But I think that the friction losses of the proposed system would be considerable. Also, the
suggested diaphragm pump has several structural limitations: it is comparatively large in
diameter and therefore quite unsuitable for a borehole; it must be secured at the bottom of the
borehole against the pull of the connecting rod a very impractical proposition. The pump is not
suitable for large heads of water; the 15' (5m) head suggested in the example has little practical
application. Because the moving structure and the connecting rod are quite heavy, they will
absorb a substantial portion of the available energy. It seems likely that the diaphragm of of the
pump will not last long. And since the pump has to be immobilized at the bottom of the well,
changing the diaphragm could be very difficult.
The support structure requires welding difficult to do in the average village.And a rubber
compound is needed to mate some surfaces also difficult to find in a village.
As given, the curve of the wind speed plotted against water delivered at a 10' head will apply
only in the best conditions.
There is no provision for governing or braking systems, which are necessary to protect the device
in very strong winds.
3.Performance Tests of Savonius Rotor, by M. H. Simmonds and A. Bodek, Brace Research
Institute Technical Report No. 5.
The method for testing the rotor is fairly accurate and appropriate.
The power coefficient plotted against tip speed ratio for various wind power machines shows
correctly that the rotor has the lowest coefficient of performance (is the least powerful).
Various test curves included in the report are very useful to a designer and will help with making
an intelligent decision as to whether the machine will work in a given wind condition.
The conclusions given in the summary, however, imply that the rotor is suitable for pumping
water in relatively low wind speeds which I believe to be untrue.
4.An Investigation Into the Suitability of Savonius Rotor for the Use as a Power Source in
Underdeveloped countries, by A. N.
Bymer. Imperial College of Science and Technology, London S.W.7.
The report describes an exercise in building and testing a S-rotor.
This rotor was placed horizontally, which is not a typical position for the rotor.Due to various
difficulties, the errors in reading are very high. The report gives a limited bibliography and
attempts to make an evaluation of economic merits of the rotor. The general conclusions are that
the machine is not very powerful; but may be suitable for pumping limited amounts of water.
5.The S-Rotor and its Applications, by S. J. Savonius.Mechanical Engineering Vol. 53, May
1931, No. 5.
The author describes his earlier work and his experimental and theoretical comparison of various
wind machines with the S-rotor.
He claims 30% efficiency for his S-rotor against 20% as the highest theoretical maximum for all
vertical-shaft airwheels, calculated by Professor Betz. The author himself states that "Either the
author's tests and results were altogether at fault, or in making their theoretical calculations
Professor Betz and the German School of aerodynamic experts had overlooked something of
importance." From the results of numerous tests by others, it is rather evident that Savonius'
"tests and results were altogether at fault."
The optimum tip speed to wind speed ratio of about 1.0 found by Savonius seems to be correct;
this is confirmed in tests by others.