Kammback

A Kammback — also known as "Kamm tail" or "K-tail" — is an automotive styling feature. The rear of the car slopes downwards before abruptly cutting off with a vertical surface. A Kammback minimizes aerodynamic drag while maintaining a practical shape for a vehicle. The Kammback is named after German aero-dynamicist Wunibald Kamm for his work developing the design in the 1930s.

Kammback on a 1969 Fiat 850 Coupe

A Kammback reduces fuel consumption and improves performance at higher speeds.

Origins
1950 Nash Airflyte
1952 Borgward Hansa 2400

As the speed of cars increased during the 1920s and 1930s, designers noticed automotive aerodynamics.[1] In 1922, Paul Jaray patented a car based on a tear-drop profile (i.e. a rounded nose and long tapering tail) to minimize aerodynamic drag created at higher speeds.[2][3] The streamliner vehicles of the mid 1930s — such as the Tatra 77, Chrysler Airflow and Lincoln-Zephyr — were designed according to these discoveries.

However, the long tail was not a practical shape for a car, so automotive designers sought other solutions. In 1935, German aircraft designer Georg Hans Madelung showed alternatives to minimize drag without a long tail.[4] In 1936, a similar theory was applied to cars after Baron Reinhard Koenig-Fachsenfeld developed a smooth roofline but with an abrupt end at a vertical surface, effective in achieving low amounts of drag similar to a streamlined body.[3][5][6] He worked on an aerodynamic design for a bus, and Koenig-Fachsenfeld patented the idea.[7] Koenig-Fachsenfeld worked with Wunibald Kamm at Stuttgart University, investigating vehicle shapes "provide a good compromise between everyday utility (e.g. vehicle length and interior dimensions) and an attractive drag coefficient".[3][5] In addition to aerodynamic efficiency, Wunibald Kamm emphasized vehicle stability in his design.[5] He proved mathematically and empirically the effectiveness of the design.[8]

In 1938, Kamm produced a prototype using a Kammback, based on a BMW 328.[9] The Kammback, along with other aerodynamic modifications, gave the prototype a drag coefficient of 0.25.[10]

The earliest mass-produced cars using Kammback principles were the 1949–1951 Nash Airflyte in the U.S.A. and the 1952–1955 Borgward Hansa 2400 in Europe.[5]

Aerodynamic theory

The ideal shape to minimize drag is a teardrop. However researchers including Kamm found that abruptly cutting off the tail resulted in minimal increase in drag.[3] The reason for this is that a turbulent wake region forms behind the vertical surface at the rear of the car. This wake region mimics the effect of the tapered tail in that air in the free stream does not enter this region (avoiding boundary layer separation), therefore smooth airflow is maintained which minimises drag.[9]

Kamm's design is based on the tail being truncated at the point where the cross section area is 50% of the car's maximum cross section,[3][11] which Kamm found represented a good compromise—by that point the turbulence typical of flat-back vehicles had been mostly eliminated at typical speeds.

The Kamm tail presented a partial solution to the problem of aerodynamic lift, which was becoming severe as sport car racing speeds increased during the 1950s. The design paradigm of sloping the tail to reduce drag, carried to an extreme on cars such as the Cunningham C5-R, resulted in an airfoil effect lifting the rear of the car at speed, that could result in instability or loss of control. The Kamm tail decreased the area of the lifting surface while creating a low pressure zone underneath the tail.

Usage
1964-1969 Ford GT40
1974-1985 Citroën CX
2000-2006 Honda Insight
2009-2015 Toyota Prius
2011 Audi A7

In 1959, the Kamm tail came into use on full-body racing cars as an anti-lift measure, and within a few years would be used on virtually all such vehicles. The design had a resurgence in the early 2000s as a method to reduce fuel consumption in hybrid electric vehicles.

Several cars have been marketed as Kammbacks, despite the profile not adhering to aerodynamic philosophy of a Kammback. These models include the 1971–1977 Chevrolet Vega Kammback wagon,[12] the 1981–1982 AMC Eagle Kammback,[13][14][15][16] the AMC AMX-GT and the Pontiac Firebird–based "Type K" concept cars.[17][18][19][20][21]

Cars that have had a Kammback include:

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gollark: <@151149148639330304> If bees are not deployed, a Bee Poll hsa no effect.
gollark: I wonder if I can somehow work in POTAT-O5 clearance.
gollark: [REDACTED - POTAT-O5 CLEARANCE NECESSARY]
gollark: Maybe next we should make a Bee Council to veto bee actions.

