While I source new information for the P-38 Lightning I decided to revisit and update the Grumman F6F Hellcat and the Bell P-39 Airacobra Cad/Ordinate datasets. This work relates to the empennage for which I have decided to make the Autocad DWG and a PDF copy of these documents available for download.
These drawings are preliminary Basic Layouts for early release. The 3D CAD model updates will only be available to those that have previously purchased a copy from me directly. Though these won’t be finalised until nearer the end of May 2022. I shall contact the buyers directly in that respect.
I am also in the process of tidying up the Ordinate datasheets to make them easier to read. The datasheets list the ordinates for each frame/station profile in both Inches and Millimetres with a second sheet that extrapolates this data and compiles the data as X, Y, and Z coordinates for input into any CAD system. These X, Y and Z coordinates have initially 3 columns for each ordinate which is ideal for Mechanical systems like Autodesk Inventor plus an additional concatenate column which combines all coordinates comma-delimited for Multiple Point input into Autocad.
Other CAD/Ordinate Datasets:
These CAD/Ordinate packages are designed to help you kickstart your own projects. All the dimensional research has been done for you, which will save you weeks of work.
For more information drop me a line at: hughtechnotes@gmail.com
I can obtain a small number of key dimensions from the panel drawings which will not be enough to achieve an accurate full profile. I do hope someone has a copy.
I have tried all the usual sources for this information without success.
I can’t offer you much for the drawings but I am willing to share the comprehensive ordinate study and cad material when this project is complete.
Further Request: Photos of Wing Tip Required:
The wingtip trailing edge has a tab extension as a consequence of the connection of the top and lower panels. I am curious as to how this extension integrates at the extreme tip of the wing. If anyone has any close-up photos for the wing tip I sure would appreciate a copy.
Let me know if you can help. Email hughtechnotes@gmail.com
Update: 21st May 2022:
I have not had much luck with sourcing the above material. The Mold drawings would certainly have been enormously helpful in determining an accurate ordinate model. There is a Plan B, though it is going to be a fairly intensive search for every morsel of information that can be gleaned from the individual part drawings, manuals and reports that collectively will give me enough to achieve an accurate definition of the FWD Boom and Engine cowl surfaces.
An example would be the Scoop web plate profiles shown above to achieve some surface definition in those areas. I am currently working on the Landing Gear doors which will help define the lower surfaces. This is a lot of work which unfortunately means this will not be ready until much later in the year. I don’t do guesswork, if the ordinate point does not exist it is not on the model.
If anyone has any information that can assist me with these ordinate points, please, please do get in touch.
New Ordinate/CAD Project: The Lockheed P-38 Lightning is an American single-seated, twin piston-engined fighter aircraft that was used during World War II. Developed for the United States Army Air Corps by the Lockheed Corporation, the P-38 incorporated a distinctive twin-boom design with a central nacelle containing the cockpit and armament.
This project will dissect the complexity of the aircraft dimensions with fully developed spreadsheets, CAD models and drawings. I have drifted back and forth on this project over the last few months, studying the blueprints in detail to determine the best way of presenting the data in a usable format.
Surprisingly the wings are probably one the most complex parts of this study. The complexity comes about as a consequence of how the dimensional data has been recorded. For example, the wing chord is at a dihedral angle of over 5 degrees with the wing ribs actually perpendicular to the ground plane.
When we define the wing ribs we are actually working on a vertical plane angled to the wing chord line with the main beam and rear shear beams perpendicular to the chord on section. We also have the dimensions for the basic wing airfoil profile. Initially, I will record the rib dimensional information and generate the correct array of points at each Station. Then I shall calculate the airfoil profile at each station based on the given formulae Yu = YuT+(YuL-YuT)A. This should give us a means of verifying the tabulated data, for example; the table values for the Main Beam on 35% chord should match with the calculated airfoil values.
