▁ ▁Vor one zh ▁M V - 6 ▁ 6 - cy l inder , ▁air - co o led , ▁invert ed ▁in - line ▁engines ▁mounted ▁at ▁the ▁front ▁and ▁rear ▁of ▁the ▁fus el age ▁nac elle , ▁driving ▁ 2 - bl aded , ▁variable ▁pitch ▁prop ellers . ▁ ▁The ▁sharp ly ▁t aper ed ▁wings ▁supported ▁tail - bo oms ▁which ▁in ▁turn ▁supported ▁the ▁tail plane , ▁elev ators , ▁fin ▁and ▁rud der . ▁The ▁wings ▁also ▁hous ed ▁the ▁ret ract able ▁main ▁under car riage ▁units ▁which ▁ret ract ed ▁in wards . ▁The ▁nose ▁under car riage ▁was ▁attached ▁to ▁the ▁front ▁engine ▁mount ing ▁and ▁ret ract ed ▁rear wards . ▁ ▁Arm ament ▁of ▁the ▁S AM - 1 3 ▁was ▁intended ▁to ▁be ▁ 4 x ▁ ▁Sh K AS ▁machine - g uns : ▁two ▁in ▁the ▁fus el age ▁top ▁deck ing ▁firing ▁through ▁the ▁prop eller ▁disc , ▁and ▁one ▁at ▁each ▁end ▁of ▁the ▁wing ▁centre - section . ▁ ▁Oper ational ▁history ▁First ▁flow n ▁in ▁ 1 9 4 0 ▁by ▁Nikol ay ▁D ▁F ik son , ▁the ▁S AM - 1 3 ▁proved ▁difficult ▁to ▁handle , ▁requiring ▁long ▁runs ▁to ▁take ▁off ▁and ▁land , ▁with ▁poor ▁clim b ▁performance ▁and ▁low ▁ce iling . ▁ ▁After ▁the ▁first ▁flight ▁and ▁subsequent ▁tests , ▁the ▁poor ▁flying ▁qual ities ▁of ▁the ▁S AM - 1 3 ▁were ▁being ▁addressed ▁when