A diesel powerplant development program for airships

Abstract

This paper explains the approach that Westinghouse Airships Inc. has taken in selecting an advanced technology 2 stroke diesel powerplant for consi&ration as a future enhancement for the Skyship and Sentinel series airships. It also outlines the current state of development of the selected Zoche diesel (currently running on the test bench in 4 cylinder form) and the further program that will bring the 8 cylinder variant to production readiness in the medium term. Finally, the paper addresses the dramatic advantages that this new propulsion should bring to the airship and the author's belief that this program could represent an opportunity for a major performance breakthrough for airships. The term high specific power output used in this paper refers to diesel engines with a power to ratio in excess of 0.5 hp per lb. As any student of airship history will be aware, the high performance diesel is no newcomer to the field of airship propulsion. The majority of the German Zeppelin rigid airships, the UK's RlOl and the USA's Los Angeles, Akron and Macon were powered by diesel engines of the German Daimler-Benz or Maybach types (with the exception of the RlOl which was powered by Beardmore Tornado engines). However, since the demise of that generation of rigid airships and the advent of World War 2, virtually all airships have been powered by gasoline piston engines, a recent exception being the Goodyear GZ-22 with its gas turbiine engines. This continuing dependency upon the gasoline piston for current airships is, in the author's opinion, a consequence of there having been no viable alternative production powerplant available in the power range appropriate to today's d e r airships. It is noteworthy, however, that one of the few current large volume (2.5 million cubic ft) airship development programs, Westinghouse Airship's ARPA YEZ 2A, will employ the world's only production, high specific power output diesels in the 2000 hp range the Italian CRM BR2AI for its main cruise propulsion system. This paper seeks to demonstrate that reliable, high specific power output diesel engines will be available in the medium term for today's smaller (100,000 to 500,000 cubic feet) range of airships and explains Westinghouse Airship's approach to selecting a suitable candidate diesel powerplant, the Zoche type ZO 0 2 4 and the company's on-going development program with Zoche. . . . e for the A l Why search for a modern high specific power output diesel when there are numerous aircraft gasoline piston and gas turbine engines available in the 100 to 500 hp range? The answer lies principally in one factor fuel consumption, although there are, of course many other additional advantages for the diesel engine. One, if not, the main attribute of the airship for military missions is long endurance. For long endurance missions (e.g. in excess of 16 hours) fuel can become more dominant than weight. Fig. 1 overleaf indicates that for the YEZ-2A the breakeven point in terms of engine installation plus fuel weight between the current best diesel and gas turbine installations is at approximately 24 hours mission endurance (accordingly, the YEZ-2A has twin diesel cruise and a gas turbine sprint engine). Below that endurance the gas turbine installation is preferable, above that and the diesel increasingly has the advantage. The best gasoline piston engines typically provide endurance at a level between the diesel and the gas turbine. With d e r airships, due to the very light of the Zoche engine, the installed of the Zoche diesel is virtually identical to that of typical 400 hp turbines, which coupled with a lower SFC at all speeds, means that the breakeven point at which the diesel becomes superior to the turbine occurs at zero hours. I I 0 I I I I o a 1 0113 ON STATION However, Fig. 1 only holds good for high specific power output diesel engines. The average modem, medium performance turbocharged diesel (e.g. power boat or high performance industriai engine) would be unacceptably heavy and bulky. Simiily, automobile diesel engines are too small in power output terms and still would be of unacceptably low specific power output. Table 1 below provides comparative data for powerplant in the power range appropriate for airships in the 200,000 to 2500,000 cubic ft size range. The part load (20% power) SFCs are particularly of interest in so far as it is at these modest power levels that an airship tends to operate in 'on-station' mode.