Flier bearing bow mounted on paper (8)
I believe the answer is:
aircraft
'flier' is the definition.
(I've seen this before)
'bearing bow mounted on paper' is the wordplay.
'bearing' becomes 'air' (both can mean an attitude or pose).
'bow' becomes 'arc' (both can mean a curve).
'mounted' shows that the letters should be reversed in order (in a down clue, letters mounted up).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'paper' becomes 'FT' (the Financial Times newspaper).
'arc' in reverse letter order is 'cra'.
'air'+'cra'+'ft'='AIRCRAFT'
(Other definitions for aircraft that I've seen before include "Planes" , "Aeroplane, helicopter etc" , "Flying machines" , "Eg, seven four seven or Airbus" , "Eg, plane, helicopter, etc" .)