Kammback

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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[edit]

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[edit]

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[edit]

High-performance cars[edit]

Kamm-tailed competition car: Ford GT40

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

Mass-production cars[edit]

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:

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.[24][25][26][27][28]

Hybrid mass-production cars[edit]

As the Kamm tail's low drag helps improve fuel consumption, it features on hybrid cars designed for maximum economy, for example:

References[edit]

  1. ^ "Paul Jaray 1889-1974". Coachbuilt.com. Retrieved 9 June 2014. 
  2. ^ Hucho, Wolf-Heinrich (1987). Aerodynamics of Road Vehicles: from fluid mechanics to vehicle engineering. Butterworths. pp. 19–20. ISBN 978-0-408-01422-9. 
  3. ^ Gowans, Alan (1981). Learning To See: Historical perspective on modern popular/commercial arts. Popular Press 1. p. 360. ISBN 978-0-87972-182-4. 
  4. ^ a b c d Eckermann, Erik; Albrecht, Peter L. (2001). World History of the Automobile. SAE International. pp. 115–117. ISBN 978-0-7680-0800-5. Retrieved 9 June 2014. 
  5. ^ Montgomery, Bob (8 August 2007). "Designing a spin for the tail end of things" (fee required). The Irish Times. Retrieved 8 December 2011. 
  6. ^ Bush, Donald J. (1975). The streamlined decade. George Braziller. p. 109. ISBN 978-0-8076-0793-0. 
  7. ^ Ludvigsen, Karl (Fall 1967). "Automobile Aerodynamics: Form and Fashion". Automobile Quarterly 6 (2). 
  8. ^ Ihrig, Ron (3 December 2004). "Part 3: Production, Physics, Politics - Only the Strong Survive - German Design History". Car Design News. Retrieved 9 June 2014. 
  9. ^ Taylor, Rich (September 1981). "Searching for the Perfect .10". Popular Mechanics: 158. Retrieved 9 June 2014. 
  10. ^ "Kamm Back". Auto Repair About. Retrieved 9 June 2014. 
  11. ^ "BMW Press Release dated 27 March 2007. "BMW at Techno Classica". Archived from the original on 27 May 2007. Retrieved 9 June 2014. "Kamm was a key figure in the design of the body for this . . .car, which was built specially for the Mille Miglia 1940."" 
  12. ^ "Victory in Italy". bmw-motorsport. 9 June 2014. Archived from the original on 7 December 2007. "Giovanni Lurani and Franco Cortes have to retire on lap seven with their BMW 328 'Mille Miglia' Kamm coupe." 
  13. ^ Editors of Consumer Guide (17 May 2007). "Iso Grifo". auto.howstuffworks.com. Retrieved 9 June 2014. 
  14. ^ "Ford Mk IV". Ultimate Car Page. 9 June 2014. "...cut-off 'Kamm' tail" 
  15. ^ Nye, Doug (2004). Dino, The Little Ferrari. Motorbooks. p. 110. ISBN 0-7603-2010-1. "...a cut-off Kamm-theory tail..." 
  16. ^ Stevenson, eon (2008). American automobile advertising, 1930-1980: an illustrated history. McFarland. p. 221. ISBN 9780786452316. Retrieved 9 June 2014. 
  17. ^ "History of the 1981 AMC Eagle". AMC Eagle Den. Retrieved 9 June 2014. 
  18. ^ Ernst, Kurt (10 March 2014). "Lost Cars of the 1980s – 1981-1982 AMC Eagle Series 50 Kammback". Retrieved 9 June 2014. 
  19. ^ Witzenburg, Gary; Miller, Moss (September 1980). "Driving the new AMC Eagles". Popular Mechanics 154 (4): 100. 
  20. ^ Stevenson, eon (2008). American automobile advertising, 1930-1980: an illustrated history. McFarland. p. 221. ISBN 9780786452316. Retrieved 5 January 2014. 
  21. ^ "AMC Gremlin X". Car & Driver 22: 104. 1977. "... The distinctive Kamm-back profile was left untouched..." 
  22. ^ Leffingwell, Randy (2002). Mustang: The Original Muscle Car. MBI Publishing. p. 126. ISBN 978-0-7603-1349-7. Retrieved 9 June 2014. 
  23. ^ Langworth, Richard M. (2000). Complete Book of Collectible Cars: 70 Years of Blue Chip Auto Investments 1930-2000. Publications International. p. 29. ISBN 9780785343134. Retrieved 9 June 2014. "...new-for-'79 Spirit liftback; Kammback was an updated Gremlin." 
  24. ^ "Kamm Tail AMX". Car and Driver 14: 99. 1968. Retrieved 9 June 2014. 
  25. ^ Mitchell, Larry G. (2000). AMC Muscle Cars. Motorbooks. p. 23. ISBN 9780760307618. Retrieved 9 June 2014. "...with a chopped-off rear end that was known as a Kamm-back." 
  26. ^ Editors of Consumer Guide (15 November 2007). "Chevrolet Camaro and Pontiac Firebird Concept Cars". auto.howstuffworks.com. Retrieved 9 June 2014. 
  27. ^ Wilson, Bill (26 March 2014). "The Pontiac Kammback: Innovation vs. Convention". Boldride. Retrieved 9 June 2014. 
  28. ^ Stone, Matt (August 2009). "Pontiac Trans Am Greats: We Shall Never Pass This Way Again". Motor Trend. Retrieved 9 June 2014. 

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