3D Printing: P-51 Tailwheel

3D Printing: P-51 Tailwheel:

I’m back after a few months dealing with a difficult period of my life. I would like to take this opportunity to thank those that stepped up to the challenge and supported me through this time.

Many moons ago I developed a series of CAD models for the P-51 Mustang Tailwheel mechanism initially to study the mechanical operations and also to clarify an otherwise obscure area that is not clearly defined on the NAA drawings.

At the beginning of 2021 I had the good fortune to obtain an Elegoo Mars pro 3D printer which just sat in the cupboard until now. Getting my life back on track I unboxed this and setup for my first print which invariably had to be one the many CAD models from my research. The part selected is the Housing for the Tailwheel spindle. Part # 73-34004.

These parts are accurately modeled from the NAA drawings so I was unsure how well they would print at 1:4 scale particularly the thin wall elements.

The first image shows the preparation using the Lychee Slicer program with the layers set to 0.05mm. I added a generous amount of supports to maintain the print integrity using the Auto support feature with a few manually added for good measure. The Resin I used was the Elegoo Water Washable Green which has worked very well. I am rather pleased with this print as I had read many horror stories of problems that folks encountered with this type of immersive printing which made me a tad anxious before I eventually decided to take the plunge.

This printer is capable of printing with a layer height of only 0.02mm which is quite extraordinary but as it took 4 hours to print this model at 0.05mm I doubt if I will venture to printing at a finer pitch as the time would be excessive. I don’t plan to print all the Tailwheel components as my budget for resin is limited but I will print a few more to determine the limitations; if any; of resin 3d printing.

Talking about the future I should note that I am currently sourcing new material for the P-51 Mustang and hopefully to start a brand new project for the F7F Tigercat.

If you are interested in the Tailwheel models check out the bottom section of this post for details.

On a personal note it is good to be back working on these projects and please do not hesitate to comment or drop me a line with any queries. hughtechnotes@gmail.com.

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Technote: Autodesk Inventor 2022 Part Model States

Technote: Autodesk Inventor 2022 Part Model States

In a previous Technote I briefly introduced the work method for Derived parts that provide the capability of managing model states i.e. from Forged part to machining; as separate part files. This was included in a discussion on the P-51 Mustang Tail Wheel down position modeling.

Inventor 2022; just released; now has a feature called Part Model states which will enable you to manage manufacturing operations, dimensional variations and simplified representations all on one part file.

Check out the introductory video on The Autodesk website for more details on this feature as well as more information on the latest release of Autodesk® Inventor®. This is packed with user-requested updates and enhancements to help manage your design process, speed up your connected engineering workflows and reduce repetitive tasks.

Whilst Autodesk Inventor is not normally associated with the Aviation industry it has a very advanced 3D toolset that adapts well to this industry as I have demonstrated in the many Technotes throughout this blog. So do checkout my previous articles on using Inventor in this environment and drop me a line or comment below. More information on Inventor 2022 and specific tutorials on utilizing the host of features within Inventor will follow.

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Recycling Project: Repurpose Construction Site Waste

Recycling Project: Repurpose Construction Site Waste.

I haven’t posted for a while due to research for a number of environmental and recycling projects. The projects involve researching design options to see how we can repurpose/recycle Construction Waste materials like timber, insulation, paper etc.

This post is just to let everyone know that I am still here and working away in the background and also as an introduction to my new project. Aviation projects of course are still work in progress.

Anyway getting back on subject: The Recycling or Upcycling project is based on maximising usage of material that would otherwise not be considered for alternative purpoes. As the typical timber waste from sites vary considerably it is critical for the new designs to be able to utilise the smallest offcuts that would not otherwise be a consideration.

I can’t go into too much detail right now but the essential elements will comprise unique lattice structural forms as well as composite design features to maximise strength and practicality. Historically, recycling construction waste is actually fairly common however it is mostly restricted to creating furniture and small garden utilities. The principal idea of repurposing for garden buildings or offices is not so common due to the technical challenges of effective use of small sized materials…until now.

I plan to crowdfund the construction of a number of these designs shortly. If anyone is interested in supporting these projects please drop me a line.

