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By: - 29th December 2013 at 16:21 Permalink - Edited 1st January 1970 at 01:00
So why are there hardly any intercontinental jetliners with aft-mounted engines?
Engines are too big and heavy. The structure would mean the fuselage is heavier than sensible, the wing moves nearer the rear of the aircraft so the tailplanes needs to be bigger. Which moves the c.g. further back, which means the wing must be even nearer the rear of the aircraft, which means the tailplanes need to be even bigger which means the structure needs to be heavier...
Oh, and the engines mean you need a T-tail, which is heavier than a conventional tail, which moves the wing nearer the rear which etc etc...
Is it for ease of maintenance - easier access to the turbofans on larger aircraft?
Partially.
Are there aerodynamic disadvantages to aft mounted jets on bigger airframes?
No, the clean wing is aerodynamically advantageous. Albeit not by much in the case of good wing/pylon integration.
edit: Oh, and jet-pump fuel feed to aft mounted large engines is a bollox, so you automatically incur a lot of hazardous and catastrophic safety issues with your fuel system. The size of the CRJ engines coupled with the real length between wing and tail means can get away with a jet pump system, which will deliver fuel when the engines are running - entirely passively. That would not be the case for the widebodies.
edit2: An advantage of rear-mounted engines is a shorter undercarriage - which allows easier use of a built in stairway. Single-aisles now have automated stairways built in too - this was a big deal for the likes of Ryanair. But for loading/unloading widebodies, such approaches aren't really feasible, so the undercarriage height isn't so big a deal, and funnily enough can come with service access advantages.
By: - 30th December 2013 at 12:21 Permalink - Edited 1st January 1970 at 01:00
Mr Amiga500 has given a very comprehensive answer.
If you think about the physical size of the B777's engines relative to the fuselage, it would be difficult to imagine them slung on the back underneath a t-tail. When this layout was more common back in the 1960's, turbofan engines were much smaller and cigar-shaped (and noisier - one of the reasons they were put there).
I love the look of the layout, though, and view the VC-10 as probably the most beautiful airliner ever built but, like three-engined configurations, rear-mounted engines on full-size airliners have been consigned to the history books for many economic and technical reasons.
By: - 30th December 2013 at 17:19 Permalink - Edited 1st January 1970 at 01:00
The CRJ and F70/100 were developements of existing rear engined jets...Challenger/Fokker F-28 where rear engined was the way it was done during their development and in the case of the Challenger, the style for BizJets, which is still the case.
Newer Regional Jets seem to favour the underwing mounted.
It is easier to offer different engines on under wing pod mounted as rear fuse mounted does need more engineering to change.
Posts: 242
By: LERX - 28th December 2013 at 10:06
I've been wondering about differences in jet engine configuration/placement on intercontinental aircraft vs regional jets.
Almost all modern intercontinental jets I can think of:
747 / 767 / 777 / 787
A330 / A340 / A380
Il-96
have underwing turbofans
But many (of course not all) regional jets have their turbofans mounted aft:
Embraer ERJ-145 series / Bombardier CRJ200 / CRJ700 series / Fokker 70/100
The only intercontinental jetliners with rear-mounted jets I can think of are the VC-10 & Il-62 which are now rarities :(
So why are there hardly any intercontinental jetliners with aft-mounted engines? Is it for ease of maintenance - easier access to the turbofans on larger aircraft? Are there aerodynamic disadvantages to aft mounted jets on bigger airframes?