Author: Hugh

2D Draughting to 3D Models

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2D Draughting to 3D Conversion

2d to 3dTechnical drawings, detailing the specifics of your design can be critical for the communication both internally and externally. We can transform your 2D CAD or fully dimensioned legacy paper drawings to 3D Models using our experienced engineers to ensure drawings are 100% accurate and adhere to the most relevant standards and protocols.

3D Cad models will be fully inclusive of manufacturing tolerances as specified. New 2D drawings will be derived from the 3D model, dimensioned and denoted as original.

Attributes and BIM IFC data can be incorporated according to your engineering and company standards for Structural, Mechanical, Building Services and Equipment projects.

We normally use the Autodesk Inventor but are equally capable with all the Autocad based products from which we can provide native format model files or various other formats to suit your requirements, including DWG, IFC, STEP and STL.

We can provide CAD modelling services for your restoration project, adhering to all appropriate standards and design specifications.exit

The Journey

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The Journey:

This blog has been about the journey cataloging my passion for historical aviation design and construction. Its about the geometry; the ordinates and plans, about the designs and construction; from wood and canvass to full metal and alloy and the inspirations for the designs. The sheet metal work, the manufacturing, the mechanics, materials, electrics and hydraulics.

Its been an interesting time studying the different aircraft construction techniques and design methods. The different approaches to how different designers organise and develop the designs on the drawing board, sometimes accumulating 100o’s of drawings for a single aircraft…an admin challenge that even today would be quite daunting.

Not all my work has been published here, only a few examples that I think may be of particular interest. The evolution of the FW-190 to Ta-152, the various marks of the Spitfire, the early design characteristics for the Tiger Moth, the Mustang P-51 conic research and mathematical analysis culminating in a broad spectrum of research material that lays the foundation for the next chapter in my work.

I have learned a lot from this work which has been both challenging and frustrating. Its tested the limitations of my knowledge and the CAD systems we have come to rely on so much in our designs today.

Not many of the archive drawings sets I have are representative of a complete aircraft, often missing key information or simply illegible; though the latter sometimes can be overcome by studying other aspects of the design. I am often asked if I would consider creating an entire aircraft design in CAD that could actually be manufactured and whilst the answer is of course yes I would be reluctant to spend the considerable time required for any aircraft for which we have many flying examples.

Having said that Operation Ark was setup to undertake such a task for an extinct or rare aircraft depending on availability of sufficient design data. This work is still in progress and will take a while to resource, evaluate and fund such a project.

In the interim I have received a new set of archive material for an aircraft that was used extensively by Russia on the Eastern front which will be featured here in a few months time.

For now there wont be many updates but please do drop me a line as its always good to hear from the many readers of this blog about their own experiences in the exciting world of historical aviation.

de Havilland Tiger Moth DH82: Fuselage Gussets

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de Havilland Tiger Moth DH82: Fuselage Gussets

Looking back through a previous project for the Tiger Moth I had some notes relating to the fuselage gussets. The rear fuselage is a bit of a puzzle when it comes to the strengthening gussets at the truss joints.

2015-09-19_13-22-38This is a scrap view of the de Havilland rear fuselage drawing on which I have indicated 3 gusset locations. The first thing that comes to mind is that for each joint the diagonal truss member is at a different angle but the gusset plate in each case is the same part number.

2015-09-19_13-24-50On this same drawing, we have an enlarged detail view showing the minimum weld requirements for each of these gusset joints which cannot be achieved if the gusset plates above are all the same size!

In fact, for 2 of the three joints, the gusset plate extends beyond the diagonal truss member making it impossible to achieve the weld criteria. This is actually quite clear in the first image and modeled in the following.

2015-09-19_13-44-35I started my engineering career on the drawing board so I understand why in many cases they have done this to maintain consistency of parts and minimise variations, but if its not fully engaging then its bound to be less effective.

As you can see in the model the gusset plate is not even close to the center of the strut and certainly would not achieve the 0.25″ weld.

2015-09-19_13-29-27Another odd example is the bottom truss end gusset where it splices with the front fuselage truss.

This is actually detailed as a flat plate on the dH drawings, but for it to fit correctly it needs to be jogged; as shown; to coincide with the diagonal struts, otherwise, you would have to fill the gap with weld.

The material thickness for the tubes and the plate are less than 1mm, so depositing large amounts of weld in these areas is not advised.

The gusset plate also fits flush with the end of the tube and is noted on the drawing as requiring an edge weld. I think if I was designing this I would have the plate set back from the end of the tube allowing a full profile weld all around.

