Some numbers
TShort said:
Another thing to consider is that some additional strength is provided by the nesting of the dimples over a countersunk skin sitting flush on the rib.
I'm no engineer so I don't know how much difference this would make...
Thomas
Thomas ... the numbers are well known from the MIL-Handbooks for aircraft design.
A selected portion is here, copied from an old 1995 posting of mine on the Matronics List.
-------------- old 1995 post ---------------------
Following is the equivalent data for YIELD strength (in this case, defined
as a permanent set of 0.005 inch)
YIELD strength of 3/32 MS20426AD flush rivets in 2024-T3 (values in lbs.)
Sheet thickness ----- Dimpled ------- Countersunk
0.032 -------------- 209-------------- 132
0.040 -------------- 209 -------------- 153
0.063 -------------- 209 -------------- 213
This is actually a worse % loss than the ultimate loads, giving a 33% loss
in 0.032, and a 27% loss in 0.040. The previous post's figures were for
ultimate strength (failure), while the above are those loads that would
cause a small permanent set.
YIELD strength of 1/8 MS20426AD flush rivets in 2024-T3 (values in lbs.)
Sheet thickness --- Dimpled ------- Countersunk
0.040-------------- 367-------------- 231 (*)
0.063-------------- 506-------------- 321
(*) this is a "knife edge condition", and not approved.
(Note: Not approved by Mil-Spec. - but approved by the FAA AC43-13 ... gil A)
----------------- end old 1995 post ---------------
The strength differences are substantial, but Vans has approved both configurations.
gil in Tucson ... who likes actual numbers....
Sorry about the formatting... I can't seem to insert blank spaces...