For this project we were tasked with developing our CAD skills in an area of our choice. I decided that a good challenge would be to model a hydrofoil in fusion 360. I chose the hydrofoil (a design by neilpryde) because it is something that I am interested in making a carbon version of, and it is a tricky shape to model with many complex curves.
After some research, I discovered that the best way to make the shape of the front wing is to mark several points on the wing and draw out their cross sectional profiles and then use a 3D sketch as the guide rails to perform a loft between the profiles. However, I found that this wasn’t very intuitive in fusion and after quite a while ended up switching to solid works to finish the model. I also discovered that in Solidworks it is possible to do Computational Fluid Dynamics (CFD) modelling whereas its not possible in fusion.
I didn’t manage to get the lofting to work properly (Every time I tried a loft, I got the error message saying the guide rails were not connected to the profiles) so I decided to change my approach and used fillets and chamfers to get an approximation of the shape of the wing. I then modelled all the other parts of the hydrofoil and put them together in an assembly. Finally I exported this as a .SLDPRT file so that I could model it all as one body using the inbuilt flow dynamics add in.
I specified the variables: the water velocity, density, flow direction and the goal points of the study: the net force in the x axis, the net force in the y axis and the coefficient of drag of the foil. I then ran the simulation.
Once the software had finished its calculations, I chose to display the results as velocity of the water travelling over the foil (colour coded: red is faster, blue is slower) and also the vectors of the water travelling over the foil (blue arrows).
The results are as follows:
Coefficient of drag: 0.8
Force in X: -27.4 Newtons (to the right)
Force in Y: 1984 Newtons (Up)
The force in X means that my design is slightly asymmetrical. It is producing more lift on the left side of the wing than on the right which is causing a horizontal force. If I was to make this foil in this way, it would be tricky to sail because in order to go in a straight line I’d have to counteract this sideways movement with my body weight. I believe this lack of symmetry was caused by the way I designed the foil wing: I ended up using chamfers and fillets instead of a loft like I originally wanted to and the fillets on the front overlapped in an odd way meaning one side was different to the other. Because of this I am going to try and model the wing with lofts again.
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I decided this foil because it is very popular among windsurfers and it has a slightly more complex inverted gull-wing shape that I thought would be a good challenge to try and improve my fusion skills. Another benefit of this is that Slingshot provide top down and front on drawings of their wings on their website, so I was easily able to trace over these to get my initial outline.
I managed to practice using the 3d intersection curve feature in fusion and I watched a few tutorials to help as well. This enabled me to produce a 3d sketch for the front edge of the wing: it follows the line of the vertical sketch in the front plane and the the bottom sketch. From my previous attempt at using lofts I really struggled to get the bottom of the wing profile (for the loft) to snap to these lines. In order to fix this issue, I also used the intersection curve to project up a few lines from the bottom of the wing sketch. This ensured the lines met the front and back edges of the wing.
I only did this on one side because I can mirror the final body later. This line will be my front guide rail for the loft. I then used the projected straight lines to draw wing profiles at intervals. I couldn’t get any data for the actual wing profile that slingshot use for their foil. However, I did some research on hydrodynamics and wings. I found that aerofoil shapes are pretty transferable across to hydrofoils and that the american National Advisory Committee for Aeronautics (NACA) in america has a huge database of wing profiles that are free to use. 
My research into this area suggested that a flat bottom foil with a long tapering trailing edge would be best. This is because this creates a very high lift at low speeds (which will mean an earlier takeoff) and this appears to be similar to the slingshot foils profile. I was then able to loft this wing shape using the profiles and the 3d sketch as a guide rail. Below is a render of the CAD, I experimented with the rendering aspect of fusion and applied the texture of carbon fibre to the model (the material the wing is made of ) I also played around with the lights and back grounds of the rendering to try and make the model look as good as possible.
CAD File link: https://a360.co/2yreILW
