Undersea Vehicle Autopilot Off Weight Design Compensation

A service issue that can adversely affect the performance of many undersea vehicles in general application is either over or under weight operation. Depth keeping precision can be impacted when a vehicle is launched at a weight different from that specified in the nominal flight control system design. As a result, overall maneuvering performance and the vehicle application objectives can be significantly impacted. This paper presents a compensation method based on simple expansion of the vehicle’s autopilot depth controller trim schedule. Expansion is defined relative to a vehicle’s nominally fixed weight-buoyancy flight control equilibrium trim design point and refers to practical variances in both net buoyancy and buoyancy-weight center geometric offset. This implementation requires only a simple, highly feasible, dry dockside launch under/overweight measurement for operational flight static reference. Off weight compensation is enabled by a priori determination of the vehicle’s steady speed, straight-horizontal flight path, body pitch, and elevator trim angles when subjected to the expected set range of weight-buoyancy variations. The method and implementation are outlined. A depth step change maneuver, using a high fidelity autopilot-software-in-the-loop maneuvering simulation, is examined to verify the implementation feasibility and effectiveness.