Ordinates

NAA B25 Mitchell: New Project

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

CaptureE

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).

B25 STRINGER

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.

B25 Ordinates

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%.

B25 WING CHORD

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.

b25wing9

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:

B-25 OUTER WING2

To develop this:

B-25 OUTER WING

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

P-51 Ordinate & CAD

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P-51 Ordinate & CAD Package: 

A comprehensive overview of the Ordinate/CAD package for the P-51 Mustang B,C and D aircraft. This package is the result of over 2 years of extensive research and development incorporating everything I know about the ordinate information pertinent to the P-51 Mustang; now available for download.

Fully Dimensioned Layout Drawings (Autocad 2d):

These are my CAD files that you can use for your own projects. These files are being made available for personal use only and not for commercial gain. Detailed layouts, fully dimensioned.

51j

engine mount revb

Tip 1: The Engine Mount drawing is a good starting point when setting out your CAD model. This will establish the fuselage datum points, Thrust line, Engine mount locations, and Firewall.

The dimensions for this have been triple checked. Incorporates information extrapolated from 6 different documents.

Tip2: Did you know you can work with inch and mm dimensions in the same model. If you happen to be using an mm template and wish to input inch dimensions then just type in the value followed by the unit type; either “ or in. So for 1 3/8in enter exactly as shown including space and vice versa if working in the inch template and using mm just quote mm units.

Over 228 Autocad 2D Point Profiles Derived from Spreadsheets:

These are my CAD files (DWG) that you can use for your own projects incorporating the point data. These files are being made available for personal use only and not for commercial gain. 2D profiles of all frames for wings and fuselage.Ordinate DWG profile

Ordinate Spreadsheets: 1000’s of Ordinate Point Coordinates (mm and inch):

These are my Excel spreadsheet files that you can use for your own projects. These files are being made available for personal use only and not for commercial gain. All ordinate points painstakingly entered by hand in both mm and inches. Data is sorted and extrapolated to derive 3d coordinates for direct input into most CAD systems.

Original Military Specs AN & MS (fair share) with Dimension Spreadsheets:

Standard specifications and dimensions for parts including turnbuckles, bolts, nuts washers etc. 3D CAD models of these parts are available separately as a collection; refer to the CAD library tab. Relevant parameters are recorded in spreadsheets that can link to CAD models.

2019-10-06_17-03-01The full Ordinate/CAD dataset will literally save you 100’s of hours of tedious work and is available online. For further information please send an email to hughtechnotes@gmail.com 

This Ordinate/CAD dataset is only available from my blog. All work and research were done by me. All spreadsheets and DWG files are fully editable.

Models on CGTrader:

Alongside the ordinate and dimensional research I also have a large number of professionally prepared 3D CAD models for the P-51 Mustang now available for download on CGTrader.These include the Tailwheel assembly for the P-51 Mustang. All parts, including all internal components, nuts, bolts, washers, and pins modeled to original standards. Tailwheel CAD assemblies on CgTrader:

P-51 Mustang TW Shock

exit These CAD models include fully itemized layouts for each assembly.se

As usual please get in touch at the following address for all inquires HughTechnotes@gmail.com 

Messerschmitt: Bf109 Ordinates

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Messerschmitt: Bf109 Ordinates:

I recently received an inquiry from a museum regarding ordinate datasets for the Bf109. As I previously mentioned in this earlier post the archive I have has a lot of data that was done by others…so I figured it was quite comprehensively covered.

Anyway, I decided to have a closer look and see what was actually documented and how well it aligned with known data. It turns out to be a bit of a muddle. Although the data is quite well presented I have uncovered a number of inconsistencies and anomalies which I will need to resolve.

8-109.000 G-2 Flugzeug Zuss 2

What I thought would be a quick response to an inquiry has initiated a much more intensive study which admittedly I had not planned for. I will go back to basics with this one, using the existing data as a reference and develop a new set of ordinate data for the Bf109 similar to how I approached the Mustang P-51 project.

