SEVERAL UNUSUAL PROPULSION SYSTEMS

Abstract

ABSTRACTThe paper describes several unusual propulsion systems that can be used in underwater vehicles such as torpedoes, propelled mines, anti‐torpedo weapons, underwater launched missiles, submarine signals, decoys, et cetera. One of the devices also has a potential for ship propulsion. The unifying theme in this report is the principle that, at short ranges, the size of the propulsion hardware is much more important than the fuel consumption rate. This principle applies even more strongly at high vehicle speeds. An application of this idea to short‐range torpedo‐like vehicles led to active consideration of rockets for underwater propulsion. At short ranges, the rocket fuel and hardware are significantly smaller and lighter (considered together) than the fuel and hardware for a conventional system. A program is now being completed to develop an engineering data base for the use of rockets under water.The somewhat surprising weight and volume advantages of using rocket motors for short‐range missions, despite their high fuel consumption, leads one to speculate whether or not an intermediate system can be devised that would have a small hardware weight and volume (not so small as a rocket). Such an intermediate system could have an advantage over both rockets and conventional systems at most ranges of interest.The first and most straightforward of the intermediate systems is the “Jet Tip Propeller.” It integrates a single‐stage reaction turbine of the HERO type with a propeller. This integration achieves small hardware size and weight, but because of the resulting inefficiencies the fuel consumption rate is about one‐hall to one‐fourth as great as that for a rocket or about ten times greater than that for a conventional propulsion system.It can be shown that the fuel consumption of a rocket could be reduced dramatically if a modest flow of the ambient seawater could be added to the rocket exhaust in the “right way.” Many attempts have been made to exploit this possibility, but most have failed because their inventors ignored some implicit assumptions made in analyzing the problem.The water piston propulsor, a complete propulsion system which successfully meets all of the assumptions and is a variation of the water piston concept, is only a prime mover. It is a high efficiency, low speed, single‐stage turbine while the other propulsors discussed previously can be used only on vehicles the size of a large missile or smaller. The water piston turbine, however, can be used on ship as well.This report discusses three such systems that have been investigated at the Naval Surface Weapons Center.