[1][2] Founded by Herbert Beaujon in the 1970s, Beaujon Aircraft has published the designs for eight ultralight aircraft and marketed seven of them in book form under the name How to Build Ultralights.
Apart from general performance calculations, stress analysis, and other general design requirements, it really shines in the detailed illustrations of aluminum tube building.
It lacks in one area though: it does not show how to cover the craft with either sailcloth or dope & fabric.
[1]Beaujon's designs have been described as "beautifully simple" and have been used to construct many flying examples.
[1] Beaujon has made the plans for one of his earlier designs, the wooden winged, three axis control Enduro available for free download as 25 JPEGs.