McLaren Design
GB - New Zealand
Car Designers - Can Am in 60ies
THAT THE 1967 M6A McLaren Can-Am sports cars were so fantastically successful was in no small way the result of a very unsuccessful Can-Am season in 1966. The team returned determined to do much better the following year and the fact that Bruce McLaren won the Can-Am Championship with teammate Denny Hulme close behind in second place (winning five out of the six races with fastest laps everywhere they went) is some measure of the McLaren team's determination!
We were fortunate in being able to draw on a fair amount of experience from within the organization and during March 1967 there was debate about the various features to be incorporated in the new cars. As well as designing a new chassis, we had decided to do our own engine work. The engines were basically Bartz-modified Chevrolets assembled by us and incorporating a few of our own ideas. Lucas fuel injection was fitted to the 6-liter engines, with much of the work being done by Gary Knutson and Bruce himself.
The choice of transmission lay between the ZF 5DS-25 gearbox and the then-new 5-speed Hewland LG gearbox. For several reasons the LG box was very attractive and it was selected. This was a decision we never regretted, for it proved to be a reliable transmission and gave the driver a satisfactory gear change movement.
Our tire suppliers were Goodyear and our liaison with them during the design and development of the car was very close. Both British and American Goodyears were available and it is interesting that the British tires proved ideal for formula racing while the American tires were best for Can-Am racing. These latter tires were based on the 1967 Indy-winning Goodyears. The rear tires we used were immense and initially created a sensation, but by the end of the series they looked quite normal!
Having defined the engine, transmission and tires and obtained the services of world champion-elect Denny Hulme, in addition to Bruce, it remained to combine all these items together with a chassis and we decided to forsake the simple spaceframe and go monocoque.
The basic features of a good racing car are straightforward. It must accelerate quickly to a high top speed with braking and cornering power to match performance. Further, the car should be in every way pleasant to drive as well as being simpIe to construct and maintain. It should also stay in one piece. Laying down these ideals is the easy bit-their realization in terms of engineering are rather more difficult. One presumes that all designers are seeking the same ends but a glance at the various cars in any form of racing indicates the wide divergence of opinion on how these same ends should be reached.
It is also obviously worth putting in a lot of effort to make a car as light as possible, but the compromise between lightness and strength is about the most difficult factor in racing car design. If one errs toward high strength the car becomes heavy and uncompetitive. Equally, if one errs toward lightness the consequences can be dangerous. To complicate matters, it is frequently impossible to calculate accurately the loads encountered by some of the components. What, for example, is the load on a lower front transverse suspension link as a car understeers into a curb under braking at Monaco? It is possible to get some idea of the forces involved, but in no way as accurately as one might like.
The optimum compromise of the several aerodynamic requirements for a Group 7 car is difficult to achieve. The factors involved are numerous and frequently tend to contradict one
another. It is far from being a question of building a low-drag.
body and then eliminating the snags. However, it is interesting that the quicker Can-Am cars are beginning to show a similarity of body shape, suggesting that the same discoveries are being made and the same ideas put forward independently in several places. Progress in tire technology has been so great in recent years that suspension systems which were fine a few years ago are now undesirable. With the great wide tires now in use, one might think it sensible to keep the tires upright at
all times, and the conventional independent system is quite incapable of doing that under normal circumstances. A De Dion axle does keep them upright and might prove to be the suspension system of the future. However, the singular reluctance of the major racing car manufacturers to adopt it suggests that it has some inherent disadvantages and that the conventional system has some less-obvious advantages.
After March's thinking and talking we started to design and build the cars in April, the process from a clean sheet of paper to the first test run taking 11 weeks.
The fiberglass body was built by Peter Jackson and his men at Specialized Mouldings. A quarter-scale clay model was first made and then modified until it was the shape we wanted. Templates were taken at intervals along the model and converted to full scale. A wooden mock-up of the chassis was built, the body sections fitted to it, and the full size body constructed in clay. From this the body molds were taken.
