▁would ▁be ▁replaced ▁by ▁only ▁ 2 5 0 ▁aircraft . ▁The ▁Air ▁Force ▁had ▁attempted ▁to ▁replace ▁the ▁C - 1 3 0 ▁in ▁the ▁ 1 9 7 0 s ▁through ▁the ▁Advanced ▁Med ium ▁S TO L ▁Transport ▁project , ▁which ▁resulted ▁in ▁the ▁C - 1 7 ▁G lob em aster ▁III ▁that ▁instead ▁replaced ▁the ▁C - 1 4 1 ▁Star l if ter . ▁The ▁Air ▁Force ▁Research ▁Labor atory ▁fund ed ▁Lock he ed ▁and ▁Bo eing ▁demonstr ators ▁for ▁the ▁Speed ▁Ag ile ▁concept , ▁which ▁had ▁the ▁goal ▁of ▁making ▁a ▁S TO L ▁aircraft ▁that ▁can ▁take ▁off ▁and ▁land ▁at ▁spe eds ▁as ▁low ▁as ▁ ▁on ▁air fields ▁less ▁than ▁ 2 , 0 0 0   ft ▁( 6 1 0   m ) ▁long ▁and ▁cru ise ▁at ▁Mach ▁ 0 . 8 - plus . ▁Bo eing ' s ▁design ▁used ▁upper - sur face ▁blow ing ▁from ▁embedded ▁engines ▁on ▁the ▁in board ▁wing ▁and ▁blow n ▁f laps ▁for ▁circul ation ▁control ▁on ▁the ▁out board ▁wing . ▁Lock he ed ' s ▁design ▁also ▁used ▁blow n ▁f laps ▁out board , ▁but ▁in board ▁used ▁pat ented ▁revers ing ▁e ject or ▁no zz les . ▁Bo eing ' s ▁design ▁completed ▁over ▁ 2 , 0 0 0 ▁hours ▁of ▁wind t unnel ▁tests ▁in ▁late ▁ 2 0 0 9 . ▁ ▁It ▁was ▁a ▁ 5 ▁percent - scale ▁model ▁of