• PLYMOUTH SUPERBIRD: THE RICHARD PETTY CONNECTION!

    Our man on the track, Stephen Cox, talks with Richard Petty about his connection to the winged Superbird.

    It has been claimed that Plymouth’s legendary winged ‘70 Superbird was the brainchild of NASCAR champion Richard Petty. The rumor has been around for decades but I’ve never found anyone with first-hand knowledge who could absolutely confirm or deny that the car’s origins truly began with The King of Stock Car Racing.

    But opportunity knocked a couple of weeks ago when Petty was in attendance at the Mecum auction in Kissimmee, FL, which I co-host for NBCSN. I found him relaxing backstage late in the show and hollered, “Hey, King!” Although I don’t know him well, he looked up with his trademark smile and immediately held out his hand.

    I asked him point blank whether he was responsible for the development of the Plymouth Superbird. Petty paused and laid the back of his hand across his brow. “Well, let me get the dates right.”

    “We knew in 1968 that Dodge was building a wing car. So I went to Plymouth and asked if they were gonna build one and they said, ‘No.’ I told them that I’d like them to work on one and they said, ‘No, you’re winning all the races anyway.’”

    True, Petty had been dominant, winning 27 of 49 Grand National races en route to the championship in 1968. Rather than cough up the additional funds to stay current in NASCAR’s burgeoning aero wars, Plymouth was content to let Petty struggle against increasing odds.

    Undeterred, Petty tried another angle. He asked if he could stay within the Chrysler family and simply move over to Dodge and drive the new Charger Daytona winged car for the 1969 season. Plymouth flatly refused.

    “So I said, ‘Either build me a wing car or I’m walking across the street,’” Petty continued. “They said, ‘Sure, go ahead.’ So I did.”

    That same afternoon Richard Petty personally walked into Ford Motor Company’s front office. Ford executives took no risks, signing Petty to a one-year contract on the spot. Petty finished second in the points chase while winning ten races for Ford in 1969. It was enough. He didn’t have to return to Detroit to beg Plymouth for a winged car. This time, they came to him.

    “The head man from Plymouth came walking into my shop,” Petty continued. “He said, ‘What do we need to do to get you back? I said, ‘Give me what I’ve been asking for.’”

    Plymouth pledged to have a new winged car completed for Petty in time for the 1970 NASCAR season. Rather than re-inventing the wheel, they chose to use a modified version of the wildly successful Dodge Charger Daytona platform. Under NASCAR’s homologation rules, a limited number of Superbird street cars were built and sold through Plymouth’s dealership network.

    Behind the wheel of the car built specifically for him, Richard Petty and his Plymouth Superbird won 18 of the 40 races in which they competed in 1970, led nearly half of all laps and won nine pole positions. Despite being produced for only one model year, the road-going version of the Superbird became a legend in the annals of musclecar history.

    Today, a concours-ready Plymouth Superbird will routinely draw bids from $100,000 to $300,000 at auction. They remain among the most collectible musclecars ever built.

    “So there you go,” Petty told me with a smile. “That’s how it happened.”

     

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  • Electric car charging rip-off?

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    Ministers are preparing to tackle overpriced electric car charging over fears that it can cost as much to run a green vehicle as a diesel car.

    Reforms set to be introduced next year will make roadside pricing for electricity – which can reach £7.50 for a half-hour charge – more consistent, so motorists are not put off buying environmentally friendly cars.

    The new rules will give drivers easier access to public charge points and set common standards for pricing.

    Ministers are preparing to tackle overpriced electric car charging over fears that it can cost as much to run a green vehicle as a diesel car

    The environmental audit committee said that ministers would fall short of a target of ensuring that 9 per cent of new cars and vans were classed as ultra-low emission vehicles by 2020.

    Its report predicted that without reform, green vehicles would at most account for only 7 per cent of the car and van market by 2020.

    Motoring journalist and spokesman for the FairFuelUK campaign, Quentin Willson, told The Times: ‘We have seen some rapid chargers cost almost £7.50 for a half-hour charge. That strikes me as far too expensive and can almost bring costs up to a comparable level of running a diesel car.

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  • RACING’S GREATEST UPSETS: 1966 TRANS-AM ENDURO!

    Stephen Cox blogs about Shelby American’s legendary Group 2 Mustang racers, Part 3 of 3.

    John McComb ordered a new car for 1967. The choice was easy. Given his success in the 1966 Group 2 Mustang, he ordered a new notchback for 1967 to pick up where he left off with the Shelby program. The ‘67 Mustang was the model’s first major redesign and the car gained both size and weight. McComb didn’t care for either.

