▁speed ▁ratio ▁more ▁nearly ▁constant . ▁Oper ating ▁closer ▁to ▁their ▁optimal ▁tip ▁speed ▁ratio ▁during ▁ener get ic ▁g ust s ▁of ▁wind ▁allows ▁wind ▁tur b ines ▁to ▁improve ▁energy ▁capture ▁from ▁sudden ▁g ust s ▁that ▁are ▁typical ▁in ▁urban ▁settings . ▁ ▁In ▁contrast , ▁older ▁style ▁wind ▁tur b ines ▁were ▁designed ▁with ▁heav ier ▁steel ▁bl ades , ▁which ▁have ▁higher ▁in ert ia , ▁and ▁rot ated ▁at ▁spe eds ▁govern ed ▁by ▁the ▁AC ▁frequency ▁of ▁the ▁power ▁lines . ▁The ▁high ▁in ert ia ▁buffer ed ▁the ▁changes ▁in ▁rotation ▁speed ▁and ▁thus ▁made ▁power ▁output ▁more ▁stable . ▁ ▁It ▁is ▁generally ▁understood ▁that ▁noise ▁increases ▁with ▁higher ▁bla de ▁tip ▁spe eds . ▁To ▁increase ▁tip ▁speed ▁without ▁increasing ▁noise ▁would ▁allow ▁reduction ▁the ▁tor que ▁into ▁the ▁g ear box ▁and ▁generator ▁and ▁reduce ▁overall ▁struct ural ▁loads , ▁thereby ▁reducing ▁cost . ▁The ▁reduction ▁of ▁noise ▁is ▁linked ▁to ▁the ▁detailed ▁aer od ynam ics ▁of ▁the ▁bl ades , ▁especially ▁factors ▁that ▁reduce ▁ab rupt ▁st alling . ▁ ▁The ▁in ability ▁to ▁predict ▁st all ▁restrict s ▁the ▁development ▁of ▁ag gress ive ▁aer od ynamic ▁concepts . ▁Some ▁bl ades ▁( most ly ▁on ▁Ener con ) ▁have ▁a ▁wing let ▁to ▁increase ▁performance ▁and / or ▁reduce ▁noise . ▁ ▁A ▁bla de ▁can ▁have ▁a ▁lift - to - drag ▁ratio ▁of ▁ 1 2 0 , ▁compared ▁to ▁ 7 0 ▁for ▁a ▁sail