Question:What is a KAMM BACK?

-One of AMC's unique designs.
-A Pontiac Firebird show car.
-Used in competition bicycles.
-Advantage for hybrid powered cars.
-The rare Chevrolet Vega wagon.
-Aeronautical engineering benefit.
-Design feature found in race cars.

Answer: It is all of the above!

The "Kammback" is a design type named for the German aerodynamics engineer Wunibald Kamm. He worked with another engineer and developed a test car incorporating a unique design. This was based on a formula "that drag begins to increase after the rear of a car's cross-sectional area is reduced to fifty percent of the car's maximum cross section" (http://autorepair.about.com/library/glossary/bldef-513.htm). On the other hand, less drag (or air turbulence) means there is less resistance to forward motion. Thus, higher efficiency is achieved and there is an increase in the maximum velocity of the car.

However, to better understand the origin of the Kammback, it is first necessary to examine the development of automobile design.

In the beginning, automakers were mainly concerned with improving the mechanical aspects of their cars. Styling of the body evolved around a given chassis, drive train, and passenger area structure. Most of the popular early cars followed standard box-type design elements. Even external items and accessories, such as lights and fenders, were simply attached to the box body wherever it was needed or convenient.

It took a Hungarian engineer, Paul Jaray, to establish the form and function design concepts that established the modern automobile. Jaray studied the air-resistance of vehicles. His 1922 patent provided the basic aerodynamically efficient shape of a round nosed and taper tailed automobile. (http://www.katylon.com/harisauto/x_archive/jaray/jaray.htm) However, this shape is impractical for normal vehicles due to the length required for the car's tail.

It is worthy to contrast the influence of the advanced airship design on Jaray's automobile patent with the common box approach that was used by contemporary automakers -- for comparison, a high line 1924 Cadillac Landau is shown. Likewise, the very rudimentary Ford Model T was a sales success and remained in production through 1927. It was hardly a testament to innovative styling by that time. All the popular designs of that era produced massive air turbulence and their nearly vertical backs created a partial vacuum. Their bodies caused drag that functioned as an invisible anchor to the automobile's forward movement at higher speeds. However, increasing performance of racing cars -- beyond engine and mechanical development -- soon became an important consideration. Cars with wind cheating bodies could beat high powered box designs. Paul Jaray took the lead in combining the aerodynamic behavior of autos and airplanes.

The next phase in this research was undertaken by Baron Reinhard von Koenig-Fachsenfeld, an outstanding aerodynamics engineer. His goal was to reduce the turbulence, or drag, caused by the shape of the automobile. He worked on experimental cars in a Stuttgart (Germany) wind tunnel. As a result of his research, he developed a chopped off tail and patented this design in 1936. Dr. Koenig-Fachsenfeld proved that having a shorter tapered rear end makes for worse airflow at the rear of the car, compared to a sharply sheared tail where drag coefficients as low as 0.20 were achieved in experiments. (http://www.design-classic-cars.de/jaray/fachsenfeld01.html) His design incorporates a smooth roofline with a taper in the automobile's body that is then whacked off at the rear end. Thus, at higher speeds, the air flow acts as if the full tapered "tail" patented by Jaray was still there. Koenig-Fachsenfeld's aerodynamic solution proved to be very effective, as the design managed to keep the air flow from becoming turbulent.

At the same time in the USA, Walter P. Chrysler supported innovative automobile designs. His interest was so great that he established a wind tunnel at his firm's Highland Park, MI, research facility. The fruit of his investment -- to push ahead automobile technology -- was the 1934 Airflow. This was a pioneering design in numerous areas. For example, the chassis packaged both the engine and passengers much more forward than was common in contemporary cars. These major modifications allowed Chrysler's stylists to apply more efficient teardrop, or aircraft, aerodynamics to the shape of the body. The Airflow models had smooth tapered lines with the two-door having the most extended fastback tail. These innovative models followed the principles established by Jaray, but these streamlined "cars of tomorrow" were not popular with consumers.

On the other side of the Atlantic Ocean, Koenig-Fachsenfeld continued his work with a German Professor, Wunibald Kamm, who developed a prototype in 1938. It was a rather large-sized four-door sedan that featured the sharply truncated rear end design. Kamm's test car represented a good compromise between a low air resistance and every day automobile practicality.