    “Even though the ’67 car had a wider track, it was a heavier car, so I don’t really think the wider track helped,” McComb said. “The ’66 car was just a very reliable, quick car. I always thought the ’66 was better than the ’67 anyway.“

    While awaiting delivery of the new car, McComb pulled his old mount out of the garage to start the new season. It still ran strong, competing at the Daytona 300 Trans-Am race on February 3, 1967 and in the 24 Hours of Daytona the following day. In March, McComb returned to familiar grounds and took second in the amateur A/Sedan race at Green Valley, and again participated in the Trans-Am event the following day. The car’s final race under McComb’s ownership was the Trans-Am at Mid-Ohio Sports Car Course on June 11th.

    His new racecar became available just days later and McComb sold the #12 Group 2 Mustang to Keith Thomas, a Kansas native who had shown considerable ability winning club races throughout the region. Thomas campaigned the car against stiffening competition in the A/Sedan Midwest Division, ironically finishing second in the championship hunt only to John McComb’s new car.

    This gave the #12 Group 2 Mustang a unique place in road racing history. Not only did it claim a share of John McComb’s A/Sedan championship by scoring points for McComb early in the 1967 title chase, but it also clinched second place in the same series in the hands of Keith Thomas. By virtue of Thomas’ runner-up standing in the series, the car earned a second invitation in the AARC at Daytona where it scored yet another top five finish.

    Keith Thomas continued driving the #12 Group 2 Mustang in 1968 and 1969, finishing third in the series both years. Although the car was now well past its prime, Thomas set a new A/Sedan track record while winning at Wichita’s Lake Afton Raceway. He continued to rack up wins at places like Texas International Speedway, Oklahoma’s War Bonnet Park and the SCCA Nationals at Salina, Kansas throughout the late-1960s.

    Now sporting a new livery, the car ran a limited schedule from 1971-73, after which it was retired from auto racing. The car traded hands later that year and again in 1978, each time distancing itself a bit more from its proud past while being repeatedly repainted and renumbered. Finally, in 1984, the car came into the possession of car collector Gary Spraggins. By this time its true identity had been lost and Spraggins was unsure of its provenance. He bought the car anyway.

    Spraggins recalled that the Mustang had been repainted in “school-bus yellow” with black Le Mans stripes. There were no Shelby markings to be found anywhere on the car, but still Spraggins suspected that the vehicle might be something special. He noticed several items that were unique to Shelby GT350Rs, including the Cobra intake manifold, the Holley 715 carburetor and the A-arms that had been relocated to lower the car by one-inch. Mechanically, everything about the car screamed “Shelby” although no one really knew for sure.

    The moment of truth came when Spraggins took the car home for a closer inspection. “When I raised the trunk lid up, of course, the inside of the trunk area was black, but you could see the Le Mans stripes overspray down in there,” Spraggins remembered.

    “Oh, man, I knew what those colors represented – Shelby cars. And I got some paint remover and lightly put it over the black Le Mans stripe on the trunk and wiped it off, and there was the prettiest blue Le Mans stripe there. It’s like, oh, my gosh!”

    Spraggins immediately wrote to the Shelby American Automobile Club, describing the car and asking if the VIN could be verified as a Shelby product. The response came on November 12th.

    “Looks like you’ve found one of the original Shelby 1966 Trans-Am cars,” the letter began. “Your car was originally sold to Turner Ford in Wichita, KS. I think they may still be in business…”

    SAAC national director, Rick Kopec, signed the letter. And so did Carroll Shelby.

    Spraggins could barely contain his enthusiasm and quickly set to work restoring the car to its original 1966 livery and condition, not realizing that an aging John McComb had also entertained the idea of finding his old mount. He just didn’t know where to look.

    “I was very excited at that time that I had found a needle in a haystack,” Spraggins said. “Nobody knew anything about these cars, so in order to track down the original driver – you know, John McComb – I just started calling information in the Wichita area.”

    On a hot summer afternoon in late-July 1985, the telephone on John McComb’s desk rang again. On the other end was car collector Gary Spraggins calling with the surprising news that his famous #12 Group 2 Mustang had been found. When McComb saw photos of the newly restored Mustang, he said, “My immediate reaction was, ‘That’s my car!’ What a super job you have done on it.”

    When asked to critique the restoration and help them convert the car to its precise 1966 condition, McComb confessed to a pair of secrets that he’d kept for nearly 30 years.

    “We cheated in two places on the bodywork. One was on the lower front valance where the license plate goes. We took those two little tabs off and opened it up a little. We also opened up the front fenders just a little. We rolled the inner lip around a welding rod to give it more strength for nerfing. We never got caught on either one.”

