- This is test one.
The Catesby Tunnel in Northamptonshire, England
used to be for trains.
It was built by the Victorians in 1897,
but fell into disrepair after the line that went through it
was closed in the '60s.
It was abandoned for many years,
but now it's a vehicle testing facility.
You know a wind tunnel?
This is a more realistic version of that
where the air isn't moving, but the car definitely is.
- So Catesby Tunnel is 2.7km long.
It's got a cross section of 42m², perfectly straight.
It's quite an amazing feat considering
the Victorians built it without a laser level.
Obviously the surface of the earth is curved,
but Catesby Tunnel is flat.
So if you put a laser line along it,
we're within 3mm of being off that laser line.
But when we first inquired about repurposing Catesby Tunnel,
it was totally derelict.
They'd ripped up the track, they'd taken away the ballast,
they'd destroyed the drainage.
So at the far end,
the tunnel was actually knee-deep in water.
There were no facilities or utilities here.
There were bats living within the tunnel
that we had to tread carefully around.
So at the far end of the tunnel, they've actually got their own "bat hotel".
When we test outside,
we've got the wind, we've got the rain, we've got other vehicles,
we've got lumps and bumps in the road.
We want to remove those and make this controlled a condition
as possible so that the test
is only seeing the changes that we're looking for.
- We're doing a "coast-down test" here.
Julian got the car up to 130km/h,
very quickly(!), and then he took his foot off the accelerator
and just let it coast in neutral.
This tunnel's long enough that there'll be a couple
of minutes before he has to touch the brakes.
From that, you can work out the drag and friction forces,
which is really useful data for car manufacturers.
- Because Catesby Tunnel is a bit different to a normal wind tunnel,
we have to collect data on board.
We can't use GPS,
because we can't see the satellites in the sky.
The approach that we've come to is an image-based system.
- There's 1200 tags now in the tunnels
and they are 5m apart, and they've been surveyed
to within a few millimeters, each position.
And then we measure the time it takes
to go between each tag,
and that's picked up by this high speed camera
that's working a hundred times a second.
And that gives us a very high accuracy
for speed of about a hundredth of a kilometer an hour.
The tunnel is a fantastic place for this kind of measurement,
because there is no extraneous sunlight
and sunlight is very difficult to cope with
when you are working with infrared.
- But I said that this was test one,
and it was, I wasn't lying.
But like any video about cars,
you didn't see it from just one angle.
There were camera shots from all around the tunnel
to get different angles and keep it interesting.
There were shots from cameras that were attached
to the car with suction cups
for dynamic shots from almost impossible angles.
But this is a proper glossy car video.
We don't want to see those suction cup cameras from outside,
and beside, we've only got two of them,
and we don't want to see the camera operator
in the back either 'cause he's not there.
There's got to be a little bit of unreality to this
that no one will notice once it's all edited together.
So when I said this is test one, that is actually true.
This right now is test one,
but the shots from outside, we haven't filmed them yet.
We're going to have to go back and forth
in this tunnel 15, 20 times
before we've got every angle we need
to make this look interesting.
So I had a thought.
Do those cameras actually affect the results?
If you've got a camera on the outside of your car,
how much more fuel are you actually using?
How's that for timing?
- Good timing.
Spot on!
- Typically, we go out and back for a test
and average over both of those sections.
We have a turntable at each end.
The turntable takes about 20 seconds to turn around.
We don't have access at the far end of the tunnel,
so we have to turn around inside.
It saves doing an Austin Powers 37-point turn at the far end.
- So exactly the same test the other way.
- Yes.
- Okay.
Go for it.
- In order to get the best accuracy,
the driver has to be very consistent
and he has to do the same thing time after time.
You have to drive in a very straight line.
So any deviation, that adds to the distance
and the drag that the car's experiencing.
You can start off at pretty much any speed,
as long as it's above the start of your coast-down speed.
You want to let the car settle a bit,
because the moment you put it into neutral,
the car will start to rock backwards and forwards a little bit,
and all these little things all add up.
- Is that a garage door opener?
- It is. - Just for the turntable?
- Yeah. - That's nice.
- Smart.
- I feel like this needs the music from "Thunderbirds."
- So the whole idea of Catesby Tunnel
is to create constant atmospheric conditions.
We shut the doors at both ends
and we seal the tunnel
so that there's no wind coming through it.
Because we're surrounded by earth,
it actually means that the temperature within the tunnel
is within one or two degrees all year round.
We had the Aston Martin Valkyrie in the tunnel,
we've had cyclists in here during drafting,
which is fairly unique,
something that you can't do in other places.
One of the biggest issues is
what happens if there's an accident in the tunnel
and how do we get to them?
So throughout every test, we have a fire safety team on site.
They're there to respond if there is an accident.
- There is a very slight gradient to this tunnel
and while I'm sure some of the marketing team
would be very happy if it was perfectly flat,
turns out there is a little bit of an advantage
to that gradient,
because drag increases with the square of speed,
but friction increases linearly.
So if you have one test going very slightly downhill
and one test going very slightly uphill,
in theory you can separate those two factors
out from each other with a lot of maths
that I do not understand.
- The Catesby Tunnel surface is an asphalt surface,
typical of an A-road that you would see outside,
but just finished to as high tolerance as we can get.
- I do like how you stick
to one side of the tunnel, like it's a two-way road.
- It just seems wrong barreling that fast
down the center of a road.
- Yeah.
- And also, for consistency,
for the aerodynamic wake.
- Oh of course, it'll be different depending
on where you are in the tunnel.
So I've been kept in the dark for about 20 minutes now
while you wrangle data.
What do we have?
- Well, this is an example of one of the coast-down tests.
The dark blue line is the speed.
So that's us accelerating rapidly up to 130,
then pop it into neutral and then coast down to about 40.
- And then brake so you don't hit the barrels.
- And then brake so I don't hit the barrels.
- So we had four or five runs with a clean car.
- Yeah.
- We had five, six runs with the GoPros
in varying configurations.
So we've got some sort of drag from some sort of camera.
- Yes, exactly. - Alright.
- And you can see, from 130 to 120 kilometers an hour,
it took 7.04 that time and 7.03 that time.
So a hundredth
of a second difference. - That's so close.
- You wouldn't get that outside.
- Yeah. - It just wouldn't happen.
And then with the GoPros on,
from 130 to 120, took 6.98 and 6.97.
Again, hundredth of a second difference.
- Yep. - Incredible.
But there is a very noticeable difference
between having a clean car
and when you've got the GoPros on the outside.
It's measuring just a small difference of about 0.8% between the two.
- And does that map to fuel usage?
- Yes. - And this is not the most scientific test.
We did a couple runs, the GoPros were all over the place,
but there is enough drag from them
that you can measure it in there?
- Yes. - And there would be some effect on fuel.
- Yes. Now of course, we were using the ideal car for this test,
because the weight doesn't change from test to test.
- Right, it's electric. - Whereas,
in a fossil fuel car, of course, you've got to make sure
that you don't let that tank go too empty.
And there's lots of things you have to take into account.
- Yeah. So there's roughly 0.8% more drag on the car
from sticking a couple of GoPros somewhere.
- Yes, absolutely.
- That's the closest I've got to science in a long time.
Thank you very much.
- No problem. Thank you.