The Increbible Chaparral 2J
by Dick Rutherford
This article appeared in the 1970 program guide for the Monterey
Castrol GTX Grand Prix. It was reprinted from Corvette News.
The car you see on the next four pages
is perhaps the most incredible race car ever designed and built.
It's the new Chaparral 2J. It promises to revolutionize everyone's
ideas about race cars. Unless, of course, some spoil sports get
together and ban it.
The Chaparral 2J will generate more corning
power and more braking power than any Group 7 car today. And unless
othr Group 7 constructors follow suit, as they did with the wing,
the Chaparral 2J should continue to enjoy its outstanding edge
in vehicle design for longer than one season. And even if Hall's
competitors come up with a similar car in 1971, they still won't
have the benefit of Jim's testing and de-bugging.
The 2J is the result of Jim Hall's quest
for a new race car a vehicle project begun in the middle
of the 1968 season. The goal was deceptively simple: Find an "outstanding
edge" in vehicle design. The "outstanding edge"
is a design that will circulate any given race car faster than
The search for the outstanding edge took
Hall to novel spoilers and the celebrated wings. The main reason
for the wing was to generate downforce. Some automotive writers
wondered publicly in print why the wings were attached directly
to the rear suspension rather than to the body. Hall wanted the
downforce generated by the wing concentrated on the suspension
for greater adhesion. With this effect, he reasoned, the car should
be quicker through any given turn. When the winged and spoilered
Chaparrals ran right, they were. Mechanical failures kept the
winged beasties from proving the total worth of the spoiler concept,
and the structural failures of competitors' wings let to their
ban by the SCCA.
Wings and spoilers were one experiment
with downforce. Both, unfortunately, have severe limitations and
at best are only a compromise between aerodynamics and downforce.
The downforce generated at slow speeds is, in actual practice,
Another area of exploration was fourwheel
drive. It, too, was found wanting. As were other areas of engineering
research. The goal was to provide measurably more downforce without
affecting the aerodynamics and drag associated with wings and
spoilers. Not just aminute increase in downforce; a whole huge
hunk of improvement. Enough downforce to equal a minimum of 50%
more vehicle weight, without the extra weight penatly. What Jim
was seeking was the equivalent downforce of 1,000 or more extra
pounds without adding any weight. Sounds impossible.
The reason for the added downforce was
simple. To improve the tire adhesion. Not only in the corners,
where the quickest way through is best, but on the straights where
they accelerate and decelerate. Jim wanted to keep the car glued
to the track. A simplistic solution would be to add 1,000 pounds
to the gross vehicle weight. But who ever heard of a 2,500-pound
Can-Am car? Or, more absurdly, a competitive fully loaded cement
truck Can-Am entry? No, pure weight piled and heaped on downforce
all right, but when you try the first time to turn . . . or stop
. . . it's all over.
In search of elusive downfoce, previous
Chaparrals have sprouted front and rear spoilers, diviing planes
forward on the fenders, front fender vents over the tires, movable
rear spoilers, radiator air exits and fabled wing. All of these
experiments resulted in only small amounts of downforce.
Sometimes during the thinking process in
1968 the idea jelled about a ground effects vehicle, only in reverse.
Most people know GEV's will hover on a cushion of air and skim
over land or water. What would happen if the fans were reversed
so that instead of hovering, it clung? Novel. New. Untried. Off
to the computer to see what design parameters were involved. Programming.
Reprogramming. An explosion of arithmetic disgorged from the computer
to give Chaparral cars what they wanted to know. Jim Hall, his
chief vehicle engineer Don Gates, the talented crew have created
a car that clings, literally, with huge suction fans.
The 2J has tremendous amounts of static
downforce; more than 1,000 pounds of downforce on the tires plus
the static vehicle weight. The effect is the same as adding 1,000
pounds of weight for the tire adhesion without carrying that extra
weight with you during a race.
They made the rear portion of the car a
gaint vacuum reservior. Shirts extended from the bodywork to the
ground on all four sides, and cover the rear wheels, as the pictures
show. In the rear, behind the enlarged ZL-1 Corvette engine which
drives the car, are the two vane-axial fans powered by an additional
small two-cycle engine. When the fans are running the evacute
a large area under the car, and it's this suction which provides
the incredible downforce. The skirts, made of General Electric
Lexan, are articulated to move independently of each other to
maintain the best possible seal between car and ground.
Testing proved the idea. You could almost
say it works like sucking on a straw. Only instead of the 1/8"
area inside a straw, imagine a 5,000 square-inch straw. If you
could reduce the pressure inside the Chaparral "straw"
by only .18 PSI (that's point one-eight), you'd get about
900 pounds static downforce working on the 2J. And that 900 pounds
of downforce created by the suction works whether the car is standing
still or hurtling down a long straight. Add approximately 150
pounds of aerodynamic downforce created by the 2J's design at
120 mph and the net downforce effect exceeds 1,000 pounds, total.