What makes this odd is that for other aspects of this aircraft design they have gone into great detail with gussets elsewhere, clearly dimensioning jogs with separate plates for individual joints.

I should note that there is an insert piece required to close the main tube which is not modeled yet.

When I study these aircraft designs, whether it be the Ta152, the Mustang, Spitfire or the Tiger Moth I try to understand the reasons why things are done the way they are. In many cases it could be driven by manufacturing criteria, availability of materials, expediency, a need to minimize variation or in some cases just down to the individual draftsman.

There is some debate about the effectiveness of these gussets and whether or not they are actually required. I have no opinion on these debates, the fact remains that they are part of the design and with some minor dimensional adjustment can be fitted correctly in compliance with the specified criteria.

I quite like the Tiger Moth, it is a practical design with many examples still flying worldwide. I hope that someday I can collate the necessary information to finish this project.

tm uc

NAA P-51D Mustang: Carb Air Scoop

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NAA P-51D Mustang: Carb Air Scoop

In an earlier post I discussed in some detail the progression of model development for the Carburetor Air Scoop (Lower Cowling) inlet and I mentioned that the final Air Scoop would be uploaded upon completion. Earlier Post : Air Scoop Prelim work:

It has actually been completed for awhile; I just forgot to upload it!

So here it is and if anyone has attempted to model a complex surface of this type you will understand how difficult this can be. Needless to say the Freeform T-Splines were invaluable in obtaining the correct surface.

The surface model is attached to over 300 ordinate points with numerous contour and fairing curves generated in preparation for the final surface modelling.

The data was first prepared in a spreadsheet; listing all ordinate points in mm and inch dimensions from which I extrapolated the 3D coordinates for each point; essentially creating a point cloud.

The ordinates were imported into Autocad, analysed and then the points grouped accordingly to define the contours and fairing lines.

This was then imported into Inventor and the surface painstakingly built up in each separate square grid attaching all the ordinate points. There was no easy way of doing this; I know I tried!

I am delighted to have finally completed this particular model having consumed many hours trying various methods to get it just right.

Project Cad Technote: Sheet Metal Bending in CAD

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Project Cad Technote: Sheet Metal Bending in CAD.

Sheet Metal Work is an interesting subject to which I could no doubt devote an entire blog to. Fortunately for us we don’t have to as this topic is covered in detail by the many professionals working in this industry.

However understanding some of the key principles is imperative to ensure that our CAD models created from the aviation manufacturers drawings are correct as the dimensions given do not always suit the CAD development process.

One particular aspect relates to something the Sheet Metal guys refer to as the Outside Setback. The Outside Setback is the distance from the apex of the outside mold lines to the tangent point of the outside radius. When the sheet metal is bent the inside radius pulls the edge of the material away from the apex of the bend.

2015-08-30_12-39-11Typically on many occasions we will have a developed profile for the part which is to be bent to the required profile with only a few dimensions noted to achieve this including a bend coincidence point and angle.

2015-08-30_12-13-10The image on the left is indicative of many situations that arise when working with the manufacturers drawings. It is not unusual for a dimension to be given to the projected point at “A” which understandably is important to ensure the part mates properly with another.

However in Inventor; for example; we only have selections at 1,2 & 3 for “folding” a part from a development sketch and no option to define the stated “Dim” to the point of coincidence; which therefore may not provide the desired result. We may of course have the angle, material thickness and usually the inside radius.

2015-08-30_12-19-11Its not practical to select points 1 & 2 but it may be possible to use point 3 if we know the OSSB dimension.

In Inventor this is the middle option from the sheet metal fold dialogue. In this case we have specified the complimentary angle (97 degrees).

In order for this to work we need to calculate the dimension OSSB. The smart guys in the sheet metal industry have this stuff all worked out and have an easy equation that we can use to ensure consistent accurate results.

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B> denotes the complimentary angle which must be less than 170 degrees.

IR is the Inside radius and MT is the material thickness. (the dot in the middle by the way is multiplication).

2015-08-30_12-25-18From this equation we derive the value for OSSB which we will deduct from the Dim value provided on the drawings, thus giving us the correct location of the fold line at point 3 above.

In this example the dimension from the manufacturers drawing is stated from the hole center, which has been adjusted to locate point 3 by deducting the value OSSB.

It works perfectly and we now have a folded bracket from a development plan that complies with the stated drawing dimensions.

I should note that some CAD products take this into account and provide the necessary options for developing this folded model but where we have limitations a touch of maths goes a long way to achieving the desired result.

In this example the hole is very close to the bend causing a slight deformation. This could initially be drilled to a smaller diameter and reamed after bending or we could simply use a smaller bend radius; if permissible!

