Kammback

A Kammback is a car body style that derives from the research of the German aerodynamicist Wunibald Kamm in the 1930s. The design calls for a body with smooth contours that continues to a tail that is abruptly cut off. This shape reduces the drag of the vehicle.

"Kammback" is an American term. In Europe the design is generally known as a Kamm tail or K-tail.

History

Paul Jaray experimented and developed streamlined car body work in the 1920s. His innovative body design featuring a low-profile teardrop shape with a long tail minimized the air resistance of passenger cars.^[1] Better highway systems being built in the 1930s called for higher automobile cruising and top speeds, thus, automobile designers focused on the aerodynamic characteristics of cars.^[2] Wind tunnel tests showed that a true tear-drop shaped body offered only a slight improvement in efficiency to the Chrysler Airflow design. In 1935, Georg Hans Madelung, a German engineer, professor, and aircraft designer, showed that a vehicle does not need a long tapered tail at high speeds.^[3]

Freiherr Reinhard Koenig-Fachsenfeld "developed a body style whose tail was cut off to form a flat rear surface" to reduce the air turbulence caused by the apparently streamlined, but steeply raked roofs of cars that used Paul Jaray's principles.^[4] He worked on an aerodynamic design for a bus, and Koenig-Fachsenfeld patented the idea.^[5]

In 1936, "further research by the FKFS—Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart (Stuttgart Research Institute for Automotive and Automobile Engine Technology), under the direction of Wunibald Kamm, proved that vehicles with the so-called K- or Kamm tail, following Koenig-Faschsenfeld's lead, offered a good compromise between everyday utility (e.g. vehicle length and interior dimensions) and an attractive drag coefficient".^[4] In addition to aerodynamic efficiency, Wunibald Kamm also emphasized vehicle stability in his design.^[4] He proved mathematically and empirically the effectiveness of the design.^[6] The Kamm-back, or K-form, was a body with a smoothly contoured front that continues to an abrupt vertical flat surface in the rear.^[7]

The earliest use of "Kamm" to describe an automobile body incorporating this design was the prototype 1940 'Kamm' Coupe based on a BMW 328 chassis.^[8] The earliest mass-produced cars that used Kammback principles were the 1949–1951 Nash Airflyte in the U.S. and the 1952–1955 Borgward Hansa 2400 in Europe.^[4]

Aerodynamics

Kamm-tailed 4-door: Citroën CX

While the realities of fluid dynamics dictate that a teardrop shape is the ideal aerodynamic form, Kamm found that by cutting off / flattening the streamlined end of the tear at an intermediate point, and bringing that edge down towards the ground, he could gain most of the benefit of the teardrop shape without incurring such a large material, structural, and size problem. The airflow, once given the suggestion of the beginning of a turbulence-eliminating streamlined teardrop tail, tended to flow in an approximation of that manner regardless of the fact that the entire tail was not there. This is called the Kamm effect.^[9]

There is controversy about the proportions of a true Kamm tail. According to the classic definition the tail should be cut off where it has tapered to approximately 50% of the car's maximum cross section,^[10] which Kamm found represented a good compromise—by that point the turbulence typical of flat-back vehicles had been mostly eliminated at typical speeds. Thus a minivan is not a Kammback, and neither are numerous cars that have truncated tails.

Automakers’ use of the term "Kammback" has diminished as Kamm's principles have become more generally assimilated into modern car design.

Kammback examples

High-performance cars

Kamm-tailed competition car: Ford GT40

The Kamm tail was used on many high-performance and competition cars, such as:

• 1940 BMW 328 "Mille Miglia" Kamm coupé^[11][12]
• 1952 Cunningham C-4RK
• 1961 Ferrari 250 GT SWB Breadvan
• 1962–1964 Ferrari 250 GTO
• 1963 Aston Martin DP215
• 1963–1974 Bizzarrini Iso Grifo^[13]
• 1965–1968 Ford GT40 ^[14]
• 1965–1970 Aston Martin DB6
• 1968–1973 Ferrari 365 GTB/4 ("Daytona")
• 1968–1976 Ferrari Dino ^[15]
• 1970–1975 Citroën SM
• 1970–1977 Alfa Romeo Montreal
• 1972–1982 Maserati Khamsin
• 1968–1973 Chevrolet Corvette

Mass-production cars

1969 Fiat 850 Coupe

AMC Eagle "Kammback" all-wheel drive

The 1971–1977 Chevrolet Vega Kammback wagon featured a Kamm tail in its liftgate.^[16]

The 1981–1982 compact two-door hatchback version of the AMC Eagle was also named a Kammback.^[17][18] It retained the "mini-wagon look" of the AMC Gremlin, but with much larger quarter glass, and rear window^[19][20] that derived from the AMC Spirit's two-door sedan body style.

Kamm (and Kamm-like) tails can be seen on numerous mass-production cars, such as:

• 1962–1978 Alfa Romeo Giulia
• 1965–1971 Aston Martin DB6 ^[21]
• 1966-1974 Saab Sonett II and III ^[22]
• 1969–1971 Fiat 850 Coupe and Sport Coupe
• 1969–1976 Triumph TR6 ^[23]
• 1970–1978 AMC Gremlin ^[24]
• 1970–1986 Citroën GS
• 1970–1978 Datsun 240Z, 260Z, 280Z
• 1971–1989 Alfa Romeo Alfasud
• 1970–1993 Alfa Romeo Spider
• 1971–1977 Chevrolet Vega Kammback Wagon
• 1971–1973 Ford Mustang ^[25]
• 1974–1991 Citroen CX
• 1979–1982 AMC Spirit and Eagle 50 sedans ^[26]
• 1984–1991 Honda CR-X
• 1985–1996 Autobianchi/Lancia Y10
• 1991–1998 Mazda MX-3
• 1999–2005 Audi A2
• 2001–2008 Volvo S60
• 2004–2009 Citroën C4 Coupé
• 2011–present Hyundai Veloster

Several automakers including American Motors (AMC) and General Motors (GM) have publicized certain models with truncated tails as "Kammbacks" even though they do not meet the classic "50% cross-section" definition, i.e. the AMC AMX-GT and Pontiac Firebird–based "Type K" concept cars.^{[27][28][29][30][31]}

Hybrid mass-production cars

Honda Insight

Opel Ampera - European version of the Chevrolet Volt

The Kamm tail-type design reduces drag and it is a feature on some hybrid cars that include:

• 2000–2006 Honda Insight ^[32]
• 2004–present Toyota Prius ^[33]
• 2010–present Honda Insight (2nd generation) ^[34]
• 2011–present Honda CR-Z ^[35]
• 2011–present Chevrolet Volt ^[36]

References

External links

• Robinson, Peter; LOCI Ltd (2002). "The Pininfarina 1800". LOCI Ltd. Retrieved 9 June 2014.  - an explicitly Kamm-influenced design which informed the Citroën CX and Rover SD1
• Ziemnowicz, Christopher (2004). "The Origin of the Kammback Design". Archived from the original on 15 April 2012. Retrieved 9 June 2014.