Davis and Oates 



DISCUSSION 



H. D. Ranzenhofer 



Grumman Aircraft Engineering Corporation 



Bethpage, Long Island, New York 



Generally, the paper is excellent, in that it presents a full and detailed pic- 

 ture of De Havilland's work on the FHE-400 hydrofoil ship, in terms of the ap- 

 proaches used and the results obtained. The tiioroughness of the work is attested 

 to, in part, by the extensive use of both fixed and free models in the development. 



The analysis in some respects, parallels that used at the Grumman Aircraft 

 Engineering Corporation in our work in the hydrofoil field. 



It is interesting to note that the authors' conclusions as to the complexity of 

 the craft equations of motion when using the method of small perturbations are 

 identical to ours. 



Another item of significance is the use of the surge degree of freedom in 

 the analog computer program. From the results obtained, it may be inferred 

 that, for the foilborne cruising conditions, craft forward velocity can be assumed 

 constant, thus eliminating the surge equation. For our work in the design and 

 development of hydrofoil autopilots, this assumption was made. However, the 

 surge equation is useful in studying takeoff and landing performance if hull lift 

 and drag terms are included. A possible limiting factor here is the amount of 

 analog equipment available; it was found in our work that the addition of the 

 surge equation and associated terms required a 50% increase in a five degree 

 of freedom analog program. 



A point of criticism is the omission of the lift and drag equations from the 

 discussion of the approach using forces and moments. These forces comprise 

 the major portions of the total force and moment terms, X, Y, z, L, M, and N in 

 Eqs. (1) through (6) and in our opinion would be of interest to others in this area. 



The frequency response charts form a valuable basis for performance com- 

 parisons with other hydrofoil craft, but only if identical wave length-to-height 

 ratios are used for all craft, or if wave lengths are normalized to foil base or 

 another suitable craft parameter. 



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