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Technote: Spherical Wind Turbine

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Technote: Spherical Wind Turbine (Updated 2nd April)

You probably realise by now that outside of Aviation, I have an interest in many types of engineering projects from HiFi Audio systems to wind turbine design.

I am captivated by the numerous projects created by the extraordinary Robert Murray-Smith, which are showcased in his many YouTube videos. Unfortunately, Robert is no longer with us, and his passing is a great loss to the community. Rest in peace.

One of his videos featuring the O-Wind Spherical turbine sparked my interest, and the latest version inspired me to explore how spherical wind turbines could be developed in CAD. Link to Roberts video: O-Wind Turbine

This screenshot features the latest O-Wind Turbine, which is designed for omnidirectional operation. This means it can capture wind from any direction, making it particularly suitable for urban environments. While the design is visually appealing, I share Robert’s curiosity about why it appears that the ducts are closed.

You might also be curious about the vertical slats seen along the bottom faces. I believe their purpose is to house the generator components within the sphere. Additionally, these slats may help with cooling and provide structural integrity.

Here’s my take on a spherical wind turbine!

You start with 2 circles of equal diameter perpendicular to each other as shown. Within the circles, we can construct a trapezoidal type form where all the red lines are of equal length. The Blue lines are for the first 4 ducts, where the length of the longest blue line is equal to the trapezoid red lines. The duct surfaces are shown in the second image.

The remaining 4 ducts are located on the trapezoid diagonal lines. The eventual surface must be correctly aligned with the main vertical axis; to do this, we construct a 3D line that intersects the main vertical Z-axis and is perpendicular to the sloped red line. Check that the 3D line intersection with the axis is coincident with the circle datum point. I would normally just create a plane from the datum point and select the 2 end points of the red line, but I felt it was important to describe the intent. In the second image, you can see the duct’s planar surface that is perpendicular to the axis of rotation.

Mirror that surface across both vertical planes to complete the development of the ducts.

Now that we have all the duct openings located, we need to think about the duct cover surface lofts. First, we need to create a lofting guide rail, which is the arc shown in the first image above, along the smaller blue line drawn earlier. Essentially, rinse and repeat for all guide rails at the top and bottom, and loft each section in turn.

Once that is all done, you should end up with something similar to the above. I have shown a shaft through the vertical centre for reference. As mentioned earlier, this is just my interpretation of how a spherical wind turbine could be constructed.

To check that the geometry is correct, it is advised to measure the area of each resulting surface, and they should all be exactly the same. Note the actual duct faces on the real object are shown cut back…if desired, this is easy to do with a surface setback 10 or 15 degrees and trimming the duct face. I didn’t do that, and I will explain further why.

We now have the basic geometry from which we can explore options for finishing the ducts. I keep thinking about the enclosed duct space evident in the actual O-wind and Robert’s comments about the Venturi effect that seem absent from this model.

Well, I think I have a solution to that as well.

If we trim back the duct cover and create an opening as shown above, we can induce the Venturi Effect. This is simply done by creating a work plane on the vertex shown, tangent to the duct cover surface and drawing a circle for the cutout. The 3 baffle plates shown in red are only partially extruded so as not to cause too much turbulence, but sufficient to maintain structural integrity and direct airflow. For this proposal to work, there would be no benefit in cutting back the duct opening at an angle. The Venturi Effect applied in this manner would also add a degree of lift, further improving the performance and therefore efficiency of a spherical turbine of this type.

One additional benefit of this approach is that air circulates over the internal surfaces. If these surfaces include fins, we could create a heat sink effect, allowing the movement of the turbine to draw hot air away from the embedded generator. I have only modelled in one Duct as shown above for reference…it would be interesting to see what you can do with this design.

Disclaimer: I am reaching out to express my concerns regarding the recent unavailability of the model that Robert had generously made publicly accessible. I have a feeling that this change may have been prompted by someone’s request. I would like to clarify that this model draws inspiration from existing spherical wind turbines as part of a CAD development exercise. I hold a deep respect for the innovative work surrounding these turbines and wish to emphasise that my intention is not to reproduce or replicate their design. Thank you for considering my perspective on this matter.

Update 2nd April 2026:

I have made some minor changes to this design.

The Venturi effect opening is modelled with a slight curve added to the underlying surface to improve airflow. I have also adjusted the size to 225mm diameter, allowing more internal space for a flux generator while maintaining parameters suitable for 3D printing.

Also, I actually tilted the front duct face back 15 degrees to be more tangential to the adjacent surface. The entire assembly comprises 4 parts; 2 as drawn on the left and 2 to opposite hand on the right.

