Re: REFLECTOR: Wing attach bolts

[Peter Beaty <PETER.J.BEATY@usa.dupont.com>]

Just a word of caution here.  You want to be sure you are getting the same
ultimate tensile strength (UTS), yield point (YP), ductility and toughness.
 You can infer ductility from the UTS/YP ratio, but you cannot be totally
certain, because material properties play a role here.  

Also, I would be loathe to sacrifice toughness (resistance to developing
shear cracks) unless I knew for sure I was getting the equivalent (NOTE: I
didn't say "better"!) material properties.  Rolled threads are important in
resisting the start of shear cracks in the thread root, but so are the
material properties, ductility and toughness, which resist the propagation
of cracks once they start.

Finally, the extra bolt length is a positive feature, whether the designers
realized this or not.  The extra length provides extra bolt stretch when
tightened, and this better resists loosening.  We use this technique all
the time in designing equipment, especially when vibration is present.  The
extra stretch may not be needed for our wing bolts, but why "throw it away"
if it's a free-bee?

None of this may matter, IF the bolts have a large safety factor (SF).
But, strange things happen to bolts, like getting loose, and then all bets
are off, as the SF drops to 1.0 or less.

Good topic!  Comments?

Pete Beaty
Std Wing RG-E a-building 


At 06:23 PM 05/25/1999 -0700, you wrote:
>David Brown wrote:
>> 
>> I am bolting my wings on for what I hope will be the last time before
>> flight. I have the STD wing. The AN8-30a bolts are requiring between 6 and
>> 7 thick AN816 washers in order to keep the locknuts from bottoming out.
>> 
>> I'm thinking of replacing the bolts with -26 or -27 length. Has anyone else
>> had this problem?
>> 
>> Dave Brown
>  Dave I had the same problem, corrected by using a 1/2" shorter bolt.	 
>i used an SAE grade eight bolt with a yield strength of 130000 PSI     
>and a 150000 tensile, also has rolled threads. This exceeds the AN     
>specs. I would use AN if
>available.
                      
>Regards, Al
>Faison
>