Based on the teardrop shaped Rumpler four seat road car, this was the first mid-engined grand prix car.  It was designed with a low frontal area and a teardrop shaped fuselage to reduce drag.  The purpose of a teardrop shape is to keep the air flow boundary layer attached which reduces negative pressure wake and therefore form drag.

In 1934, Dr. Ferdinand Porsche further refined the teardrop shape in this mid-engined grand prix car.  Later, the cockpit was fully enclosed to pursue speed records.  A 545 hp blown V16 powered the fastest version to 267 mph which then crashed.  The record breaking coupe was susceptible to cross winds and had lift at speed.

Far ahead of his time, Michael May was the first to use a wing to increase overall grip of the car.  He mounted a cockpit-adjustable wing in the middle of this mid-engined, 1500 cc, 125 hp Porsche.  In practice, this novice driver in his winged car challenged the most powerful cars of its day, but it was not allowed to compete.

In 1961, a V6 mid-engined Ferrari spyder was the first to use a spoiler on the rear deck.  The spoiler "welled up" the airflow on the deck creating a high pressure area and thus reducing lift at the rear.  The spoiler was widely used in the 1960's and a prime example was the Le Mans-winning Ferrari 250P.  Tire advances allowed 1 G cornering in the early 60's.

Reviving teardrop streamlining, this fully enclosed coupe incorporated a downward sloping "fastback" rear deck.  Unfortunately, the original had no rear spoiler (but was added later).  Typical of cars in its day, its curved under nose was believed to help the car "cut through" the air as a boat hull "cuts through" the water. 

The Ford GT40 was first car to "trim out" both front and rear lift through the use of spoilers.  Like its predecessor the Lola GT, the GT40 was a low frontal area fastback design (although its fastback notched slightly between the rear window and deck).  While its "untrimmed" shape had front and rear lift, a front spoiler (directing air to the radiator) reduced the "ramming" and "wedging" of air under the nose and the rear spoiler kept the flow attached to the notched rear deck.

In 1967 the rules were changed to permit a narrow windshield.  The Ford GT40 Mk IV was designed with the entire cockpit narrowed to reduce frontal area and therefore drag.  Its fully lowered nose profile was an integrated solution to minimize front end lift.  This car also used slab sides.

In 1966 Jim Hall brought the wing back to increase rear grip.  He incorporated a cockpit-adjustable rear mounted wing on his Chaparral 2E open cockpit Can Am car.  In 1967 his Chaparral 2F endurance coupe used a rear wing and its lowered nose achieved negative front lift.  In following years, wings were widely used (particularly in open wheeled cars).  Tire advances at this time allowed 1.3 G cornering without aerodynamic assistance.

In contrast to the downward sloping fastbacks of its day, its horizontal rear deck and spoiler produced negative rear lift.  While the high tail increased drag somewhat, the gain in negative rear lift and stability were given higher consideration.  With its low nose, the Lola achieved negative front and rear lift without wings.  The Lola T70 was the first coupe to eliminate front and rear lift by means of an integrated nose and tail design.  In 1969, the Mk IIIB nose had a bottom lip, in essence an horizontal splitter, further restricting air under the front.

These two cars were developed and raced in a 5 liter limited production class (25 copies).  The short tailed versions of both cars optimized the low nose and high tail of the Lola T70 and incorporated fixed rear wings.  The Ferrari 512M had a full rear wing and some versions of the Porsche 917 had either a partial or full rear wing.

This 1100 hp open cockpit Can-Am car further optimized negative lift at the expense of drag.  With a "shovel" nose and a cantilevered slotted flap rear wing over its "long tail," the car produced 2200 lbs of down force and 2 G on the skid pad.  While the additional drag restricted the car to only 230 mph, the 917/30 is probably the greatest non-ground effects, open cockpit car to date.

In 1979-80 I tested 1/12th and 1/10th scale cars in a University of Washington fixed ground plane wind tunnel.  Inspired by the open wheeled Lotus 78/79 ground effects cars, my mid-engined models incorporated a venturi bottom in a full bodied coupe.  The best configurations produced negative front and rear lift drawing flow from both the front and sides over a flat mid section bottom.  As it turns out, the Lola T600 was being developed at the same time. 

Patterned after the Lotus 78/79 open wheeled cars, this was the first successful IMSA GTP coupe employing full "venturi bottom" ground effects.  A large rear "diffuser" draws high speed low pressure air through the "throat area" under the middle of the car.  This 600 hp car, along with most GTP cars in the 1980's, also had a low nose, horizontal splitter, slab sides, downward sloping rear deck and rear wing.

