said concavity at said trailing end of said concavity having a depth sufficient to accommodate said impeller such that a central hub of said impeller is positioned at an elevation substantially equal to an elevation of {HEAD ~ said output shaft} of {TAIL ~ said engine} 
said concavity at said trailing end of said concavity having a depth sufficient to accommodate said impeller such that a central hub of said impeller is positioned at an elevation substantially equal to an elevation of { HEAD ~ said output shaft } of { TAIL ~ said engine }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL