▁al umin um - al loy ▁cyl inder ▁heads . ▁An ▁R - 7 5 5 E ▁variant ▁was ▁developed ▁for ▁use ▁in ▁hel ic op ters . ▁ ▁Vari ants ▁R - 7 5 5 A 1 The ▁base - line ▁direct ▁drive ▁production ▁version . ▁R - 7 5 5 A 2 3 0 0   hp ▁variant . ▁R - 7 5 5 A 3 Sim ilar ▁to ▁A 1 ▁but ▁with ▁Sc int illa ▁magnet o es . ▁R - 7 5 5 B 1 De - r ated ▁version ▁of ▁the ▁R - 7 5 5 A ▁to ▁drive ▁a ▁fixed ▁pitch ▁air s cre w . ▁R - 7 5 5 B 2 De - r ated ▁version ▁of ▁the ▁R - 7 5 5 A ▁to ▁drive ▁a ▁variable ▁or ▁cont roll able ▁pitch ▁air s cre w . ▁R - 7 5 5 E Up - r ated ▁engine ▁with ▁reduction ▁g ear ing . ▁R - 7 5 5 E H Develop ed ▁to ▁power ▁the ▁Jacob s ▁Type ▁ 1 0 4 ▁Gy ro dy ne . ▁ ▁App lications ▁ ▁An ahu ac ▁T au ro ▁ ▁Be ech craft ▁Model ▁ 1 7 ▁St agger wing ▁( B 1 7 L , ▁C 1 7 L , ▁E 1 7 L ) ▁ ▁Bo eing - Ste ar man ▁P T - 1 8 ▁Kay det ▁ ▁C ess na ▁AT - 1 7 ▁Bob cat ▁ ▁C ess na ▁