AN Bolt Configurator
Airforce Navy (AN) bolts, washers, and nuts have long been the standard hardware used in American aircraft. Steel AN bolts are heat treated to meet or exceed 125ksi in tensile strength and 75ksi in shear strength. In comparison, standard 18-8 stainless steel bolts generally only have a tensile strength of 70ksi. Using AN grade hardware is an absolute must when designing or repairing an aircraft. Non aircraft certified hardware is not only weaker but its strength can also vary and it may fail unpredictably. We won't get into the history behind AN hardware since it's already been covered in detail in this article by Ron Alexander. Alexander also does a great job of explaining the specs and sizing of AN hardware so here's an example for quick reference:
AN means the bolt is manufactured according to Air Force-Navy specs.
4 identifies the diameter of the bolt shank in 1/16" increments
8 identifies the length of the shank in 1/8" increments
A means the shank of the bolt is undrilled (no letter here means a drilled shank)
While designing our airplane, we struggled finding detailed CAD files for all the different sizes of AN bolts. These CAD files would allow us to insert the bolts into our final Onshape assembly and get a more accurate CG and weight estimate. We manged to find a limited selection of CAD files from McMasterCarr but it still lacked a lot of the sizes we needed. To solve this issue we created our AN Bolt configurator which automatically configures an AN bolt based on the entered specifications. With the exception of a couple known issues listed below, it's accurate to +-0.001".
Known issues and notes:
As the end of the thread closest to the bolt head, it ends abruptly instead of gradually tapering off. As long as you aren't manufacturing bolts based of our configurator, this should have a minimal effect on bolt mass.
The spacing of the shank hole for AN7 and AN8 bolts hasn't been verified
There is no chamfer on the shank hole
Not all combinations have been verified and thread length and other longitudinal tolerances may increase as the shank length approaches the larger values. The shorter shank lengths have been checked for accuracy but I would consider anything over -20 experimental.
Using the AN Bolt Configurator is easy. Simply select the bolt size and shank length from the upper left hand drop down menu. You also have the option for a drilled head and shank for safety wire or a cotter pin respectively. The corrosion resistance option just adds a small dash on the bolt head to signify the bolt is corrosion resistant. Once all your settings are in, right click on "Part 1" in the lower left hand parts list and click export. Choose your desired file type and export settings and you're good to go. You can also make an easy remix our bolt generator simply by duplicating the public Onshape document.
*Editors note: the thought processes and design choices presented in this article don't necessarily represent those implemented into the final design and are subject to change. Flight Club Aerospace is a group of amateur students with no formal education in any fields of engineering. We present this information for educational purposes only, with the understanding that it is not to be re-created without adequate professional oversight and mentorship. For our latest designs and updates, please see our most recent blog posts.