months 2 weeks 9 hours ago) and read 3068 times:
Quoting OldAeroGuy (Reply 27):
I believe that 14,400 lb is total thrust rather than thrust per engine.
Thanks, makes much more sense! I'm used to specs listing thrust per engine... should have read a bit closer.
By the way OAG, do you have any thoughts on the wing bending relief issue? I thought it was fairly well established as an important design consideration. You tend to be on top of these things!
OldAeroGuy From United States, joined Dec 2004, 2818 posts, RR: 61 Reply 29, posted (10 months 2 weeks 8 hours ago) and read 3061 times:
Quoting Dw747400 (Reply 28): By the way OAG, do you have any thoughts on the wing bending relief issue? I thought it was fairly well established as an important design consideration.
I don't understand the following comment.
Quoting Bsergonomics (Reply 23): The wing-bending argument is irrelevant in the current age of material sciences
Perhaps Bsergonomics will explain in more detail.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
HAWK21M From India, joined Jan 2001, 27758 posts, RR: 61 Reply 30, posted (10 months 2 weeks 7 hours ago) and read 3020 times:
Quoting SEPilot (Reply 21): That is actually an advantage; the more you can distribute the load over the wingspan the easier it is on the wing spars.
Considering the Weight of the Engines & the fuel on the outboard side,The wing root attachments would need to cater to a lot of weight.
Understandably no match for the An124 though in terms of wing root attachments load bearing capabilities
regds
MEL
Bsergonomics From United Kingdom, joined Jan 2002, 462 posts, RR: 0 Reply 32, posted (10 months 1 week 6 days 21 hours ago) and read 2865 times:
The comment about wing bending is being taken out of context.
Firstly, wing bending is important, but not paramount. The amount of wing flex on the A380 is simply astounding, but it does not adversely affect the airworthiness of the aircraft. That is due to the advaces in material science.
If you mount the engines further outboard (i.e., in the modern 'standard' configuration), you need extra strengthening on the wing spars in order to cope with not only their weight when the wings are unloaded (i.e., on the ground) but also due to the twisting moment caused by having underslung engines. If you bury them within the wing, close to the fuselage, both of these elements are eliminated, resulting in a considerably lighter wing due to the reduction in wing spar mass. It has the additional benefit that, in the event of the loss of one or more engines on one side, the yaw effect is considerably reduced.
Secondly and as stated above, one of the major benefits of mounting the engines further outboard is that it reduces wing flutter. If a 737 had 2 Comet-style engine mountings, the flutter would either limit cruising speed/VNE, or significantly increase fuel consumption (and, so, cost per passenger), or reduce the aircraft's lifespan (with inherent increases in through-life costs, particularly related to increased maintenance checks).
To cut a long story short, the current 'standard' configuration is due to accidents of history. Boeing tried the outboard configuration, and it worked. The Comet crashed due to its windows and, in the process, killed off the British civil aircraft production industry. Airbus more or less copied the Boeing configuration (I know I'm going to get shot down for that statement, but...). End result? Everyone has concentrated on refining what they are already doing. There have been no real lasting innovations in engine placement in the last 60 years (OK, the Trijet was tried but, ultimately, it died due to maintenance issues).
This isn't meant to mean that the inboard configuration is better than the outboard one, nor vice versa. It simply means that, due to accidents of history, the competition was 'called off' for reasons that had nothing to do with the argument under discussion. If the Comet had had small oval windows, we may have had an entirely different 'stndard' aircraft configuration today.
The definition of a 'Pessimist': an Optimist with experience...
SEPilot From United States, joined Dec 2006, 3936 posts, RR: 24 Reply 33, posted (10 months 1 week 6 days 19 hours ago) and read 2821 times:
Quoting HAWK21M (Reply 30): Considering the Weight of the Engines & the fuel on the outboard side,The wing root attachments would need to cater to a lot of weight.
I don't understand your point. My point is that any weight that is carried directly by the wing is not transferred through the wing root attachments. And if that weight is distributed over the span of the wing, it does not add stress to the spars.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Tdscanuck From Canada, joined Jan 2006, 5639 posts, RR: 56 Reply 34, posted (10 months 1 week 6 days 17 hours ago) and read 2794 times:
Quoting Bsergonomics (Reply 32): If you mount the engines further outboard (i.e., in the modern 'standard' configuration), you need extra strengthening on the wing spars in order to cope with not only their weight when the wings are unloaded (i.e., on the ground) but also due to the twisting moment caused by having underslung engines. If you bury them within the wing, close to the fuselage, both of these elements are eliminated, resulting in a considerably lighter wing due to the reduction in wing spar mass.