The plan is to record the dimensions as noted, vertical, horizontal and chord aligned in inches and millimetres exactly as defined on the original blueprints. Then I will extrapolate the X, Y, Z, coordinates for each point taking into account the chord angle of 2 degrees so that we can simply transpose these points directly into CAD at the correct positions relative to the origin point where the Nose Ref Line intersects with the Fuselage Ref Line.
The other caveat to all this is the 0% chord line is actually set back from the leading edge. There is yet another table of dimensions that relates the curvature of the leading edge to the 0% chord line. Ultimately to define the wing ordinates will involve a lot of work and then checking to ensure accuracy and correct alignment with the airfoil claculated profiles. At the end of the day, it is about making sense of all this fragmented information into a workable solution that makes it easier to interpret and use in any CAD system.
This is essentially how I work with all these Ordinate/CAD datasets. It is not just about recording information but also to check that the information works and that the end-user can transpose this into whatever system they are using. It is quite common for the information on the blueprints to be obscured, missing or simply illegible which usually requires a fair amount of time searching for answers. To complete this project I estimate something in the region of 300 manhours.
Update: 26th April 2022:
I have not yet decided on how best to present the Wing Ordinate dataset. I am looking at establishing check tables that will effectively compare the noted tabulated dimensions on the Blueprints with the calculated values. Also, we need to derive locational information directly from the wing plan CAD drawing for the Rear Shear beam and do a calculated check. Just to give you some idea of where I am going with this see screenshot below. As I mentioned above, the information on the drawings is fragmented so it is important that the excel spreadsheet data is presented in a clear and legible manner. Just now it is a bit of a muddle.
A quick update: Have rearranged the spreadsheet now with calculated values in lieu of listed values so the CAD model will be considerably more accurate. Calculated values are in blue text.
The rest of the Rib station tables will be added with similar calculated values and then I shall create a second worksheet with the airfoils for each corresponding station. The final sequence will be the extrapolation of 3D Ordinate points from a single datum so it will be possible to build an entire wing just from one collection of X, Y, and Z coordinates in one step. At least up to STA 254…still need to figure out the intricacies of the wingtip geometry.
Ordinates for each wing STA profile are calculated and recorded as shown. The highlighted rows at the 35% chord, are checked with those corresponding values listed in the tables above from the Lockheed original drawings. By the way, the drawing on the right is the Basic Layout Engine Mounts…there are 2 variations on this; both of which will be developed.
In the above screenshot, I have highlighted 2 minor corrections to the wing rib locations. They should be the decimal value for 85 11/16″ and 106 5/16″.
Update 3rd May 2022:
Have made good progress on the datasets for the Wing, Boom and Engine Mounts. Whilst working on this project I thought it may be prudent to compile an assembly list for each aircraft type for the basic dimension layouts as shown below. I plan to do a Technote shortly updating work methods using the ordinate dataset from Excel spreadsheets and include information on Sketch coordinate systems; manipulating the X, Y, Z-axis locally…so look out for that.
There seems to be a theme developing here…following on from my efforts to organise the chaos of large blueprint collections I endeavoured to continue my efforts with a long-overdue update to the P-51 Drawing register.
The P-39 Airacobra register was a breeze by comparison to this P-51. That was only a matter of 4-5 hours of work which was aided by the fact the drawing filenames were already fully described…all I had to do was add the Film Index numbers alongside the filenames. The P-51 on the other hand only had obscure filenames that were somewhat inconsistent…which meant this exercise ran into a few days. Occasionally my enthusiasm tends to thwart common sense!
Getting back to the P-51 Drawing register. The update is now inclusive of hyperlinks contained within the excel spreadsheets that will open the associated drawing. This is a huge step forward in managing and working with such a large archive and though it took ages it is a major improvement.
As you can see LINKS have been added to the right column (J) with hyperlinks recorded in column L. This column is hidden but can easily be viewed by using the option to UNHIDE. The Film Index reference is the actual microfilm reference hard coded onto the original film which differs from the actual filename that was generated when the film was scanned.
I should note at this stage that a number of folders in the archive will require renaming as Excel does not like #hashtags in naming conventions. The download section includes a word document describing the file-naming convention.
