Technote: Clean Up 3D Scans

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Technote: Clean Up 3D Scans:

In 2019, I wrote an article about my experiences using photogrammetry and its applications in historical aviation research. For those interested, the article can be found here: Photogrammetry. Having delved into this fascinating subject over the years, I thought I should share some tips and associated YouTube videos that can help with the preparation of scans for 3d printing.

Museums often embrace exciting scanning techniques to safeguard their precious artefacts, such as the cutting-edge use of laser scanners and the fascinating method of photogrammetry. These innovative approaches not only help preserve history but also bring it to life in new and captivating ways! You will find many museums on sites like Sketchfab with large collections of these artifacts availble for download.

You might be curious as to why the first two links lead to websites featuring armoury models. In addition to my personal interest in armour and weaponry from the Middle Ages, this subject also illustrates the typical surface profiles similar to those of historical aviation aircraft and their components.

In today’s world, nearly everyone carries a mobile phone, and many of these devices come equipped with high-resolution cameras capable of capturing stunning photographs. This feature proves especially beneficial for those interested in photogrammetry projects, which require detailed imaging to create accurate 3D models. Using a mobile phone for this purpose is particularly advantageous when visiting museums, as it allows for discreet photography without disrupting the exhibit or disturbing other visitors. This non-intrusive method enables enthusiasts and professionals alike to document artefacts from various angles, enhancing their ability to analyse and reconstruct their dimensions digitally.

One of my favorite subjects to capture in photogrammetry is droptanks. They are often rusty, making them ideal subjects for this technique. Other great items to consider include guns, torpedoes, and aircraft engine cowls. While you may not have complete access to all sides of a cowl, remember that you only need half of the profile to recreate it effectively. It is also a good idea to carry with you a plastic ruler that you can use for scale later.

Getting back on subject to cleaning those scans, let me introduce you to the Jousting helmet.

My workflow starts with the Inspector feature in Meshmixer, a free download from Autodesk. This will throw up a bunch of different issues, as illustrated. The blue refers to small holes or inverted faces, the red are potentially problematic areas for resolving, and the magenta identifies loose, unattached meshes. At this stage, you could just run the Auto Repair All, and Meshmixer will do its best to resolve those highlighted issues. Sometimes, though, the results can be unpredictable and may add additional meshing that you don’t want.

Don’t despair, as you can be selective with this tool and initially fix the blue-highlighted areas by clicking on each of the blue orbs. You could click through each of the magenta orbs and select each of the unattached elements one at a time, but there is a better way.

Using the select option, we can isolate the unattached elements quickly and efficiently. First, select an area using a medium-sized brush and double-click to select all attached meshes. A single mouse click will only select mehes within the specified brush diameter. Once selected, go to MODIFY>INVERT to invert the selection to group the unattached items. Then go to EDIT>DISCARD to remove all those unattached items.

This is also a useful technique for tidying up groups of meshes.

Here, I have selected a row of meshes, essentially a channel cut line isolating the chaotic mass of meshes. Using the above technique to then select the entire body and invert, I can easily remove that mass. Taking my time, I would go around the interior and tidy up the spurious collections of meshes one mass at a time.

For reference, a good YouTube video explaining this in more detail “Meshmixer Clean a Scan”

Sometimes with photogrammtery the conversion programs will attempt to enclose large areas, commonly the base or unscanned regions.

If you need to remove sections like this, selecting the meshes directly and discarding works fine, but you can also just create a perimeter channel, invert and discard accordingly.

Ultimately, we desire a continuous, defect-free surface suitable for applying thickness for 3D printing.

Before we apply a material thickness, we need to be sure the object is correctly sized. First, we need to identify the actual size of the imported model using the INSPECTOR> UNITS/DIMENSION command. Then go to EDIT>TRANFORM to scale the object to the desired size. For this example, I kept the size within the boundary limits of my 3D printer.

For wall thickening, usually a minimum of 1mm is the recommended value, but for this example, I set it to -0.8mm (twice the nozzle size), and it printed just fine. The thickness is applied using the SELECT>EDIT>EXTRUDE combination, and be sure to select “NORMAL” and “OFFSET”. Don’t go crazy with the wall thickness, as any interior surfaces will thicken accordingly and may exceed the gap between the inside and exterior faces, causing some odd surface anomalies.

Export the model to STL, and it should be ready for 3D printing. Sometimes the walls may be thinner than expected due to the process described, in which case, be sure to have the Thin Walls option selected in the slicer.