I have already started with the Horizontal Stabiliser and part of the way through the Vertical. The tables will essentially be a reconstruction from the Messerschmitt drawings and then compiled to develop the X, Y, Z ordinates for transfer to CAD.

bf109

 

NAA P-51D Mustang: Landing Gear Dims

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NAA P-51D Mustang: Landing Gear Dims

I am currently working on the Landing Gear geometry dimensions to check the data for accuracy. During the course of this research, I thought it may be of interest to share some Excel formula for converting angles shown in Deg Min Sec to decimal degrees and vice versa.

p-51 Landing Gear

The plan angle for the OLEO Strut relative to 25% wing chord is 4° 32′ 35.14″ as shown in the above sketch which translates to 4.543094 degrees.

The accuracy of the angles and dimensions in the NAA documentation is rather good with small deviations occurring of only 0.003mm when developing this in CAD. I should note this deviation is negligible and for all intents and purposes can be ignored. However, I like to get this stuff right so I have set about developing the landing gear dimensions to be as close as possible to be exact.

As I have already developed the cad geometry I measured the same angle above from the CAD system which is now giving me 4.54309673 degrees.

In Excel:

excel table

Starting from the left; in column A; I have input the angle from the cad system, then systematically converted to Deg, Min, Sec in separate cells and then converted back to a decimal angle in column E.

The equations for each cell are as shown below:

p51 Landing gear eq

Just enter the equation in the cells denoted; so for the first equation, this would be in cell B2. The latter equation works fine without parenthesis, which I included just to keep the equation tidy.

The Landing gear geometry will be recorded in a separate spreadsheet and added to the P-51 Ordinate Package. Mustang P-51 Ordinates

P-51D LG

Grumman F6F Hellcat: Ordinates:

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Grumman F6F Hellcat: Ordinates:

I have come across some interesting information that has provided some clarification of the cowl ordinates. This has enabled me to further the progress of the F6F Hellcat project.

I have also verified the fuselage ordinates which I have subsequently updated. This project is now looking rather good with wings, front nose ring, air scoop, cowl and of course the fuselage ordinates now complete.

F6F-3

As you can see some preliminary work has also been done on the tailfin which will be closely followed by the horizontal stabilizers and eventually the canopy.

It is unlikely that there is sufficient information to fully complete the Tailfin and Horizontal stabilisers ordinate datasets due to the lack of dimensional data for the tail components. At this stage, the best I can do is locate the 2d plans for this area and hopefully return to this project at a later date when more information becomes available. It has been a challenge getting this far with the project.

Hellcat Ordinates/CAD datasets.

Now available online; a comprehensive package comprising detailed spreadsheets (mm and inch) with supporting Grumman ordinate blueprints, Autocad DWG and original Inventor assembly and part files. The entire package covers 90% of the aircraft geometry. See previous posts for detailed discussions on the development.

For all enquiries please email me for details at hughtechnotes@gmail.com.

Grumman F4F Wildcat: Wing Ribs:

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Grumman F4F Wildcat: Wing Ribs:

Recently I received an email asking if I had done any work with the Grumman F4F Wildcat. As I do have an archive for this aircraft it was indeed on my to-do list. This inquiry prompted me to have a closer look at the archive to see what information was available to derive a working ordinate dataset.

F4F Wildcat

Similar to the P-39 the archive does not contain tabulated data but the part drawings do have the ordinate dimensions. Working to derive an ordinate dataset from part drawings as you can imagine is quite intensive work as you first have to collate the drawings and then develop the profiles in CAD and then extract the point data to a spreadsheet. A complete reversal of the normal process.

The work I was doing for the F6F Hellcat previously was not a priority task so I decided to do some development on the F4F Wildcat, starting with the wings. This threw up a few surprises as the wing rib dimensions were not relative to the wing chord as you would normally expect, instead, they were from a Base datum line. I had not seen this before and it transpires that the reason for this is because the wing ribs are actually not perpendicular to the wing chord. They are in fact perpendicular to wing datum line.

