PANEL DISCUSSION-AIR CUSHION 



VEHICLES, HOVERCRAFT, AND 



SURFACE EFFECT SHIPS 



James L. Schuler, Panel Chairman 



The Chairman opened the meeting by stating the purpose, introducing the 

 major participants, and briefly outlining the general areas to be discussed. The 

 purpose of the meeting was to exchange ideas, concepts, and opinions on air 

 cushion vehicles, hovercraft, and surface effect ships. The large number of 

 attendees precluded general discussion. However, the leading participants were 

 requested to make a few introductory remarks designed to provoke questions 

 and dialogue. A summary of the remarks is as follows. 



The first problem in defining a vehicle is defining the mission, size, speed, 

 and pay load to perform the required tasks. Once these are known, the technical 

 problems concern (a) structure, arrangement, power, thrust, and lift and (b) 

 control and stability. The technical areas of most interest to the hydrodynami- 

 cist are (a) propulsion, thrust, and drag, (b) internal flows, and (c) stability and 

 control. 



A full-cushion craft is quite accurately represented as a moving pressure 

 field. This theoretical treatment is more representative of reality than using a 

 moving pressure field to represent a displacement ship. The theoretical drag 

 must then be corrected for appendages, if applicable. The major difficulty is 

 how to realistically treat the degradation of performance in a seaway with the 

 attendant wave impacting and spray drag. 



Comparing the sidewall craft to the nonsidewall craft introduces new prob- 

 lems concerning frictional resistance of the sidewalls, possible cavitation, and 

 control dynamics. Sidewalls should improve directional stability but could 

 complicate steering. Sidewalls should reduce lift power requirements but could 

 introduce surge in the air supply system due to wave-pumping action. 



Following the preceding remarks, Mr. House was asked to present some 

 comments and lead a discussion on some aspects of machinery selection. He 

 made several important points (see Tables 1 and 2 and Fig. 1). One is that the 

 use of lightweight power plants leads naturally to consideration of marine gas 

 turbines. These machines are costly and require long development cycles. 

 This leads the vehicle designer to select proven prime movers and this (to 

 some extent) tends to yield craft designed around one or more existing ma- 

 chines. Recent developments, such as blade cooling techniques, will improve 

 the performance of existing machines as we move forward in time. 



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