▁power ▁vs ▁disc ▁load ings , ▁higher ▁red ▁star ) ▁compar able ▁to ▁hel ic op ters ▁and ▁general ▁av iation ▁aircraft . ▁ ▁During ▁hover ▁and ▁transition , ▁the ▁attitude ▁of ▁the ▁aircraft ▁can ▁be ▁man eu ver ed ▁by ▁thrust ▁vector ing ▁of ▁the ▁two ▁jet ▁engines , ▁which ▁control ▁y aw , ▁roll , ▁and ▁pitch .( See ▁pitch ing ▁moment ) ▁The ▁differential ▁forward ▁thrust ▁of ▁the ▁two ▁j ets ▁controls ▁y aw , ▁and ▁the ▁differential ▁up ward ▁thrust ▁controls ▁roll . ▁The ▁addition ▁of ▁two ▁up ward ▁thrust s ▁controls ▁pitch . ▁The ▁angles ▁of ▁jet ▁no zz les ▁can ▁be ▁rot ated ▁to ▁adjust ▁the ▁forward ▁and ▁up ward ▁vectors . ▁A ux ili ary ▁j ets ▁may ▁be ▁needed ▁to ▁accur ately ▁control ▁the ▁attitude . ▁ ▁Trans ition ▁▁ ▁The ▁low ▁disc ▁loading ▁ann ular ▁lift ▁fan ▁system ▁introdu ces ▁trem end ous ▁momentum ▁drag ▁and ▁nose - up ▁pitch ing ▁moment ▁during ▁the ▁transition ▁from ▁V TO L ▁to ▁cru ise . ▁Before ▁the ▁aircraft ▁reaches ▁a ▁speed ▁for ▁sufficient ▁aer od ynamic ▁lift , ▁it ▁needs ▁extra ▁power ▁to ▁overcome ▁the ▁momentum ▁drag ▁and ▁nose - up ▁pitch ing ▁moment .( See ▁pitch ing ▁moment ) ▁According ▁to ▁the ▁CF D ▁simulations , ▁the ▁maximum ▁requirement ▁for ▁jet ▁thrust ▁with ▁the ▁aid ▁of ▁a ▁sk irt ▁in ▁transition ▁is ▁ 0 . 4 4 8 ▁of ▁the ▁aircraft ▁weight , ▁which ▁can ▁be ▁satisfied ▁by ▁tur bo fan ▁engines ▁with ▁a ▁thrust