Identifying Interior Meshes:

This may or may not be relevant, but sometimes when tidying up models from a third party, you occasionally find combined models with a lot of interior surfaces. There is an interesting video showing you how to fix this using Ambient Occlusion in Meshlab by Terry Simmons-Ehrhardt

The End Goal:

After creating a tidy meshed model, you can import it into CAD, in my case, this would be Inventor. This model can then be used to generate contours for further CAD development.

For this example, I have imported the Walter PPK scan. When using Inventor to work with scanned STL or OBJ files, the model must first be converted to workable surfaces or solid models after import. Autodesk Inventor uses a 3rd party add-in called Mesh Enabler, which is availablehere. Fusion also has the capability of working with imported scans, which does not require any special add-ons.

When selecting the type of conversion, always select the Solid option. Even though it may fail to compile a solid first time around, it does give you standard surface meshes to work with. The other option for a composite surface is less workable and occasionally frustrating to work with.

Once you have a solid mass or a workable surface, you can identify key vertices to facilitate contour development for further design.

I chose medieval helmets to illustrate the principles mentioned earlier because they are excellent subjects to practice contour development workflows. They share similarities with aviation subjects and are also engaging to work with.

Grumman Goose: Hand Crank Gearbox

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Grumman Goose: Hand Crank Gearbox

It is not common for blueprints to be almost illegible, and without a Parts catalogue, understanding the mechanisms and operations of assemblies like Gearboxes can be challenging. This was the case with the Tail Wheel assembly I built for the P-51 Mustang and, of course, the current work in progress, Landing Gear Hand Crank Gearbox for the Grumman Goose.

I became captivated by this unique gearbox upon discovering its remarkable dual function: it not only raises and lowers the main landing gear but also manages the tail wheel’s movement. However, delving into the blueprints left me with more questions than answers regarding its intricate operation. Intrigued by its complexity, I decided to construct a working model and evaluate its operational characteristics firsthand.

The Gearbox consists of a central shaft featuring an ACME thread along which the Traveler Collar for the tail wheel moves. Additionally, it includes a bevel gear that powers the main landing gear struts, as illustrated. At the base, the ratchet lock offers two positions: one for raising and the other for lowering the landing gear.

I am eager to explore the operational parameters and the criteria for calibrating this gearbox to ensure smooth operation and timing. The available blueprints and installation manuals do not clearly outline how this setup is configured, so I will need to rely on some trial and error.

To successfully complete this assembly, we still need to finalise several crucial details, particularly the assortment of nuts, bolts, and washers. Fortunately, I have access to an extensive library of parametric parts, ensuring that I can efficiently source the exact specifications required for this project.

Developing these assemblies requires a significant investment of time and effort, but I believe this investment is invaluable. Often, manufacturers’ documentation is either unclear, incomplete, or entirely absent, which can create challenges for maintenance and operational staff. By constructing detailed CAD assemblies, we create a visual representation that not only clarifies the intricacies of the components but also serves as a critical resource in the field. This practice can facilitate more efficient troubleshooting, enhance understanding of the system’s functionality, and ultimately improve the overall safety and effectiveness of operations. By proactively addressing these documentation gaps, we ensure that maintenance teams are better equipped to perform their tasks with confidence and precision.

In previous articles, I shared my aspirations to develop a 1/16th scale RC model based on this project. I realised that this gearbox configuration could serve as inspiration for creating a scaled version that would operate using a single servo to raise and lower the model’s main landing gear and tail wheel.

Update: 28th Jan 2026: Spur Gears

The Spur Gears and Splines dimensions are shown as “over pins”, the diameter of which are 0.140 in.

CAD software generally does not facilitate this type of dimensioning for gears, so first we have to determine the important gear parameters using online calculators like this one at Zakgear.com:

The Diametral Pitch is 12 (number of teeth/pitch diameter), which we then input into the CAD gear calculator. To match the calculated diameters from the Zakgear website, we need to adjust the Addendum to 0.800.

By overlaying the CAD data onto the Zakgear data, we achieve a good match. It may only require microdimensional adjustments within stated tolerances to ensure perfect alignment for a correct setup.

Restoration Insights: The Risks of Working from Blueprints

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Restoration Insights: The Risks of Working from Blueprints

Restoration projects…is working directly from blueprints a good idea?

A company I know is currently restoring a P-40N aircraft, and I came across several posts where they highlighted concerns about the alignment of the fuselage frames. The misalignment was approximately 1/8 inch (3.175 mm), which is quite significant. From their posts, it seems they are working directly from the blueprints.

