Can Am Series Chaparral 2J when brought to race at Watkins Glen - it's first race 1970
USA
So once again the famous Chaparral Road Show is on the march in a big way. Plain white pickup trucks with Texas plates will be seen in Can-Am paddocks, and the peasant dazzling Sabrejet with the blue and red markings will be winging in to land at nearby airports. This aspect of Jim Hall's Midland Mafia always impresses, even when it is not accompanied by something wild and wonderful from the mystery-car factory. With the appearance of the 2J car, the show is complete and it is something to behold.
But is it the Chaparral show... or is it really the Chevy show, with Jim Hall instead of Dinah Shore? In fact, the new 2J "Chaparral" was conceived and constructed, in all its essentials, at the Chevrolet Engineering Center in Warren, Michigan. Jim Hall's fabled Great Stone Face taciturnity has never been more appropriate than it is now, when he's being placed in the embarrassing position of having to graciously claim paternity, in public, for a concept and car that he adopted, not fathered.
But be that as it may, the 2J "Vacuum cleaner" is a marvelous idea and it is only surprising that it has not been applied to racing much earlier.
Actually, the vacuum cleaner concept was around long before the FIA announced a height reduction on wings and sent all the Can-Am competitors scrambling for some new "unfair advantage." It goes back, in this incarnation, to the invention at GM Styling of a new kind of ground-effect principle otherwise known as an air-bearing or air cushion or hovercraft-christened (in the inimitable GM manner) "Hovair" by its creators. They found that by blowing air down through a vehicle or object, you could form a pressurized layer of air that would lift it free of the surface and allow the object to move very easily. Many others have made air cushion devices; the Hovair was unusual in giving high lift at very low pressures and air-delivery
volume. Frigidaire even used it for a time on the bottoms of their refrigerators to allow the housewife to move these appliances around the air being provided by the exhaust side of a vacuum cleaner. Obviously, with the suction side of a vacuum cleaner applied, the refrigerator would not have moved sideways for King Kong and Godzilla working together, and that may have been what triggered a novel notion in the mind of GM's Harry Mackie. Suck air through the Hovair pad, he thought, and you could create great object/ground adhesion. A little 3-wheel demonstrator was made to show what it could do, and on December 24, 1961 a patent application for the device was properly recorded in Washington.
Some years later, Pontiac tried a reversc Hovair pad under the rear axle of an experimental drag racing car and found that the problem was one of keeping the force levels down; not building them up. Up to a point but only up to a point-tires grip better if they're forced down against the pavement. That better grip can be used for acceleration, braking and cornering. But after a certain amount of gripping work is demanded of them, they'll begin to slide no matter how much force is applied downward (probably because the side-load exceeds the sheer strength of the rubber). The wider and larger the tire, the bigger the contact patch on the pavement and the more work it will do before sliding as the total downforce is increased. The Chaparral 21's suction fans generate a lot of downforce, and that's why the car wears the widest rims it will accept and the widest of Firestone's racing tires.
When Jim Hall took delivery of the Chevrolet experimental car that was to become the Chaparral 2J, its rear wheels were exposed, in conventional fashion, and suction was being applied over an area that was the width of the car and the length of the body between wheel arches. The suction fans were mounted low at the sides of the body, flanking the engine and individually driven. This arrangement did give substantial downforce, but there was some doubt (said doubt arising during tests last February) that the way the fans had of throwing dirt high in the air would be appreciated by racing authorities. Also, Hall and his chief vehicle engineer, Don Gates, felt that it' a lot of downforce was good, more would be even better.
Over the following four-month period, the GM Exp./Chaparral 2J was rebuilt at the back. Its fans were mounted at the extreme rear, as in the photographs presented here, with their drive engine between them. The arrangement was reluctantly arrived at, because it placed some 200-pounds of fans and engine high in the air, cantilevered out over the tail. But there wasn't much choice, considering the problems inherent in any other layout.
