Ground effect, from spheres to Formula 1 – History

The first systematic studies on this type of influence are placed at the turn of the 1920s, and they have by object i airfoils of the planes: it was experimentally noted that the wings had a lift increase close to the ground and this allowed pilots to perform take-off and landing maneuvers at lower speeds. Neither more nor less, the same advantages that birds have always enjoyed when detaching or approaching the ground. The first theoretical studies, attributable to various authors, C.Wieselsberger , TO. Zahm And R.Bear (1921-22), confirmed that the pressure differential on the wing, back-belly, in those conditions, was wider: the flow under the wing, having more low and therefore pressures more highgave rise to a sort of “air cushion“. Not only that, progressing with the analyzes, it was discovered that the soil, attenuating the eddies at the tip of the wings, it helped to reduce the energy dissipated in the generated contrails, resulting in a smaller one induced resistance overall. In summary, when you went below a certain altitude, comparable with the wingspan of the aircraft, the efficiency of the wing improved, with the ratio Fp/ Fr (lift / drag) growing up to double compared to that in free air.

In the context of insiders, the expression “Ground effect”(Implying on the wing) he began to identify these phenomena… with a benevolent character. The data aroused interest and would hardly have remained without specific exploitation: in fact, at the end of the 1950s, the first special aircraft made to fly at very low altitudes, from 25 to 50% of the wingspan, naturally on the sea given the obstacles of all kinds present on dry land. They were sort of seaplanes but with specific shapes and airfoils. Above all, the Russians believed in this technology to create some large means of transport, even in the military field, given the collateral advantage inherent in low-altitude flight that allowed them to escape radar localization. Ekranoplano (or screen plane) is the term coined to denote them. Their low flight altitude, which was the only possible one for the larger vessels, made them classified as “fast ships”, therefore regulated by the maritime navigation code. However, the interest in this type of transport has considerably decreased over time, and still remains only for smaller vehicles, in niche commercial applications. Returning to the authors TO. Zahm And R.Bear, it seems that, in addition to the aforementioned experimentation, they also tried a wing with an inverted profile, always close to the ground: also in this case they noted that the lift value, this time negative (downforce), increased due to this proximity, but they did not deepen, not glimpsing any kind of practical utility for this configuration. In fact, even in the contemporary world of land transport, aerodynamic research, already much less advanced than that for air transport, had a more empirical character and was solely aimed at reducing drag. Only at the end of the 1950s did the first changes begin, starting from the world of motor racing, did interest also begin in deporting aerodynamic forces. Returning to the research on the Soil Effect, in 1946 LM Milne – Thomson published a text entitled Theoretical Hydrodynamics in which there was also the study of the aerodynamic behavior of a sphere: they detected in the wind tunnel that passing from the movement in free air (no lift) to that near the ground, a deporting force was born; they also measured the relative coefficient C.pmax= -0.375, practically with the sphere in contact. The theoretical treatment clarified the role of the soil: by restricting the passage section of the air under the sphere, locally increased its speed with the consequent decrease in pressure. From the pressure field on the surface of the sphere, no longer symmetrical in the vertical plane, the downforce was born. An experimentation of the same phenomenon detected by Zahm and Bear, but the sphere instead of a wing facilitated the theoretical setting and the practical development of the calculations. A further step will be made by prof. John Stollery of Imperial College London, which in 1969with the publication of the research “Forces on bodies in the presence of the groundHe further investigated the effects of the soil. It was the fruit of the assignment received from Donald Campbell who wanted to build a vehicle to break land speed records. The shape being tested in the wind tunnel was of the “streamlined” type, similar to a symmetrical airfoil. In addition of course to the data on the resistance to advancement, the Soil Effect was highlighted, with a mapping complete lift and above all downforce, as both the height from the ground and the incidence vary. The data were also quite reliable because Stollery had obtained them by carrying out the tests in the wind tunnel of the Institute of him which, a few years earlier, had had the moving walkway. In the F1 world, were these experiences known? From testimonies of the time it seems not, and in any case if someone had been aware of them they had not considered them interesting for application in F1. It took a few more years for them to be rediscovered autonomously and above all with the addition of a decisive accessory: the flaps mobile side seal. We are at the epilogue of history. Peter Wrightperhaps the main architect of the application of the Soil Effect in F1, in the same period in which Stollery published what was described above, was working on the BRM under the guidance of Tony Rudd: the latter had been struck by the rapid proliferation of ailerons in F1 but also by their danger, so he was convinced that it was interesting to test the effectiveness of an alternative solution: two wing stumps to be mounted on the sides of the car which at the time were still in the shape of a spindle. Wright was the aerodynamicist who had to develop them, the tests were also conducted on the track by modifying one BRM P126-V12: the result was not striking, the load produced was low but with good efficiency. However, his studies were soon interrupted because the group broke up, Rudd switched to Lotus (industrial) and Wright to Specialized Moldings, a synthetic composite manufacturing industry. Evidently, however, Wright had been struck by these wing-shaped side pontoons, so much so that, the following year, 1970, he proposed them to Robin Herd who had turned to them for the bodywork of the first one March F1 the 701.