The hyperlinks are plain text entries originally copied from the development process that utilised the Vlookup function referencing a separate spreadsheet. I had considered including the separate spreadsheet in the download section but I think that just over-complicates things. About that development process!! It may be prudent to provide a quick overview of how things were developed.
The Development Process (briefly)
The initial process was to extract the filenames from Windows Explorer and deposit those records into a separate spreadsheet. The way to do this is to select all the files in the folder and click the Copy Path option in the windows explore toolbar.
Paste this into a spreadsheet and then remove the first part of the path (highlighted) so the location parameters now become a relative path to the root folder. This was done using the Replace (CTRL+H) function by copying the highlighted portion and applying a null space to all of the records.
This is now the actual hyperlink path which we need to associate with the actual Film Index. As mentioned above the Film Index is recorded on the scanned images and therefore a fair amount of manual intervention is required to record this value in column A. Using the Vlookup function necessitates that we use the column on the left for the value sought to return the value on the right. As you can see from the many tabs on this spreadsheet I filtered out all the filenames from every folder and then proceeded to populate the column in each case with the Film Index number…that drove me nuts!
There are several ways of accessing the values using Index and Match or even Indirect in conjunction with Vlookup…but we shall stick with the simple option of using Vlookup.
The Vlookup function asks for an initial lookup value; in this case “I10” then it asks for the corresponding Table Array; essentially the array of data from which to search. In this example, the array is defined as the values from the spreadsheet called “FILELIST” Tab “A” from cell A1 to B1043. The “2” refers to the column from which to extract the value you are seeking…which refers to the second column. “False” is for an exact match to the value in I10.
The Link is simply the =HYPERLINK function referencing the value in column K with a text value defining the label “LINK”.
You can combine the HYPERLINK function with the VLOOKUP in one formula like this…though it does take a fraction longer for the link to open.
That’s the basics of how this was done. using Indirect in conjunction with Vlookup enables you to search for the tab designation from a tab list that would look through the entire spreadsheet for the sought value. I didn’t think this was necessary for this exercise.
I mentioned the folder name changes that are required for this to work. The 3 main folders should now be changed to P-51 Mustang D01, D02 and D03.
The updated drawing registers will be available for download this evening so watch this space for an update.
As usual, the spreadsheets are fully editable so you can adapt the data to suit your own requirements. I would note that the Vlookup formulae are not embedded within these drawing registers as the hyperlinks are just copied text values and not live links. The recordset “FILELIST” is not available for download but if you would like a copy to play around with Vlookup or similar then please just drop me a line.
Update (earlier than expected)
The updated P-51 Mustang Drawing Registers are now online and available for download. Please let me know any comments or feedback.
This folder also includes the Aviation Manufacturers Standard Parts file which I am trying to consolidate as they tend to pertain to more than one aircraft.
Comments or feedback as usual to hughtechnotes@gmail.com
Another project that is long overdue is a drawing register for the P-39 Airacobra. This will be an Excel spreadsheet complete with drawing number, description and a link to the actual drawing file.
Assuming you have the P-39 folder arrangement as default the links will work fine.
The spreadsheet contains multiple worksheets each designated according to the folder name. The names are tabbed along the bottom to open each worksheet. The links will open the connected file in Adobe Acrobat so make sure you have the Acrobat Reader as a minimum.
The spreadsheet is still work in progress which hopefully will be available for free download this evening. The spreadsheet needs to be deposited in the root P-39 folder.
The spreadsheet is fully editable so you can adapt it for your own project. I should note that columns G and H are temporarily hidden columns that contain the hyperlink address…so don’t be alarmed when they suddenly pop up when you are developing your own adaptations.
To HIDE or UNHIDE a column, select the column header, right-click and select the option from the menu.
Every aircraft manufacturer has libraries of standard parts in addition to the MIL specs that are used for their various aircraft designs. These vary considerably covering a wide number of standard parts like bolts, nuts, washers, hinges, screws, grommets, extrusions etc, etc.