A fair amount of comment was aroused by the distinctive orange color scheme. This in fact was a crib from Jackie Epstein's T70 Lola which clearly impressed McLaren Racing's team manager, Teddy Mayer, whose choice the color scheme was. It had one unforseen advantage-apparently it showed up very clearly in a racing car mirror and as a result slower drivers moved out of the way fairly rapidly as they spotted the bright orange flash.
On completion of M6A-I, which was to be Bruce's race car, the car was handed over to Tyler Alexander, who was to be in charge of it through its development and also while it was raced. We decided to run the car first at Goodwood. This is a popular test track in England because it presents many difficulties to the car; a driver who knows Goodwood well can cover many aspects of the car's performance there. In general, it is a fairly safe place to have a "moment."
The official lap record was held by Clark and Stewart at 1 min 20.2 sec, in 1500cc Lotus-Climax and BRM Formula 1 cars respectively. In the multi-tubular McLaren 1B with the Oldsmobile engine, a fastest lap of I: 17.2 had been set. The unofficial lap record belonged to Gurney and Brabham at 1:15.4 in their 1967 Formula 1 cars, although the number behind the decimal point varied with the person giving the information! By a little extrapolation (i.e. guesswork), we felt that to be competitive in the Can-Am series we would have to get down to 1:13.5. We reckoned other people might be able to if we couldn't. .
Our deadline for the first run of the car from the beginning had been Monday, June 19th. Somewhat to our surprise and pleasure we were able to spend a gloriously sunny June 18th lounging on Bruce's lawn-most of us had almost forgotten what the sun looked like in the previous weeks!
We had decided to run the car initially without the body in order to avoid interference of too many aerodynamic phenomena. In fact we had built one aerodynamic factor into the car and so in one direction Bruce was unable to utilize the car's potential to the full. On that first Monday Bruce recorded a lap at 1:16.2 while running in the car and carrying out a 200-mile regularity run to try and break the chassis.
During the second week of testing, the body was added and Bruce lapped consistently around 1:14.5. Toward the end of the development program, with Bruce and Denny driving the car, both got below 1:14, with Denny marginally quicker at 1:13.4.
Early in the car's life we also ran it for 200 miles on the roughest track we could find - Snetterton - and nothing broke.
A fair amount of research was devoted to the car's body our level of aerodynamic ignorance was remarkable. We had several ideas for closing our flow system at the tail, and therefore carried out a systematic series of experiments with wings, spoilers, and tabs. Suffice it to say that we ended up with a fairly conventional rear spoiler with an adjustable twin tab.
In our aerodynamic work so far, we have found existing theory and both scale and full-size wind-tunnel work unsatisfactory in many ways. In order to obtain some data which would be fairly realistic, we set up a- series of pressure tappings over the internal and external surfaces of the car. Bruce drove the car at about 150 mph while I recorded the appropriate pressure readings in the passenger's seat together with their variation with speed, and under acceleration, braking and cornering. The first lesson to be learned was that all future, McLaren racing cars will have to be a great deal more comfortable! On the first day along I racked up 23 individual bruises.
From the passenger's seat I also took readings of suspension behavior. When I was studying the rear suspension I had to lie on my stomach facing backwards in-order to peer at the wheel and links. I used the roll hoop to the left hand and the filler cap to the right to counter the 1.2g lateral acceleration. Bruce had been experiencing a handling characteristic through one of Goodwood's quick right-handers which we were at a loss to understand without more evidence. Approaching the corner in question Bruce shouted above the wind roar that he was really going to pitch it in. He did! As the car's back end began to break away, I felt a great thump on mine. This seemed odd until I realized that Bruce was trying to apply opposite lock to correct the slide only to find my
back side blocking the movement of his hands!
Looking back on this incident I am surprised to recall, as the car got steadily more out of shape, a feeling of calmness rather than terror, and having enough time to argue that if Bruce couldn't get us out of this problem, nobody could. It was fascinating to see the complex combination of throttle bursts, steering movements, and brake applications that sent us spinning harmlessly down the center of the track.
