▁will ▁couple ▁the ▁structure ▁to ▁the ▁flow ▁field ▁- ▁thus , ▁design ▁tools ▁must ▁evol ve ▁to ▁model ▁these ▁non linear ities . ▁ ▁Standard ▁modern ▁tur b ines ▁all ▁f url ▁the ▁bl ades ▁in ▁high ▁wind s . ▁Since ▁fur ling ▁requires ▁acting ▁against ▁the ▁tor que ▁on ▁the ▁bla de , ▁it ▁requires ▁some ▁form ▁of ▁pitch ▁angle ▁control , ▁which ▁is ▁achieved ▁with ▁a ▁sle wing ▁drive . ▁This ▁drive ▁precisely ▁angles ▁the ▁bla de ▁while ▁with standing ▁high ▁tor que ▁loads . ▁In ▁addition , ▁many ▁tur b ines ▁use ▁hyd ra ul ic ▁systems . ▁These ▁systems ▁are ▁usually ▁spring - loaded , ▁so ▁that ▁if ▁hyd ra ul ic ▁power ▁fails , ▁the ▁bl ades ▁automatically ▁f url . ▁Other ▁tur b ines ▁use ▁an ▁electric ▁serv om ot or ▁for ▁every ▁rot or ▁bla de . ▁They ▁have ▁a ▁small ▁battery - res erve ▁in ▁case ▁of ▁an ▁electric - grid ▁break down . ▁Small ▁wind ▁tur b ines ▁( under ▁ 5 0   k W ) ▁with ▁variable - p itch ing ▁generally ▁use ▁systems ▁operated ▁by ▁cent rif ug al ▁force , ▁either ▁by ▁fly we ights ▁or ▁geometric ▁design , ▁and ▁employ ▁no ▁electric ▁or ▁hyd ra ul ic ▁controls . ▁ ▁Fund amental ▁g aps ▁exist ▁in ▁pitch ▁control , ▁limit ing ▁the ▁reduction ▁of ▁energy ▁costs , ▁according ▁to ▁a ▁report ▁from ▁a ▁coal ition ▁of ▁research ers ▁from ▁univers ities , ▁industry , ▁and ▁government , ▁supported ▁by