When you plan to pull a vacuum inside a box, you make that box strong unless you want it to collapse. The 2J box is made of .25-inch aluminum honeycomb, and it is strong. Unhappily, it is also gruesomely slabsided, and it is going to have to stay that way until someone finds a way to form compound curves in honeycomb.
This new section was Dzus-fastened to a monocoque structure that is very deep through the center because that portion, still unpainted at the Glen, is a major load-bearing section. Hatches in the sides meet the door requirements, of the rules. Longerons extending rearward from this section embrace the Chaparral-Chevy engine, a 465 cubic incher, and the 3-speed-p1us-torque-converter transmission.
The 2J's suspension is conventional: at the front like that of the 2H and like the 2E/G at the rear. They're laid out to counter nose-dive on braking and tail squat on acceleration; both of these being activities that would upset the skirt system more than would be convenient. And while wheel travel is three inches up or down from design height, that is the stance of the car with the fans pulling, with the car sucked down 1.5 inches from its trim with all systems shut down. The car has what appear to be very heavy springs, and that big, drop when the fans are huffing away is an indication of the very high downforces being attempted.
Let's look at this suction system, and at the fans particularly as they are a key element. You might recognize them on sight, if you're just back from 'Nam, as they are radiator cooling fans from an M-I09 self-propelled Howitzer. They have 17-inch blades, are aluminum castings, and are made by the Pesco Products Division of Borg-Warner, whose catalogue says that each fan can pump 9650 cubic feet of air per minute when spun 6000 rpm, and maintain a static pressure of 11 inches of water, or 0.4 psi.
Driving two of these fans, through cogged rubber belts and magnesium sprockets is the best engine Chaparral could find for the job: a German - made JLO two-stroke, air-cooled twin imported by Rockwell, with a rated 45 hp at 5500 rpm. In testing, this engine was absolutely reliable after being rigged with a capacitor-discharge ignition system to overcome problems caused by dirt getting into the points of the conventional coil ignition.
The fans are evidently operating at slight under-drive, relative to engine speed (about 5000 rpm) as their gross horsepower requirement at 6000 rpm is 52 hp-more than the JLO will deliver, at present. But that should still be enough to maintain a vacuum of 0.3 psi under the 2Js skirts when the car is at rest or moving slowly. The advantage of having an auxiliary engine is, of course, that the downforce is present at all times-especially at low speeds, where the extra downforce is most effective (and where wings don't work at all).
Now, about those skirts, which border the area where the downforce is generated. Obviously, the closer they conform to the road the morc effective the suction from the fans will be. But in being close to the road; they inevitably make contact at times, and to allow this without having the skirts bent or broken, they are made out of General Electric's very tough Lexan plastic. The side skirts are simple .090-inch sheets su spended from lever arms that adjust their height in response to suspension movement through push-pull cables. In other words, the side skirts go up and down with the wheels, and the rear skirt is linked to them at its ends.
The front skirt presents the greatest problem. It runs across the car just behind the front wheels, and it is crucial. The fans work hard to pull air out of the chamber, while the car's forward motion tries to ram air into that chamber under the front skirt. That skirt must, and does, rub hard against the ground while the 2J is moving. It can do this, at acceptable wear rates, because it is composed of a row of 12 thick Lexan plaques, which trail sharply back from the underbody (each on its own plastic hinge, backed -by two others similarly hinged in a way that uses combined spring and vacuum pressures to keep that trailing edge down against the pavement).
To minimize the ex tent of the problem with which this forward skirt must cope, the 2J's body is shaped to scoop as much air up and over as possible. Also, there arc transvcrse rubber strips under the car's nose to further break up the air flow.
The front skirt's segmented construction allows it to adjust for road contour, and the individual plaques have enough length to accept some wear, with 'a new set being fitted for each race, or as required depending on the measured wear rate. They successfully survived 200 miles of testing at Hall's own Rattlesnake Raceway, but I'll bet the Chaparral crew has some new numbers to consider after Watkins Glen.
