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Once a 19th-century railway route, Catesby Tunnel is all set to revolutionise aerodynamic testing in the UK

By Matt Bird / Saturday, 3 September 2022 / Loading comments

For decades now, what the public sees of aerodynamic testing has become very familiar. There’s a static car in a chamber, fan gusting wind over it to indicate how the vehicle carves through the air. A good deal of faith has been placed in the procedure, though obviously in the real world a car doesn’t remain still the whole time. What’s needed to accurately measure everything studied in a wind tunnel – set to become even more important as far as EV range is concerned – is a real-world wind tunnel with lab-controlled conditions. Catesby Tunnel looks set to be that facility.

A few miles from Daventry, the tunned was first used by steam locomotives in July 1898. As was the thing for Victorian engineering, it was on an epic scale: 30 million bricks were used to build Catesby, which measures a perfectly straight 2.7km in length, with a cross-section 8.2m wide and 7.8m high. Closed to trains in 1966, the tunnel has just undergone a multi-million-pound transformation by Aero Research Partners, which includes laying a dead flat road surface, to make what’s described as a ‘state-of-the-art aerodynamic vehicle testing facility’. It’s the first of its kind in the UK, and only the second in the world. 

Essentially, it aims to be the best of both worlds. Catesby Tunnel is the real world (as opposed to it being mimicked in a conventional wind tunnel) but allows for the atmosphere to be controlled in a way that’s never possible with weather and wind changes in the actual real world. And, well, if it’s good enough for Multimatic to book out a whole chunk of testing time then it must be good. And not just conveniently located near its Brackley UK base.

To prove the point, Multimatic has already been to Catesby Tunnel with Andy Priaulx and a Mazda RT24-P. Done 120mph in it, too. The important discovery, however, was that the aerodynamic data from the tunnel showed ‘a high level of correlation to that existing performance data’, the stuff taken from CFD development, full-size wind tunnel testing and actual races. Which is encouraging.

Over to the professionals for an expert view on the old Victorian tunnel. Larry Holt, founder of Multimatic no less, is in the video. He said: “Compared to conventional wind tunnels, this is better because it’s real… In a moving ground plane wind tunnel, the car is stationary and the wind is blown over it by a massive fan and flow conditioning set-up, and a belt is arranged to move under the car at a coordinated speed.  It’s a very sophisticated configuration but the car is still stationary and that constitutes the not totally real piece.  What Catesby facilitates is the measurement of the aerodynamic performance of a vehicle actually moving through the real world.”

“The problem with a car moving through the real world is that it is subjected to influences like gusting wind, rain and other changing environmental conditions that effect air density; all of the variables that come with testing in the real world. Catesby provides the real world without the weather. You have a moving car, a real road surface, a controlled environment and we can run 24 hours a day, whatever the season. It is a perfect 2.7kms of controlled atmosphere. That’s the kind of consistency you need when you are chasing incremental gains.” See, just like we said. Priaulx added that it was “odd to jump into a race car and drive flat out through a 2.7km tunnel” – rather him than us on that job.

Though Catesby Tunnel is open now, Multimatic has snapped up a lot of the available test time. Given its aforementioned proximity to Brackley and the plethora of motorsport operations close to Silverstone, it wouldn’t be a surprise to hear that the new facility is fully booked before long. What a brilliant thing. 


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