I don't believe this is right. Although having the engines outboard will increase the wing root moment when you're parked on the ground, I'd be really surprised if that's the limiting load for the wing. If it is, then yes, you'd have to increase the spar strength. But all of the ultimate load wing tests I've ever seen are bending wings up (flight load), not down (ground load), which means that that critical load is the flight ultimate load. In that case, the engine weight is helping you by reducing the wing root bending moment.
In addition to that, I'm pretty convinced (primarily based on the DC-10 banjo fitting) that the total spar weight increase because the fitting you'd need to carry the spar loads around the engine for an in-wing engine would grossly overshaddow any weight savings you got in the outboard part of the spar.
I'd love to see some counterexamples (that use high-bypass fans) but something doesn't smell right about this.
Quoting Bsergonomics (Reply 32): It has the additional benefit that, in the event of the loss of one or more engines on one side, the yaw effect is considerably reduced.
This is certainly true, and I strongly suspect this is a significant driver in any trade study for exactly where to put the engines on the wing. You've got multiple competing factors, and since adverse engine-out yaw drives tail volume, this must be a consideration.
SEPilot From United States, joined Dec 2006, 3936 posts, RR: 24 Reply 35, posted (10 months 1 week 6 days 16 hours ago) and read 2760 times:
Quoting Bsergonomics (Reply 32): To cut a long story short, the current 'standard' configuration is due to accidents of history.
I would argue this. I know that Boeing has constantly played with all kinds of configurations, and I strongly suspect that all of the other manufacturers have as well. The fact that all new airliners follow pretty much the same configuration is because it is the one that works the best. Aerodynamic principles are not dependent on who discovers them; they function exactly the same for Airbus as they do for Boeing (or anyone else, as well.) And just because planes look alike (this also applies to the earlier discussion about the German origins of engine pods) does not mean that one is copied from another; it is perfectly possible for two different designers to independently come up with the same arrangement as the optimum.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Starlionblue From Greenland, joined Feb 2004, 13570 posts, RR: 68 Reply 36, posted (10 months 1 week 6 days 12 hours ago) and read 2679 times:
Quoting Bsergonomics (Reply 32): If you mount the engines further outboard (i.e., in the modern 'standard' configuration), you need extra strengthening on the wing spars in order to cope with not only their weight when the wings are unloaded (i.e., on the ground) but also due to the twisting moment caused by having underslung engines.
I agree with Tdscanuck in challenging this. The wing tends to bend over backwards and wing twist is actually counteracted by slinging the engines forward.
Putting the engines outboard enables a lighter spar.
Tact Is For People Who Aren't Witty Enough To Be Sarcastic
HAWK21M From India, joined Jan 2001, 27758 posts, RR: 61 Reply 37, posted (10 months 1 week 6 days 5 hours ago) and read 2550 times:
Quoting SEPilot (Reply 33): it does not add stress to the spars.
The load on the wing root would be much more for a longer span wing & fitted with Engines too,add the outboard distribution of fuel load.
true there are stringers/spars in the wing to distribute the load,but the wing root would be taking a higher load that normal in such cases.
regds
MEL
Alessandro From , joined Dec 1969, posts, RR: Reply 38, posted (10 months 1 week 6 days 1 hour ago) and read 2487 times:
Quoting Bsergonomics (Reply 32): Airbus more or less copied the Boeing configuration (I know I'm going to get shot down for that statement, but...). End result? Everyone has concentrated on refining what they are already doing. There have been no real lasting innovations in engine placement in the last 60 years (OK, the Trijet was tried but, ultimately, it died due to maintenance issues).
This isn't meant to mean that the inboard configuration is better than the outboard one, nor vice versa. It simply means that, due to accidents of history, the competition was 'called off' for reasons that had nothing to do with the argument under discussion. If the Comet had had small oval windows, we may have had an entirely different 'stndard' aircraft configuration today.
No they didn´t, the engine pod designs for the A300 was bought from McDonnell-Douglas.
Sure the Il-62 and Vic-10 later had 4 engines stacked in the back, Comet didn´t kill the British civilian airspace, the independence of colonies did.
SEPilot From United States, joined Dec 2006, 3936 posts, RR: 24 Reply 39, posted (10 months 1 week 5 days 23 hours ago) and read 2440 times:
Quoting HAWK21M (Reply 37):
The load on the wing root would be much more for a longer span wing & fitted with Engines too,add the outboard distribution of fuel load.