Throughout my experience in the industry, I have encountered occasional dimensional errors in the blueprints of nearly every project I have been involved in. This recurring issue fuels my passion for my work. I strongly believe that dedicating time to meticulously developing these designs in CAD is essential for uncovering any anomalies before fabrication begins. This proactive approach not only enhances the accuracy of the final product but also ensures a smoother assembly process. However, I recognise that this level of diligence may not always be feasible due to various constraints.

For example, if you are building the fuselage frames and one of those is 3mm out of alignment, you naturally assume that it is incorrect. That may not always be the case because, as the assembly progresses, there may be factors that are as yet unclear that influence this misalignment, or it could simply be a mistake. You won’t know for sure until all the parts are assembled.

Consider for a moment the following example from the Grumman Goose Tail Wheel blueprints.

I have intentionally highlighted the revision box to indicate Revision H. This revision specifically documents the change in dimension from 6.5 inches to 6.25 inches. If we examine the other dimensions, the blueprint specifies that the centre axis for the fork should be set at a 45-degree angle. Additionally, the key setting out dimension is 5.25 inches, measured horizontally to the intersection of the vertical axis and the centre of a 1.25-inch radius.

This immediately rings an alarm bell…to achieve a 45 degree fork with the dimensions shown, you would expect that 6.5 inches is in fact correct and that in this case the 6.25 inch is not. But yet it was the only purpose in this revision to record a change to 6.25 inches.

The tilde “~” indicates that this dimension is approximate, but for this to be a revision would suggest that the actual dimension is closer to 6.25 inches than it is to 6.5 inches.

To ensure all key dimensions align with the blueprint, particularly noting that the 6.25-inch measurement is approximate, the setout for the Tailwheel Fork should follow the above depiction. However, we now have a concern: the vertical post is meant to extend to the diagonal intersection and be welded to the curved plate’s interior. As shown in Detail B, the edge of the posts is too close to the fork’s edge, while the blueprint indicates they should be positioned further inward. Additionally, the actual component, seen in the following screenshot, reveals that the heel of the fork is more bulbous than the blueprints suggest.

There was a reason for the 6.25-inch revision, though we do not know it at this time. Therefore, in order for this to be correct and meet all criteria, something other than the 6.25-inch dimension should change.

Honestly, I’m not sure what the correct answer is here. Unless I can physically get my hands on the real thing, this will likely remain a conundrum. I will retain the CAD design as it is for now, which serves my intended purpose to demonstrate the deployment parameters of the Tail Wheel and provide clarity on the assembly configuration.

I recognize that the dimensions in most blueprints are generally accurate, with only a few exceptions. When budgets and schedules are tight, it may not be practical to explore entire assemblies in CAD before fabrication. However, in cases where discrepancies are identified, I recommend examining all relevant assembly components in CAD. This will help in identifying the correct solution and understanding all influencing factors before making any changes.

Grumman Goose Project Updates

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Grumman Goose Project Updates:

I am currently working on a series of updates to the Grumman Goose project. This will include full surface modelling and comprehensive assemblies for the Landing Gear and Engine Nacelle.

The surface panelling is being implemented in a series of carefully planned stages to effectively accommodate the significant variations in surface contours that occur along its length. To achieve optimal curvature continuity for the surface panels, I have undertaken the modelling of multiple fairing contours, each meticulously designed to ensure a seamless integration with the underlying structure. This approach not only enhances the aesthetic appeal but also ensures structural integrity, as it allows for precise adjustments that align with the dynamic shifts in the surface geometry.

The Landing Gear will be fully modelled, including detailed working mechanisms that will later be the driving parameters for a deployment simulation.

I am currently exploring various options for replicating the components as high-quality 3D prints. This initiative is part of a future project aimed at demonstrating operational criteria in a tangible, physical form. I plan to utilise advanced 3D printing techniques and materials to ensure accuracy and durability in the prototypes. Additionally, I will conduct thorough testing to assess their functionality and performance. This approach will not only enhance the visual presentation but also provide a practical, hands-on experience.

As a basic test to check the viability of the project, I 3D printed the front cover of the secondary gearbox to see how it worked out.

Part #9632 front cover. Printed on an Elegoo Centauri with 0.12 layer height using PLA+ filament. The surface was surprisingly smooth with good dimensional accuracy. Eventually, I will print all the internal gears and check operational criteria.