Update: Mustang P-51 Project & Operation Ark

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Update: Mustang P-51 Project & Operation Ark

The Mustang P-51 project is on hold whilst we review the CAD systems we will use for Operation Ark. To date we have utilized both the Autodesk Inventor & the Dassault Solidworks for our projects and research. We have another contender for the project which is Solidedge, until recently this was not a viable option but the latest version ST8 exhibits many of the features we would need.

Operation Ark will be a long term project requiring many man hours of work to research and build literally thousands of models, so it makes no sense to have different CAD products for this project. There is also a cost consideration as the project will rely entirely on goodwill and donations to support our efforts and assist with  CAD software.

Collaboration technologies and access to rendering farms for final processing of the CAD data are also key considerations. We have received offers of support from a few fellow enthusiasts to help with the Cad model developments and rendering; the latter being from Bilby…thank you very much for your support. Some comments from fellow enthusiasts:

From Alan “I love your Operation Ark initiative, and would be more than willing to play a role in any capacity.”

From John; “ARK is an extremely important project and I congratulate you on your vision.”

From Beaufort: “…I am really impressed with what you do and I can see that massive amount of time that you put into it. I also love the design specifics of these aircraft…”

Operation Ark Project Status:

Lockheed_Vega_5

This project is attracting a lot of attention, with many positive responses as noted including suggestions of alternative aircraft for consideration. One of which is the Lockheed Vega , which is a unique aircraft and was; in many respects; ahead of its time.

This is actually a good example for Operation Ark as the only remaining examples are located in the USA with only one flight worthy example, though further research would suggest that number could well be 2. The location alone excludes a large number of enthusiasts from actually ever seeing one either as a static exhibit or in flight!

That is part of what Operation Ark is about, removing geographic constraints and bringing access to everyone; the complete aircraft with everything modeled right down to the nuts and bolts. An exact replica in 3D that can be interrogated online as assembled or as individual components. We are also contemplating extending this to include additive or 3d printing technologies to build a half size replica, making the parts available to interested parties.

WEB11667-2010pBut this is only one of the aircraft being considered and whilst a likely candidate for selection; specifically as we have access to the manufactures drawings; our preference would be for one that does not exist or has only 1 example in existence like the Ta152.

The project though is entirely dependent on the availability of the original manufacturers drawings and specifications, which is our current priority!

Even when we do have access to materials they first have to be evaluated, which incurs a cost for scanning of microfilm archives and then reviewed for completeness. This process is rather costly but ensures that we don’t commit to a particular aircraft that we can only partially build. Usually where we have incomplete datasets we will endeavor to source the missing data elsewhere before we actually exclude the aircraft from selection.

All the research and work published here to date has been done voluntarily in the hope that it will help other enthusiasts.

Topology optimization and additive manufacturing

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Topology optimization and additive manufacturing

This is probably a slight divergence from the main subject of Historical Aviation though it does align well with the underlying research philosophy relating to the how and the why of how the aircraft designs develop from concept to manufacture.

Engineers have always strived to maximize efficiency with materials, reduce weight and improve manufacturing…the shape and form being integral to that same desire.

Thus today we have many tools at our disposal that have evolved to interrogate and simulate our designs before they become a real world object. In recent years Topology Optimization, an industry term that Wikipedia defines as “A mathematical approach that optimizes material layout within a given design space,” could be a critical motivator to create industrial designs more efficiently with less material…an ideal environment for the aircraft designer.

In my day job as an engineer I am always looking for new tools to help me make my designs better and more efficient. In my studies of historical aircraft designs I attempt to get into the designers mind and understand the motivations and inspiration for the aircraft designs.

So I am naturally curious about the many influences that impact the design process and the tools available to do that job.

This is a link to a youtube presentation on Topology Optimization..just because it is; for me personally; an incredibly interesting technology…enjoy!

Solidthinking Inspire; Topology Optimization

2015-08-17_22-23-48

Republic XP-47J Superbolt

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In my endeavours to research the forgotten aircraft of the war eras and the remarkable people that designed, built and flew them I came across this article on the Republic XP-47J Superbolt.
What is important; apart from the fact that this aircraft recorded the highest speed in level flight for a propeller-driven aircraft in 1944; is the tribute noted in the response column by the daughter of the pilot; Mike Ritchie who made that historical flight.
Perhaps the XP-47J should be added to the list for the Operation Ark project.

