How significantly is the fuel burn increased?
It depends. If the engine is like that, allowing the blades to spin without power (windmilling) then the increase is significant. If a streamlined cover is fitted (pics in the database) then it's rather negligable.
Could a 747 with spare engine make a longer flight such as LAX-SYD nonstop?
is already cargo-restricted on a base 744 AFAIK, cargo would be even moreso with the ferry engine. A 744ER, which can fly the route without cargo restriction normally, would have one carrying the engine. On less demanding routes like LAX
, there would be no problem.
But how is the engine attached to the structure? is there a special pylon that has been designed for the occasion, or does the plane originally carry provision to attach an extra pylon underneath the wing?
There is provision for a pylon there AFAIK.
Can it carry other types of engine, or just the one the a/c uses?
I've only seen aircraft carrying their own engine type. I would assume any engine would be possible, but the only airplanes that I believe can do it are 747s and DC-10s, which use the same basic engines. With narrowbodies, they wouldn't be far enough away from home to need the extra engine, and the only widebodies that don't use the same basic CF6/RB211/Trent/PW4000 family are the A340 (which can't carry a 5th) and the 777 (which can't carry a third because the engines are too frickin' big)
Is that aircraft particularly made for these transport or all 747s capable of this ?
I would assume it is a factory-optional feature, like selecting a different engine type or additional fuel tankage. It seems to be something the majority of airlines, especially ones that fly to some seriously far-out destinations (like Air France and the various overseas departments) would select.
If the 747 had 5 engines wouldn't the aircraft be unbalanced ?
No because the 5th isn't running and the drag concequence is negligable, and could be cured by tapping the other side's throttles back a tad from the side carrying the engine, or by FADEC (full-authority digital engine control) automatically.
Now if the aircraft had 6 engines, wouldn't the wings AND the aircraft be heaver and be harder to maneuver?
I don't believe the 747 or DC-10 (the other plane that can do this) is certified to carry 6/5 engines.
And finally, can you carry pax on those such flights?
Absolutely. It's not an inherantly dangerous procedure, which is the criteria that blocks passengers off planes.
Are there any other restrictions/limitations involved?
If the plane is at the edge of its performance envelope as far as range/payload, then yes, one or the other would be restricted. If we're talking about a 744 on JFK
, then no.