The engine nacelle is still very much a work in progress, which I will feature in a future post. Following the example of the SU-31 project, the Grumman Goose will also be available in a 1/16 scale version suitable for RC projects.

For reference, this is the Landing Gear Assembly Drawing #12600.

Landing Gear Deployment Positional Representations:

This drawing, created in Inventor, utilises positional representations in the assembly to illustrate the Landing Gear deployment.

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.

Preserving Memories: A Personal Journey Through 35mm Film

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Preserving Memories: A Personal Journey Through 35mm Film

I haven’t posted in a while due to personal reasons. During this time, I’ve been browsing through my extensive film archives and reflecting on cherished memories. Alongside family and friends captured in many rolls of film, I also have a comprehensive collection of aircraft photographs spanning the last 40 years.

From sleek fighters and vintage prop planes to experimental designs and airshow spectacles, each frame tells a story of engineering, elegance, and airborne ambition. These images aren’t just pictures; they represent moments suspended in time, chronicling my lifelong fascination with aviation.

However, as the years pass, the urgency to preserve these images grows. Film curls, fades, and gathers dust. Scanning them digitally isn’t just about convenience—it’s about safeguarding history, honouring friends and family, and unlocking the full potential of each shot. Therefore, I decided to explore options for digitally scanning these libraries to preserve both personal memories and the history of aviation.

This led me to design a new type of 35mm film holder for digital scanning—one built not only for precision but also for passion. It’s a tool that respects the fragility of film while delivering the flatness, fidelity, and ease needed for high-quality digital scans.

From top left:

Film Holder, Film Holder with Hood, Film Holder with optional Diffuser, Film Holder with Spacers to fix location on CineStil Light box, 35mm Mounted Slides sit on top and held in place by magnetic Hood and finally a plan view of the complete assembly.

This Film Holder is designed to be Resin printed on the smallest build plate using the minimum amount of Resin. For the prototypes, I am using the Anycubic ABS-Like. It features an S-Curve guide track for the negative or slide film strips. This S-Curve is actually a mathematical matching of second-degree curves to ensure surface continuity instead of 2 tangent arcs. This S-Curve removes the physical curves typically found in film strips to ensure flatness at the viewing window. The S-curve is not a new innovation; in fact, I have examples of film holders for the rather old Epson 4870 flat-bed scanner, which has this feature, but only for 120 film.

Incidentally, second-degree curves are essentially the building blocks that define the conic profiles of the P-51 Mustang.

I did some research on current commercially available options. Most off-the-shelf film holders suffer from a few persistent issues:

  • Curling and warping of negatives, especially older or heat-exposed strips
  • Inconsistent flatness, leading to soft scans and uneven focus
  • Enclosed loading slots that risk scratching or misalignment

As an aeronautical engineer and product redesign specialist, I saw an opportunity to rethink the film holder from the ground up—merging mechanical precision with modern usability at minimum cost.

I still have the copy stand to design and, of course, get my hands on a 1:1 macro lens. I currently have access to a friend’s camera and lens setup for a few days for testing, but in the long term, I need to try and raise funds for a more permanent camera and lens solution…currently looking at the Sony A7 III with 70mm Macro…a full frame, rather expensive, but worthwhile combination to achieve the optimum reproduction fidelity of the original.

I will update this post shortly with images of the final product…so watch this space!

For more information or inquiries, please drop me a line at: hughtechnotes@gmail.com

Update 17th Sept 2025: Some Renderings of the final product showing the configuration for mounted 35mm slides:

Footnote:

Of course I am still continuing my work on various aircraft ordinate studies, which will also now include the full DWG profiles for every listed fuselage frame and wing ribs. That is a lot more work than I intended with these packages, as the dimensional information is already listed in spreadsheets. I appreciate that not everyone has access to CAD and perhaps not the experience to develop profiles from spreadsheets; instead, they just want to get something made…so the information needs to be more accessible and usable.

Preserving Aviation History: Documenting Aircraft Dimensions

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Aircraft Dimensional Data Documentation: Help Support This Initiative.

1. Project Title:

Aviation CAD TechNotes: Documenting Historical Aircraft Structures

2. Executive Summary:

This project aims to document and preserve dimensional data for historical aircraft, currently working on models such as the P-47, FM2, and Grumman Goose, alongside two glider projects. Utilizing archival blueprints—often of suboptimal quality—we employ precise digital reconstruction techniques to ensure the accuracy of aircraft structural data. The goal is to support restoration efforts, research, and educational initiatives in aviation history.