    Eventually, even Carroll Shelby was reunited with the newly restored #12 Group 2 Mustang at a car show in the mid-1990s. He recognized it instantly. “This was the last year I was really interested in racing,” he lamented to Mustang Monthly.

    “We had won Le Mans in 1966 and then the Trans-Am series came along. A lot of our good guys had moved on to other things because we had been winning for so many years.”

    When it came to North American road racing, the Group 2 Mustangs were Shelby’s last stand. Largely forgotten by car collectors worldwide, these amazing racecars won the first Trans-Am title for Ford and were among the most dominant sportscars their era. They left an indelible imprint on the American road-racing scene of the 1960s. Then they simply disappeared.

    Standing at the car’s freshly repainted rear fender, Shelby crossed his arms, took one last glance at the #12 Group 2 Mustang and gave a long sigh. “After 1966, we were concentrating on building volume. Unfortunately, the racing programs didn’t have much priority after this.”

    NOTE: All photos are courtesy of Mecum Auctions. The driver in the cockpit photo is owner/driver John McComb preparing for a race in the late-1960s.

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  • Tyre friction and self-affine surfaces

    The friction generated by an automobile tyre is crucially dependent upon the roughness of the road surface over which the tyre is moving. The theoretical representation of this phenomenon developed by the academic community over the past 20 years has been largely predicated on the assumption that the road can be represented as a statistically self-affine fractal surface. The purpose of this article is to explain what this means, but also to question whether this assumption is in need of some generalisation.

    To begin, we need to understand two concepts: the correlation function and the power spectrum of a surface.

    Surfaces in the real world are not perfectly smooth, they’re rough. Such surfaces are mathematically represented as realisations of a random field. This means that the height of the surface at each point is effectively sampled from a statistical distribution. Each realisation of a random field is unique, but one can classify surface types by the properties of the random field from which their realisations are drawn. For example, each sheet of titanium manufactured by a certain process will share the same statistical properties, even though the precise surface morphology of each particular sheet is unique.

    Let us denote the height of a surface at a point x as h(x). The height function will have a mean <h(x)> and a variance. (Here and below, we use angular brackets to denote the mean value of the variable within the brackets). The variance measures the amount of dispersion either side of the mean. Typically, the variance is calculated as:

    Var = <h(x)2> − <h(x)>2

    Mathematically, the height at any pair of points, x and x+r, could be totally independent. In this event, the following equation would hold:

    <h(x)h(x+r)> = <h(x)2>

    The magnitude of the difference between <h(x)h(x+r)> and <h(x)2> therefore indicates the level of correlation between the height at points x and x+r. This information is encapsulated in the height auto-correlation function:

    &#958(r) = <h(x)h(x+r)> − <h(x)2>

    Now the auto-correlation function has an alter-ego called the power spectrum. This is the Fourier transform of the auto-correlation function. It contains the same information as the auto-correlation function, but enables you to view the correlation function as a superposition of waves with different amplitudes and wavelengths. Each of the component waves is called a mode, and if the power spectrum has a peak at a particular mode, it shows that the height of the surface has a degree of correlation at certain regular intervals.
    Related to the auto-correlation function is the height-difference correlation function:

    C(r) = <(h(x+r)−h(x))2>

    This is essentially the variance in height as a function of distance from an arbitrary point x. This is a useful function to plot graphically because it represents the difference between the auto-correlation function and the overall variance, as a function of distance r from an arbitrary point x:

    C(r) = 2(Var−&#958(r))

    Which brings us to self-affine fractal surfaces. For such a surface, a typical height-difference correlation function is plotted below, (Evaluation of self-affine surfaces and their implications for frictional dynamics as indicated by a Rouse material, G.Heinrich, M.Kluppel, T.A.Vilgis, Computational and Theoretical Polymer Science 10 (2000), pp53-61).

    Points only a small distance away from an arbitrary starting point x can be expected to have a height closely correlated with the height at x, hence C(r) is small to begin with. However, as r increases, so C(r) also increases, until at a critical distance &#958||, C(r) equals the variance to be found across the entire surface. Above &#958||, C(r) tends to a constant and &#958(r) tends to zero. &#958|| can be dubbed the lateral correlation length. In road surfaces, it corresponds to the average diameter of the aggregate stones.

    To understand what a self-affine fractal surface is, first recall that a self-similar fractal surface is a surface which is invariant under magnification. In other words, the application of a scale factor x → a⋅x leaves the surface unchanged.

