258 : H. Von Schertel 
The length of a route between two points which can still be operated advantageously in 
competition with an airline is also dependent on the economic maximum speed of the hydro- 
foil boat. Preference obviously will be given to the airplane if it requires much less time 
for the trip and if both the airplane and the hydrofoil company charge the same prices. 
Assuming a maximum speed for the hydrofoil boat of 75 knots and for the medium-distance 
airplane a block speed of 360 knots, it can be safely predicted that for all distances beyond 
300 nautical miles, for which the hydrofoil boat needs more than four hours, travellers will 
prefer the airplane with its 50 minutes of flying time, even counting the time lost getting to 
and from the airports. 
It can be expected that under the existing circumstances the longest economically 
favorable distance for the hydrofoil boat lies between 300 and 400 nautical miles. Although 
quite a lot of publicity has been given to the idea of a future Atlantic hydrofoil service it 
appears very improbable, if not impossible, that hydrofoil boats will ever be suitable for — 
this task which can be much better accomplished and with better economic results by 
modern airplanes. 
NOTATIONS USED 
= vertical acceleration 
= span of hydrofoil 
= chord of hydrofoil 
=- submergence below water surface 
= foil distance 
= weight 
= speed in ft/sec or in knots 
= 0.5lpv” = dynamic pressure 
b?/S =. aspect ratio 
= fuel consumption 
D/qS =: drag coefficient 
L/S = lift coefficient 
‘drag of hydrofoil 
= lift of hydrofoil 
w= wavelength 
= Froude number 
=- wave height 
= motor power 
=- projected foil area 
= orbital sensitiveness 
= wing characteristic 
= displacement 
= angle of incidence 
= weight density of water 
= dihedral angle 
= wave slope 
= y/q = mass density 
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PHY APNSMNVSRBHOHSVUAAWAOQVCSCPEwe™ ee 
