I noticed on this video of an A380 landing in rain that reverse thrust was applied to only the inboard engines. Do the outboard engines not have reverse thrusters? If they don't, then why not? If they do, then why not use them on a slippery landing?
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$\begingroup$ IIRC they do not have trust reversers on the outside engines, as the engines are far away from the centerline. This means that the force of the thrust reversers would place a very large bending moment on the wing, which would require stronger (and heavier) wings $\endgroup$– ROIMaisonMar 15, 2015 at 13:38
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$\begingroup$ @ROIMaison: Thank you. You might want to post that as an answer so that I could accept it! $\endgroup$– dotancohenMar 15, 2015 at 13:48
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$\begingroup$ The thing is that I'm not sure if this correct (and if this is the only reason) I'd prefer backing if up with resources before posting it as an answer :) $\endgroup$– ROIMaisonMar 15, 2015 at 13:50
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$\begingroup$ @ROIMaison: The bending moment is not the problem - if the regular thrust can be transferred, reverse thrust can be as well. FOD is the problem. $\endgroup$– Peter KämpfMar 15, 2015 at 13:53
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$\begingroup$ @Peter, is this true? I can image that structures are designed for a certain load (not only a certain force, but also a direction), and I'm not sure if this also means that the structure is as strong in the opposite direction $\endgroup$– ROIMaisonMar 15, 2015 at 14:05
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1 Answer
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Yes, the outboard engines do not have reverse thrust to avoid them kicking up dirt. On a regular runway they will be outside of the concrete surface, so using reverse thrust there will incur the risk of foreign object damage.
This was already covered in this answer.
answered Mar 15, 2015 at 13:51
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$\begingroup$ Thanks Peter! Apparently Google still has some work to do indexing this SE site! $\endgroup$ Mar 15, 2015 at 13:54
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$\begingroup$ @dotancohen: I found it only because I remembered it, but I have to say the SE search is doing a nice job (when you use the right search term). $\endgroup$ Mar 15, 2015 at 13:57
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$\begingroup$ You are right, I should use the in-site search too. Thank you! $\endgroup$ Mar 15, 2015 at 13:59
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$\begingroup$ Why can't the pilot(s) just avoid using reverse thrust on the outboard engines while they are over an unimproved surface? $\endgroup$– KeeganMar 15, 2015 at 16:03
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$\begingroup$ @SpongeBob: Including a thrust reverser would add weight to an aircraft that is already 5.5 tons over the promised empty weight. Initially, no thrust reverser was planned, and the inboard ones were added late in the project. Nobody felt the need to add outboard ones, too. $\endgroup$ Mar 15, 2015 at 16:06