His designs led directly to the CH-46 and CH-47. Both of these aircraft have been operational since the early 60`s, with the CH-47 still being produced today. While not aesthetically pleasing, the twin rotor design allows all of the power to be used for lift. With a traditional helicopter, part of the power is used for the tail rotor to counteract the torque of the main rotor.
A design from Frank Piasecki was a total disaster in the 80`s. This was the "Helistat". It was a blimp with four H-34 helicopters attached, intended for use in the forest industry. It came apart on the ground after a test flight due to ground resonance, killing the pilot. The project was cancelled after this. In a bit of irony, this took place a half mile from where the Hindenburg crashed.