Frakes Aviation
Frakes' most significant projects were the re-engineering of two Grumman products , the Ag-Cat and the Mallard , in both cases replacing the original radial piston engines with the Pratt & Whitney Canada PT6A . 
<triplet> Ag-Cat <subj> Grumman <obj> manufacturer <triplet> Mallard <subj> Grumman <obj> manufacturer