Tunnel Vision

Philip Porter takes 9600HP on an aerodynamic adventure 

There are few adventures, even to the adventurous, in this over-regulated, namby-pamby day and age. But I have just had one.

Like most things these days, it started with an email. It was, though, an especially intriguing one.

Would we, the Jaguar E-type Club, like to supply an E-type to evaluate its aerodynamic qualities in a tunnel, not a wind tunnel but a Victorian train tunnel?

This, though, is no ordinary tunnel: it never was, and it most certainly is not today. In fact, it is unique in the world.

Some background: the Catesby Tunnel, on the route of the old Grand Central railway main line, was built in 1897 because the landowner wished to preserve the landscape and keep passing trains out of sight. The tunnel is lined with 30 million Staffordshire blue bricks, is dead straight, flat and 1.7 miles long (2.7km). After closing in 1966, presumably when Dr Beeching swung his axe and decimated Britain’s rail network, the tunnel lay disused and flooded for more than 50 years.  

I offered my Fixed Head E-type, 9600 HP.

Driving down a very rural narrow strip of tarmac road gives no clue as to what lies ahead but takes one to the entrance to Catesby Tunnel. Not surprisingly, as this is a very serious, and rather clandestine, engineering facility, it is all very low key on the outside. Indeed, it is discreetly anonymous.

The car and I were ushered into a smart area with the appearance of an industrial unit. Here I was introduced to a succession of people who explained their roles including the fire crew.

I was given a safety briefing. A laser would be in operation as part of the test equipment, and it was emphasised that protective, heavily tinted goggles must be worn, to avoid going blind. The three-man fire crew assured me they would be on standby and if there was a fire, ‘We will come in and get you out’.

I could not help thinking that the car was rather more important than me!

The whole exercise had the feel of preparing to go on stage. And I was about to venture into the unknown to add a further certain frisson. Clearly danger was part of the cocktail.
Next I was driven through the tunnel in an SUV and the turntable at the end was demonstrated. The tunnel is quite dark with only minimal lighting. The surface is superb. 

At a certain point, we stopped and alighted at the halfway spot. This is where all the clever equipment lives, and I was given a demonstration. A squall of bubbles floated across the tunnel with the laser aimed at them. With the goggles on, there is little to see. However, watch it afterwards on a phone camera and you can see the bubbles which are green.

So, then the time had come for my solo run in the E-type. Engine fired up. Goggles on. The entry gates were opened and we were ‘released’.

I had been instructed to stick to 60mph which proved quite tricky because, with the heavily tinted goggles on and virtual darkness all around, I struggled to read the speedo.
Also, it was not overly easy to realise where you were in nearly two miles of dark tunnel, a statement that sounds rather inane. The ‘action point’ where the bubbles emerge was tricky to spot but I was also keen to film it so held my small video camera in my left hand. I had no idea whether I had caught the green mist as, with the goggles on, you have no idea but I was pretty confident I had passed that location.

Shortly after I saw the distance boards which gave a countdown to the end of the tunnel. I slowed and parked carefully on the turntable. I had been armed with a small device which I pressed to revolve us back into line to make the return run.

This done, I was asked to do a second run for the photographer. Perched in the back of a suitable vehicle with an open tailgate, he had a very bright lamp pointing straight at me. Again with the goggles on that was particularly challenging as, blinded by the light, it was not easy to see the photographer’s vehicle just a few feet in front. Furthermore, I could only see his hand signals – closer, move left, move right, closer still… – when his hand wafted in front of the lamp. Nevertheless, we succeeded, and he seemed happy.
When I could, I was also taking stills through the windscreen, and by reaching out of the open side window and pointing in the vague direction of the front!

With the runs completed and the data captured, I departed this amazing set-up and headed for home, about an hour and a half away. The conditions were appalling with exceptionally heavy rain. As I steamed up the outside lane overtaking all the modern cars, I could not help reflecting how Sayer’s inspired work had allowed the Jaguars at Le Mans to dominate thanks to the speeds they achieved on the 2.5-mile long Mulsanne Straight.

Some weeks later, I received the results for the tests and appraisal of the E-type design. Of course, much of the data is far too technical for me, and I suspect, most members.  
‘The side velocity section shows,’ stated the findings, ‘that the car flow is largely attached, which is a credit to the designer, which was designed using such primitive methods such as wool tufting.  The thickening of the boundary layer, entrained air and flow circulation can be seen from the velocity vectors. It should be noted that this flow separation and recirculation is significantly less than the majority of modern day cars, particular with the trend surrounding modern SUVs.

‘The tear drop or airfoil type shape tends to accelerate the air over the top of the vehicle and the fastback type rear end of the vehicle results in a downwash at the back of the car. This velocity and pressure differential leads to two counter rotating longitudinal vortices. The airfoil shape allows the E-type to be relatively low drag but that could lead to the production of unwanted lift and decrease the stability.

‘The largest energy losses within the wake are the result of the wheel wakes and vortical structures.  Modern techniques allow us to visualise these losses and help improve the efficiency of vehicles further.’

So, there we have it, assuming this technical talk makes sense to you.

In an ideal world, we would compare a Fixed Head with a Roadster, and the E-type with its contemporaries, and with more modern machinery. However, at a daily rate of (from memory) something like £25,000 to hire the facility, including the crews, that is not likely to happen, alas.

The significance of the images are, I have to say, way beyond me but, and the engineers would probably be appalled by this statement, they make great art.

It was all a tremendous experience. More importantly, the results appear to flatter the E-type and only add to the aura of Malcolm Sayer’s stunning E-type design.   

By Philip Porter