L.J.K.
Setright
THE
THIN EDGE OF THE WEDGE was at just about the right height to chop off a USAC
official at the ankles; and at a maximum slicing speed of 198mph on
Indianapolis, the Lotus-STP contender should have cut clean. Whoever won and
whatever happened after Spence’s death the Lotus-STP contender will still repay
close examination – a flying scarlet slice two inches linger than a Cortina,
one inch narrower in the track than a Toronado and probably faster round
corners than anything that has ever been built before.
On
the day when I saw The Wedge, a day that began with an urgent telephone call
rousing me from my bed and summoning me to Hethel. Hill was only reaching a
mere 170mph down the straight of the private test track adjacent to the Lotus
factory. On the other hand the car was proving decidedly skittish because it
was running on tyres that were new and unscrubbed, their treads not yet flat
and so far making contact with the road over less than 80 percent of their
considerable width. To tell the truth, those 12.75 by 15 Indys looked a bit too
wide for the 9.5in rims to which USAC regulations limited the car, but all the
monumental tractive effort had to be got through to the road somehow and an
ample acreage of stable tread rubber was the only way.
For
much the same reasons the car was a four-wheel-driver, with ideas by courtesy
of Harry Ferguson Research Limited. Superficially the transmission layout might
have had a lot in common with the Jensen that we all know and love, but the
detail differences were surprising. The Lotus, with its 50/50 weight
distribution fore and aft, also had 50/50 distribution of torque – unlike the
37 front / 63 rear arrangement of the Jensen and other four-wheel-drive cars.
More surprising still, the third or center differential was not of the
limited-slip variety, apparently because it just didn’t seem to be necessary.
More accurately, it was not operating as a limited-slip diff but could be made
to do so just by movement of a lever. According to Maurice Phillipe, the
French-sounding Londoner who designed the car, they may get round to that in
the future, and may even experiment with different balances of torque front and
rear; but basically he believes in fair shares for all, and in giving the front
tyres as much work to do as they can take.
Phillipe
has been chief designer of Team Lotus racing cars since 1965, and it is
interesting to find that he is not too keen on overdoing torsional stiffness of
the hull structure. There are all sorts of good reasons for making a car as
stressed-skin pseudo-monocoque, but high torsional stiffness is not necessarily
one of them. The Lotus-STP Indy car rated about 3000 lb/ft per degree, a lot
less than the incredible 35,000 claimed for the SPT-Paxton turbo car that so
nearly won at Indy in 1967. Phillipe does not believe that figure, which is
certainly an extraordinary one; the 1966 Mallite McLaren was quite exceptional
among racing cars in having a torsional stiffness of 10,000lb ft/deg, the Lotus
33 better than average at something like 2400. Jack has shown us the way,
said Phillipe, reminding me of what the Brabham designer Ron Taurenac told me
18 months ago: the stiffer you make your chassis the more precise your
engineering has to be, the more perfectly balanced your springing, the more
consistent your damping, the more difficult in sum to keep all four wheels on
the road through a fast bend – and if a wheel is not on the road, what good is
it?
What
indeed? Never mind the tractive effort, never mind the cornering power, the
driver of this car was going to need his brakes, and it would rather help if
the tyres were on the road at the time.
At
least those front brakes did have an advantage denied to most other racing cars
in that they were connected by a differential, one of the ancillary benefits of
four-wheel-drive. The differentials at the front and rear were ZF multiple
affairs built into spiral bevel final-drive gearboxes by the same manufacturer.
Phillipe said that they had not been set to lock up fully on the first car,
meaning presumably that they had not been given that degree of preloading in
the clutch plates that is optional in a ZF diff. This is rather surprising, for
clutch pleat preloading is the only mode of slip-limiting in the ZF disc
differential that is not dependent on a degree of reaction at the axle shafts,
so it is the only thing that prevents one wheel spinning wildly if it becomes
completely airborne. Either I misunderstood the man or else the Indy surface is
really smooth.
Certainly
the suspension of the Lotus should have been able to iron out bumps: total
wheel movement was no less than seven inches, though the car as presented for
examination at Hethel could not have been properly set up since the front
springs at static deflection wee so long as to leave no ride height adjustment
available, the abutment collar round the concentric damper being at the very
limit of its thread travel. Even so, the thin end of The Wedge was getting
noticeably nearer to the ground under braking; and if the car were lowered much
further it could always been used for sweeping up the pits after the race.
