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Every time I have landed on a airplane reverse thrust is needed, but what if the runway is 18,000ft long. Because if the runway is longer couldn't you save fuel by not using the reverse exhaust

Ethan
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  • Please everybody stop reporting my questions as bad because if I get anymore bad question reports then I can't ask questions anymore and I absolutely love this website. Its better than google giving me answers more explained than google can give me. I am only 14 years old and I am curious about airplanes and hope to be an aerospace engineer so please do not report my questions as bad thank you. – Ethan Aug 07 '15 at 20:49
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    We are not saying your questions are bad, just that they have been asked and answered before (or at least someone thinks so). The idea is that people with the same questions can find answers. You can use the search box at the top right to see if similar questions have already been asked. If there is already a question asked, then you get to learn the answers without the trouble of asking a new question. – fooot Aug 07 '15 at 20:52
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    If you have searched, or have read the "possible duplicate" link, and feel your question is different, then feel free to edit your question to clarify what your new question is asking and indicate why it's different than the one being referenced. If you look through the comments on older questions, you'll see this has happened many, many times, and is an expected behavior. – FreeMan Aug 07 '15 at 20:54
  • If you are interested in what methods planes use to stop, this question is also related. – fooot Aug 07 '15 at 20:54
  • I just changed my question to be more different. – Ethan Aug 07 '15 at 20:57
  • I already know how reverse exhaust works I am just curious to see if you really need it on a longer runway – Ethan Aug 07 '15 at 20:59
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    The first question I linked also includes when it needs to be used, and the second one talks about how useful different braking methods are. – fooot Aug 07 '15 at 21:03
  • I'm just going to keep this question up guys, but I did take down some of my recent questions. – Ethan Aug 07 '15 at 21:05
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    I think most of your questions aren't too bad. The search function on this website isn't the best so it may be hard to find out if someone else already asked your question. Usually google is better, especially if you put site:aviation.stackexchange.com in the search field, restricting the search to this site. – DeltaLima Aug 07 '15 at 21:41
  • The current wording of the question seems different than the duplicate suggested. So I'm voting to keep this one open. – mins Aug 08 '15 at 00:53
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    @Ethan I am glad you are here and participating in the site! If your questions get closed, we still like you, but part of what makes this site so great is the high quality standard. Take it as an opportunity to edit your questions to be better, more clear, and original. – digitgopher Aug 08 '15 at 01:28

2 Answers2

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Reverse thrust is never needed.

A reverse thrust is relatively complex thing that can easily fail and for this reason when deciding whether an aircraft can land at some runway, the calculations are done without assuming reverse thrust. And of course the stopping distance for aborted take-off is also without thrust reverser, because if your engine failed, it won't provide any.

The reason to use reverse thrust is to reduce wear of the brakes and tires. The kinetic energy of the aircraft is huge and when it gets converted to heat in the brakes, they can get pretty hot. So if available, pilots always use reverse thrust to ease the brakes.

But it's not a big deal if not available. Thrust reversers are on MEL (minimum equipment list) for most if not all aircraft meaning the aircraft can be dispatched with thrust reversers inoperative. The brake wear will be higher from the more intensive braking, but it is better than having a plane wait for spare parts at some remote location.

Regarding long runways, there is almost always a possibility to turn off the runway earlier, which often saves time for the aircraft (shorter route to taxi) and makes the runway available for next aircraft sooner. So pilots usually still want to use some reasonable braking.

Jan Hudec
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    Don't you mean they are NOT on the MEL? – TomMcW Aug 07 '15 at 22:48
  • An example where you hardly feel the pilot brake, let alone use the reversers, is runway 14 at LNK. It's 8,750ft long, the only sensible exit to the terminal is at the far end and traffic is very light. A typical passenger plane flying into there is something like a CRJ-100, which requires barely half that runway length even at MTOW. – David Richerby Aug 07 '15 at 23:22
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    @TomMcW Nope - it's a slightly confusing name, but it would be impractical to list every piece of equipment / nut and bolt on an aircraft so the MEL only lists pieces of equipment (With caveats as required) that aren't required. – Dan Aug 08 '15 at 09:10
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Aircraft don't need thrust reversers on a long runway, in fact they often don't need it at all. It just helps in decelerating, reducing the wear and tear of the brakes and tires. That comes at the cost of fuel, but it saves on downtime replacing brake discs and tires.

Another reason to use the reverser is that sometimes it saves taxi time to take an earlier runway exit. This saves fuel and time = money.

DeltaLima
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