▁transition . ▁ ▁A ▁later ▁jet - power ed ▁design , ▁the ▁Ryan ▁X - 1 3 ▁Vert ij et , ▁first ▁fle w ▁in ▁ 1 9 5 5 . ▁ ▁Two ▁pro tot ypes ▁were ▁made , ▁both ▁fle w , ▁made ▁successful ▁trans itions ▁to ▁and ▁from ▁horizontal ▁flight , ▁and ▁land ed . ▁ ▁The ▁final ▁test ▁flight ▁was ▁near ▁Washington ▁DC ▁in ▁ 1 9 5 7 . ▁ ▁An ▁inher ent ▁problem ▁with ▁all ▁these ▁tail - s itter ▁designs ▁was ▁poor ▁pilot ▁visibility , ▁especially ▁of ▁the ▁ground , ▁during ▁vertical ▁descent ▁and ▁landing . ▁This ▁led ▁to ▁the ▁concept ▁being ▁abandoned ▁once ▁a ▁more ▁practical ▁form ▁of ▁V TO L ▁appeared , ▁in ▁the ▁form ▁of ▁thrust ▁vector ing . ▁ ▁An ▁U AV ▁does ▁not ▁suffer ▁the ▁problem ▁of ▁pilot ▁attitude . ▁The ▁D orn ier ▁Aer ody ne ▁is ▁of ▁du cted - fan ▁configuration ▁similar ▁to ▁a ▁cole opter , ▁and ▁a ▁test ▁U AV ▁fle w ▁successfully ▁in ▁hover ▁mode ▁in ▁ 1 9 7 2 , ▁before ▁development ▁was ▁dis cont in ued . ▁ ▁Studies ▁and ▁wind ▁tunnel ▁models ▁were ▁made ▁of ▁a ▁tail - s itting ▁version ▁of ▁the ▁F - 1 6 ▁that ▁would ▁be ▁ship ▁based , ▁but ▁any ▁further ▁development ▁was ▁abandoned ▁due ▁to ▁the ▁large ▁thrust ▁requirement , ▁and ▁the ▁need ▁for ▁extensive ▁appar atus ▁to ▁handle ▁take - off ▁and ▁landing . ▁ ▁List ▁of ▁tail - s it ters ▁ ▁See ▁also