The Work in Progress aviation projects include datasets for the L23 and L33 gliders…watch this space.

In the interim please continue to support this site through donations or purchase of Ordinate and Blueprint packages.Without your help I would not be able to undertake the Aviation research and new important projects like this one.

Contact me at hughtechnotes@gmail.com

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I have recently noticed that certain online sites are making available Industry Standard specifications for sale. You dont need to pay for this stuff as it is freely available online, where you can get virtually any spec you may need for historical and for new aviation projects here:


Aircraft manuals. Again dont be paying crazy money for these. Those same companies are charging upwards of $10 for a copy of a manual. Instead drop me a line I may already have it.

I also have the full compliment of HAWM workshop manuals; which are the original scans. Perhaps consider supporting the research that is done here. There are 27 manuals in this collection, covering everything you need to know about aviation workshop practice.

As usual all enquires to hughtechnotes@gmail.com

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P-39 Airacobra Recovered from the Black Sea

P-39 Airacobra Recovered from the Black Sea

“SIMFEROPOL, September 25. / TASS /. An expedition of the Russian Geographical Society (RGO), together with the Russian Ministry of Defense, lifted a Bell P-39 Airacobra fighter from the bottom of the Black Sea from the regiment that took part in the air cover of the Yalta conference of leaders of the anti-Hitler coalition in 1945, a specialist from the Expeditionary Center of the Ministry of Defense Anatoly told TASS on Friday Kalemberg.”

As many of you know I am a huge fan of the P-39 Airacobra. So I was particularly interested to read these reports of the recovery of this P-39 from the Black Sea. These are the links to the articles I have read so far from various news publications.

Links to the articles:



If anyone has any further information to share on this project please drop me a line and I will feature updates in future articles; perhaps even progress on the restoration.

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Popular Technotes!

Popular Technotes…

I have run this blog for almost a decade now in order to pass on and share my research and technical know-how related to the amazing designs of historical aircraft.

The blog is a journal to document my experiences on this journey with articles on the various aircraft designs interspersed with a bunch of Technotes. There’s a lot of stuff so I thought it may be prudent to compile a list of the more popular technotes to date:

Technotes Selection:

  1. Technote: Inventor Sketch Datum: The importance of selecting the correct datum points when offseting work planes.
  2. Technote: Inventor face Draft: This uses a part from the P39 that required facedrafts, similar to forging and catsing requirements.
  3. Technote: Positioning Holes in Complex Surfaces: Complex surface hole positioning.
  4. Hoppers: Surface Modelling for Mass Containment: Slightly off-topic but nevertheless relevant; describes the best way to model hoppers for mechanical handling projects.
  5. Technote Sopwith Pup: Spar Clip Technote: An article discussing some of the design vagaries for the Sopwith Camel as well as in-depth use of sheet metal development.
  6. Technote Bell P-39: Modelling Curved Cockpit Glass: Inventive use of Inventor design features to develop complex cockpit glass.
  7. Technote: Bell P-39 Creating Wing Fillets: 3D Sketches and workplanes used to develop the complex flanges for the P39 wing fillets.
  8. Technote: Sheet Metal Bending in CAD: General technical details for sheet metal bends.
  9. CAD Library: A large selection of CAD resources.
  10. Other Blog: Pioneering modular workflow and design solutions for use of 3D CAD in Substation design for the Power Industry that defied “expert” optinion. Prior to my work on this subject there was no viable solution for this industry. This was a long time ago but much of the subject matter is still pertinent to the industry today.

Theres a bundle of other interesting stuff and discussions on CAD, design as well as a number of articles on Excel.

I came across a site that provided a link to this blog describing it as a “guy that does CAD from aviation blueprints”. Actually they could not be more wrong. Sure there is a stack of CAD related stuff but the serious work is researching and compiling accurate dimensional data. Did you know for example that the top of the rear fuselage for the P-51D Mustang has only 4 verifiable ordinate points…prior to my documenting this no one actually knew this. The ordinates came from blueprints, reports, manuals and letter correspondence..the latter consumed a lot of time. I am probably only one of a handful of people who has actually studied every single drawing in the P-51 Mustang archive. This is serious research not just CAD!

