In early 1976, spurred on by a disappointing lack of pace of the ageing Lotus 72 the previous season and the indifferent performance of the current Lotus 77, Lotus founder and principal design engineer Colin Chapman wrote a 27-page document detailing some new ideas on low drag air penetration. Having studied the de Havilland Mosquito fighter bomber, he had paid close attention to its wing-mounted radiators and the hot air outlets designed to induce lift. Chapman realised that, inverted, such a system could give significant downforce. Careful examination of Bernoulli's principle of fluid dynamics confirmed his thoughts on the effects of an upturned aeroplane wing profile fitted to a car, and he handed the document to his head of engineering, Tony Rudd.
Rudd appointed a team to work on the project: chief designer Ralph Bellamy, vehicle engineer Martin Ogilvie, and aerodynamicist Peter Wright. Rudd and Wright had previously worked for BRM, and before joining Lotus in 1970 had done a design study into the possibility of an inverted wing profile fitted to one of their cars. Wright remembered their work and brought it into the project.
Wright set about experimenting with F1 car body shapes using a wind tunnel and a rolling road, when by happy accident he began to get remarkable results in one of the models. Closer inspection found that as the rolling road's speed increased, the shaped underbody was being drawn closer to the surface of the road. Wright experimented with pieces of cardboard attached to the side of the model car body, and the level of perceived downforce produced was phenomenal. The results were presented to Chapman, who gave the team free rein to come up with an F1 chassis design.
After a round of design sketches, engineering drawings, and further wind tunnel work at Imperial College, the car was put into production. Five examples were built, codenamed John Player Special Mk. III, otherwise known as the Lotus 78, which appeared in July 1976. Mario Andretti wanted to introduce the car early, possibly at the Dutch Grand Prix that year, but was overruled by Chapman, who did not want other teams discovering what Lotus had achieved.
The 78 was loosely based on the Lotus 72, sharing the same basic wedge shape and internal layout, but featuring detailed aerodynamic improvements, better weight distribution, and a longer wheelbase. It had a slimmer, stronger monocoque made from aluminium sheet and honeycomb, developed from the 77. The bodywork was made up of fibreglass body panels with aluminium used to strengthen the chassis at points.
Based on Bernoulli's discoveries, the underside of the sidepods were shaped as inverted aerofoils, in the same vein as conventional wings but on a much larger scale. By shaping the floor of the car in this way, the team could accelerate the air passing through the gap between the ground and the underside, thereby reducing the air pressure under the car relative to that over it. This created significant underpressure, effectively sucking the vehicle down and forcing the tyres harder onto the track. Copying the Mosquito's radiator design, the radiators were positioned so that the hot air escaping would pass over the upper bodywork of the car, creating even more downforce.
The greater downforce on the tyres gave more grip and thus higher cornering speeds. This ground effect had the advantage of being a low drag solution unlike conventional wings, meaning that the increased cornering ability was not compromised by a decrease in straight-line speed.
To begin with, brushes were fitted to the base of each sidepod to keep the low pressure area under the car. When these proved insufficient, Lotus tried plastic skirts, but these abraded very quickly; finally, moveable rubber skirts were developed which proved very effective. The sliding skirts sealed the gap between the sides of the car and the ground, preventing excessive air from being sucked into the low pressure area. Andretti described driving the 78 as if it were "painted to the road."
The fuel tanks were three separate cells: one behind the driver and one in the midsection of each sidepod. The sidepod tanks could be controlled from the cockpit, used to fuel the engine separately or together, improving performance and weight bias in cornering. The suspension setup from the Lotus 77 was used, designed for quick changes in geometry to suit specific circuits.
A significant limitation was that the low pressure area under the car was found to be too far forward, requiring a very large rear wing that produced considerable drag at high speeds. This was especially noticeable on fast tracks such as Hockenheim and the Österreichring, where the Ferraris and McLarens were much faster than the 78. Ford provided development versions of the Ford Cosworth DFV to compensate, increasing the car's speed but also sacrificing reliability. Andretti suffered no fewer than five engine failures in 1977, which cost him the world championship to Niki Lauda, even though he had won four races and taken six pole positions to Lauda's three wins and two pole positions. Eventually a smaller wing was designed in time for the Italian Grand Prix, which cut the drag factor significantly and allowed Andretti to take a popular victory.
Another problem was the rear suspension, which remained directly in the path of air exiting from the rear of the sidepods, affecting the stability of the back of the car and causing oversteer.
The 78 was introduced at the first race of 1977 and proved to be the class car of the field that season, winning five races. The car proved relatively easy to set up and modify, with particular attention paid to the undercar aerodynamics and their interaction with the track surface. It was obvious the Lotus 78 had some special feature: when the car worked well, it was almost uncatchable, as proved by Andretti and Gunnar Nilsson winning the race in Belgium.
Other teams scrambled to replicate its performance for 1978. They were confounded because Chapman and other members of the Lotus team offered any number of explanations to obfuscate the real reason for the car's pace, and the side skirts hid the underside from view.
The 78 remained a winner in early 1978, with Andretti and Ronnie Peterson scoring a win each and another three pole positions before the car was replaced by the Lotus 79, which was as far ahead of the 78 as the 78 had been ahead of the rest of the field in 1977.
The 78 saw one further works team start. Owing to damage sustained to his 79 in practice, Peterson was forced to use the reserve car, 78/3 (JPS-17), to qualify for the 1978 Italian Grand Prix. The car had not been maintained or developed by the team as they concentrated on the 79, and was hurriedly prepared for the race. Although his teammate Andretti predictably took pole position, the slower 78 qualified only fifth. Peterson was caught up in a massive start-line accident, which resulted in his car ramming the barriers nose-first, completely destroying the front end. Peterson later died owing to complications arising from the treatment he received following the crash.
The original development prototype, 78/1 (JPS-15), was sold to Héctor Rebaque. He ran this car through his Rebaque privateer team in World Championship events during 1978 and 1979, and in non-Championship races into the early 1980s.
In all, the Lotus 78 took seven wins, nine pole positions, and scored 106 points in its career.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.
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