William Pearce's avatarOld Machine Press

By William Pearce

In mid-1942, Republic Aviation Corporation initiated a design study to lighten their P-47 Thunderbolt fighter for improved performance. The Thunderbolt had been steadily gaining weight as the design matured, while comparative enemy aircraft, like the Focke-Wulf FW 190A, were much lighter. Republic officially proposed a light-P-47 to the Army Air Force (AAF) on 22 November 1942. On 1 April 1943, the AAF gave Republic a letter of intent to purchase two light-weight P-47s, and the contract was officially approved on 18 June 1943. This new aircraft was designated the XP-47J.

Republic XP-47J front An early image of the Republic XP-47J before the Superman nose art was applied. Note the cooling fan vanes around the spinner inside the cowling.

As with all P-47s, Alexander Kartveli was the main designer of the XP-47J, and he was assisted by Murray Burkow. The XP-47J was similar in appearance to a P-47B, but it was…

View original post 1,100 more words

NAA P-51D Mustang: Fuselage: Conics

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NAA P-51D Mustang: Fuselage: Conics

In the preceding article I had some fun with polynomials and how they could be useful for determining a smooth fit spline for the development of the Mustang fuselage. As a follow up to that article I wanted to share some research relating to conics.

The Mustang P-51 was the first aircraft to be completely defined by conics. The designer Edgar Schmued worked with Roy Liming to mathematically analyze the Mustangs shapes, tangents and curves. Conics were used by NAA as far back as 1932 though many of the techniques and equations we use today however were not actually in use until 1959.

The Bézier curves for example were based on the Bernstein polynomial which had been known since 1912 but its application for graphics was not understood till much later. Bézier curves were widely publicized in 1962 by the French engineer Pierre Bézier, who used them to design automobile bodies at Renault. The study of these curves was however first developed in 1959 by mathematician Paul de Casteljau using de Casteljau’s algorithm, a numerically stable method to evaluate Bézier curves at Citroën.

So I started to wonder how did Edgar Schmued and Roy Liming actually apply conic principles and what methods did they use for the Mustang design!

The documentation I have available for the Mustang Wind Tunnel models gives us a clue at the geometric construction for the fuselage frames. The designers used smooth conic sections with key parameters controlled by longitudinal shoulder and slope control curves. The longitudinal curves defined fullness and tangency values for the conics from forward to aft of the fuselage. The P-51 designers found that this technique allowed them to accurately control sectional areas to secure the required effects for lift, drag, stability, and overall performance.

2015-08-03_22-50-45

Here we see a scrap view from the wind tunnel models, showing clearly the development of the conic constrained by 2 tangent lines and a third Shoulder Point as a known point on the designed curve.

The intersections of lines extended from the Max Half breadth point and the Lower Ship Centre point illustrate a drafting technique for creating the finished curve for the lower section of a fuselage frame.

Hugh P-51 ConicsTaking this method further we can describe a curve using a series of extended lines to define any point on the curve as shown in my Cad drawing.

This is my interpretation of a technique for the drafting of a typical Mustang fuselage frame. I haven’t seen this technique applied to a full fuselage profile and whilst the design information I have suggests a similar approach by the Mustang designers I can’t verify that this was the actual technique used.

It is not possible within the scope of this article to go into the detail of this technique, but suffice to say that selecting only 3 points for the lower and upper sections contained within tangential lines provides the basis for accurately determining any other ordinate point on the particular curve. I have uploaded a short video on Youtube here: Drawing a Conic

This is actually a lot better than using the polynomial equations for frame geometry as they only give you a best fit approach based on the tabled ordinates; with limitations; whilst this construction technique will allow the flexibility of defining any point on the curve to an unprecedented degree of accuracy when created in CAD…it works!

So what else did these visionary guys do? I am really keen to further research the mathematical approach that Edgar Schmued and Roy Liming used in the other aspects of the aircraft design and uncover the methods that made the Mustang unique.

It is my hope that by sharing my research and developments that this will inspire others to also research the work of the designers from this era and hopefully in some small measure encourage support for our project “Operation Ark”.

2015-08-06_03-06-27Update: I must have spent a full day browsing through the archives to find more information that would assist with understanding the conics development and thankfully I came across this NAA lines drawing for the cowl on P-51C (NA-103).

This shows the development and tangent lines for everything including the shoulder lines and the fairing lines as well as the main profile contour lines.

Its very important to spend time verifying the information used for developing these designs to validate the research. Sometimes I could spend days just looking for small scraps of information just to verify one dimension, which happened quite a lot on the Ta-152 project!

Full profiles drawn in Autocad from comprehensive excel spreadsheet ordinate collections now available for download. See this article for details.