Posted in Aviation, Donate, Ordinates | Tagged | 1 Comment

Grumman JRF Goose: New Project

Grumman JRF Goose: New Project

Just started a new project to determine the structure ordinates for the JRF Goose. Typically for the Grumman drawings, this will require resources from a combination of tabled ordinate data and extrapolated dimensions from the individual part drawings.

With the NAA drawings for the B25 Mitchell I was spoiled as these guys tend to love ordinate tables and it is much easier to develop the data spreadsheets whereas the Grumman guys tend to fragment the information over several drawings. The wing ribs, for example, are actually in 3 separate drawings; the nose, intermediate and tail-end.


Why Ordinate datasets are important;

I spend a lot of time developing these datasets as a record of my research that can be utilised for various purposes including development of CAD 2D and 3D models. As an engineer, I know from experience that when the skeletal framework of an aircraft is correct then everything else will fall into place. I often see modellers dive headfirst into creating 3d part models and end up encountering problems with alignment and fits.

It is therefore prudent to first check the geometry prior to committing to 3d modelling…it will save you a lot of time, frustration and work in the long run.

The datasets already completed for the P-51 Mustang and the B25 Mitchell have been used by restoration companies, researchers, modellers and RC enthusiasts. The criteria for each group vary so it makes sense to provide the correct geometry in formats that can be translated to any engineering systems in a manner that can be used according to their specific needs.


The Goose Dataset:

The above cross floor drawing is an example where the ordinates are first compiled in a spreadsheet in both inch and millimetre formats. The core data is then extrapolated to determine the workable X, Y, Z coordinates. This is an interesting aspect of the aircraft design as the cross-floor profiles share similarities with the sister aircraft, the J2F Duck. Where I have cross-references between similar aircraft this information will also be included on the spreadsheet as a record of data resources.

goose wing2c

The wings; as mentioned; are compiled from 3 different sections for the nose, intermediate and tail-end which require 3 sets of tables for each rib and then consolidated.

The ribs once integrated into the CAD assembly are then checked at each ordinate point to verify alignment with the neighbouring profiles to ensure accurate alignment. Occasionally the originating data is unclear so it is absolutely essential to continually check neighbouring associations to achieve accuracy.


The wing tip float: as well as the float profiles; depicted in the image above; I will also be studying the support structure and relationship with the wing.

This ordinate set will comprise the dimensional data as spreadsheets and as 2d DWG cad profiles for every frame and rib. For the main fuselage, the drawings will contain the key dimensional information in lieu of the usual spreadsheets due to the complexity of the frames. All other areas; wings, cross floor, nacelle and empennage will have both spreadsheet data and drawings.


These datasets are designed to help you get a heads up on your own aviation projects and as a resource for research. I do this work and research so you don’t have to…so please consider supporting my efforts. Thank you.

Update 3rd June 2020:

Have been quite busy figuring out the vagaries of working with the Grumman drawings. They are generally quite good but to be honest the inclusion of a few more ref dimensions would not go amiss! The development of the tail fin and rudder required referencing 3 separate drawings in order to ascertain the correct relationships between the fuselage, tail fin and rudder.

Goose Tail

I also noticed a number of incorrect dimensions during the development of the fuselage and tail. When this happens it is imperative to cross-reference various associated drawings and sometimes even the Structural manual to determine correctness. This is actually where a lot of time is consumed in sorting these issues.

For the wing the ordinates are being checked as the profiles are developed. Part of this process involves developing key structural components as 3d models to ensure that the profile ordinates align correctly. In the following image it shows that the ordinates points align as expected with the red points (intermediate wing section) on the aft of the front beam web and the yellow wing nose points fall on the forward face.

goose wing 1

I am not planning to fully model this aircraft only where necessary to investigate alignments.

TechTip: It can be frustrating working with Grumman drawings…take nothing for granted. The wing ribs as mentioned comprise 3 drawings, the Nose, Box Section and Intermediate. For the sake of complicity I shall refer to them as Nose, Mid and Rear.


