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Raymer says:

Landing is much like taking off, only backwards!....Note that the aircraft weight for landing analysis is specified in the design requirements, and ranges from the takeoff value to about 85% of takeoff weight. Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency.

What is the meaning of the last sentence: "Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency"?

How is the aircraft design is affected by such different needed kind of weight?

(Source: Raymer: Aircraft Design – A Conceptual Approach Chapter "17 PERFORMANCE AND FLIGHT MECHANICS" Paragraph “17.9 LANDING ANALYSIS ”)

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    $\begingroup$ If you're landing backwards, you probably shouldn't be flying in that strong a headwind! $\endgroup$ – Dan Hulme Jun 14 '16 at 13:05
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End-of-mission is a time- (and case) dependent term. Your mission could end under a variety of circumstances. If your mission is to carry passengers from point A to point B and you have an uneventful flight, then end-of-mission and landing are the same thing. But (as stated above) if you have an emergency at some point, you might need to abort the mission. If this happens, then you are likely to end-up dumping as much fuel as necessary to get to your landing weight, because said end-of mission weight and landing weight will not be the same.

Here is an oversimplified example: Aircraft AC has MTOW of 100,000 kg and a MLW of 50,000 kg. The same aircraft has to get from point A to point B, without releasing cargo or ordnance. During the mission AC burns 100 kg of fuel per minute. Ten minutes after departure the pilot realizes that he has forgotten his watch and needs to land immediately. Now after 10 min flight AC weighs 99,000 kg. Since the mission is about to end before MLW is reached (99,000 ~= 50,000), the captain can either dump some fuel or circle around until AC's weight is at most equal to MLW.

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  • $\begingroup$ Thank you Peter Hristov, so how does this difference affect the deisgn for weight or for weight? $\endgroup$ – d.pensopositivo Jun 14 '16 at 12:04
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    $\begingroup$ If you take the example of a fighter or reconnaissance aircraft the difference is apparent, lets take the reconnaissance aircraft, the mission could be map out section y of country z. In this case you have the take-off weight, fuel used during the flight to the mission, start of the mission (maybe supersonic) then the end of the mission. Finally you fly back to base and land. $\endgroup$ – Brilsmurfffje Jun 14 '16 at 12:33
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    $\begingroup$ If it's a commercial passenger flight, "end-of-mission" might be considered docking at the jet-way or hard stand, and shutting down the engines. Depending on what airport you land at, which runway you land on, and what gate you park at, a fair amount of fuel could be burned during taxi, therefore "EOM" weight would be less than landing weight. $\endgroup$ – FreeMan Jun 14 '16 at 12:37
  • $\begingroup$ @d.pensopositivo Maybe the most significant alteration would be the requirement for a fuel jettison (dumping) system. As you add equipment on board, your weight will inevitably creep up. Take a look at FAR 24.1001, FAR 25.119 and 25.121. Of course some large aircraft do not have FD systems and thus the popular loiter in a case of emergency occurs. $\endgroup$ – Peter Hristov Jun 14 '16 at 12:54
  • $\begingroup$ I'm still not understanding the logic of the line of reasoning of this sentence : "Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency.''. What doest it mean? Does it mean that If L. W. is the same of E.O.M. weight when landing, the aircraft have to dump a lot of fuel? $\endgroup$ – d.pensopositivo Jun 14 '16 at 14:05

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