When I was working on the P-51 Mustang Tailwheel mechanism I was forever jumping back and forth looking for the various standard parts which was a nightmare due to the large number of files in the archive. This was further complicated as the file names were the scan numbers and not the drawing names. So I figured it was time to get this stuff organised.
I have worked through the archives for the Grumman F4F Wildcat and F6F Hellcat and extracted the Standard Part drawings and renamed them with the correct drawing designations. I have also done a similar exercise for the NAA P-51 Mustang.
The actual drawing filenames have been adjusted slightly to make sorting easier (by group) and make the names more legible. Where for example we have 1E48; this is denoted as 1E-48…the 1E is the alpha-numeric group designation with the numerical sequence suffix. This just makes it easier to read when you have hundreds of files in the same folder.
The excel spreadsheet is a register with the different manufacturers’ part drawings listed on separate sheets in one workbook. This is tabbed along the bottom of the spreadsheet. It is envisaged that each set of drawings as listed will include a download link to an online resource to access the files. This download link for the collection of standard part drawings is located on the top right of the spreadsheets.
The NAA Part Drawings also include the previous specification identifier as some of the earlier blueprints still refer to this number.
This is an evolving project and will be continually updated as more information becomes available with the inclusion of other manufacturers data. Currently, over 400 part drawings are registered. For further information please drop me a line at hughtechnotes@gmail.com.
P-51D Mustang: 3D Instrument Panels: Updated 11 June 2022
P-51 B and D Instrumentation Panels are now available online as a separate package. This package includes all below noted Instrumentation Panels 3D CAD models in STP, STL and 3D DWG formats with associated dimensioned 2D drawings and PDFs. Note the hole positions are listed in a tabulated form on the drawings which can be extracted for CNC work.
Also included is a copy of the original NAA instrumentation drawings for reference.
Update 20th June 2022: All Instrument panels now also include the Parasolid X_T format. The complete package is available for download, get in touch at hughtechnotes@gmail.com.
Early Version P51D: 106-51002
Later Versions: 109-516002, 109-517002
Update 15th Feb 2022
For P-51B Mustang: 97-51002
3D Model Views:
For further information drop me a line at hughtechnotes@gmail.com.
Occasionally when trying to Emboss text in Inventor the command will fail. Most likely the problem will relate to intersecting lines for the font style..invariably it will tell you why it doesn’t work.
This can be very frustrating with few solutions other than reconstructing the font style would be apparent. However, there is a way to resolve this…well at least the particular font I am trying to use for the P-51 Mustang instrument panels. In a previous article, I had opted for an alternative to the MS33558 TTF as this font style is flawed.
I have now found something more compatible and it is called TGL0-17 ALT. This is actually very close to the MS font…however I have still encountered problems.
The solution is to first open the text editor in Inventor and select the font type, set the height, width and spacing. You may need to select Exact for the latter and type in a value to achieve the correct spacing instead of using the defaults. Once you are satisfied with the formatting close the text editor and try to emboss it. If the emboss fails move on to the next step.
Select and open the text editor again and this time highlight all the text, then copy and paste this into MS Word as Text Only. Refresh the font style by selecting an alternative and then select again the TGL0-17 ALT. Copy and paste back into the Inventor text editor, close it and voila now it will emboss.
Before you ask, I have absolutely no idea why this works only that it does in this case So next time you have a problem embossing text in Inventor try this workaround and see if that works for you.
This is a sheet metal part for the P-39 Airacobra (#12-509-052) sent to me by a fellow enthusiast for comment. Before I get immersed in discussion on this subject I would just say that this part is a cable cover that is unlikely to be under any substantial stress and thus would probably be fine as modelled.
The part comprises 2 tabs, one on the top and one on the bottom. It is the fillet radius that I will focus on. The first bend is offset from the edge of the plate. The drawing specifies a 5/32″ (4mm) radius for the fillets at the intersection of the top tab and the main body which overlaps the sheet metal bend. The originator has taken this literally and attempted to create a finished fillet of 5/32″.
