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Lynn writes " All
one had to do was pay more money to get the higher weight limit. Flying
at either weight was safe "
Lynn's comments underscore the general
misunderstanding about gross weight. Every pound of cargo (extra fuel,
passengers, baggage) you load into an airplane makes that plane less
safe. Part of the confusion is due to the way an airframe is rated for
load in Gs. Wing spars are tested at a certain load and then this load
is converted into G's assuming a given gross weight. Increase the gross
weight and the wings break off at a lower G load.
Given enough horsepower, the correct CG and a long enough runway you
could load a IV-p to 28,500 pounds and it would still fly, that is
until you pulled back on the stick and saw 1.05 Gs, at which point the
plane would get lighter by two wings. It is interesting to note that
the stall speed would equal Va at this load and the takeoff speed would
exceed the flap and gear deployment speeds.
Recently a well loaded IV entered a thunderstorm and fell out the
bottom in pieces. Had the plane been lightly loaded or flying below Va
this may not have happened. Once you exceed Va, the safety margin is a
function of load. More weight, less margin, so while "either weight"
may be safe, the lighter weight is safer. Using a higher gross weight
does NOT increase the airplanes ultimate load capability. Increasing
the gross weight from 2,900 to 3,550 decreases the ultimate G load
capacity from 8.8 to 7.2.
Weight also increases stall speed, with the attendant bad consequences.
Weight also decreases speed, also bad.
So, increasing load decreases safety, and we have already seen at least
one case of an in-flight structural failure. Unless you laminate the
airworthyness certificate to the extreme fiber of the wing it will have
NO effect on the ultimate strength of the aircraft. The arbitrary,
progressive increases in gross weight will eventually end in death,
possibly yours. Engineering lore is fraught with incremental increases
that eventually fail catastrophically (e.g. Tacoma Narrows Bridge). It
is a pattern and habit that must be resisted even if that resistance is
characterized as hysterical by some.
Is that enough "information"?
Regards
Brent Regan
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