The Piasecki Helistat crashed due to structural failure of the low grade pipe work used to connect the H-34 fuselages to the blimp.The idea was to prove the concept before building a definitive version.Moral....don't do things on the cheap ( I still have a piece of the fabric saved from when I met the chief pilot quite a few years ago).
P.S. The Brantly was a lovely helicopter to fly,with a good safety record and a popular trainer in its day.