F4F Wing Ribs

This next image shows a simplified sketch of how the dimensions are shown on the Grumman drawings. Note also that the vertical divisions are dimensions fore and aft of the “0” line (which I take to be the vertical datum) and not percentage breakdown of the cord length as expected.

F4F Wing Ribs2

This raises all sorts of questions as to why Grumman designed the wing structure in this manner. I cannot think of any performance or manufacturing benefit in doing so. You can also see in this scrap view from an actual Grumman drawing how the dimensions are to the baseline and not the chord line.

F4F Wing Ribs3

I posted a similar question on the WW2 Aircraft forum, so hopefully, someone will enlighten me on this unusual design feature.

Update: Solved!

The wing ribs are perpendicular to the Wing Datum line, which is 1.6 degrees from the Thrust Line (essentially the design horizontal axis) that aligns with the fuselage Thrust Line. It transpires that the various wing components are dimensioned relative to any one of 5 different datums depending on their function.

2018-09-16_01-23-03

Update Sept 2018: Work in Progress:

F4F Aileron 2

2018-10-06_19-18-41

Grumman F6F Hellcat: Cowl Ordinates

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Grumman F6F Hellcat: Cowl Ordinates:

I may have been a tad over-optimistic in my previous article on the F6F ordinates when I mentioned there was a good chance the Grumman ordinate data would be complete. The one exception is the cowl, although there is an ordinate drawing for the cowl the table itself is just a black blob, completely illegible. However, I checked the part drawings that make up the cowl which is quite well detailed so I made a start on the nose spinner ring.

The spinner ring main model is fine and here it is derived into the air scoop construction model. The construction requires numerous contour lines as each ordinate needs to be manually checked due to the poor quality of the original Grumman drawing scan.

Cowl nose ring3

This ordinate drawing is not deliberately blurred by me, this is how it actually looks like. The main dimension is almost legible just the fractions that are problematic. The process will require evaluating each contour line and curvature check, both horizontal and vertical as shown in the above image.

I am hopeful of achieving a good result with this model which will probably take a few days to complete.

Update 27th August:

F6F Cowl Nose Ring2

I have now determined the correct ordinates for each of the seven profiles. Notice the lower profiles have been artificially extended to the center ring, which will give me better results when lofting. After lofting a surface the plan then is to remove the mouth of the air scoop (blue) and apply the finishing flange to the inner edge.

F6F Cowl Nose Ring80

The ordinates are recorded in a spreadsheet with the x,y,z coordinates extrapolated as I previously did for the wings and fuselage.

Update: 12 Sept 2018:

Cowl Ring Cowl Nose setout dimensions verified.

F6F Ring Cowl Nose

Ordinate Dataset Completed: Wings, Fuselage and Front Air Scoop.

The F6F archive of scanned Grumman documents comprises over 7000 drawings in PDF.

Grumman F6F Hellcat: Wing Ordinates

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Grumman F6F Hellcat: Wing Ordinates

I wrote an earlier article on my work with the F6F fuselage ordinates which I have recently updated. Whilst revisiting the archive I also came across the Grumman wing ordinate drawings and decided to develop those as well. I was reluctant to do this as the original drawings were not that great.

Thankfully it was not as bad as I first suspected, though it has taken me over 7 hours to painstakingly enter each ordinate manually to tabulate the ordinates in Excel.

F6F Wings

I still have to interpolate the data to generate the appropriate X, Y, Z coordinates; set out from the 35% chord; which I will endeavor to do over the next few days.

F6F wings 2

To verify the ordinate dimensions the following equations are applied. The chord length is for any wing chord whilst the LER is only applicable from station 75 to station 252.

f6f calcs2

To be honest the F6F Hellcat was not even on my to-do-list but a conversation with a colleague about the F6F performance characteristics prompted me to have a closer look at the archive. Surprisingly it is very possible that this archive may have sufficient information to generate an entire aircraft ordinate set, which is quite rare.

f6f

I will update this post when the wing model is complete, so come back soon.

