jessman
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A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 12:48 pm

Jets with two engines have them either wing mounted (777)
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or tail mounted(MD-80).
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Jets with three engines have either two on the wing and one in the tail(MD-11)
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or all three on the tail (727)
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Why do jets with four engines only have them mounted on the wings(B747)
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.
Why no two wing mounted/two tail mounted jets?
Have there been any designs for a jet with two wing mounted/two tail mounted engines?
Just curious  Smile
 
deltaffindfw
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 12:52 pm

This could be close!


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[Edited 2003-11-09 04:53:31]
 
USAFHummer
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 12:53 pm

you forgot the VC-10/IL-62/Lockheed Jetstar class...four tail-mounted engines...

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An-225
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 12:55 pm

You're forgetting something.


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fanofjets
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 1:33 pm

I imagine that a design with two wing-mounted and two tail-mounted engines would pose center of gravity problems affecting handling or efficiency or both.

Here are some other engine configurations; none of these saw widespread use-
Two engines in pods and two on wing tips:

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Four engines buried in wing root:

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Photo © Daniel M Dunn



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Photo © Alan



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Two unusual two-engined configurations-

Two engines in tail:

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Photo © Sergey Riabsev



Two engines in wing roots:

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N243NW
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 1:35 pm

Why no two wing mounted/two tail mounted jets?
Have there been any designs for a jet with two wing mounted/two tail mounted engines?

The question that our friend Jessman is asking is not "Why aren't there any jets with all four engines on the tail?".

I assume the aircraft would just be too complicated with the configuration (different styles of pylons, nacelles, etc.) and too hard to maintain (the mechanics would have to check both the wing-mounted and tail-mounted engines, however it seemed to work for the DC10 & L1011). I don't, however, see any significant advantages for this configuration compared to others, but I have turned the idea over in my head more than once before. There is also the chance that by the time that any aircraft manufacturers might have thought of this (if they ever did), the commercial jets became more simple and efficient with only two engines. Any other ideas or details would be appreciated, as I'd also like to know of your thoughts or facts!
-N243NW Big grin
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jessman
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 1:44 pm

I must admit, I did completely forget about the four tail mounted engines. I have never seen one of those aircraft in real life.
But that does make me wonder, are the two inside engines hard to get to? It seems like they would be a problem to maintain.  Smile
 
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 2:22 pm

There have also been 4-engine aircraft with the engines mounted on top of the wings - there was an experimental USAF transport in that configuration. I don't remember who built it, but I believe that it's on display at the Pima Air Museum in Tucson. The Gemans also built a small jet with two pod mounted engines slung above the wings - a Fokker I believe. I think that designers have hung engines just about anywhere you could possible hang an engine over the years. Wasn't there an early USAF bomber that had its engines pod mounted on the forward fuselage?

jet's
 
L-188
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 2:25 pm

You also forgot mounting two engines over the wing.


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How about a single engine over the cabin?


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Coronado990
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 2:32 pm

Regarding the two engines on the wing, two engines on the tail design: I would think the engines mounted on the sides of the tail would tend to suck in the exhaust from the wing mounted engines. Probably not a good thing. The DC-10 engine sat up high enough to avoid this problem.
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 7:45 pm

Don't forget these:


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nudelhirsch
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RE: A Different Style Of Four Engined Jet?

Sun Nov 09, 2003 7:55 pm

I'm not an expert in aircraft design. I could imagine, that the engine position is actually influencing flight stability and flight behavior of the plane.
Seeing the two-eng wing-mounted as a "normal" way, 4 on the wing still pretty normal, DC-10-style to increase vertical maneuverability (is this a word???) by a third centered thrust. I read in a book, that this layout helped a crew to land a DC-10 wihtout rudders, to control bank by the wing engines, and descend and levelling out by the tail engine.
I also read, that there is an effect, which uses the exhaust stream of the engine to flow over the wing, creating more uplift.
It probably also depends on engines on the market and their power. If, like Coronado mentioned, exhaust in inflow wouldn't be a problem - what sense would it make to mount 4 engines to a 737 - two on wing, two on tail - would probably be great looking, but probably no sense in economical ways.
See also the thread about why the BAE146 has 4 instead of 2 engines...

The DC-10 had pretty big engines, and placed in a triangle, which would, like mentioned enable the crew to use the the engines for steering. I don't think, a "4-engine, 2-wing 2-tail concept" would provide these effects as well.

Just my stuff, I really am not an expert, this is what I gathered by reading and thinking. Interesting thread though!
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rthrbeflying86
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RE: A Different Style Of Four Engined Jet?

Mon Nov 10, 2003 12:01 am

I read in a book, that this layout helped a crew to land a DC-10 wihtout rudders, to control bank by the wing engines, and descend and levelling out by the tail engine.

Probably a book about United 232.
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jessman
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RE: A Different Style Of Four Engined Jet?

Mon Nov 10, 2003 5:42 am

For the design I was thinking a jet along the size of a A340. It seems to have engines that would be small enough to be mounted onto the tail.
With all the different places designers have put engine, I would have thought this would have been tried.
I suppose the exhaust thing could be a reason.
Some pretty cool pics have been put up on this thread. That's great.  Smile
 
jgardiner
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RE: A Different Style Of Four Engined Jet?

Tue Nov 11, 2003 1:40 am

One advantage of mounting the engines on the wing is that the weight is used to counteract the aerodynamic forces that want to twist the wing. This way the wing structure can be made lighter.

Another advantage is that mounting the engines on the tail limits the amount that you can stretch the fuselage.


 
mandala499
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RE: A Different Style Of Four Engined Jet?

Tue Nov 11, 2003 6:28 am

Engines on the wings = Balanced weights centered around the wing/cg/cl.
Engines on the tail = Nose heavy... resulting in long nose and short tail...

Combination... have you compared the DC10/MD11's wing position relative to the overall body with a 777 ? Now slap another engine on the tail and see that wing move further back... In the end, you might aswell have 4 engines on the tail, or on the wing. Not to mention the maintenance complications. 2 engines with all the connections on the top, and 2 engines with connections to the side... Hmmm, sounds like a nightmare to me...

And we haven't even gone into the potential use of cabin space if the engines are on the wings!...

Mandala499
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