On Thu, 25 Sep 2003 10:25:50 -0700, (Harry
Andreas) wrote:

In article , "Jeff Crowell"
wrote:

Mike Marron wrote:
I doubted that ... B) the pod fasteners were designed to take
shear loads in the threaded area.

I did not "doubt" what you said about them "four bolts running
straight up into the airframe."

FYI, Mike, shear loads are 90 degrees to the long axis of the bolt.
Loads aligned with the long axis of the bolt are tensile loads.

I read that whole convoluted thread with amusement earlier this
week when I returned from travel. So much figurative arm waving...

As a long time mechanical engineer, let me point out a few things
I saw when reading the whole distended session:
1] someone (MIke?) was absolutely correct when he said that bolts
should never be loaded in shear across the threads. There are
special bolts with unthreaded shanks for shear loading.
2]someone said bolts are roll threaded to increase strength, that
is incorrect. the reason roll threading is used is that it does not
create as bad a stress point as cut threads. Cutting threads cuts
across grain flow and roll threading pushes the grain around the
thread. No increases in strength, but less of a decrease.
3] It is perfectly reasonable that 4 bolts going straight up into the
airframe take the entire loads of a pod. Pod mounting points are
primarily loaded in bending with only a little shear. This is overcome
with tensile strength, not shear strength.
4] any good designer can transfer pod flight loads into the airframe
anyway, without putting the entire load through fasteners
5] cadmium is plated onto fasteners to prevent galvanic corrosion
with aluminum in the airframe
6] pre-loading the bolts puts the structure in compression.
Subsequent flight loads unload the compression before the
structure goes in tension. All this depends on the load paths.
7] I have some experience with "little hooks" and different alloys
and different heat treatments. Size doesn't necessarily matter.

When a layman looks at lugs (what I call the assembly/loop the pylon
"hook" circles around) and one is a little smaller than a little
finger, and the other is as big as a thumb the size difference made me
wonder what was going on.

Something for everyone to consider. Everyone has been focused on a pod
coming off an aircraft by the attachment point of the pylon to the
aircraft. Bolts sheared, etc of the adapter plate. (I forgot what that
was called - MWA?

How about the lug on the pod, the plate the lug screws into and how
that plate is attached to the pod?

I don't remember ever sending in the lugs for nondestructive testing
(magnaflux) at Ubon 1967, Korat 1968-70, nor Tyndall 1972 where we
flew the ALE-2 chaff tanks and the ALQ-72 pod on T-33s.

BUT we got caught at Det 1 4677 DSES at Holloman AFB during a mini ORI
for not testing the lugs on our ALE-2 chaff tank spares we kept around
for use on TDY EB-57s around 1973. I can't remember the specifics, but
I think it was a new requirment.

A couple pods ripped off F-4s in SEA because of lug failure in say
1972/73, and they make it a requirment to test all ECM lugs in the Air
Force no matter what they are used on?