To outline the 2J's capabilities, I'll estimate that it can hold a 0.3 psi vacuum through the up to 80 mph speed range at which it's designed to perform best. Applied over the approximately 7400 square inches of skirted chamber, that amounts to 2220 pounds of downforce. That is, as it happens, over the gross weight of the car with its 85-gallons of fuel (15 of them in a separate tank, mixed with oil, for the JLO engine) and with Stewart in the cockpit. So Jim Hall could have unveiled the 2J with it hanging upside down from the ceiling, the JLO shrieking away.
With the original, abbreviated chamber, the 2J had enough downforce to corner at a lateral 1.8 G. Best figures for winged Can-Am cars are down in- the 1.5 G. range. Hall says that with the extended chamber, up to 2.0 G. should be attainable. And a major difficulty is simply finding a driver who can use the extra half-G.
Jim doesn't think he's up to it: "I'm driving just like I always did, but I just don't seem to be going fast".
Jackie Stewart should be very fast with the car, if he preseveres. Setting the fastest lap in,
the Can-Am race at Watkins Glen was a remarkable achievemcnt, as it came at the end of the second-dozen laps ever turned by that car / driver combination.
Special test days at the Glen were wasted, because Stewart discovered all too early that stones sucked up from the recently resurfaced track lodged in the fan sprockets and flipped off the drive belts. A protective guard was made to shield the belts while other problems were diagnosed: overheating of the huge rear brakes. and persistent vapor-locking of the JLO's Tillotson carburetors. Bathed in engine heat from below, and trapped under Lexan above, the JLO was complaining - although like the skirt, it had kept going through the 200-mile test at Midland.
On race day, after a six-hour pounding it got during Saturday's race, the Watkins Glen course was a far cry from Rattlesnake Raceway's smooth asphalt. And sub-par power from the JLO gave the 2J an underskirt depression of only 0.1 psi for a downforce of some 750 pounds - which is about what the McLarens get from their wings. Even this modest force, with the track deterioration; was enough to cause unexpected tire wear. Then brakes started acting funny again, and the JLO vapor-locked itself into silence. Finally, Stewart missed one of the tricky shifts with the "automatic" box, which scrambled its internals, and the day was done. It was a mixed debut for the 2J.
Before the race was over, the white trucks were headed back to Texas with the asphaltcoated 2J hulk. They were, it was said, to skip the race at Edmonton to get ready for Mid-Ohio, where its low- speed grip would shine far more than it had at the Glen. At least, it should do better at Mid-Ohio.
But is the 2J Chaparral inhcrcntly too heavy and complex (and with complexity, unreliable) to make the grade as a race-winning car and not just as a curiosity? Very possibly, in its present form. And that's what - a lot of people are hoping. The other Car-Am competitors hope it will just go away, like a bad dream, because they don't even want to think about having to build similar cars to stay competitive. They won't get much help from the authorities, who do not seem inclined to ban the fan in the absence of a clear safety
hazard. There was some talk about this aspect whcn news of the 2J first went around, but such fears proved groundless. Peter Revson, who followed the 2J closely in his Lola during the early laps, reported no special problems from debris or heat. In fact, it may be that the close - fitting rear of thc 2J is a superior container for stones that, with other cars, come squirting back from the tires.
What happens if a fan quits in a corner? Experience so far indicates that they lose speed slowly enough for the driver to compensate. This may not be true if the 2J driver ever manages ultimate cornering power - in which case the drop would be from 2.0 to 1.3 G. within a second or two and that is a lot to compensate.
In displacement-limited racing (everything but Can-Am) the size of any fan engine will have to count toward total displacement, and you can just see the computer - users like Porsche charting trade-offs between power diverted to the fans for traction and that reserved for speed. They would probably vary this for diffcrent courses, with a big one at Brands Hatch and none at Le Mans. The only constant here would be the constant use of the computers to keep up with the problems.
So maybe that means the future belongs to the computer users? Does it? Keep an eye on the Chaparral 2J. It may provide the answer to a question it has asked.
Author: ArchitectPage
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