3. Objectives:

  • Digitally reconstruct and verify the dimensional data of historic aircraft.
  • Provide comprehensive documentation for restoration, museum displays, and aerospace research.
  • Develop methodologies for extracting accurate data from degraded blueprints.
  • Expand the available reference library for aviation researchers and engineers.

4. Significance & Impact:

  • Historical Preservation: Ensures that legacy aircraft remain accurately documented for future generations.
  • Educational Contribution: Supports aerospace research institutions and museums with validated technical data.
  • Technical Innovation: Implements advanced CAD techniques to refine aviation blueprint analysis.

5. Methodology:

  • Collection and analysis of historical blueprints and microfilm archives.
  • Use of CAD software to recreate accurate aircraft structures.
  • Cross-referencing archival data with existing dimensional records.
  • Collaboration with restoration experts to validate findings.

6. Challenges & Solutions:

  • Suboptimal Blueprint Quality: Implement specialized image enhancement and measurement techniques.
  • Funding Limitations: Seek partnerships with aviation museums, historical organizations, and aerospace institutions.
  • Data Validation: Engage with experts to cross-check reconstructed aircraft dimensions.

7. Funding Request & Justification:

The project has been independently funded to date, but rising operational costs present financial challenges. Support is requested to sustain ongoing research, enhance documentation quality, and facilitate broader distribution to historical and aviation institutions.

8. Potential Collaborations & Sponsorships:

  • Aviation Museums: Partnerships for data preservation and restoration projects.
  • Educational Institutions: Opportunities for research integration and student engagement.
  • Aerospace Industry Experts: Validation and application of documented data.
  • Fellow Enthusiasts and Donors: Acknowledge contributions, engage in peer-to-peer discussion and provide technical support where applicable.

9. Conclusion:

This initiative offers a critical contribution to aviation history by preserving precise structural data of historical aircraft. With adequate funding and institutional partnerships, the project will continue advancing research and documentation efforts for aviation scholars and engineers.

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Contact Hugh Thomson via email: hughtechnotes@gmail.com.

P-39 Fuel Tank Covers and Filler Cap

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P-39 Fuel Tank Covers and Filler Cap

The P-39 restoration project is still very much a work-in-progress. The latest addition to the project is the Fuel Tank Covers and Filler Cap. When the existing components were removed there were visible signs of corrosion so it was decided to replace the inner mounting rings as well as the covers/caps.

Each cap assembly consists of an inner mounting ring, a Goodyear-type sealing ring, and cover plates. It is important to consider the varying thicknesses of the sheet metal at each location, as this can lead to slight differences in the profiles of the mounting rings. Typically, when we develop these types of parts, we mark the holes in situ based on existing hole patterns to ensure a proper fit. This is usually done because the holes are evenly spaced between two known locations, which can vary during manufacturing. However, for these covers and caps, we have precise knowledge of the hole locations, allowing us to ensure an accurate match.

The flush rivets used throughout are the 35R1 Bell standard, featuring a 120-degree countersink designed for thin sheet materials. An equivalent Boeing standard for this type of rivet is also available. In the assembly drawings, I have spaced the components apart to enhance clarity. I should note that the drawings shown are still a work in progress.

Update: Ready for issue:

This is the final assembly, typical for the fuel tank covers and caps.

The lower ring features an Elastic Stop Nut Gang Channel. It is presumed that this channel was designed according to Bell standards when it was constructed. I have examined various companies that supply similar Gang Channels; however, the hole centers in their standard components differ slightly from our specifications. I suspect that we will need to have a bespoke fabricated item to meet our requirements.

It may be possible to purchase Elastic Stop Nuts and retaining springs from companies like Howmet Aerospace and create a channel to match the design in the second image below. I will provide an update later on how we will proceed.

I will also soon be able to provide you with more information about the P-39 restoration and a gallery of images showcasing the latest work.

F4F/FM2 CAD Updates

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F4F/FM2 CAD Updates

I have added new updates to the FM2 CAD/Ordinate dataset, completing assemblies for the Aileron, Outboard Flap, and Inboard Flap. In addition to the 3D CAD models, we have the fully dimensioned 2D drawings defining the profiles for all ribs.

Wing Layout and Rib Profiles:

The wing ribs comprise 3 separate rib profiles for the Leading edge, Mid-section, and Trailing edge. The detailed drawings show the complete profile and the individual component profiles separately. This will identify the blueprint drawing number in each case and the related blueprint scan file name.

