Alan Lis has the technical back ground to do justice to this
side of the sport. We posted this item during Le Mans
week 2003: it does help to explain why the Bentleys were
about to do so well.
Elleray & Gene Varnier - On The 2003 Bentley Speed 8
Bentley has produced an all new race car for the 2003 Le
Mans 24 Hours. Peter Elleray, the team’s chief designer,
and Gene Varnier, the assistant chief designer, spoke with
Alan Lis about the project – at the Le Mans Test Day.
We’re posting this to coincide with Tom Kristensen’s
provisional pole lap of 3:32.843, on June 11.
did work start on the 2003 car?
Elleray (right) : Probably a lot longer
ago than most people realise. Proper design work started in August
2001 but I had a scheme for a new car even earlier than that,
before the 2001 race, that didn’t get ‘fleshed out’ until
after that first race. It was a very basic layout that didn’t
really look like the 2003 car, but most of the ideas like running
torsion bars at the rear (and everything else for a smaller rear
end) were pretty much in place from day one. In August 2001 Gene
drew most of the rear end and I did an early layout of the chassis,
which subsequently changed a bit, but the basic front end with
torsion bars and dampers was on that original scheme. The shape
of the cockpit and the aerodynamics changed a bit after that,
once we got into the wind tunnel, but the basic concept was there
at that time.
has it taken so long to produce a car?
PE: A decision was made to update the 2001 car
for the 2002 race so that occupied everybody’s efforts
for about six months.
Gene Varnier: We didn’t get back into
the new design until February 2002 because we had to wait for
the go ahead to do a complete new car, but by May 2002 we were
doing wind tunnel work for the new car.
the 2003 Bentley differ from the 2001 and 2002 models?
PE: It’s the next generation car and it’s
very different from the previous models, with the main influence
coming from what’s been going on in the design of open
top prototype cars - particularly in the management of the air
exiting the front diffuser and trying to make that work on a
coupe body with doors. Of course the mechanical design had to
be reworked for Michelin tyres.
GV: In fact I had schemed and detailed uprights
for Dunlop tyres and issued the drawings before the Michelin
deal came along, so we had to stop that work and revise the geometry
for a new tyre manufacturer. The changes needed to produce the
characteristics required by the Michelins meant new pick up points
on the gearbox and the chassis and manufacturing was already
fairly well progressed on those elements by then.
car is obviously a departure from the previous model in the
aerodynamic approach. What advantages has this provided?
PE: The aerodynamic package is such that we
can run the car in a lot of different ways. We can use more downforce
with same drag as the old car, low drag or a range of other options.
In aerodynamic terms, the old car was limited by its front end:
the new car has a front end that can offer a lot more if we choose
to use it or we can trade it off for running a lot less drag.
The 2003 car is a lot less sensitive to ride height and rake than the old car.
It probably has lower reserves in terms of cooling, the older car was well
over cooled, while the new one is closer to the edge in that respect.
was the wind tunnel programme done?
PE: At the Swiss Aircraft Industry tunnel in
Emmen. The team doesn’t have a dedicated aerodynamicist
so I did that work myself. If you have a good look down the Le
Mans pit lane it’s clearly nothing revolutionary. We had
some help from Audi with collecting test data but as far as coming
up with an aerodynamic concept and developing it, I did that.
gains have you made in efficiency over the older car?
PE: I wouldn’t like to reveal any figures
and in fact it would be difficult to do that because in some
parts of the aero map big gains have been made, in other parts
less or no gain. The old car was pretty respectable in the Porsche
curves, which is the high speed aero part of the track - and
on top end - but there were other areas that weren’t as
good as they could have been so those were where we did a lot
new front end configuration, with air flowing through the
front suspension, arrived at early on in the design process?
PE: I had two options and that was one of them.
On a coupe with a wider chassis and a turbocharged engine, you
have a limited amount of space for coolers. You can’t just
strap a bigger radiators on because you don’t have a sufficient
head of air. Really the design decided itself, if you are not
going to take your cooling flow from where we had it on the original
car, you end up either taking all the air from the front diffuser
or creating other holes. If you do this, the only place you have
holes is through the front suspension.
structural differences between the 2001-2 and the 2003 cars?
