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Recreating a 20th century car using 21st century technology

XJ13, Building The Legend, Jaguar

My intention was to create a facsimile of Jaguar's unique XJ13 - as it was in 1966/67 and before it was rebuilt in 1972/73. It had to be rebuilt after it was badly damaged on the eve of its first public appearance in 1971. My aim was to recreate the car as faithfully as I was able and as a tribute to the genius of its designer, Malcolm Sayer.

During the rebuild by Abbey Panels in 1972/73, certain aspects of the car were altered and it lost its "pure" form as originally envisaged by Sayer. One of the more obvious "enhancements" was the addition of flared/widened wheelarches. The XJ13 log records this was done primarily for "cosmetic reasons". There are many differences between the car I wanted to recreate and the car as it stands today.

Undoubtedly, the current car is unique and has continuous history linking it back to the one and only original. It may have been described as a, "Jaguar-built replica" by authors Viart & Cognet in their 1985 book, "Jaguar - A Tradition of Sports Cars" (page 318), with forward by William Lyons himself, but I personally feel this may be a little unfair as most of the underlying structure was salvaged and re-used (with the exception of certain floor and sill sections - the original sections were originally painted black and are likely to have been been replaced). The engine installed in the car today is a different engine to the one originally installed in the XJ13 in the Spring of 1966 but it remains one of the very few prototype quad-cam engines that have survived and was installed in the car in period. OK, the body may be completely new, and different in some respects to the original body, but there can be no doubt that the car gracing the Jaguar Heritage collection can describe itself as the unique Jaguar XJ13.

What I am attempting to create can only ever be a facsimile and homage to the original XJ13 and its designer Malcolm Sayer. There is, and always has been, one Jaguar XJ13.

So - how to set about recreating a car which doesn't exist anymore?

Contrary to what you may read from certain replica manufacturers over the years, there are no "blueprints" for the car. Jaguar, on their part, have never allowed sufficient access to the car to enable detailed measurements to be made. Again, this is despite statements to the contrary by certain replica builders. Indeed, a replica made by the very talented Rod Jolley which passed into the hands of the late Jaguar Specialist Tim Waddingham, bears a brass plaque claiming the replica was produced "with the co-operation of Jaguar". The inaccuracy of the replica compared to the original bears testament to Jaguar's unwillingness to allow intimate access to the car. The closest anyone got to the car may have been Bryan Wingfield whose car eventually ended up in the Walter Hill Collection. However, this car was notoriously "wrong" in may details - including a rather "snub-nosed" appearance. The latter does indicate how difficult it is to replicate the complex curves of the car simply by reference to photographs - even with privileged access to the car itself and for a man with undoubted car-making skills.

OK - there are no "blueprints" and no chance Jaguar will allow sufficient access to the car so where do you go from here?

Fortunately, Jaguar Heritage very kindly granted me access to XJ13-related documents in their archive. However, although the archive is now professionally managed by Anders Clausager and his team, this has not always been the case in the past and many documents may have gone missing in the intervening years. Although Jaguar Heritage's archived documents give valuable clues to the car's build and history, I have had to dig deeper and extend my search further afield. A breakthrough came the best part of a year ago when a collection of original documents came to light containing actual data describing the original car's construction. This has since been supplemented by previously-unpublished photographs taken during the car's build in 1965/66. It is my wish to eventually deposit these documents in the Jaguar Heritage Archive for the benefit of future historians.

What are these documents exactly?

These documents contain critical measurements used by Jaguar to build the car. They are likely to have originated from Malcolm Sayer himself. Just to explain ...

Malcolm Sayer, as I reported in a previous post was very much a man “ahead of his time”. There is much talk nowadays of Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) but it seems that as early as the 1950s Sayer had developed his own longhand version of similar techniques. He kept his calculations and means of representing complex shapes mathematically very close to his chest and there is little information on his methodology available today. Paul Skilleter reported that Cyril Crouch, who worked in the Body Drawing Office in Sayer’s time, recalls him “using Chambers seven-figure log tables to calculate all the shapes, as one would do on a computer now.”

