▁This ▁technique ▁was ▁successfully ▁used ▁on ▁many ▁early ▁H A WT s . ▁However , ▁on ▁some ▁of ▁these ▁bla de ▁sets , ▁it ▁was ▁observed ▁that ▁the ▁degree ▁of ▁bla de ▁pitch ▁t ended ▁to ▁increase ▁aud ible ▁noise ▁levels . ▁ ▁Vor tex ▁gener ators ▁may ▁be ▁used ▁to ▁control ▁the ▁lift ▁characteristics ▁of ▁the ▁bla de . ▁The ▁V G s ▁are ▁placed ▁on ▁the ▁air fo il ▁to ▁enh ance ▁the ▁lift ▁if ▁they ▁are ▁placed ▁on ▁the ▁lower ▁( fl atter ) ▁surface ▁or ▁limit ▁the ▁maximum ▁lift ▁if ▁placed ▁on ▁the ▁upper ▁( high er ▁cam ber ) ▁surface . ▁ ▁Fur ling ▁Fur ling ▁works ▁by ▁decre asing ▁the ▁angle ▁of ▁attack , ▁which ▁reduces ▁the ▁induced ▁drag ▁from ▁the ▁lift ▁of ▁the ▁rot or , ▁as ▁well ▁as ▁the ▁cross - section . ▁One ▁major ▁problem ▁in ▁design ing ▁wind ▁tur b ines ▁is ▁getting ▁the ▁bl ades ▁to ▁st all ▁or ▁f url ▁quickly ▁enough ▁should ▁a ▁g ust ▁of ▁wind ▁cause ▁sudden ▁acceleration . ▁A ▁fully ▁fur led ▁tur bine ▁bla de , ▁when ▁stopped , ▁has ▁the ▁edge ▁of ▁the ▁bla de ▁facing ▁into ▁the ▁wind . ▁ ▁Lo ads ▁can ▁be ▁reduced ▁by ▁making ▁a ▁struct ural ▁system ▁so fter ▁or ▁more ▁flexible . ▁This ▁could ▁be ▁accomplished ▁with ▁down wind ▁rot ors ▁or ▁with ▁cur ved ▁bl ades ▁that ▁tw ist ▁naturally ▁to ▁reduce ▁angle ▁of ▁attack ▁at ▁higher ▁wind ▁spe eds . ▁These ▁systems ▁will ▁be ▁non linear ▁and