I have noticed that the A380 only uses the two engines closest to the fuselage to reverse thrust to brake. Are all four engines the same (i.e.: could they theoretically swap engine 1 and engine 2) or are the inside ones different from the outside ones?
In general, would the outside ones have reverse capabilities if they were installed on the inside or are they different types of engines?
O Airbus A380 comes with two engine choices:
The thrust reversers are not part of the core engines. The reversers are developed by the company which produces the engine nacelle, in this case Safran Nacelles. They developed nacelles for both engine variants for the A380, including the first electrically actuated reversers:
Safran Nacelles nacelle systems equip the Airbus A380 powered by four Rolls-Royce Trent 900 engines or four Engine Alliance GP7200 engines. [...] they are the first in the world to have a thrust reverser with an Electric Thrust Reverser Actuation System (ETRAS®).
(fonte: safran-nacelles.com)
(fonte da imagem: safran-group.com)
Não, the nacelles for the outer engines are different from the inner ones to save weight. Este artigo diz:
Four nacelles were developed for the A380: one inboard nacelle (with a thrust reverser) and one outboard nacelle (without), for each of the type's two engines, the Rolls-Royce Trent 900 and Engine Alliance GP7200.
As ymb1 pointed out in the comments, this is confirmed by the type certificate for the Trent 900:
At engine certification, the engine has been approved for use with Aircelle Thrust Reverser Unit (TRU) at the inboard engine positions (part numbers ASE 0010-XX-0 for the left hand installation and ASE 0050-XX-0 for the right hand installation) and for a Fixed Fan Duct (FFD) in the outboard engine positions (part numbers ASE 5010-XX-0 for the left hand installation and ASE 5050-XX-0 for the right hand installation).
The TRU and FFD do not form part of the engine type design and must be certified as part of the aircraft type design.
e também para o GP7000:
This engine is approved for use with Airbus thrust reverser system P/Ns (left and right) L78DR130000xxx / L78DR230000xxx and with Airbus fixed fan duct P/Ns (left and right) L78DR140000xxx / L78DR240000xxx.
Airlines normally maintain what are called Engine Build Units (EBUs) in their spare engine pool. The engine will be pre-assembled up to the point where variations in position on-wing have to be accounted for. Components beyond that point are only installed at the time the engine is installed on-wing.
Designers try to minimize engine "handing", mirror image configurations of things like plumbing, heat exchangers, etc, so the EBU can be built up to the most complete assembly possible, ready to be slapped on in a crisis.
On something like the 380, to the extent that reverser related components can be installed on the EBU, the airline will probably have a choice of:
The choice will be based on a global cost business case.