Somebody recently asked me, "What the heck is that 'AC 43.13' thing you keep referring to?"
AC 43.13 is the common shorthand for the FAA's Advisory Circular 43.13: "Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair." This advisory circular is the official bible on how to inspect, modify, or fix aircraft of almost every construction type. It is also commonly used as a reference guide in the detail design of new aircraft.
As amateur builders of experimental aircraft, we are not legally obligated to comply with all the directives of AC 43.13. However, we are definitely obligated to take all reasonable precautions to ensure that our aircraft do not present a danger to either ourselves or to others. The easiest way to meet this obligation is to follow the guidelines of AC 43.13 wherever practical, and to rely upon engineered and tested practices in all other cases.
There are obviously some aspects of the HP/RS gliders that are inherently contrary to the somewhat conservative guidelines of AC 43.13. The bonding of wing skins with epoxy, the use of rigid PVC foam for wing and tail ribs, and the use of Monel pop rivets are a few good examples. However, for every exception to AC 43.13 that is applied to the HP/RS gliders, Dick Schreder put a ton of effort into testing those materials or processes and determining that they were acceptable for a specific application.
Also, please note that the methods, techniques, and practices described in AC 43.13 are not just the "official" way of doing things. They are also usually the best and most effective way, and more often than not the least expensive way as well. AC 43.13 was developed by real A&P mechanics and aeronautical engineers, and really does reflect a focus on keeping real airplanes safe and operational. Admittedly, there are some controversial aspects to it, such as recently-added verbiage that declares urea-formaldehyde glues obsolete for wooden aircraft repair (tell that to the Sequoia Aircraft people!). But for the most part it's good information.
You can buy printed copies of AC 43.13 at most aviation book stores or pilot shops. You can also download copies of AC 43.13 off of the Web from a variety of sites. Two such sites are:
The official FAA server, which is slow and poorly indexed:
http://www.faa.gov/avr/afs/300/pdf/
and
Jim Pratt's Frequently Asked Questions about Amateur-Built Aircraft, which is faster and a little better organized:
http://www.moneypit.net/~pratt/ac43/
In order to use the files from either the FAA site or Jim Pratt's site, you'll need to have Adobe Acrobat installed on your computer. You may also need WinZip or some other program to extract files from .zip archives.