In this image, you can see that the exit profile has become more uniform with the addition of the curved profile. This is still a surface model, and each quadrant is designed to be compatible with a 3D printer with a bed size of 254 mm x 254 mm. The files for this latest version start with the prefix OMNI 11.

Apply 1.2mm thickness to the primary surfaces to obtain a solid, printable turbine, like this (not available for download)…

I have decided to make this model available as a free download for others to explore the fascinating world of CAD and its application in wind turbine design. For personal and educational uses only. The Omni 10 CAD model is 190mm in diameter, the Omni 11 is 225mm dia and are available as 3D DWG and IGES formats. DOWNLOAD LINK

Please consider making a small donation to help support my work on Aviation projects. [PAYPAL LINK]… thanking you in advance..

Inquiries as usual to hughtechnotes@gmail.com

Technote: 3D Printing-My Perspective

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Technote: 3D Printing-My Perspective

Recently, I acquired the Elegoo Centauri printer, and I would like to share some details about my experiences using it for aviation projects. When I received this printer, it actually sat in its box for about a week, as I was not quite ready to deal with the vagaries of FDM printing until fate intervened. I was also swamped with updates to the Grumman Goose and FM2 ordinate studies alongside development of the P-47. I didn’t really have much time for anything else.

Then the unexpected happened: my computer suffered a catastrophic hard drive malfunction. I opted to send the hard drive to a specialist company for data recovery; though technically I could have done this myself, the data was too important. So, having time on my hands, I set up the Elegoo Centauri and did some 3D printing.

I have been using resin printers for a few years, but I have never tried FDM printers. I used to believe that resin printing was the ultimate form of 3D printing when it came to dimensional accuracy and surface finishes, which FDM printers couldn’t match. However, I now realise I was mistaken!

This Elegoo Centauri is, quite frankly, a really good printer, a bargain at less than £300.

As I had an old laptop, I was still able to access my email and online accounts, but running any substantial software was out of the question on an antiquated version of Windows. So what I did was send CAD files from my online backup to my son-in-law, and he would slice them for me and send me the G-code for printing. This was sufficient for me to get started and explore the vagaries of FDM printing. Later, of course, when I got my hard drive sorted and my computer back up and running, I was then in a position to address several questions from my first foray, and this is what I will share with you today.

P-39 Airacobra – Planes of Fame:

As many of you know, and as previously covered in various posts on this blog, I have been assisting Planes of Fame with their P-39 restoration project. Where possible, replacement parts are manufactured to the original material specification; however, in some areas, particularly the cockpit control units, it was decided to opt for 3d printing replica parts. This is a static restoration, so this is quite acceptable. Though I often wonder with the plethora of advanced printing materials, whether 3d printing could be an effective replacement for flight-worthy restorations.

One of the first parts I printed when I got my computer back in working order was the Exhaust Stacks. Previously, I have had a post already on this, but the reason why I decided to print this was to explore metallic finishing options and acceptable material thicknesses.

Planes of Fame has access to an industrial-grade 3D printing facility using engineering-grade filament, the results of which are shown in the second image above. I figured that there was no way I could replicate that level of quality on a budget printer, but surprisingly, the Elegoo Centauri did remarkably well just using PLA+.

When I developed this CAD model, the exhaust wall thickness was set to 1mm…this was to make it easier for Planes of Fame to adjust the minimum wall thickness to suit the industrial printing preferences. I actually decided to initially print this at the 1mm wall thickness to see how well the Centauri handled thin walls. I was pleasantly surprised that, other than a few minor imperfections, the print came out really well. However, as this exercise was more about exploring metallic finishes, I decided to print it at 1.6mm wall thickness to give me some latitude for sanding. The black version in the first image shows the result of applying Filler Primer; 2 coats of sanding with 80, 120 and 320 grit sandpaper, and then applying 2 coats of black gloss. To achieve the metallic finish shown in the second image, I rubbed in graphite powder. There are several cosplay videos on YouTube showing how this was done on items like the Mandalorian helmet.

The surface should ideally be completed with a clear coat, but I don’t have any of that. The finish, I think, is quite dark and could be improved to be more aluminium-like if the paint were Gloss Grey instead of Gloss Black. I shared these details with Planes of Fame; I understand they may opt for the latter.

Custom Supports:

For the Exhaust stacks, I used the slicer Organic Tree supports, which were fine, but there was some stringing evident on the inside surface. I decided to explore options for custom supports instead to achieve better results. Again, working with a P-39 part, this time the pilot seat top support bracket. I should note that Planes of Fame has this same model; however, they will be making this from aluminium.

