Peter Elleray & Gene Varnier - On The 2003 Bentley Speed
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
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.
So why 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
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.
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.
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 of work.
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
GV (right): The new chassis is bigger but the weight
is the same as the previous model.
Why is the chassis bigger?
PE: The redistribution of space for machinery and
man. The bellhousing got shorter, the chassis got longer.
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.
Is the engine
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.
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 or performance?
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
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 front bars.
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.
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.