Swaan and Wahab 



7. Wiegel, R. L., c.s., "Research on Annular Nozzle Type Ground Effect Ma- 

 chine Operating Over Water"; "Operation Over Waves," Hydraulic Engi- 

 neering Laboratory, University of California, Berkeley, 1963. 



8. Gumming, J. D., "Research in Annular Nozzle Type Ground Effect Machine 

 Operating Over Water"; "Water Surface Configuration," Hydraulic Engi- 

 neering Laboratory, University of California, Berkeley, 1963. 



9. "Tests with a Flying Model of a Ground Effect Machine SKMR-I 'Hydro- 

 skimmer'," Seakeeping Test Report no. 121, Netherlands Ship Model Basin, 

 August 1963. 



10. "Tests with a Model of a Ground Effect Machine SKMR I 'Hydroskimmer' 

 Flying Over Regular Waves," Seakeeping Test Report no. 157. Netherlands 

 Ship Model Basin, July 1964. 



DISCUSSION 



W. A. Crago 



Saunders -Roe Division of Westland Aircraft Limited 



Wight, England 



For reasons of commercial security it is relatively rare for practical data 

 obtained on models of full scale hovercraft to be published and I personally 

 would like to say that I was, therefore, very pleased to see this excellent paper 

 by Mr. W. A. Swaan and Mr. R. Wahab. 



This is all the more interesting to me because in the Saunders-Roe Tanks 

 we spend a fair proportion of our time testing hovercraft. 



We now have full scale area model test results for the Nl, N2, N3 and 5 full 

 scale variants of the N5 (these are craft ranging in weight from 7 to 37 tons) and, 

 with this background, I can confirm that the type of test reported in Mr. Swaan's 

 paper, using dynamically scaled free models, can give results which correlate 

 acceptably well with data obtained in the full scale regime, although as a result 

 of our experience we would prefer not to use a model quite so small as the 

 N.S.M.B. Hydroskimmer because of scale effects in the jets. 



The N.S.M.B. model test philosophy, in which the propulsion propellers are 

 not represented is, I feel, acceptable except in cases where the propellers can 

 affect the flow into the fan intakes. The way in which the fan intake flow is rep- 

 resented is important because the intake flow geometry determines the moment 

 arm at which the momentum drag acts. This moment affects the crafts runnir^ 

 trim and this in turn affects the drag. Correct representation of the intake flow 

 is thus essential. 



712 