What
the nose didn’t scoop up the air intake for the oil cooler would, for it was
beneath the driver’s seat, the heat exchanger matrix being beneath the small of
his back and the air finally emerging from the same cowling as did the engine
exhaust. Vanes in the duct turned the exhaust somewhat backwards, so that as
well as providing some downthrust to keep the car on the road they produced
some forward thrust as well; this cannot have amounted to a great deal,
however, since the total residual thrust of the exhaust gasses after they had
given up most of their energy to the turbine was only about 60lb.
Something
rather more forcible that that is necessary to make sure that the car never
showed any tendency to become airborne, even at the highest speed of which it
was capable. This is why it was wedge-shaped; not merely to provide the sharp
nose and blunt posterior that are fashionable, but also to ensure that no
aerodynamic lift was engendered by the passage of the body through the air at
high speeds. I am bound to admit that the shape of the Lotus caused me no
little satisfaction, for it is just two years ago that I suggested in the pages
of CAR that an awareness of what aerodynamicists call area-rule theory should
govern the design of the high-speed car body, and that a wedge shape seemed
most appropriate to the cars designer’s needs. Since then, Messrs Marsh and
Adams have produced the sports-racing Marcos prototype of satisfyingly
cuneiform shape, and now here was Mr. Phillipe admitting that the
cross-sectional area of the tyres, being greater than that of the body, forced
the air to accelerate over the nose of the car and thus create a region of
relative low pressure, so that the shape of the Lotus was (despite the marked
negative incidence of the wedge) only just succeeding in allaying the onset of
positive aerodynamic lift at the front.
While
we are on the subject of aerodynamics, it might be worth wile reminding
ourselves of the virtue of the NACA type of air intake, increasingly common on
racing cars and serving on this Lotus to lead air inside the body to a heavily
lagged plenum chamber from which the engine could inspire. Before the invention
of this peculiar flush intake of approximately triangular planform, aircraft
designers were forced to build air intakes for the then new jet engines as
great ugly protuberant snouts whose forward-facing apertures were at some
distance from the flanks of the fuselage so as to avoid the choking effect of
the boundary layer of air close to the surface of the fuselage. The NACA intake
presents no frontal area at all, but is of such a shape as to strip away the
interfering boundary layer, rolling it up into two vortices that conveniently dive
into the hold at the last moment along with the greater mass of faster-moving
air which pushes its way in without impediment. This extremely cunning design
found its way from jet aircraft to the flanks of one or two streamlined
motorcycles in 1954, and was then taken up by Connaught for their unsuccessful
streamlined Grand Prix car. Vanwall really put it on the map among
four-wheelers, and very soon after that it made its Lotus debut on the bonnet
of the Super 95 Elite. Nowadays you find it all over the show, but very seldom
is it aligned with local airflow – more often it points dead ahead regardless
of what the air is doing.
There
was not much danger of anything so meretricious appearing on the Indianapolis
Lotus. Nearly everything was as it should be and where it should be, though
there cannot have been much merit to having the breather from the
final-drive casing exhausting into the driver’s compartment and it was a little
disquieting to observe the presence of two large steering dampers. In almost every
other respect the car was of compellingly beautiful design and construction;
its only too easy to make glib references to aircraft standards of manufacture,
but in this car such standards were certainly being approached. Design
ingenuity and manufacturing skill had gone hand in hand: witness the main
longitudinal transmission shaft linking the central differential to those at
front and rear – it was free to flex, yet there was not a universal joint
anywhere in it. Here were shades, if you will, of the solid-shafted V12 Grand
Prix Mercedes-Benz of 1938/9. The 1939 car developed nearly the same maximum
bhp as did this turbo-shaft Pratt and Whitney STN 674 turbine, and remained the
world’s fastest racing car from its inception until 1951. Had it ever been
taken to Silverstone, it could have lapped the circuit at about 101 mph; but of
course the Lotus Indy car could have gone much faster than that. In fact during
early trials it lapped Silverstone faster than it had ever been lapped before,
with poor Mike Spence hopping out of his BRM and into the Lotus at every
possible opportunity and ending up lapping a second faster than Hill. All that
two-pedal driving of the Chaparral could have been so useful to him…