I suspect that the drawing is actually referring to a 5/32″ radius as it would be for the developed flat pattern because doing so otherwise; due to the bend being offset as illustrated on the cad model; this introduces stress points.
The images show the irregular continuity which creates angular edges that essentially become focussed stress points. It is often best to try to achieve smooth continuity both for bending purposes and of course when in use. What they did was sketch a face profile; which included the specified radius (#1)and then proceeded to adopt the standard commands to build the flanges. Technically it is not wrong but as the manufacturer’s drawing does not contain a developed flat pattern it is often misinterpreted…the radius should perhaps be applied to the pattern before bending.
Similarly, at the bottom tab, we also have irregular continuity as shown at #2.
I rebuilt this model to address these issues and you can see how a small change in modelling technique can obviate some of these issues.
The images show the developed pattern with the original cad model on the top and the new version on the bottom. At #3 the outline of the tab would be difficult to cut with the small taper before the fillet, whereas the lower profile at #4 is easier to cut with no stress points. Similarly for the base tab at #5 and #6. I should note that the bottom tab radius is not specified so I opted for the default minimum which fits nicely before the bend lines.
There are several ways to do this with the easiest being accomplished by using the Unfold command on a square flange and then applying the fillet before refolding. The option I have used here is first to draw an extended flange as part of the initial face sketch, create the first part of the model as a Face then apply the 5/32″ fillet before bending along a predetermined bend line sketch.
The sketched tab outline is a lot bigger than is required which of course can be trimmed once the tab is complete. You can see the extents of the tab on the initial sketch…you only need to add a plane at that point to trim. The resulting fillet is a smooth continuity with no obvious stress points.
Understandably the designers wished to increase the amount of material at the bend to maximise strength so it is advised to try to achieve those goals. As I said before, for a cover like this it is probably not too critical if we only applied a small fillet but for framing and structural elements, it may be critical.
One quick note on the 2 vertical flanges…the drawing specified an internal radius of 5/32″ which to be honest is unworkable as the resulting bend would overlap the bottom tab…in this case, I opted for the minimum specified.
At the end of the day, it is down to the interpretation of the designer intent. For the majority of sheet-metal drawings, they often do not include developed flat patterns but may contain information that is actually applicable to the flat pattern and not necessarily the finished folded profile.
Today I had an interesting conversation with a University lecturer on utilising historical blueprints as a resource for learning 3D CAD. I have been involved in similar discussions in the past and I do think they are an ideal source for those that are beginning this journey. I once helped a college to develop a curriculum for their students learning CAD on the principle that they would be more engaged in the learning process if they were developing a real-world object that they could actually relate to.
It does make a lot of sense and I would encourage new users to seriously consider the many benefits of using blueprint resources for learning. A typical aircraft design covers complex mechanical items, hydraulics, electrical, sheet metal, moulds, integration with external resources such as Excel spreadsheets as well as familiarising the end-user with tolerance application. Never mind the added benefit of how to prepare quality, fully dimensioned 2D drawings. All disciplines in one package!
I work with a lot of different CAD systems, not just Inventor, though the main reason for using Inventor is because it is accessible as a trial product more so than many others and that this industry is not one normally associated with Inventor…so it is a nice challenge. Occasionally, particularly with other CAD systems, I tend to evaluate them using the blueprints as source material to cover the many aspects of their functionality.
The blueprint archives are not expensive when you think that you could get 10000 blueprints for a small amount of money. The downside of having so many blueprints is finding what you need to help with your learning task. The P-51 Mustang blueprints come complete with a fully detailed drawing list which helps enormously. The P-39 blueprints are roughly sorted into categories which helps in this respect. The Fw190 and Bf109 sets are also very good but as they are in German this sometimes can be counterproductive if it is not your first language.
I am currently putting together a free random collection of a dozen or so blueprints from the various Aviation archives that will give you an introduction to real-world applications and a head start on your project. Just drop me a line at hughtechnotes@gmail.com.
Aviation CAD TechNotes 