Wrong. The wing distributes lift over its span; any weight that gets distributed over the span is lifted directly, almost like a balloon. That weight does not figure into the wing-fuselage interface; it is borne entirely by the wing.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Moriarty From Sweden, joined Jan 2006, 114 posts, RR: 0 Reply 40, posted (10 months 1 week 5 days 22 hours ago) and read 2417 times:
Just a note:
Quoting Alessandro (Reply 24): The Comet was a world-leader that was killed by its windows, not by the airframe, nor by the engines. However, there is a good lesson to be learned from the Comet - don't mount your engines next to each other. If one lets go, it's liable to take the other one with it.
Concorde... among others. The Concorde crash was a result of a chain of events, one of them was the fact that the engines are/was close to each other.
I assume there are similar risks with the Bone, T-160 and so on. However, not sure how many incidents/accidents that are related to one engine being too close to another on those models.
VC10 From United Kingdom, joined Nov 2001, 1182 posts, RR: 20 Reply 41, posted (10 months 1 week 5 days 17 hours ago) and read 2312 times:
Quoting Moriarty (Reply 40): assume there are similar risks with the Bone, T-160 and so on. However, not sure how many incidents/accidents that are related to one engine being too close to another on those models.
You can possibly enlighten me on accidents were both engines have failed due to being along side each other, but I cannot think of any at the moment, however that does not mean there were not any. Whilst accepting that close engines can cause common problems from ingestion, again I cannot think of a serious incident and I was on aircraft [ for thirty years] that all had engine along side each other.
The Concordes problems was their proximity to the landing gear wheels rather than to each other
Also pylon engines have not got a blameless record here as I seem to remember that on two 747s a single engine coming detached took it's adjacent engine with it [ El Al, & China Airlines ]
Now getting back to the Comet then some possible reasons for buried engines are:-
1] The original jet engines thrust was so small that every thing had to be done to reduce weight
2] Putting engines in the wing allowed the designers to have a shorter Landing gear so saving weight, as with pylons the gear has to long enough to allow the engines to clear the ground. I can assure the Comet was low on the ground requiring you to duck if you walked under the wings.
3] With inboard engines the yaw on an engine out case was a lot less so requiring less rudder , which caused less drag in the engine out case which was quite important if you did not have much engine power to start with. If I remember correctly the original B707 was considered to be lacking in directional control with an engine out and so had extra fin area and boosted rudder from the 400 series on.
From a maintenance point of view working on a buried engine can be a pain, but what I do remember was that when working on the engines your arms would ache like mad as your arms were always above your head. However engines could be changed with a lifting gantry that sat on the top of the wing so no crane required
Talking now about the Comet 4 [even an codger like me was not old enough to work on the Comet 1 ] Fuel was carried in integeral tanks in the wings, which leaked like a sieve, and in addition to that there was a bladder tank in the fuselage centre section
Dw747400 From United States, joined Aug 2001, 975 posts, RR: 1 Reply 42, posted (10 months 1 week 5 days 11 hours ago) and read 2162 times:
Quoting Bsergonomics (Reply 32): Firstly, wing bending is important, but not paramount.
Remember, "wing bending relief" is not the same thing as wing flex. Its all about balancing the loads in an optimum fashion, regardless of how the wing flexes.
Tdscanuck From Canada, joined Jan 2006, 5639 posts, RR: 56 Reply 43, posted (10 months 1 week 5 days 11 hours ago) and read 2157 times:
Quoting SEPilot (Reply 39): Quoting HAWK21M (Reply 37):
> The load on the wing root would be much more for a longer span wing & fitted with
> Engines too,add the outboard distribution of fuel load.
Wrong. The wing distributes lift over its span; any weight that gets distributed over the span is lifted directly, almost like a balloon. That weight does not figure into the wing-fuselage interface; it is borne entirely by the wing.
This isn't exactly true. Although SEPilot is right that the wing is holding itself up, so the wing weight isn't transferred through the wing/fuselage joint, the moment on the wing root does go up as you make the wing longer because the center of lift is moving outboard. The force is the same but it's got a longer moment arm, so the fuselage sees more moment. You can counteract this with wing twist to keep the center of pressure at the same lateral station, but then you're changing more than just wing length.
Viscount724 From Switzerland, joined Oct 2006, 10707 posts, RR: 9 Reply 44, posted (10 months 1 week 5 days 10 hours ago) and read 2146 times:
Quoting VC10 (Reply 41): Quoting Moriarty (Reply 40):
assume there are similar risks with the Bone, T-160 and so on. However, not sure how many incidents/accidents that are related to one engine being too close to another on those models.
You can possibly enlighten me on accidents were both engines have failed due to being along side each other, but I cannot think of any at the moment, however that does not mean there were not any.
