Gliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne . 
<triplet> Gliding <subj> air sport <obj> subclass of <triplet> unpowered aircraft <subj> Gliding <obj> use <triplet> gliders <subj> unpowered aircraft <obj> subclass of