Hydrofoil Craft 



TOPIC 2 



A detailed presentation by J. Z. Lichtman (Naval Applied Science Labora- 

 tory, Brooklyn, N.Y.) was given in connection with cavitation erosion, resist- 

 ance of propeller and hydrofoil structural materials. Lichtman presented 

 several graphs showing the relative performance of samples of Titanium 621, 

 17-4 PH(1025) steel, HY 130, Cunisibe 18, Mn-Ni bronze, Mn bronze and HY 

 80, as well as the effectiveness of elastomeric coatings. He concluded that the 

 resistance to cavitation erosion of several propeller and hydrofoil structural 

 materials has been determined using high-velocity (rotating disk) and vibratory 

 (magnetostriction) apparatuses. The materials were rated on the basis of their 

 relative resistance. None of the structural materials were as resistant as high- 

 strength elastomeric coatings, inlays or overlays, suggesting the use of elas- 

 tomeric patches in local areas where erosion of structural materials occurs. 

 The erosion of non-corrosion-resistant ferrous alloys was increased signifi- 

 cantly in sea water, in comparison with fresh-water exposure due to electro- 

 chemical (corrosion) effects in the former liquid. The use of a sacrificial 

 zinc-anode cathodic protection system decreased the erosion of these alloys to 

 values within the range associated with fresh-water exposure. (Further details 

 should be sought directly from the Naval Applied Science Laboratory.) 



There were no discussers of this vital topic, which is so essential to the 

 operation of transcavitating hydrofoils. 



Professor T. Y. Wu (California Institute of Technology) abstracted a de- 

 velopment of a quasi-steady planing of delta wings by R. K. DeLong and A. J. 

 Acosta. Professor Wu pointed out that this study was indeed new, in that hereto- 

 fore a nonstationary flow theory had not been attempted for planing craft. Agree- 

 ment between measurements and theory was found to be good for angles of attack 

 up to 10°. Agreement would be better at larger angles if the nonlinear terms 

 could be doubled. The influence of reduced frequency was noteworthy. Out- of - 

 phase forces were well predicted, but in-phase forces were lower than measured. 



D. Savitsky (Stevens Institute of Technology, Hoboken, N.J.) asked if there 

 were any physical interpretation of the in-phase lift results at very low reduced 

 frequencies. He noted that analysis of experimental planing data for cases of 

 slowly applied vertical velocity could not be analyzed simply as a change in trim 

 or angle of attack, but, rather, it is necessary to calculate a higher effective for- 

 ward or planing velocity to explain the large increase in lift due to a vertical 

 velocity component. In contradistinction to wings, the planing body not only 

 changes angle of attack with heave velocity, but also its wetted length. At low 

 reduced frequencies, these two effects can be accounted for by calculating a 

 higher steady- state planing speed. 



Professor Wu generally deferred answers to the questions to the authors 

 who were not in attendance and offered some copies of the paper to any who may 

 be interested. 



Next, a description was given of a new high-speed water-tunnel facility and 

 hydrofoil tests in cavitating conditions at the Centre d' Etudes Aerodynamiques 

 et Thermiques de Poitiers in France. This prepared work, read by Professor 



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