Every drawing will be available as a full size Autocad DWG. All rib profile offsets are listed in a comprehensive Excel spreadsheet.

Unlock Precision with Aircraft CAD/Ordinate Data

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Unlock Precision with Aircraft CAD/Ordinate Data:

The CAD/Ordinate datasets are designed to offer detailed documentation of the dimensional information pertaining to the core profiles of various aircraft components. This includes elements such as fuselage bulkheads, cowls, vertical stabilizers, horizontal stabilizers, wings, rudders, flaps, ailerons, and elevators. Essentially, these datasets provide all the dimensional information needed to develop the main profiles for aircraft construction.

The research studies were conducted to fill in important gaps in information and to clarify unclear details. Often, data on blueprints can be difficult to read, making it necessary to record and analyze the bulkhead or rib profiles in CAD. This process helps accurately determine the correct dimensions.

The examples of ordinate dimensions above are not necessarily the worst; in fact, there are truly poor examples that exist. To tackle these issues, we should start by recording the known dimensions in Excel and making educated guesses about the worst examples. Next, we can create each profile in CAD. This CAD profile will give us a clear visual representation of any anomalies in the curvature, which can be further analyzed through curvature analysis to identify low and high spots. This process is done for every rib and bulkhead profile where we have ordinate dimensions.

The spreadsheets above are typical examples of CAD/Ordinate datasets. The first spreadsheet contains the Ordinate record for the P-38, while the second one features the Aileron sheet for the FM2. You may notice a Linear Regression analysis table included in the FM2 sheet. Initially, determining the individual profiles of the ribs or bulkheads is just the first step; we now need to assess the assembly of all these components and check for proper alignment.

Each drawn sketch profile in CAD will serve as the border for containing a surface patch.

There are two primary reasons for doing this. First, it provides us with a plane that can be converted into a working surface, which can be utilized in any CAD product. Secondly, it provides us with a tangible element that we use to check assembly cross sections at key locations for alignment checks.

For example, consider the wing of the FM2. The wing assembly has been converted into a part file, and cross-section sketches were created at various chord locations: 30%, 60%, 70%, and 80%. Each sketch utilized the “Project Cut Edges” function to generate a cross-section of each rib. As shown in the second image, the array of lines representing the rib cross-sections provides a visual aid to identify high and low spots on the wing assembly. By creating a surface plane for each rib, we were able to generate these cross sections effectively. There were a few high and low points, which were double-checked and rectified.

If we require additional verification and strive for precision, we could use Excel’s Linear Regression to generate the coordinates for a Best Fit Line and make adjustments as needed. However, this approach may be excessive since our primary goal is to clarify the original blueprint data and apply it to identify appropriate rib and bulkhead profiles within acceptable parameters.

We can also use Linear Regression to give us an overview of how the ordinate profiles align with one another and to identify any discrepancies. Typically, acceptable parameters are within +/- 0.01 inches (or 0.254 mm), as specified by the dimensions on the blueprints, which usually only provide accuracy to two decimal places. Sometimes, as was the case with the P-51 and P-38, we had key design parameters that allowed us to calculate the exact profiles for each wing.

Validating dimensional data is crucial because the actual wing construction may not always match the accepted specifications. The design specifications for the FM2 call for a NACA 23015 airfoil at the root and a NACA 23009 airfoil at the tip. You might be surprised to learn that the NACA 23009 is a modified version of the standard 23009. Nothing is therefore assumed or taken for granted.

The CAD/Ordinate datasets are the result of extensive and thorough research and analysis, often taking many months of work, sometimes around the clock. These spreadsheets include every known ordinate dimension for various aircraft, gathered not only from blueprints but also from manuals, reports, and even correspondence. The CAD/Ordinate packages also include various 3D CAD models in various formats, including 3D DWG and fully dimensioned 2D DWG. All documents provided are fully editable so you can adapt the information to your work processes.

For more details on using the Ordinate spreadsheet data for your own CAD systems, see my earlier post here: Ordinate Overview

With over 45 years of experience in structural and mechanical engineering, my expertise influences everything I do.

In summary, the purpose of the CAD/ordinate datasets is the result of intensive work and research to provide the user with correct usable data that can be utilized in any CAD system.

When you buy CAD/Ordinate datasets and Blueprint collections from me, you support my ongoing research to provide the most comprehensive and probably the most accurate dimensional information about various aircraft. This blog and my research work would not be possible without your support.