Perhaps you should try some spelling variations:
"unmanned arterial vehicles" » "unmanned arial vehicles", "damaged arterial vehicles", "unmanned area vehicles", "unmanned aerial vehicles", "unmanned aethereal vehicles"
"skinned arterial vehicles" » "skinned aerial vehicles", "skinned aethereal vehicles", "skinned arial vehicles", "guided arterial vehicles"
"unmanned aerial vehicle" » "unmanned aerial vehicles"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("unmanned arterial vehicles") OR ("skinned arterial vehicles"))) OR ("unmanned aerial vehicle")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"unmanned arterial vehicles\") OR (\"skinned arterial vehicles\"))) or (\"unmanned aerial vehicle\"))".
• Removing quotes may allow a broader search: (((( unmanned arterial vehicles ) OR ( skinned arterial vehicles ))) or ( unmanned aerial vehicle )).
• Adding a wildcard symbol may retrieve word variants: (((("unmanned arterial vehicles") OR ("skinned arterial vehicles"))) or ("unmanned aerial vehicle"))*.