In essence, these documents consist of a mass of numbers defining fixed points in 3D space. For example, a particular single point on a body surface can be defined as:

"X inches from an origin on the floor at the front of the car; Y inches up from the floor; Z inches from the centreline of the car"

As an example of data for one part of the car, the following original document indicates how the curvature of the windscreen was defined.

XJ13, Building The Legend, Jaguar

Original data - definition of outer windscreen surface.(Data obscured). © Jaguar Heritage - reproduced with permission.

At the start of my project I discovered that Pilkingtons claimed to have located the original metal jig used to manufacture the original 1966 XJ13's windscreen. I commissioned a windscreen from them and this gave me a unique opportunity to objectively validate their claims against the original data. The finished windscreen was digitally scanned and it's precise shape was captured.

XJ13, Building The Legend, Jaguar

Digital scan of windscreen made using Pilkington's original XJ13 windscreen former.

We then superimposed the 3D points defined in the original Jaguar document. We were then able to carry out a statistical comparison of the two sets of data. During this analysis we discovered that Sayer had defined the windscreen as sitting a rather strange 32.39 degrees from horizontal. The conclusion was that Sayer found, "wherever the windscreen laid within his overall body profile was correct". More detailed analysis showed a close agreement between the windscreen Pilkingtons had produced and the original Jaguar data. The following picture shows the variance between points on the two defined surfaces - the closer to red, the bigger the difference:

XJ13, Building The Legend, Jaguar

Comparison of the new windscreen vs original Jaguar data.

The data is shown below:

MAXIMUM DISTANCE: +1.79mm -2.18mm
AVERAGE DISTANCE: 0.06mm
STD DEVIATION: 0.30mm

In short, there is an average of 0.06mm difference between the new screen and the original data - pretty good don't you agree?

This was very good news for me as it meant we could precisely locate a key section of the outer body. But more was to follow .... similar data describing original car's body shape, as well as data precisely identifying key location points for things such as steering rack, front and rear suspension, suspension arms, shock absorbers etc etc was uncovered. The latter data has proved especially invaluable in the design and ongoing build of the complete chassis/monocoque unit.

Here is an example of the type of data that shows where key components are located. It shows the precise location of the XJ13's upper front wishbone (wishbone as used in the 1964 Lightweight E-Type Jaguar). I have obscured the actual 3D data points.

XJ13, Building The Legend, Jaguar

Original document describing location of upper front wishbone in 3D space.

The above data doesn't only describe exactly where the wishbone should attach to the chassis, it also gives valuable information on the dimensions of the chassis itself. Combining data such as this with original photographs such as the one shown below allows us to precisely model the front suspension.

XJ13, Building The Legend, Jaguar

Front chassis.

Putting all this data together, along with other measurement data and contemporary photos taken during the car's build have enabled us to arrive at an excellent digital CAD representation of the 1966 original. This data was been further enhanced by discussions with those who were present and participated in the original build.

So - where to from here?

All the above data was been used to enhance the digital model of the 1966 car. Gradually seeing the 1966 car emerge from the data was a rather exciting process. The first physical manifestation of the digital data has been the manufacture of a full-size buck which is being used to manufacture the car's monocoque.

We decided to build the monocoque in steel first, just to "get it right". This all-steel monocoque was destroyed and we built one using original-spec aluminium and steel as original.

Before I finally pressed "GO" and had the body buck manufactured, I commissioned a pair of 3D-printed models of the body - one in 1:18 scale and one in approximately 1:30 scale. It is all very well being able to see the finished car on a screen but I wanted to have something I could hold in my hand. I planned to paint the larger of the two so I can see how the light catches it and how the curves measure up to the original.

XJ13, Building The Legend, Jaguar

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