The results were similar, but they were ideal for accommodating the extra fuel tanks, a requirement of March. For a few years to follow, no one proposed these forms again, but in ’76 the duo Rudd And Wright rejoined the F1 design team at Lotus… Plus there was a certain Chapman. The latest single-seaters, the 76 and the 77, had not met expectations, Chapman wanted for the 78 (1977) an in-depth aerodynamic study that took into consideration the new tendency to have wide-base cars capable of generating and exploiting the low pressure on the bottom. The studies went on rapidly, there 78 was now defined: a narrow “chisel” nose with half-wings on the sides, a partially brushed front oil cooler and side pontoons in the shape of a airfoil containing the water radiators and part of the tank. On each of them there was the air intake on the leading edge and the corresponding opening for evacuation on the upper surface, a scheme faithfully inspired by the cooling system (known in literature) of the famous bomber Mosquito from the de Havilland (1939). The two lateral wing abutments had therefore been chosen both for the load they generated, the results were slightly better than the BRM and March ones, but above all because they offered little resistance and were therefore the most efficient forms to accommodate both the radiators and portions of the tank. The last stages from experimentation in the gallery, however, they did not follow the usual practice, the turning point was around the corner: Wright’s group was noticing that the measured values ​​were no longer repetitive, the load varied. From an analysis of the scale model it was realized that its components, in wood, plasticine… were yielding, approaching the carpet. Immediately intuition from what was happening: do not try to lower all but only the side bulkheads. With some makeshift material, he quickly adapted to extend them until they touch the moving walk … and he arrived bursting the surprise. Such a “seal” drastically limited the transverse end flows which, going from top to bottom, were the cause of the low differential: the underlying pressure dropped and the load went up … all beyond all expectations. These extremity phenomena, widely knownin this particular context of minimum elongation wing had been underestimated: the bulkheads instead canceled them and made the stumps like parts of a wing with great elongation. At that point in the group he dominated astonishment mixed with the awareness of having found an extraordinary “Effect”, who knows if they called it immediately Soil effectwhich gave these wing stumps a high efficiency (F ‘p / F ‘r), higher than what they would have gotten away from the ground. In other words, if that load had been generated with ailerons in the usual positions, they would have induced a lot more resistance advancement. However, it was not all roses and flowers, on the contrary: the group began to think about systems of side seal… But with the founded fear that they came prohibited, because they can be identified as moving aerodynamic parts. From here on is the story of 78…, Considering its historical value, it deserves a separate article. In conclusion, the rational application ofSoil effectin the version with ” the opposite signs“To the one exploited in aeronauticshad entered the world of land vehicles, starting from the tiny niche racing single-seaters; Chapman, with his usual sagacity, to describe this phenomenon of physics, said:Ground Effect is something for nothing.

FP | Andrea Pesaresi

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