RussianJet
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Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 12:41 am

Like the thread title says.

The largest rear-engined planes I can think of are the VC-10 and IL-62. As higher power engines have become available over the years, why do we only see rear-mounted engines on smaller planes? Isn't there any significant advantage in the clean wing achieved by rear-mounted engines? Also, I think a larger plane with engines at the rear would look pretty cool, though I realise of course that this is not the main consideration.
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Starlionblue
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 12:52 am

Quoting RussianJet (Thread starter):
Isn't there any significant advantage in the clean wing achieved by rear-mounted engines?

Yes, but not enough to justify rear-engined widebodies.

Advantages of a rear engine layout:
- Cabin noise.
- Ground clearance.
- Clean wing.
- Less adverse yaw in engine out situations.

Advantages of engines under the wing.
- Lighter wing due to bending relief.
- Lighter wing due to wing twisting counteracted by engines.
- Easier engine maintenance access.
- Easier engine inspection during preflight.
- No need to route fuel lines through the fuselage.
- Catastrophic engine failure nowhere near critical control lines in empennage.
- No need for t-tail with consequent increase in weight and risk of deep stalls.
- No need for heavy structure around tail and aft fuselage to support engines. In a wing mounted design the loads only have to be carried by the gear.
- No need to mount gigantic engines by the tail. McDonnell Douglas will tell you there is a limit (in terms of cost) to this plan.
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RussianJet
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 1:07 am

Are there any rear-engined planes bigger than the two I mentioned?
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KELPkid
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 1:29 am

Didn't BAC have plans for a widebody with two fuselage-mounted high bypass engines? (A successor to the BAC One-Eleven). As I recall, they ended up dropping the design due to the UK's involvement in Airbus, as it would have been an A300 competitor?
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Starlionblue
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 1:44 am

Quoting KELPkid (Reply 3):
Didn't BAC have plans for a widebody with two fuselage-mounted high bypass engines? (A successor to the BAC One-Eleven). As I recall, they ended up dropping the design due to the UK's involvement in Airbus, as it would have been an A300 competitor?

Methinks you are right. I think I saw some pics in my Airbus book. But that's at home and I am not.

Quoting RussianJet (Reply 2):
Are there any rear-engined planes bigger than the two I mentioned?

Not that I can think of.
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LH707330
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 2:21 am

Quoting KELPkid (Reply 3):
Didn't BAC have plans for a widebody with two fuselage-mounted high bypass engines?

Yes, the BAC 3-11. One of the big challenges was also keeping clean enough airflow into the engines on a widebody, which is one of the reasons Boeing went with underslung engines on the 737-100, as it was 6 across and fat, so it had funky aerodynamics back there. The 3-11 vs. A300 would have ended the same way the VC10/707 debate did....
 
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AirlineCritic
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 5:42 am

Quoting RussianJet (Reply 2):
Are there any rear-engined planes bigger than the two I mentioned?

No, unless you want to count DC-10 and MD-11...
 
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 4:16 pm

Quoting AirlineCritic (Reply 6):
Quoting RussianJet (Reply 2):
Are there any rear-engined planes bigger than the two I mentioned?

No, unless you want to count DC-10 and MD-11...

OMG!!! You forgot the L-1011.     


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jumbojim747
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RE: Why No Rear-Engined Widebodies?

Tue Sep 18, 2012 7:35 pm

I think he was referring to only rear mounted engines without wing engines so the dc10 and the tristar do not count
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Viscount724
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RE: Why No Rear-Engined Widebodies?

Wed Sep 19, 2012 1:48 am

Quoting Starlionblue (Reply 1):
Advantages of engines under the wing.

Also less risk of engines ingesting ice shed from the wings/fuselage/galley and lavatory drains etc. There have been a few accidents to rear-engined aircraft from that cause, and others have shed engines. A couple of examples:


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Starlionblue
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RE: Why No Rear-Engined Widebodies?

Wed Sep 19, 2012 2:42 am

Quoting Viscount724 (Reply 9):
Quoting Starlionblue (Reply 1):
Advantages of engines under the wing.

Also less risk of engines ingesting ice shed from the wings/fuselage/galley and lavatory drains etc. There have been a few accidents to rear-engined aircraft from that cause, and others have shed engines. A couple of examples:

Forgot about that one. Then again rear-engined aircraft are perhaps less susceptible to "normal" FOD.
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thegeek
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RE: Why No Rear-Engined Widebodies?

Wed Sep 19, 2012 6:34 am

Quoting Starlionblue (Reply 1):
Advantages of a rear engine layout:

Could you add "less positive stability required" due to the need, with under low wing engines, to compensate for the pitch up moment from the engines at full thrust?
 
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longhauler
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RE: Why No Rear-Engined Widebodies?

Wed Sep 19, 2012 2:08 pm

Quoting LH707330 (Reply 5):
Yes, the BAC 3-11.

From another thread, this is some interesting info on the BAC3-11.

http://www.flightglobal.com/pdfarchive/view/1968/1968%20-%202599.html

Quoting LH707330 (Reply 5):
The 3-11 vs. A300 would have ended the same way the VC10/707 debate did....

Its a tough call, the 3-11 numbers look pretty impressive. The only drawback I see, is that it was to have RB211s, and the delays in the engine would have been a huge hurdle, much like the L1011 had to endure.

Quoting Viscount724 (Reply 9):
Also less risk of engines ingesting ice shed from the wings/fuselage/galley and lavatory drains etc. There have been a few accidents to rear-engined aircraft from that cause, and others have shed engines.

That might be a draw, as I lost an engine over South Carolina in a B737-200 due to ice buildup from a leaking lav door. And I am mean literally "lost" the engine ... it ended up in a farmer's field!

As far as ice shed from the wings, much like the MD-80s, DC-9s and CRJs of today, they require special considerations when operating in ground or air icing conditions.
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neutrino
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RE: Why No Rear-Engined Widebodies?

Wed Sep 19, 2012 3:51 pm

Quoting RussianJet (Reply 2):
Are there any rear-engined planes bigger than the two I mentioned?

Does the Space Shuttle count? Well, it does have 3 engines at its posterior, its empty weight is higher than the mentioned two and the body width is in the ballpark of the 767 which is the smallest widebody jetliner.  

Anyway, there was a proposed but never realised Double Deck Super VC-10 which would be larger and have a higher MTOW than the regular VC & the IL.

Other than that, can't think of any truely bigger/heavier ones. Maybe some obscure birds from the former USSR?
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Areopagus
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RE: Why No Rear-Engined Widebodies?

Fri Oct 05, 2012 8:00 pm

Quoting longhauler (Reply 12):
From another thread, this is some interesting info on the BAC3-11.

http://www.flightglobal.com/pdfarchive/view/1968/1968%20-%202599.html

A very interesting article. I particularly noted the use of CFRP in the structureQuoting longhauler (Reply 12):

From another thread, this is some interesting info on the BAC3-11.

http://www.flightglobal.com/pdfarchi....html

An interesting article. I was a bit surprised to see the use of carbon fiber structure for an aircraft that was to be launched in 1968. And then there is that aft-loaded airfoil that delays Mach drag rise, allowing a M 0.84 cruise speed. Wouldn't that qualify it as "supercritical"?

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