One would assume a certain degree of consistency particularly when the detail drawings relate to Station locations. For example: you would expect the STA 37.5 would be a location that would be consistent for the mid and rear sections…but it is not. For the Rear section it refers to the back face of the rear beam and for the Mid section it refers to the front face of the rear beam. So when aligning the various actions it is imperative that the connecting line is either of the chord stations on either side of STA 37.5 (ie STA 40) and not STA 37.5. It is easier for the Nose and Mid Sections as they both have ref dimensions to the common STA 25, however the rear section does not reference chord STA 25.

Seriously a few additional reference dimensions consistently applied would make working with these drawings a lot easier.

I carried out a dimensional study on the spreadsheet data to check the relationships between chord STA, 30, 37.5 and 40. It revealed a number of inconsistencies in the STA dimensions but we did have consistency with the offsets at STA 30 and 37.5 (highlight red).


I would expect that the dimensions from STA 30 and 40 would be consistent with no variation as noted on the Mid and the Rear rib profiles…however that is not always the case. Out of all the ribs only 4 were what I would envisage as being correct. This requires further in-depth analysis to determine the best solution.

This will be a lot of work but a clear example why it is important to record the data in spreadsheets so an analysis like this can be done.

Update 14th June 2020:

Fuselage Frames, Tail Fin and Rudder now complete. Horizontal Stabiliser, Stringers, Flaps and Ailerons, Nacelle and revised wings still to do.


This will be the full package, spreadsheets and drawings. The latter will be all the frames and ribs at 1:1 in Autocad DWG format as well as the full 3d model.

goose keelI seriously think this will make a great foundation for an RC model at whatever scale you desire.

Update 2oth June 2020:

With reference to the Techtip above I have revised the wing layout to correct identified anomalies with the Grumman wing rib drawings.


I first established 5 ribs that are deemed to be correct, setup a work plane at Chord STA 40 and checked the relationship with the established ribs. For reference I initiated 4 axis selected from 4 known points on the ribs. I then placed the Rib at STA 271 to act as a check. The ordinate points on the profile for this rib is within 0.04mm of the projected axis and the dimensional offset from the work plane is only 0.025mm.

Having now established correct alignments I will introduce each of the remaining ribs, then check dimensions for each one with the work plane and each of the 4 axis. The end result will be a dimensionally accurate wing.

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NAA B25 Mitchell: New Project

NAA B25 Mitchell: New Project B-25B,C,D


The North American B-25 Mitchell is a medium bomber that was introduced in 1941 and named in honour of Major General William “Billy” Mitchell, a pioneer of U.S. military aviation. Used by many Allied air forces, the B-25 served in every theatre of World War II, and after the war ended, many remained in service, operating across four decades. Produced in numerous variants, nearly 10,000 B-25s were built. These included a few limited models such as the F-10 reconnaissance aircraft, the AT-24 crew trainers, and the United States Marine Corps’ PBJ-1 patrol bomber.

This project will be another research and study effort to develop the ordinate datasets similar to the P-51 Mustang project. The ordinate data is compiled from drawings, reports, manuals, documentation and correspondence so it does take a long time to do.

For example. the above spreadsheets show the work process, starting with recording the ordinates exactly as set out on the NAA drawings. In this case, the original ordinates are in inches so a second table is created to convert this data to millimetres. The third table is the transposed version; retaining original formula cells; which is then used to extrapolate the actual X,Y,Z coordinates for input into a CAD system (the first 10 frames are shown).


This table is the stringer ordinates which follows the same convention of recording the first table exactly as per NAA drawings then converting this to millimetres. The third step is slightly different; transposing the table data in 4 sections to align the data according to stringer number.


This last table is for the wing center section. The process is similar to the previous tables with the main difference being the extrapolated X,Y,Z coordinates originate from the 30% chord. The actual location of intersection between the wing chord line and the wing reference line is calculated at 33%.


This is a lot of work just to get to this point I have spent in excess of 48 hours and I still have a long way to go. Once the frame X,Y,Z coordinates are listed they are then transferred to individual frames in the CAD system whereby they will be checked for accuracy.

There are a few ordinates that are illegible on the original drawings which will require further intensive research to determine.

To fully complete all the known ordinate spreadsheets for the B25 Mitchell I estimate will consume almost 300 hours of work. The P-51 Mustang set; created in a similar manner; was almost 3 times the number of manhours.

