Just archiving and contemplating Bernard’s tests and analysis of the crab claw sail using a home-built wind tunnel. It’s inspiring to see sketches and photos of his experimental set up, but they aren’t very accessible as of 2016. For example, you can’t find the link to his Yahoo-based “wind tunnel” data files in the English version of his analysis; the links are only at the bottom of the German version of his analysis. Once you find the files, each must be downloaded separately, and some do not have clear context. Hopefully this post will make it all easier to find, understand, and advance.
The wind tunnel
Sketch of the wind tunnel built by Slotboom.
Side view of the wind tunnel.
The 250 watt fan.
Wind speeds over the model (a flat plate in this case) were about 9 m/s.
The dual digital scales for measuring lift and drag forces.
Data and plots
Example data from the flat plate model. This sheet also explains how the 2 scales are used to measure lift and drag.
Final crab claw lift/drag plot from Slotboom’s web page. Each dot represents a 5 degree change in incidence angle (supposedly from 5-45 degrees, but there aren’t 9 dots, so the right-most dot in each curve represents 45 degrees?)…
The graph-paper version of the final plot
Final version of a plot showing effect of changing aspect ratios.
Graph-paper version of a plot showing effect of changing aspect ratios.
Examing effects of flat vs cambered models…
…and delta shapes on luff (leading edge) of model sail.
Sketches and other ideas
Final version of sketch explaining how camber is introduced as the crab claw is canted upwards.
Initial sketch of the same realization.
Thinking about what introduces different amounts of twist in a schooner’s fore and main sails.
