With the advent of nuclear submarines, U.S. Navy efforts to base helicopters aboard destroyers as a weapon delivery system increased. Limitations of storage space gave impetus to a drone concept. Piasecki proposed such a concept – the “SeaBat” – specifically designed for ease of shipboard control. In order to reduce the controller’s need to remotely fly the drone, the drone control system and rotor configuration were designed to allow the drone’s center body to keep a constant azimuth heading regardless of direction of travel. By using two pairs of tilting propellers with no cyclic control but with dual differential collective control, the machine was “omni-directional”. Its body was kept level by reference to a vertical gyro, these signals went to the differential pitch of each pair of rotors maintaining a constant heading. Each rotor-prop in a pair turned in the same direction and were balanced in torque in all positions by differential tilt angle. The other pair turned in the opposite direction.
| Type | Omni-Directional Drone |
| Engine | Lycoming VO435 6 cyl |
| Horsepower | 260 |
| Rotor Diameter | 12 ft |
| Overall Length | 26.5 ft |
| Height | 6.6 ft |
| Gross Empty | 2,220 lb |
| Endurance | 2 Hours |
| Speed | 0-92 mph |
The vehicle was not designed to carry a test or safety pilot during the tests, but a system of restraining cables suspended it safely above the ground. A vertical shaft 6 cylinder lycoming engine was utilized, and the electronic controls were made by PiAC.
Sea-Bat testing successfully demonstrated the combined electronic/mechanic ability to hover and to maintain a level attitude. The simplicity of the command and control function proved the PA-4 could be successfully operated by nonrated personnel.
Although the first Sea-Bat was damaged in a maneuver to avoid hitting an unauthorized person in the test area the development work and test program give rise to utilize its many unique features in other roles and missions.
Subsequent versions, the “Mud-Bat” and “Ice-Bat”, were designed in different sizes to meet specific mission requirements.