Update August 23:

 

I have checked the Centre section profile for accuracy and noticed one point out of alignment by 2mm towards the leading edge. Removing this point allowed the natural curvature of the spline to define an acceptable profile as shown. The curvature check shows that this curve now matches the Leading Edge Radius.

The trailing edge extends beyond the 100% Chord by 5/8th inch on the centre section (Station 0) which tapers to zero at Station 252. Drawing a straight line segment from the Trailing Edge Radius results in perfect alignment with the spline.

Centre Section Stations:

f6f ctr section

Outer Panel Stations:

F6F outer wing

It is not unusual to have a few rogue points from the tabulated ordinate data which is why it is important for a detailed analysis like this.

And here, at last, the complete wing assembly:

f6f wing assembly

Vought F4U Corsair: Ordinate Data

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Vought F4U Corsair: Ordinate Data;

About 6 months ago I received an ordinate dataset from a good friend Gary Henry for information purposes. It is a very comprehensive set for the fuselage comprising over 2800 points to define in excess of 1930 individual ordinates.

Vought_F4U_Corsair_(USMC)

I have recently updated my data processing procedure utilizing new features in MS Excel particularly the “TEXTJOIN” command which makes it a lot easier to extrapolate the X,Y,Z ordinates from large datasets. This dataset was ideal to work with the new process.

F4U Corsair Ordinates

The Textjoin function allows you to predefine a delimiter and then select either an array of data or individual cells using the Control/Mouse combination. You can see I have locked in the selected column and the top row. The units shown are inches but can easily be converted to millimeters.

F4U Corsair RevB

Due to the nature of the dataset, there is a very distinct central plane on the zero vertical plane, which of course I would filter out if I decided to progress this further as a CAD model. I don’t have enough of the manufacturers’ original drawings to develop this aircraft at this time but it sure is interesting working with other datasets.

F4u-1 sideview

The dataset is actually very good only 3 points not quite in alignment. I profiled the top and bottom contours and the contours either side of the fuselage centerline; all 4 curvatures were very smooth.

Update Oct 2018:

Recently received some new data that has allowed me to progress this project with the development of the Cabin ordinates as shown below.

F4U Cabin

F4U Corsair2

Grumman F6F Hellcat: Ordinates

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Grumman F6F Hellcat: Ordinates

I am without access to a Cad system for a few weeks so I decided to spend time reviewing my archive collection. Whilst looking through the many aircraft in the archives I came across some interesting information for the Grumman F6F Hellcat.

F6F-3_Hellcat_11_of_VF-2_on_the_catapult_on_board_the_carrier_USS_Hornet_CV-12_May_6_1944

The archive consists of a substantial number of the Grumman drawings, varying in quality from very good to very poor, though I should clarify the latter relates to only a small number of drawings. This archive includes ordinate tables for the wings and fuselage so I figured it might be a worthwhile project to attempt to decipher and create a set of ordinate spreadsheets as I have done previously for the Mustang P-51.

Hellcat ordinates

Though I rather like this aircraft it was not a priority project on my to-do-list, but having spent today studying the Grumman drawings this could turn out to be a rather challenging project.

Fuselage Work in progress:

hellcat ords 2

Update:

hellcat prelim 2I have managed to obtain a trial copy of the Inventor LT so I can now move ahead with this project. This first interpretation of the fuselage profiles is actually not bad at all. A few macro adjustments will be required to get the profiles correct, mainly due to the quality of the archive where roughly 10% of the values are very difficult to read.

Each point represents the ordinate of the longitudinal stringers which I will profile to assess the alignment and curvature as an aid to finalizing the frame ordinates. Perfecting the frame ordinates can become quite tricky at this stage, requiring constant referencing of the original drawings including the frame structures themselves which often provide additional information that can assist with this process.