NAA P-51D Mustang: Fuselage Lines; Polynomials

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NAA P-51D Mustang: Fuselage Lines; Polynomials.

This evening I spent some time looking back through some old notes I had on fuselage design, particularly Conic sections and Setting-out design theory.

Checking through the archives for the Mustang P-51 we have a design set for the wind tunnel model with a line plan showing the Shoulder Points (SP) and the “point of convergence” where the upper line of the Mustang fuselage converges with the lower fuselage line and the Fuselage reference line.

2015-07-31_03-40-50The Wind Tunnel drawings are a quarter scale but are quite accurate.

Here we can see the “point of convergence” actually defined on the the wind tunnel drawing at the scaled sta 92. Technically station 92 does not exist as it is outwith the fabric of the WT aircraft, but for convenience I have defined it!

So with this in mind I decided to undertake an experiment to calculate the “point of convergence” with the fuselage ref line according to the manufactured ordinates.

2015-07-31_12-43-55For this exercise I used the upper line of the fuselage, shown here as X,Y values starting from Station 113 and created a line chart.

I applied an third order polynomial equation to the line chart with a scientific value to 5 decimal places to increase the accuracy.

I recalculated the values of the Y ordinate to check that the formula produced an accurate result; shown in red. As you can see the resulting values are very close to the original Y values.

The last X value is the projected value I want to calculate to achieve a “close to zero” Y coordinate thus by definition being the calculated “point of convergence”. This value is 9518mm (374.725 inches) which compares quite well with the Wind Tunnel drawings showing this to be 92*4=368 inches.

Should I recreate this exercise but instead use a fifth or sixth order polynomial equation I am quite sure the resulting value for the point of convergence would be closer yet to the scaled up wind tunnel value.

Normally for this type of exercise I would work with tangent lines and the start points of the upper and lower fuselage lines from predefined Shoulder Points.

This was a bit of fun just to demonstrate how we can use the power of spreadsheets and mathematical equations to assist with developing our Cad designs.

Bf 109Update: I decided to play about with this a bit more and had a look at the fuselage lines for the Bf109. I don’t have the design “point of convergence” for comparison but decided to do it anyway to find the convergence between the Lower and Upper fuselage lines.

These points are measured from a ground datum at 800mm below the fuselage reference line.

The stations/frames are from 2 – 8 inclusive. As you can see the calculated values verify the existing ordinate dimensions with the projected “point of convergence” calculated at 4832mm from station/frame 2.

These are the fuselage lines on the vertical plane which in theory should share the same convergence point for the fuselage lines on the horizontal plane (technically plan of max width)…an exercise for some other time!

What is even more interesting is that a line equation can be used to generate a spline in both the Inventor & Solidworks cad products… as a check to verify the cad work this is enormously useful!

2015-08-01_00-02-16Another example of application would be for the frames or station profiles.

In this example I have applied a polynomial equation to a set of ordinates for the top section of station 300 for the P-51 Mustang.

This needs a full profile as an arc to achieve an accurate result, which I’ve applied as a sixth order polynomial…you cant get much more accurate than this with Excel!

Ideally we would wish to extend this arc to the max width ordinate, which would add another negative ordinate (below the base line) to the graph…for some unknown reason Excel finds it difficult to compute an acceptable polynomial with 2 sets of negative values, so I would have to transpose the ordinates accordingly.

The Mustang ordinates induce a minuscule negative curvature on the top rear fuselage frames when you create a CAD profile just using the ordinate values from the NAA drawings. Its not detrimental in anyway but it is rather annoying…so to obviate these issues I could utilize a polynomial solution to adjust the ordinates to get a positive curvature. The adjustment is micro millimeters, but hey that’s the way that CAD works.


Mustang P-51CAnother Update: Out of curiosity I recalculated; to a higher degree of accuracy; the upper fuselage line for the P-51 and contrasted that with a similar calculation for the lower line of the fuselage.

The calculated point of convergence of both lines based on a 4th order polynomial to 5 decimal places is at 9375mm and slightly above the fuselage reference line at +18mm. Factoring in error based on the original ordinates being accurate to 1/16th inch and possible error as a consequence of a higher order polynomial I think this is a reasonable result. Its interesting to note the variation with the results we got before.

This is certainly closer to the expected values based on the wind tunnel data. The squiggly line by the way on the lower part of the fuselage is the plotted max half breadths; which is rather interesting!

Confirmation; have received confirmation that the intended point of convergence for the upper and lower fuselage lines is at Sta 368, which is at 9347.2mm…this is great!!

All CAD profiles included in the P-51 Mustang Ordinate Package now available. Refer promotion here.