It didn't involve an accident, but an LX Avro RJ100 had an uncontained failure on an AMS-ZRH flight in 2004 which resulted in some damage to the adjacent engine when the engine cowling separated from the failed engine. The second engine was shut down and the flight diverted to FRA on the remaining 2 engines on the other side. http://aviation-safety.net/database/record.php?id=20040809-0
Alessandro From , joined Dec 1969, posts, RR: Reply 45, posted (10 months 1 week 5 days 7 hours ago) and read 2104 times:
Quoting Moriarty (Reply 40): oting Alessandro (Reply 24):
The Comet was a world-leader that was killed by its windows, not by the airframe, nor by the engines. However, there is a good lesson to be learned from the Comet - don't mount your engines next to each other. If one lets go, it's liable to take the other one with it.
Concorde... among others. The Concorde crash was a result of a chain of events, one of them was the fact that the engines are/was close to each other.
I assume there are similar risks with the Bone, T-160 and so on. However, not sure how many incidents/accidents that are related to one engine being too close to another on those models.
VC10 From United Kingdom, joined Nov 2001, 1182 posts, RR: 20 Reply 46, posted (10 months 1 week 4 days 23 hours ago) and read 2043 times:
Quoting Viscount724 (Reply 44): It didn't involve an accident, but an LX Avro RJ100 had an uncontained failure on an AMS-ZRH flight in 2004 which resulted in some damage to the adjacent engine when the engine cowling separated from the failed engine. The second engine was shut down and the flight diverted to FRA on the remaining 2 engines on the other side. http://aviation-safety.net/database/...809-0
Thanks for the information, which is another example to show that engines on pylons are not free from inter engine failure, however I would agree that on close coupled engines the failure of one is more likely to affect it's partner
SEPilot From United States, joined Dec 2006, 3936 posts, RR: 24 Reply 47, posted (10 months 1 week 4 days 20 hours ago) and read 1993 times:
Quoting Tdscanuck (Reply 43): This isn't exactly true. Although SEPilot is right that the wing is holding itself up, so the wing weight isn't transferred through the wing/fuselage joint, the moment on the wing root does go up as you make the wing longer because the center of lift is moving outboard.
You're right, I oversimplified. But weight added on the outer parts of the wing span reduces the moment on the wing root, especially if it would otherwise be on or near the fuselage. This has been discussed in terms of one of the advantages of a quad is having the two engines fairly far outboard reducing stress on the wing spars.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
Tdscanuck From Canada, joined Jan 2006, 5639 posts, RR: 56 Reply 48, posted (10 months 1 week 4 days 18 hours ago) and read 1966 times:
Quoting SEPilot (Reply 47): weight added on the outer parts of the wing span reduces the moment on the wing root, especially if it would otherwise be on or near the fuselage. This has been discussed in terms of one of the advantages of a quad is having the two engines fairly far outboard reducing stress on the wing spars.
Absolutely agreed. This is also why airliners burn center fuel first, to keep fuel weight outboard in the wings as long as possible.
HAWK21M From India, joined Jan 2001, 27758 posts, RR: 61 Reply 49, posted (10 months 1 week 4 days 8 hours ago) and read 1828 times:
Quoting SEPilot (Reply 39): Wrong. The wing distributes lift over its span; any weight that gets distributed over the span is lifted directly, almost like a balloon. That weight does not figure into the wing-fuselage interface; it is borne entirely by the wing.
I don't have any notes, but perhaps I can explain it better. Consider a flying wing built like a balloon, with just skin and no spars (which would require engines of zero weight for this exercise.) If you had such weightless engines, you could fill the wing with fuel up to the point where the fuel weight equals the lift capacity. Since the weight distribution would be the same as the lift distribution no spars are needed (since the function of spars is to distribute the load) at least in smooth air. Now consider the fact that the engines are quite heavy; we therefore have to add spars to distribute the weight of the engines over the wingspan. But they do not have to deal with the weight of the fuel; just the weight of the engines. Now add a fuselage, and this is now a concentrated load that must be distributed over the wingspan, and you need spars strong enough to handle it. Since the engines are in a different place on the span than the fuselage, this is no longer a simple problem; the engines will actually help counterbalance the fuselage to a small degree. But you are correct in that the most critical area is the interface between the wing and the fuselage; this is where the greatest stress occurs, but only because the fuselage is the highest load, and it acts as a very localized instead of distributed load. But the fuel in the wings essentially adds no stress to the spars at all, at least in the first order analysis. When you start considering turbulence and maneuvering loads it does enter in, but not in the static loads.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
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