The first image shows the comparison between the slicer standard tree supports and using custom supports. Looking at the circular portion, the item on the left shows an irregular surface from the tree supports, whereas the version on the right shows a much more refined, consistent surface from using custom supports. The second image shows the custom supports created in CAD.

From my experimentation with generating custom supports that a gap of 0.24mm when printing at 0.12mm layer height works quite well. There is some consensus that one layer thickness would be an optimal gap, which may be applicable if the surface is planar to the base; however, in this instance, there is a small incline, and I find that 0.24 works well with the supports easy to remove.

I also did some experimentation with another model, completely unrelated to Aviation, and this was for my wind turbine project.

Supports are necessary when the threshold angle is less than 30 degrees. Additionally, I’ve included extra supports to enhance stability, as the model may flex during printing due to the thin blades. I often find that a combination of custom supports and standard tree supports works well on more complex models.

Minimum Wall Thickness:

I touched on this with the Exhaust Stacks, and though 1mm is the recommended minimum wall thickness for 3D FDM prints, you can go thinner. There is a setting in most slicers called “Spiral Vase” or similar. What this does is produce a print with a wall thickness equal to the nozzle diameter. I tried this with a surface model for the Vertical Stabiliser for the Grumman Goose at 1:10 scale, and it actually worked quite well.

The downside is that this setting ignores any internal ribs that may be in the model and only prints the outside wall. I imagine there may be some uses for this in aviation modelling, but to be honest, without internal rib supports, there is probably too much flex. I should note that layer adhesion remains good, and the surface finish is smooth.

I intend to explore workable solutions for achieving minimal wall thickness and thus reducing the weight of model RC aircraft. As my main line of work is compiling all the known key dimensional information for the various aircraft and presenting this information in a concise, accessible format and in CAD, I see this as a natural extension of these studies.

L23 Blanik

I already have several surface models (SU-31 and L23 Blanik) that can be easily scaled and adapted to produce accurate replicas for RC flight. The key to this is when scaling to then apply material thickness to the ribs, frames and surfaces that will be suitable for 3D printing whilst maintaining structural integrity with minimal weight. My current theory is that 2 x nozzle diameter for minimum wall thickness and 3 x minimal layer thickness may work.

My work on this issue is in the very early stages, and I will dedicate a specific post to this with my suggestions and samples of the end product.

Finally: Printing Dowels:

This is something I only ever did on my resin printer due to the possibility of snapping along the layer lines. However, there is a solution for successfully printing dowels on FDM printers. I tend to use dowels a lot for aligning individual parts of an assembly.

For my desktop speaker projects, the body parts are aligned using dowels. As you can see, the dowel has 3 flat sides which can then be laid flat on an FDM print bed to enable printing with layer lines longitudinal to the axis and thus preventing splitting.

Rendering the JB2 Using Autodesk Vred

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Rendering the JB2 Using Autodesk Vred:

For quick renderings that are perfect for blog posts, I typically prefer KeyShot. It provides an intuitive workflow and a large library of environments and materials. However, the trial version has some limitations: you cannot save projects or export a rendered image, except as a screenshot. When I was recently asked to produce high-quality renders of the Republic JB2 for a museum display, I was uncertain about how to accomplish this.

These products are very expensive and far exceed my budget, so I urgently needed to find a solution. That’s when I discovered Autodesk VRED. I downloaded the software along with the accompanying asset library, and to my surprise, the trial version is fully functional. It allows me to save projects and create high-resolution renders, and it runs for 30 days.

Autodesk Vred retails at around $14000, which is extraordinarily expensive, but it is aimed primarily at the Automotive industry. Consequently, the product is packed full of features and limitless options on environments, materials, lighting and camera setups. It truly is a comprehensive and, to some degree, rather complex product, so there is a steep learning curve.

Undeterred, I set to work by reviewing tutorials, YouTube videos, and various online resources. Over the course of six days, I gained a deeper understanding of the nuances of VRED rendering. While I’m not an expert yet, the test renders started to come together, culminating in the images showcased below.

These images are not final, as I still need to work on the texture mapping and apply materials to some internal components. However, they demonstrate that it is possible to achieve satisfactory results in a relatively short time. Although the product has a steep learning curve, it encourages you to deepen your understanding of materials, textures, and lighting, which ultimately enhances your grasp of rendering processes.

I highly recommend that anyone interested in creating renders try Autodesk VRED. It offers the full functionality of a high-end rendering product, including the ability to save your projects and export high-resolution renders. The availability of a 30-day trial version is exceptional—Keyshot, take note!

I want to clarify that I have no affiliation with Autodesk, but when it comes to the accessibility of professional products, Autodesk is unparalleled. I have no problems recommending worthwhile products, like this one.