References
  1. Hucho, Wolf-Heinrich (1987). Aerodynamics of Road Vehicles: from fluid mechanics to vehicle engineering. Butterworths. pp. 19–20. ISBN 978-0-408-01422-9.
  2. "Paul Jaray 1889-1974". Coachbuilt.com. Retrieved 9 June 2014.
  3. Ziemnowicz, Christopher (2004). "The Origin of the Kammback Design". Archived from the original on 15 April 2012. Retrieved 9 June 2014.
  4. Gowans, Alan (1981). Learning To See: Historical perspective on modern popular/commercial arts. Popular Press 1. p. 360. ISBN 978-0-87972-182-4.
  5. 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.
  6. Ludvigsen, Karl (Fall 1967). "Automobile Aerodynamics: Form and Fashion". Automobile Quarterly. 6 (2).
  7. Montgomery, Bob (8 August 2007). "Designing a spin for the tail end of things" (fee required). The Irish Times. Retrieved 8 December 2011.
  8. Bush, Donald J. (1975). The streamlined decade. George Braziller. p. 109. ISBN 978-0-8076-0793-0.
  9. Ihrig, Ron (3 December 2004). "Part 3: Production, Physics, Politics - Only the Strong Survive - German Design History". Car Design News. Archived from the original on 22 July 2012. Retrieved 9 June 2014.
  10. "Kamm Back". Auto Repair About. Retrieved 9 June 2014.
  11. Stevenson, eon (2008). American automobile advertising, 1930-1980: an illustrated history. McFarland. p. 221. ISBN 9780786452316. Retrieved 9 June 2014.
  12. "History of the 1981 AMC Eagle". AMC Eagle Den. Retrieved 9 June 2014.
  13. Ernst, Kurt (10 March 2014). "Lost Cars of the 1980s – 1981-1982 AMC Eagle Series 50 Kammback". Retrieved 9 June 2014.
  14. Witzenburg, Gary; Miller, Moss (September 1980). "Driving the new AMC Eagles". Popular Mechanics. 154 (4): 100.
  15. Stevenson, eon (2008). American automobile advertising, 1930-1980: an illustrated history. McFarland. p. 221. ISBN 9780786452316. Retrieved 5 January 2014.
  16. "Kamm Tail AMX". Car and Driver. 14: 99. 1968. Retrieved 9 June 2014.
  17. 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.
  18. Editors of Consumer Guide (15 November 2007). "Chevrolet Camaro and Pontiac Firebird Concept Cars". auto.howstuffworks.com. Retrieved 9 June 2014.CS1 maint: extra text: authors list (link)
  19. Wilson, Bill (26 March 2014). "The Pontiac Kammback: Innovation vs. Convention". Boldride. Retrieved 9 June 2014.
  20. Stone, Matt (August 2009). "Pontiac Trans Am Greats: We Shall Never Pass This Way Again". Motor Trend. Retrieved 9 June 2014.
  21. "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."
  22. "Victory in Italy". bmw-motorsport. 9 June 2014. Archived from the original on 20 March 2007. Giovanni Lurani and Franco Cortes have to retire on lap seven with their BMW 328 'Mille Miglia' Kamm coupe.
  23. Editors of Consumer Guide (17 May 2007). "Iso Grifo". auto.howstuffworks.com. Retrieved 9 June 2014.CS1 maint: extra text: authors list (link)
  24. "Ford Mk IV". Ultimate Car Page. 9 June 2014. ...cut-off 'Kamm' tail
  25. Krebs, Michelle (7 March 2011). "Saab Tells the World: 'We're Still Here'". Edmunds. Retrieved 25 February 2016. ...Kamm-back tail, both reminiscent of the original Saab Sonett.
  26. Nye, Doug (2004). Dino, The Little Ferrari. Motorbooks. p. 110. ISBN 0-7603-2010-1. ...a cut-off Kamm-theory tail...
  27. Robinson, Peter; LOCI Ltd (2002). "The Pininfarina 1800". LOCI Ltd. Retrieved 9 June 2014.
  28. Leffingwell, Randy (2002). Mustang: The Original Muscle Car. MBI Publishing. p. 126. ISBN 978-0-7603-1349-7. Retrieved 9 June 2014.
  29. Larminie, James; Lowry, John (2004). Electric Vehicle Technology Explained. Wiley. pp. 8–32. ISBN 9780470090695. Retrieved 27 February 2016. At the back of the Insight the teardrop shape is abruptly cut off in what is called the Kamm effect.
  30. Zenlea, David (8 February 2012). "First Drive: 2012 Toyota Prius C". Automobile. Retrieved 27 February 2016. ...featuring the same Kammback profile as the Prius and Prius V hatchbacks...
  31. Peters, Eric (22 May 2014). "2014 Honda Insight Review". National Motorists Association. Retrieved 27 February 2016. ...a Kammback layout, meaning the roof slopes gradually backward where it meets up with a fairly tall/vertical tail section.
  32. Halvorson, Bengt (20 February 2017). "2017 Hyundai Ioniq Hybrid". Car and Driver. Retrieved 19 June 2019. Despite the Ioniq’s wind-cheating Kamm-back profile, the styling is far more conservative than that of the polarizing Prius.
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