The Lotus 56 was a racing car, designed by Maurice Philippe as Team Lotus' 1968 entry in the Indianapolis 500, replacing the successful Lotus 38.
The Lotus 56 used a modified version of the ST6 gas turbine used on the STP-Paxton Turbocar ("Silent Sam") that almost won in 1967. The ST6 was based on a small aircraft engine that would become one of the most popular turboprop aircraft engines in history. But the car itself was an entirely new and more advanced design which introduced a distinctive aerodynamic wedge-shaped body rather than a cigar-shape, just a few years before the introduction of front and rear wings. USAC, the governing body of the Indy 500, had implemented new rules aimed at handicapping turbine powered racing cars by drastically reducing the air intake size. Te Lotus 56 made up for reduced power with a sophisticated suspension design, retaining the 4wd concept of the Silent Sam, but with lighter weight, and advanced aerodynamics.
Lotus had suffered the death of Lotus' ace driver Jim Clark in a Formula 2 race in Germany. Mike Spence was killed at Indianapolis in one of 4 56's built while testing it. The remaining 3 cars with Graham Hill, Joe Leonard, and Art Pollard were entered for the race, with Leonard claiming pole position. Unlike the year before, when the STP-Paxton Turbocar easily outperformed the other cars in the race, in the race the turbine cars were relatively evenly matched with the other top contenders, much of which must be attributed to aerodynamics and the 4wd chassis design and not the turbine engine. Hill's car crashed, Pollard's car broke down, while Leonard was leading with just a handful of laps to go when the a fuel pump shaft failed. Shortly thereafter, the USAC imposed additional restrictions on turbine cars that essentially removed them from competition. For the second year in a row STP turbine cars had brought innovation to the Indy 500 and had failed to win while leading within a few laps of the end of the race. USAC subsequently banned turbine cars and four-wheel drive completely, but it was unusual enough that Mattel produced as model as the "Lotus Turbine" as one of the popular mass-produced die cast Hot Wheels cars.
In 1971 the Lotus 56 was raced in Formula 1 on occasion by Team Lotus but the large fuel tanks required to allow it to run an entire race without refueling left it overweight and uncompetitive.
The Lotus 56, while never winning a race, demonstrated the importance of aerodynamics in racing cars, along with Jim Hall's Chaparrals, and effectively set the mold for open wheeled racing cars for the next ten years. Chapman's Lotus 72 employed the same wedge nose shape and went on to win three world championships in Formula 1.
Colin Chapman developed the 56 as a potential F1 contender, part of his plan to have a single design to compete at both the Indy 500 and in Formula 1, but it was too heavy and never competitive. The car was designated as the 56B and Emerson Fittipaldi tried it in the 1971 Race of Champions and International Trophy non-Championship meetings. At Brands Hatch, during wet practice, the 56 was far and away the fastest car on the track, but the race was held in dry weather and the car was lost in midfield. At the Silverstone-based International Trophy, the car only lasted three laps of the first heat before suspension failure forced Fittipaldi's retirement. Dave Walker ran the car in the Dutch Grand Prix, and had progressed from 22nd to 10th in five laps of the very wet track, before sliding off the road and into retirement. Fittipaldi used the car again in that year's 1971 Italian Grand Prix and managed to bring the fragile design home 8th.