foam core question

[Gray E Fowler]

Mark

The idea behind a rib at the end of the tube is simply to distribute the 
load of the wing.  Without the rib, there will be a stress riser right at 
the end of the tube. A violent maneuver such as a snap could easily buckle 
the balsa skin, since the foam has such low compression strength as does 
the balsa itself.  I am sure there are people flying without a rib but I 
would advise against it. When the wing tube is bonded to the wing root and 
the "false" rib it will carry all the load. Only the portion of the wing 
past the rib will then flex creating stress at the tube termination. This 
stress is either concentrated at the very end of the tube OR distributed 
over the surface area of the rib. Because the stiffest component of the 
wing will always carry the load (the tube) any kind of stiffening strips 
inside the rib are dead weight.



Gray Fowler
Principal Chemical Engineer
Composites Engineering




"Mark Hunt" <flyintexan at houston.rr.com>
Sent by: discussion-request at nsrca.org
04/15/2004 09:16 PM
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        To:     <discussion at nsrca.org>
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        Subject:        foam core question


Sirs:
 
As a newbie to cutting foam cores, I have a question regarding how to 
strengthen the wing panel.  Does the preferred method include attaching 
some c.f. strips to the inside of the skins?  Should they extend from the 
root all the way to the tip?  I know some guys feel it is a must to also 
use a false rib near the end of the tube sleeve also?  I hear that some 
guys (r u out there Nat?) are confident without any false rib or c.f. 
under the skin....?
 
I cut the cores earlier tonight (to rebuild my 2M after a mid-air) with 
the help of a friend, and they turned out just beautiful.  I have a nice 
plan to machine a drill jig for cutting the spar tube hole...so that's 
seems to be solved.
 
Thanks in advance for the help...
 
Mark
www.geocities.com/markhunt_2000/INSIGHT
 
 

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