While we were running the car, Gary Knutson was carrying out his engine development work at the factory, except for those occasions when we were examining the engine under race conditions. Tests included back-to-back comparison of carburetion versus fuel injection, as well as the usual engine system proving. The most severe problem encountered was making the oil cooler work. Initially, the cooler received air from the left-hand inlet at the front of the tail section with the hot air exhausted to the rear of the engine bay. Structurally and aerodynamically this was a very convenient system, but unfortunately it didn't work. Eventually we relocated the oil cooler in the tail spoiler, thereby insuring a high-pressure supply of cold air on the inlet side, and low pressure on the outlet.
Looking back on the testing it seems to me that two objects were achieved: The first was to subject the car to about 2000 miles of hard running in the hope that any inherent weakness would show up . . . since our main Can-Am competitors would have well proven chassis.
The second object was to make the car more pleasant to drive which, besides its humanitarian aspect, enables the driver to drive the car nearer to its ultimate limit and to maintain that level of performance for a longer period. It is interesting that the ultimate limit of the car has remained unchanged since its inception.
We have always maintained that it is necessary to keep a full and accurate written record of all testing. Before leaving the factory on each test day, the car's various settings were recorded: toe-in, camber, casters, ride height, springs, damper settings, etc. At the track each lap was timed, together with the driver's comment~ on each of these laps and any changes carried out in consequence.
Inevitably, it was going to be a great reckoning to us when Denny Hulme came to drive the car. His background of Brabham single-seaters and Lola sports cars and GTs-all cars renowned for their handling-would make him a most critical judge. Denny's car (M6A-2) was to be maintained when raced by Don Beresford and Barry Crowe. It was not possible to run the car to its limit during its first outing at Silverstone, but Denny was still well under his own lap record in a Group 7 Lola-Chevy. With the car fully set up he drove it next at Goodwood. After a few laps he said "Leave it alone, I'll race it like that," and that summed up our development.
This, to my mind, throws considerable credit on Bruce's' shoulders, for his task had been to develop the car to a raceworthy condition and this, in Denny's eyes at least, he had achieved.
The duties of the test driver of a new race car are-in many ways similar to those of a test pilot in a new airplane, and they are just as crucial to the success of the project-although this fact is seldom appreciated. Unfortunately there is no recognized training for a test driver, and it is therefore not surprising that those who are very good are also very rare. The driver must be sensitive to the car's behavior, although there are several factors which make this difficult. It is amazing, for instance, how easy- it is to become accustomed to even the most unpleasant faults in a car if one drives it for some -time. You encounter this when someone new drives your own road car. Further, for each driver, there appear to be certain aspects of the car's performance to which he is almost blind. To some extent, therefore, the more people you can persuade to drive your race car the better, for you will usually learn something from each one.
The Mk II Ford GT is commonly held to be a pleasant car to drive and I feel that a major reason for this has been the large number of drivers who have tested it and raced it. Each added his own criticisms and suggestions until no major problems remained-at least not from the driving angle. In any case it is necessary for drivers to express the car's characteristics in words that will convey to the engineer what is taking place. In addition to his other abilities, it really would be an advantage to have a driver with a degree in English!
There are so many factors in the performance of a car which cannot be measured, either because measurement would be too complete or because the parameter is as subjective as, say, steering feel. One day we will be able to read these quantities off tapes; Ford and Chaparral are already working this way, but until -then we must rely on our test driver. Consequently, the findings of the driver are of great importance, for upon them we base so much of the car's development program.
These, then, are some of the requirements and difficulties of a test driver with a brand-new racing car. It is in addition to his tasks as company director, design consultant and race driver that Bruce undertakes the test driving for McLaren Racing, and the overwhelming success of our M6A Can-Am car reflects very closely how well he carried out his various and complicated tasks.
Author: ArchitectPage