The end result is a comprehensive list of known coordinates that will generate the requisite fuselage, wing and empennage profiles within seconds in all major CAD systems…so it definitely is worth doing.

b25 mitchell ords

Fuselage total X,Y,Z points 2x 1043 = 2086

Wing total X,Y,Z points 2x 870 = 1740

Update 7th May 2020:

Continuing the development of the B25 Ordinate dataset I now have the majority of the wing rib profiles recorded. Some reconstructive work was necessary on the outboard ribs to obviate the poor quality of the original NAA drawings.

Every legible point is added to the spreadsheets and then meticulously created in the CAD system. Where information is unclear the cad extrapolated values are closely checked against the appropriate entry on the original NAA drawing to identify matching numericals or part thereof. Once I have consistency with the graphic output and the NAA drawing information this is then entered into the ordinate spreadsheet.

The attention to detail is typical of my approach to building these ordinate sets. Nothing is taken for granted and the primary reason why these datasets take so long to develop.


b25C Mitchell

Update 12th May 2020: Project Status:

  • Fuselage: Frame Ordinates and CAD Profile 100%
  • Fuselage Stringers: Ordinates and CAD Profile 30%
  • Inner Wing: Ordinates and CAD Profile 100%
  • Outer Wing: Ordnates and CAD Profile 100%
  • Rudder: Ordinates and CAD Profile 100%
  • Vertical Stab: Ordinates and CAD Profile 100%
  • Horiz Stab: Work in Progress.

Update 16th May 2020: Empennage:

Update 19th May 2020: Rear Fuselage:

B25 Rear Fuselage

Often it is necessary to pull together several resource documents into one drawing to better understand key datum relationships as I have done here with the rear fuselage.

Update 21st May 2020: All Done:

This is a good example of what the ordinate datasets are all about.

Making sense of this:


To develop this:


The complete list of known ordinate points for the B-25 B,C,D Fuselage, Wings and Empennage are now recorded in a set of excel spreadsheets. A few additional drawings (PDF and DWG) have been created to further clarify the main datum points for aligning the main assemblies and a 3d Autocad drawing of full assembly profiles.

  • Fuselage: Frame Ordinates
  • Fuselage Stringers: Ordinates
  • Inner Wing: Ordinates
  • Outer Wing: Ordinates
  • Rudder: Ordinates
  • Vertical Stab: Ordinates
  • Horiz Stab: Ordinates
  • Nacelle Firewall: Ordinates

All enquiries please contact me at HughTechnotes@gmail.com

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Design: Robotics Project

Design: Robotics Project

I haven’t posted any updates for a while due to ongoing development of various robotic projects. Obviously, I can’t say too much about the detail of these projects that include a new robotic arm and a miniature caterpillar tracked vehicle.

I am though pleased to share with you an overview of this new Planetary gear that I have recently completed.


This planetary gear assembly is less than 2 inches in diameter capable of manipulating a 2kg load. This will be part of a family of new gears designed with different ratios according to requirements.

As a footnote, I am still working on Historical Aviation projects on request by the many readers of this blog and also some updates to existing projects but the Robotic projects are my current priority.

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P-51D Mustang: Conic Formula in Excel

P-51D Mustang: Conic Formula in Excel

A quick technote on entering a conic formula in MS Excel spreadsheets. Getting the correct syntax is critical to achieving correct results.

I am updating the ordinate datasheets for the P-51 B/C and D models to incorporate new information using the various conic formula according to the curve type. Typically with these equations, there are a number of constants to be established to input to the final quadratic formula.

excel formula 2

test equationThe original formula for one of the constants “P” is given as shown (1). If we enter the formula as prescribed in a hand calculator it will evaluate correctly but will not work correctly in Excel in this format. So we need to tell Excel to essentially divide everything in the top line by everything in the bottom by adding parenthesis as shown (2).

The bottom line shows the actual input in the excel formula bar (3).

We are continually working on updates to the Ordinate and Cad package so watch this space for new articles. There will also be in-depth tutorials on interrogating ordinate information to find max-width, tangents and matched second-degree curves as well as updates on detail drawings.

Posted in Aviation, Excel, P-51 Mustang, Technote | Tagged , | 1 Comment