there are no instrument requirements for gliders in the FAR's. So if
you have a type certified glider the only thing that governs you would
be the Handbook or the Type Certificate. For experimental, it
completely depends on your operating limitations that were issued with
your airworthiness certificate. My Cherokee's Op Lims say that I must
be equipped IAW 91.207, so I have a compass. The only reason I have a
compass is to keep the FAA happy. its a normal "whiskey" compass and
bobbles around constantly.