The downforce figures were calculated at Midland, Texas, 3,000
feet above sea level. At courses closer to sea level, like Watkins
Glen, the net result should improve about six percent.
What's it like to drive? Well, it's different
because the cornering forces are greater than any race car has
ever generated. Jim Hall says this, "The 2J's major advantage
is that it will corner faster on low-speed corners, the ones that
are 30 to 90 mph in normal Can-am cars. these corners predominate
on Can-Am tracks. It means you can leave the corner faster, with
more speed, and carry that speed down the straight." Skid
pad tests at the chaparral car's test pad show that the 2J generates
.4 to .5 more "G" force with the fans turned
on than with them turned off. Hall: "At first, the 2J was
a real shocker! Side forces (in cornering) are really impressive.
Holding your head upright becomes extremely difficult. On a normal
Can-Am car you have to bend your head over about half-way to balance
the cornering force. In the 2J the cornering forces want to bend
your head right over. We're going to have to get used to it. I've
banged my elbows and knees on things I never used to touch. Another
change in the 2J performance over past models is the quickness
and directness in steering. You get a direct change in direction
when you turn the wheel. The downforce increases the contact load
betwween the tires and the road without increasing the mass (weight)
of the car. Steering effort is high and any little change causes
a significant side force."
All of this added downforce wasn't without
some weight penelty. That added weight comes from the extra engine,
the vane-axial fans, necessary skirts and ductwork. Another problem
is that the high G loads on the car put added stress on other
components. The 2J has been designed and tested to safely withstand
2G load in any vector and/or any combination. Cornering, for example,
combines G loads in at least two or three directions. As much
as 55 percent of lap time in a Can-Am race is spent cornering
and braking. You begin to see the magnitude of Hall's concept.
The suction has minimized another probelm
on every Can-Am car: too much power. Wheelspin can be induced
at any speed up to 150 mph on normal Can-Am cars. With the 2J,
the suction virtually eliminates all wheelspin, even from a standing
start. Drag fans, take note.
What about top speed? This static downforce
system adds little drag on the car while producing tremendous
downforce in aerodynamics over wings and spoilers. And since aerodymanics
are important to top speed, not using them keeps drag at a minimum.
Various combination of fans, drives and
auxiliary engines were experimented with, but the final system
uses two vane-axial fans driven by a two-cylinder, two-cycle JLO
(pronounced "ee-lo") auxiliary engine. This method was
preferred over driving the fans from the main engine because the
auxilary engine keeps the fan speed constant. If the fans were
driven from the main engine, fan speed would vary as the main
engine speed varied; so would the amount of downforce.
Naturally the question will be asked about
failures in the fan system. Failure of one fan during the race
results in less than half the downforce loast because the other
fan would speed up to partially compensate for the disabled unit.
In the event of both fans failing, of couse, the cornering would
Fan placement was experimented with, but
the final location was at the rear. Easy maintenance is a necessity.
The entire engine and fan package can be replaced in minutes.
Simulated failures have been programmed into the car testing.
The vacuum reservior loses its effect gradually, and allows the
driver time to take appropriate action. Tom Dutton, 28, will help
test drive the new 2J. Tom's career began, appropriately, in a
B Production Corvette in 1966. His most valuable asset to the
Chaparral program is his ability to drive and diagnose a problem
and fix it himself.
To make maximum use of all this downforce,
the widest tires made mount to the 2J. Three and one-half feet
of tire width will grace the rear of the new 2J car. The car brakes
better than any previous Chaparral, too. "I simply can't
believe the braking capability of this car." says Jim Hall.
"It feels like it will decelerate about twice as fast as
any Groulp 7 car I've driven."
The 2J has set a track record at Chaparral's
Midland track, where Hall tests each of their engineering tours
de force. And Hall casually remarked that he was not driving the
car at its full potential that day.
the computer played a role in skirt design,
too. In fact, a rivalry sprang up between the live, flesh-and-blood
engineers and the inanimate computer. The design resulted in about
two parts live engineer, one part computer. Horray for people!
The goal in skirt design was to run about 600 miles without maintenance.
The closer the skirt hugs the road, the better the suction. The
Lexan material proved more durable.
When you see the Chaparral 2J, at Can-Am
races, look it over carefully. You won't see and rear wheels.
When it starts, there'll be a different sound. first, the sound
of the booming ZL-1 engine. Then the raucousness of the auxiliary
engine and fans earsplitting. And when all of this happens,
you'll see the 2J hunker down as the suction takes hold. Out on
the couse, well you wait and see.
There's never been a Can-Am car like the
Chaparral 2J. The incredible Chaparral 2J.