The baseline: multiwing/hascon 5Z


To compare the baseline design directly with the amazing new blade, you need to be able to compare it on level ground. Because I dont yet have my own rapid prototyping and testing facility I will be making a computer model of the multiwing blade and testing it against the new design in the same computer program. The thrust numbers you get out of the program can’t properly be compared to thrust coming out of the real hovercraft yet because it does not take into account things like blockage from the fan guard, driver and other real life things. In time i will write a bit about the computer model, DFDC to explain this better.

To make a model of the blade you need to find out aerodynamic characteristics at various sections along the blade, and also measure the chord and twist along the blade. To get the properties you need to cut the blade up to get sections:

To do this the chord distribution and twist of the blades is measured. the 5Z bladesand using a combination of 2D airfoil programs, xfoil/javafoil, we find the following information about it:

(specifically this is the Hascon blade but im told this is a direct rip-off of the multiwing aerodynamic shape)

The thick blunt trailing edge is neccessary for mass production reasons but gives a very high minimum drag coefficient. Ideally you want a thin knife-edge at the trailing edge, this is definitely an area that could be improved upon. To find out how hard the blade is working along its length, the geometry and aerodynamic details are put into DFDC for a typical formula 50 fan. 6 blades, at 2450 RPM with the pitch set to absorb 50Hp. From DFDC you can see that the blade is working fairly hard.

DFDC pic showing aerodynamic Cl along blade.

For all of the variations in number of blades and various duct diameters i have tried running the multiwing blade, it never appears to operate with constant Cl along the blade. Theoretically the most efficent blade has uniform lift coefficent along the whole blade span.

A great benefit of the DFDC software (apart from being free) is that you can very quickly change inputs such as blade pitch, # of blades, duct diameter etc in seconds (vs hours and $$$ needed to run CFD). The main focus for my blade design will be for the higher power categories towards 100-200HP fan systems, so I carried out a few runs with the model for a GSXR750 powered thrust fan (88 fanHp), and F1 809 powered craft (175 fanHp)

Table showing powers/ thrusts for higher power systems

Posted in: Fan design on March 31st by admin


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