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Why heavier aircrafts take longer to slow down in the air?

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Why heavier aircrafts take longer to slow down in the air?

Old 28th Nov 2012, 10:21
  #141 (permalink)  
 
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One of the thread management problems we are faced with regularly relates to the basic question of what the forum is about.
john, do you have an answer for this very interesting question ?
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Old 28th Nov 2012, 10:47
  #142 (permalink)  
 
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Bubbers you have it right

Trying to answer the question with Energy or Momentum alone, without considering the very complex subject of aerodynamics and Drag, is a very difficult thing, if possible at all.

The answer depends on about aerodynamic efficiency, and not only on the effect of having more or less mass. L/D ratio is a measure of the aerodynamic efficiency of the airplane. Similar as the efficiency of propeller blades.

An airplane flying at a less efficient AoA is wasting a larger portion of energy in the air than an airplane flying at a more efficient one.

In normal conditions, at the starting point of the experiment, the Heavy has a higher state of energy than the Light one. Due to its mass, exclusively. After we magically remove the engines and thrust disappears, deceleration starts immediately, if both airplanes keep altitude. The heavy one has more mass and , on top of that, is aerodynamically more efficient. It will then slow down more slowly. In the back side of the curve there might be cases where it would be the other way round, though.

But if we talk just about "normal" conditions, the answer is that: increased mass plus better efficiency give a slower deceleration.

Lyman

I like this thread. If you don't, why do you lose time posting here? I don't like so many other threads that I deem quite silly and I just stop reading them, like I stop reading a bad novel.
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Old 28th Nov 2012, 11:13
  #143 (permalink)  
 
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The original post just says "in the air". That isn't necessarily cruise, what about other flight conditions such as holding or approach? What speeds are you at when holding?

Last edited by HazelNuts39; 28th Nov 2012 at 11:26.
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Old 28th Nov 2012, 12:24
  #144 (permalink)  
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john, do you have an answer for this very interesting question ?

.. hard to say.

I guess we all have a slightly differing point of view.

As for me, I have naught to prove so, consistent with what those higher up the totem pole dictate, I prefer to let a thread run its course providing that folks are reasonably polite about things and play the ball rather than the player ...
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Old 28th Nov 2012, 19:58
  #145 (permalink)  
 
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I prefer to let a thread run its course providing that folks are reasonably polite about things and play the ball rather than the player ...
i think thats the obvious job of every moderator in an open forum . but what is this forum for?

imo there is not a problem when a variety of people with a variety of personal knowledge takes place in a discussion. its finally an advantage.

the problem is imo that the very most people here , especially at some subforums , claim to be some what they never are and never were. in most cases the "dreamer" is obviously a pilot with xxxxx hours on an widebody or a high degree engineer.

you will find tons of threads where "fake" people try to sell internet knowledge and manual readings compared with computer based flight simulation as actual real facts and the debate starts until the general loss in interest ends it - until a new debate starts.

this turns nearly every thread into stupidity and the " fights" come up automatically.

the rare people who really work on a flightdeck have so no use of a forum what originally might be intended for them .

today its more and more a platform for dreamcatchers . and honestly- in nowadays i do not see many reasons for what this profession is a "dream" where the dreamers catch on it.

nevertheless -i personally would strongly vote for a subforum where you have to make a proof who you are to post ( but not sure how it should be done via internet and how anonymity is given) or a profession identification in your signature after you prooved it -with postings free for everybody.

cheers !
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Old 28th Nov 2012, 20:26
  #146 (permalink)  
 
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SLF here, whom has taken years out of his life and understands the theory.

I live under the approach path in Cape Town, South Africa. Now ,being season,
Emirates & Qatar fly in a 777-300 every day. On an always straight-in approach, the engines are spooling up and down. Only the the 777s. Have A340s, A330s, 744s and the local 737s, but why only the 777s ?
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Old 29th Nov 2012, 09:07
  #147 (permalink)  
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but what is this forum for?

In a nutshell, with respect to your concerns ..

(a) inappropriate questions are moved automatically to other forums - this happens with reasonable regularity and probably is unnoticed by the majority

(b) threads which deteriorate we endeavour to get back on the rails. If that is not successful, either the thread is closed, moved or dies a rapid natural death. Occasionally, we sin bin an individual poster in the worst cases.

(c) if I get several reasonable PMs from regular and reputable posters asking for a thread to be moved, generally I go along with such requests unless there is some cogent validity in retaining the thread here

(d) the idea of restricted sub-forums comes up from time to time but has never made the grade with the folk higher up the totem pole

(e) at the end of the day, whatever we do and however we moderate, we can't please all the people all of the time ...
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Old 30th Nov 2012, 13:27
  #148 (permalink)  
 
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(d) the idea of restricted sub-forums comes up from time to time but has never made the grade with the folk higher up the totem pole

(e) at the end of the day, whatever we do and however we moderate, we can't please all the people all of the time ...
the idea of a restricted forum will surely not make the grade of the vast majority because when any serious proof of what is claimed would be introcuded the very most would lost their playground in internet dreamcatching here.

i agree that the administrators and moderators cannot satisfy everybody and will have to follow the masses for several reasons.

on the other hand these masses turn behind the anonimity of the web and free fairy taling an aviation forum in a strange direction for the last users who would like to discuss practical problems, worries , questions and suggestions of their everyday business .

nevertheless, whatever, i like PPRuNe and enjoy the reading !

cheers
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