LM, good detective work, you are correct, it is the Gluhareff Dart, designed by Michael Gluhareff. He was Chief Engineer at Sikorsky up until the 40's although he continued to have an input in numerous models. You will have no doubt seen reference to his name in Aerofiles and you can see how manySikorsky designs he was involved with.
HD, I note what you said but I have not found a reference to his involvement in the S-57. I stand corrected if you have something that indicates otherwise.
LM, over to you.