Reverse A's breakin' planes

[Gray E Fowler]

Concerns of the Reverse Avalanche damaging planes is real, but do not 
think that fatigue plays a role here.  Composites or either good or 
broken, and in the case of our planes, the damage is usually easy to see. 
As far as the CF wing tube and the fuse go, if you do X amounts of snaps, 
it does not weaken the structure with every snap, unless something is 
indeed already broken. Look for the signs of cracked glue joints and 
paint.
 The situation that would scare me are the planes that use styrofoam as a 
core material. Core sturctures work great for our planes because a 2mm 
thick core structure give an "apparent" stiffness equal to the modulus of 
a solid laminate of equal thickness without all the weight. Stiffness 
equates into a solid feeling-flying plane. This core structure, while 
having a near stiffness of the solid laminate by no means has the 
strength, and is in fact much weaker. To make matters worse, soft cores 
such as the styrofoam will buckle, and the core integrity is gone and so 
is the structural ridgidity, which means a flex, and possible structural 
failure. Such a problem would most likely show up as a chip of paint 
comming off the fuselage.
The bending of an Aluminum wing tube shows the yield strength not the 
failure strength of the aluminum has been exceeded. CF tubes have no yield 
strength only a failure strength which is higher than the aluminum.  CF 
wing tubes if exceeded in strength will go from perfectly good to simply 
broken. This will happen only once, not gradually, and that one time is 
the moment the strength is exceeded.


Gray Fowler
Principal Chemical Engineer
Composites Engineering
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