In late summer of 1938, BMW tested a prototype of the so-called 'Kamm'-Coupe based their "328 chassis". It had a drag coefficient of only 0.25 compared to the great 1940 Mille Miglia winning BMW 328 Touring Coupe with drag coefficient 0.35. (http://www.cardesignnews.com/news/2004/041203mcd-history3/) This automaker's naming of a model appears to be the earliest use of "Kamm" to publicly describe Koenig-Fachsenfeld's design patent.

Koenig-Fachsenfeld and Wunibald Kamm were also responsible for building a much smaller prototype in 1944. This compact coupe achieved a drag value of 0.314. (http://www.design-classic-cars.de/jaray/kamm.html) The airplane-like streamlined design features many innovations such as front wheel skirts and twin roof fins, but the car's aerodynamical efficiency was achieved by a radically cut off tail combined with the tapered body. These features helped to smooth the airflow behind the car. Because of its size, long hood, and truncated rear, this design could be thought as the forerunner of the Gremlin made by American Motors (AMC).

After World War II, Professor Kamm continued to espouse the truncated design. As a result, his name became attached to the chopped off rear end design -- the Kammback.

On April 1, 1970, AMC introduced Professor Kamm's design in the first modern sub-compact to the USA marketplace. The Gremlin was a significantly shorter version of the larger-sized AMC Hornet sedan without its normal trunk. However, the chopped off Gremlin design solution was not to improve streamlining, but to improve space efficiency. Thus, the Gremlin featured a Kammback-type design with an opening rear window to access the storage area behind the rear seat. The four-passenger version carried a suggested retail price of only $1959. By applying a design trick on an exixting platform, a new class of vehicle was developed. AMC was very efficient in manufacturing a variety of vehicles to serve different market segments while using common platforms and shared components.

American Motor's innovative and reliable 6-cylinder powered sub-compact was followed by a pair of 4-cylinder equipped competitors. The 1971 Ford Pinto was a conventional fastback design with a gasoline tank that exploded if the car was rear-ended. The 1971 Chevrolet Vega was General Motor's major effort to innovate. It came with an advanced aluminum block engine that later proved to have an alarming tendency to self-destruct. Mevertheless, the unique Vegas were available in three body designs that included a trim Kammback-type station wagon. This two-door wagon had more body taper than the Gremlin, but it was still not enough to gain the aero-effects as described by Drs. Koenig-Fachsenfeld and Kamm.

The Kammback "cut off tail" design continues to be popular among automobile designs. Most often, however, it only insinuates streamlining when used in production cars. It is then only a design trick to make a sporty car seem look "fast" rather than to acheve aero-efficiency. This styling is also applied to concept show cars. An extreme example was the Pontiac "Type K" wagon. Built by GM on a 1978 Firebird Trans Am, the body had almost no taper. Combined with its recessed, completely vertical back window and rear end, the Type K would have generated significant amounts of vacuum at even low speeds, thus increasing drag. This would have negated the car's high power.

However, Dr. Kamm's wind cheating principle is used in a wide variety of popular vehicles (such as the Citroen CX that was produced from 1974 to 1990), exotic and expensive sports cars (such as the Ferrari 350 GTO), the newer high fuel efficiency and "hybrid" powered cars (such as the Honda Insight with its sharply tapered body resulting in no back seat), as well as specialized race cars (such as the AC Cobra 289 Mk II Daytona coupe). On all of these, the Kamm design enhances their aerodynamic performance. The design trick even works on competition bicycles. Therefore, "all of the above" is really the answer the "What is a Kammback" question.

1982 Spirit Kammback and a Liftback visible in the background

The all-wheel drive Eagle Kammback at work in a forest (image from AMC brochure)

All sources accessed in 2004:
http://autorepair.about.com/library/glossary/bldef-513.htm
http://www.answerbag.com/q_view.php/7980
http://www.cardesignnews.com/news/2004/041203mcd-history3/
http://www.design-classic-cars.de/jaray/fachsenfeld01.html
http://www.design-classic-cars.de/jaray/kamm.html
http://www.katylon.com/harisauto/x_archive/jaray/jaray.htm
http://yarchive.net/car/aerodynamics.html
Chevy Vega image: scan from a GM sales brochure.
Pontiac Kammback image: http://www.indiemonkey.com/firebird/
Ferrari 250 GTO image: www.carsfromitaly.com/ ferrari /f_ 250 gto .html

Special thanks to Frank Swygert, publisher of the "American Independent Magazine" (AIM)
http://farna.home.att.net/AIM.html