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Pulling a Stop to Runway Overruns

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Pulling a Stop to Runway Overruns

Old 27th Mar 2006, 03:39
  #81 (permalink)  
 
Join Date: Sep 2000
Location: England
Posts: 303
Specious and Spurious Argument

MFS
In your 23 March 03:51 post you completely and purposely neglected to factor in (to the couples at work or "in play") the nose-down cumulative effects of spoilers, reverse and braking (as well as the c of g position that's tending to keep the nose on the ground).
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If you go back to the beginning of this thread, the original (and very reasonable) postulate was that
sufficient backstick could be progressively fed in so that the nose would stay down and the main-gear benefit
from the aerodynamic downforce of the horizontal stabilizer under backstick - thus gaining considerable
braking traction upon contaminated runways at higher speeds (i.e. not long after nosewheel on).
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Using convoluted math that excludes the most significant factors or (like LEM) hypothesizing with completely
imaginary figures and drawing bogus conclusions from them, is to cobble together an "argument" without any useful
substance.
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There may well be weight transference that's cumulatively in favor of the technique, but there is also (quite unquestionably) an aerodynamic downforce (on the maingear) courtesy of the backstick.
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I suggest that you should now reflect upon the fact that backstick braking is a proven methodology - and then
drive yourself even maddder trying to figure out WHY.

TheShadow is offline  
Old 27th Mar 2006, 03:47
  #82 (permalink)  
 
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,113
Originally Posted by TheShadow
MFS
In your 23 March 03:51 post you completely and purposely neglected to factor in (to the couples at work or "in play") the nose-down cumulative effects of spoilers, reverse and braking (as well as the c of g position that's tending to keep the nose on the ground).
No, I did not, because I am dealing with the delta arising from the use of the technique versus the non-use of the technique.

Whether the effect of reverse thrust is nose-up or nose down is irrelevant. The question is, what is the incremental effect of the technique: does it cause more load on the main gear or not? Whether there is an offset in overall pitching moment or not is utterly irrelevant, provided we do not have to consider the catastrophic case of causing the nose to rise such that we actually lift off again.

As long as the characteristics remain linear - which is why I keep pointing out that oleos are NEVER fully compressed, please note - the consideration must be between the DIRECT effect of increased download on the main gear, arising from the pure lever action of the tail download, and the INDIRECT effect of increased pitch attitude, increased AoA and hence increased overall aerodynamic lift. If the former is greater, there's a net benefit; if the latter, an net degradation is decel capability.

As with many things in life, there is no single right solution; on some types, depening on the characteristics, it will work. On others, it won't. On certain types it may be dependent on other factors - like weight or cg - as to what is the better option. To pretend that there is some undiscovered holy grail of truth, if only the stupid OEMs would recognise it, is to be entirely misguided. As I mentioend a long time ago, if it was that simple it'd be in the AFM data AND we'd be taking credit for it already.
Mad (Flt) Scientist is offline  

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