The 956, and its successor the 962, dominated GTP racing in the mid 1980's achieving 2.5 G on the skid pad.  The longitudinal venturi channel "bubbled up" between the front wheels to retain a constant underwing area.  Patterned after the Lola T610, a "short tail" version was complemented with a "long tail" version (actually the same length) with a shallow diffuser for high speed tracks.  While not the most advanced ground effect cars, these were the most successful cars of the GTP era.

The goal of "Project 400" was to achieve 400 kph (249 mph) with a low drag, stable GTP class car.  With its low down force underwing (1100 lb), enclosed rear tires and partially enclosed front tires, the 900 hp car officially clocked 251 mph (405 kph) in 1988 Le Mans qualifying. 

Originally developed on the TRW Jaguar XJR-6 in 1985, the Nissan GTP cars incorporated a flat mid section bottom which allowed the diffusers to draw air from the front and sides.  Capable of generating 7000 lb down force at 200 mph, the Nissan dominated GTP racing in 1988-90.  In Le Mans trim, the 1000+ hp car achieved 230 mph.

This car utilized a two tiered rear wing with the height of the bottom wing set low to act as a diffuser extension.  While diffuser length was limited by the rules, it was known from wind tunnel testing that the longer length would significantly increase down force.

The IMSA GTP class of "venturi-bottomed" cars was succeeded by other racing sanctions which featured "flat-bottomed" cars.  One example was the FIA GT1 class in the late 1990's.  These "flat-bottomed" coupes had a flat plane between the front and rear wheel center lines.  Aft of the rear centerline, the bottom could slope upwards slightly to the rear of the car (maximum of 5.9 inches).  These rules restricted the tunnel and diffuser development and overall ground effects of the cars.  An example is the 1998 Porsche 911 GT1 which had 550 bhp.

For decades cars at Le Mans have sacrificed grip to optimize for low drag (Porsche 917 long tail).  The Mercedes-Benz CLR was a GT1 class flat bottomed car which the designers attempted to eliminate down force for speed and fuel economy.  However, there was no margin of safety with the CLR because two cars "blew over" in Le Mans practice and one became air born in the race.  In these incidents the CLR was following another car at a location where there was a "falling away" of the track.  It is quite likely that turbulence from the leading car and the "angle of attack" change adversely affected the lift of sharp nose (a shape inherently prone to instability).

Historical Insights

There are a number of insights one can learn by looking back over this historical perspective.

Racing Sanctions: The Good and the Bad
Racing sanctions, their classes and rules were good because they established the incentive for competition and the development of aerodynamics.  Conversely, they did restrict development at times (moving wings, maximum diffuser tunnel length) and whole classes of cars were dropped (5 liter production coupes, Can Am cars, GTP cars) initiating "aerodynamic droughts."

Trail Blazers and Successors
Often times one car would introduce a new technique and a successor (sometimes from the competition) would have far greater success with it.  Examples include the negative lift nose and tails of the Lola T70 followed by the Porsche 917K or the ground effects of the Lola T600 followed by the Porsche 956/962.

The Aerodynamic Quest
At times there would be a step forward along with a step backward.  This was the case with the fully enclosed fastback Lola GT which had no spoilers and the Ford GT40 Mk I with its "notched" fastback.  Techniques typically progressed from small advances to all encompassing approaches.  For example, the use of spoilers to "trim out" lift (Ford GT40) was followed by integrated nose and rear deck shapes (Lola T70).  Once the top of the car was developed by the early 1970's, then the bottom was developed with ground effects (Lola T600) in the 1980's and early 90's.

More Power, Less Power, More Power
As engine development in a given racing sanction produced more and more power (sometimes over 1000 hp), the engine restrictions enforced by the following racing sanction further limited engine size and aspiration to restrict horse power (typically to 600 hp).  The developers would then squeeze out more and more power within that set of rules and the cycle would continue.

The Edge of the Envelope
What remains undeveloped at the edge of the performance envelope?  Up to the end of the GTP era, the rules limited body length so the back edges of the rear deck and the diffuser never came together.  There always existed a residual of rear "base area" creating negative pressure wake and therefore drag.  A longer length rear deck and diffuser would bring the edges together and reduce drag.  In addition, the rules never permitted movable body surfaces.  One can see that an cockpit-adjustable or load-limited diffuser would produce the best of both worlds - high down force in corners and low drag at high speeds.