Presumably you have to have a wider footbox for the 2003
car because the rule regarding that has changed since the
first car was introduced?
Yes, but it’s difficult to actually see that it’s
wider in that area even if you stand the 2001-2 car next to the
2003 car. You do have to have a certain width of footbox at the
line of the pedals, but the rules do not define their position
relative to the front wheels. So long as you have the required
width at the pedals you can continue to narrow the structure
ahead of it.
other structural differences?
PE: The chassis is built in a different way
to the previous car. Instead of being made as upper and lower
halves, it’s more of a single unit with added roll hoops.
It’s somewhat similar to an open top car and its structure
is much stronger than before. It passed the roll hoop deflection
test far better than the original car did. After the test the
2003 chassis was unmarked, whereas the original chassis, although
it passed, needed remedial work afterwards.
GV (right): The new chassis is bigger but the
weight is the same as the previous model.
Why is the
PE: The redistribution of space for machinery
and man. The bellhousing got shorter, the chassis got longer.
makes up the main structure of the car?
PE: It’s very much like a formula car,
as are most of the cars in the Le Mans pit lane. There’s
a central chassis which houses the driver and fuel, and a nose
box with the front diffuser instead of a nose box with a front
wing, as you would have on a single seater.
engine installation stressed?
PE: In the new car the engine is fully stressed
as it has been in the Audi R8 since 2000,. On the older car there
were support tubes linking the top of the rear chassis bulkhead
to the bellhousing.
GV: The old car needed the tubes because of
the layout of the chassis structure and the engine.
PE: The rear bulkhead of the new car is smaller
and that places the engine mounting points closer to the outside
of the tub, which makes for a stiffer installation.
regard to the suspension, the use of torsion bars on F1 cars
is typically to address packaging issues rather performance
issues. The original car had torsion bars only on the front
suspension, the new car has them at the front and rear. Packaging
GV: Packaging. We wanted them at the rear of
the car so we could get the rear deck as low as possible. That’s
the primary reason but if you weigh everything you probably also
get a slight weight advantage by using bars rather than coil
springs. The way we have them arranged is a fairly compact design,
which we first came up with for the front suspension of 001 (the
original car) in which the layout of the front of the chassis
was so compact that there was no room for coil springs.
the bars arranged? Some F1 cars have them running vertically
through the bellhousing.
GV: The system we have uses some of the same
components as we have in the front suspension. The principle
is the same. The bars sit horizontally on top of the gearbox
and are angled at about 30 degrees from the car’s centreline
when viewed from above. They are as easily adjustable as the
are the dampers located?
GV: At the rear they are inside the bellhousing,
again for packaging reasons to help keep the installation as
compact as possible. Right from day one we made sure that there
was good provision of cooling air for them. Positioning the dampers
in the bellhousing is actually quite an old idea: the 1980 Lotus
81 F1 car had that arrangement and when I was a Team Lotus soon
after, that design feature was carried on through a few more
models with no problems at all. So I’d say the principle
has been proved. Of course the Bentley is a closed car but it’s
not that difficult to make sure that you have decent cooling.
PE: There were many other things on the car
that we were more nervous about.
changes have been made to the gearbox?
GV: The casing is a reasonably thorough modification,
mainly due the fact that using torsion bars meant that we didn’t
need to make provision for rocker pickups. The rear wing mount
is completely different to the old car so that had an influence
too. It’s mounted on a transverse beam that attaches to
the back of the gearbox, a bit like the Lotus 79 F1 car. Internally
we’ve gone to a version of the standard Xtrac lubrication
system – the one they’ve been running on their customer
gearbox. On the original car we didn’t feel we needed that
system but when we looked at it again for the new car we decided
that some of the temperatures could be reduced by the increased
oil flow that the system offers.
The gear cluster itself is effectively the same, but with a few small modifications
that have made the shift a bit quicker.