  km / h , ▁ 1 6 1 ▁MP H ). ▁The ▁most ▁common ▁surv ival ▁speed ▁is ▁ 6 0   m / s ▁( 2 1 6   km / h , ▁ 1 3 4 ▁MP H ). ▁Some ▁have ▁been ▁designed ▁to ▁surv ive ▁. ▁ ▁St all ▁ ▁A ▁st all ▁on ▁an ▁air fo il ▁occurs ▁when ▁air ▁passes ▁over ▁it ▁in ▁such ▁a ▁way ▁that ▁the ▁generation ▁of ▁lift ▁rapidly ▁decre ases . ▁Usually ▁this ▁is ▁due ▁to ▁a ▁high ▁angle ▁of ▁attack ▁( A O A ), ▁but ▁can ▁also ▁result ▁from ▁dynamic ▁effects . ▁The ▁bl ades ▁of ▁a ▁wind ▁tur bine ▁with ▁fixed ▁pitch ▁can ▁be ▁aer od ynam ically ▁designed ▁to ▁st all ▁in ▁high ▁wind ▁spe eds , ▁causing ▁slower ▁rotation . ▁This ▁is ▁a ▁simple ▁and ▁fail - safe ▁mechanism ▁to ▁help ▁prevent ▁damage ▁to ▁the ▁system ▁by ▁excess ive ▁wind ▁spe eds . ▁However , ▁other ▁than ▁systems ▁with ▁dynamically ▁controlled ▁pitch , ▁it ▁can ▁not ▁produce ▁a ▁constant ▁power ▁output ▁over ▁a ▁larger ▁range ▁of ▁wind ▁spe eds , ▁which ▁makes ▁it ▁less ▁suitable ▁for ▁large ▁scale , ▁power ▁grid ▁applications . ▁ ▁A ▁fixed - speed ▁H A WT ▁( Horizontal ▁A xis ▁Wind ▁Tur bine ) ▁inher ently ▁increases ▁its ▁angle ▁of ▁attack ▁at ▁higher ▁wind ▁speed ▁as ▁the ▁bl ades ▁speed ▁up . ▁A ▁natural ▁strategy , ▁then , ▁is ▁to ▁allow ▁the ▁bla de ▁to ▁st all ▁when ▁the ▁wind ▁speed ▁increases .