    In contrast, a self-affine surface is invariant if a separate scale factor is applied to the horizontal and vertical directions. Specifically, the scale factor applied in the vertical direction must be suppressed by a power between 0 and 1. If x represents the horizontal components of a point in 3-dimensional space, and z represents the vertical component, then it is mapped by a self-affine transformation to x → a⋅x and z → aH⋅z, where H is the Hurst exponent. In the height-difference correlation function plotted above, the initial slope is equal to 2H, twice the value of the Hurst exponent.

    Note, however, that a road surface is considered to be statistically self-affine surface, which is not the same thing as being exactly self-affine. If you zoomed in on such a surface with the specified horizontal and vertical scale-factors, the magnified subset would not coincide exactly with the parent surface. It would, however, be drawn from a random field possessing the same properties as the parent surface, hence such a surface is said to be statistically self-affine.

    Attempts have been made within the academic literature to adopt the self-affine model of surface roughness to road surfaces, which are known to be characterised by two distinct length-scales: the macroscopic one determined by the size of aggregate stones, and the microscopic one determined by the surface properties of those stones. One such attempt, which introduces two distinct Hurst exponents, is shown below, (Investigation and modelling of rubber stationary friction on rough surfaces, A.Le Gal and M.Kluppel, Journal of Physics: Condensed Matter 20 (2008)):

    This doesn’t seem quite right. The macro-roughness of a road surface is defined by the morphology of the largest asperities in the road, the stone aggregate. Yet as the authors above state themselves, a road surface only displays self-affine behaviour “within a defined wave length interval. The upper cut-off length is identified with the largest surface corrugations: for road surfaces, this corresponds to the limit of macrotexture, e.g. the aggregate size.”

    It’s not totally clear, then, whether the macro-roughness of a road surface falls within the limits of self-affine behaviour, or whether it actually defines the upper limit of this behaviour. At first sight, the notion that a road surface is statistically self-affine seems to have been empirically verified by the correlation functions and power spectra taken of road surfaces, but perhaps there’s still some elbow-room to suggest a generalisation of this concept.

    For example, consider mounded surfaces. These are surfaces in which there are asperities at fairly regular intervals. In the case of road surfaces, this corresponds to the presence of aggregate stones at regular intervals. Such as surface resembles a self-affine surface in the sense that it has a lateral correlation length &#958||. However, there is an additional length-scale λ defining the typical spacing between the asperities, as represented in the diagram below, (Evolution of thin film morphology: Modelling and Simulations, M.Pelliccione and T-M.Lu, 2008, p50).

    In terms of a road surface, whilst &#958|| characterizes the average size of the aggregate stones, λ characterizes the average distance between the stones.

    In terms of the height-difference correlation function C(r), a mounded surface resembles a self-affine surface below the lateral correlation length, r < &#958||. However, above &#958||, where the self-affine surface has a constant profile for C(r), the profile for a mounded surface is oscillatory (see example plot below, ibid. p51). Correspondingly, the power spectrum for a mounded surface has a peak at wavelength λ, where no peak exists for a self-affine surface.

    The difference between a mounded surface and a genuinely self-affine surface is something which will only manifest itself empirically by taking multiple samples from the surface. Individual samples from a self-affine surface will show oscillations in the height-difference correlation function above the lateral correlation length, but the oscillations will randomly vary from one sample to another. In contrast, the samples from a mounded surface will have oscillations of a similar wavelength, (see plots below, from Characterization of crystalline and amorphous rough surface, Y.Zhao, G.C.Wang, T.M.Lu, Academic Press, 2000, p101).

    Conceptually, what’s particularly interesting about mounded surfaces is that they’re generalisations of the self-affine surfaces normally assumed in tyre friction studies. Below the lateral correlation length-scale &#958||, a mounded surface is self-affine (M.Pelliccione and T-M.Lu, p52). One can say that a mounded surface is locally self-affine, but not globally self-affine. Note that whilst every globally-affine surface is locally self-affine, not every locally self-affine surface is globally self-affine.

    A self-affine road surface will have aggregate stones of various sizes and separations, whilst a mounded road surface will have aggregate stones of similar size and regular separation.

    In fact, one might hypothesise that many actual road surfaces in the world are locally self-affine but not globally self-affine. For this to be true, it is merely necessary for there to be some regularity in the separation of aggregate within the asphalt. If the distance between aggregate stones is random, then a road surface can indeed be represented as globally self-affine. However, if there is any regularity to the separation of aggregate, then the surface will merely be locally self-affine. If true, then existing academic studies of tyre friction have fixated on a special case which is a good first approximation, does not in general obtain.

    Source: mccabism

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