Influences of Aeronautical Engineering at Motorsport Engineering (part II)
Hello Everybody
At the previous post, I talked about the first motorsport cars with aerodynamics generating downforce. This downforce helped the car to gain lateral acceleration in cornering, increasing cornering speed. The gains with regular front and rear wing design were not converging into the best configuration, until Colin Chapman developed the first ground effect car: the Lotus 78 (see details of this introduction into the previous article here).
At this point, when Lotus 78 ground effect car was developed, the need for ground effect downforce in Formula one (and also other categories) were the rule of a competitive car. The Lotus 79 (evolution of Lotus 78) was so dominant that every competitor tried to develop his Ground Effect car his own (not only at Formula One, but also at other categories in motorsport, like Indycars and so on).
Figure 1 - Lotus 79 Ground Effect Cat. The Evolution of Lotus 78 car that dominated the 1978 F1 season
The fight for finding downforce at the bodywork of the car came to a play. Do you remember Chaparral 2J? The concept of sealing the bottom of the car and to use an air compressor to generate low pressure at the bottom of the car was back! At 1978, the Chief Design Engineer of Brabham F1 team Gordon Murray was suffering to make a design of lateral wings to generate ground effect downforce, because the Alfa Romeo V12 engine was too wide to fit those lateral wings at the car. The Brabham BT-46 was suffering a lot from lack of downforce against the Lotus 79. The solution came after looking Chaparral 2J. Gordon Murray thought: "How about putting an air compressor into the car in order to generate this low pressure area below the car, using also this air compressor to generate cooling to the powertrain system?". With this in mind, Murray developed the Brabham BT-46 Fan car.
Figure 2 - Brabham BT-46 Fan Car
The 1978 F1 regulations permitted a moveable aerodynamic system, which must be MAINLY for cooling purposes. This MAINLY means that this is the main objective, but secundary objectives can play a role. This car, then, had sealing skirts at its bottom and the air compressor sucked the air from the bottom part of the car, creating a very low pressure area (remember the Bernoulli Principle? The higher the speed, the lower is the pressure) below the car, as seen at Figure 3.
Figure 3 - Brabham BT-46 car with the air cooling and low pressure system
This car, when raced, was unbeatable. It won the single race that he competed. In order to avoid problems (political reasons), Bernie Ecclestone (owner of Brabham Team), decided not to race this car once again (the car was legal, but other teams insisted that it was illegal). At 1979 season, this technology was banned.
What happened between 1979 and 1982 was a fight to find even more downforce from the ground effect car. With this fight to find even more downforce attended to the car structure to support even higher loads and stress. It was even harder, with the materials that the Motorsport teams used (Steel, Aluminum sheet and honeycomb, Magnesium, etc), to make structures that supports all these increasing loads without increasing significant weight. There was a compromise between downforce and weight that was limiting this increase of downforce. In addition to, the car structure must be enought to provide stiffness to bending and torsional stress at chasis, to make the car have desired weight distribution at braking and cornering phases. With higher loads, to maintain the stiffness of the bodywork, additional structures and material must be used, which increased weight.
The solution? John Barnard, as written at his biography "The Perfect Car: The Biography of John Barnard" was to adopt Composite Materials to increase the downforce without increasing too much the structure weight. This was made at 1981, at the McLaren MP4-1 - the first entire composite (Carbon Fiber) F1 car!
What happened between 1979 and 1982 was a fight to find even more downforce from the ground effect car. With this fight to find even more downforce attended to the car structure to support even higher loads and stress. It was even harder, with the materials that the Motorsport teams used (Steel, Aluminum sheet and honeycomb, Magnesium, etc), to make structures that supports all these increasing loads without increasing significant weight. There was a compromise between downforce and weight that was limiting this increase of downforce. In addition to, the car structure must be enought to provide stiffness to bending and torsional stress at chasis, to make the car have desired weight distribution at braking and cornering phases. With higher loads, to maintain the stiffness of the bodywork, additional structures and material must be used, which increased weight.
The solution? John Barnard, as written at his biography "The Perfect Car: The Biography of John Barnard" was to adopt Composite Materials to increase the downforce without increasing too much the structure weight. This was made at 1981, at the McLaren MP4-1 - the first entire composite (Carbon Fiber) F1 car!
The carbon fiber was a very strength material that was developed since the 50's. The main purpose was to offer heat resistance to jet rocket orifices. But, it was soon noticed that carbon fiber was a very strenghtfull and stiff material, much superior to tensile stress than any metal alloy. Since the 60's, the material is used to make parts of aircrafts (Turbofan jet blades, engine-mount structures, parts of wing structures, etc), at aerospace industry (rocket engines, etc) and many other applications like sweetfish fishing rods and golf club shafts.
Figure 5 - Rolls Royce RB211 Turbofan aircraft engine (1967) - the first one to adopt carbon fiber blades
Why this material was not used before at motorsport? Because it was such easy to make the cars to achieve the rules minimal weight with standard materials, before the ground effect played a role! In adittion to, carbon fiber was in development and it was VERY expensive. Until ground effect, there was no need to use such expensive material at motorsport.
The main advantages of composite material was also to have different material properties in different directions of the element structure. Let's understand it a little bit better.
At the figure below, we have the 3D Stress state (with axial and shear stresses acting on a 3D element). Considering that Carbon fiber is a 2D orthotropic material (which means that the carbon fibers are perpendicular to each other) we can simplify it into a Plane Stress:
Figure 6 - 3D Stress state simplifyed to Plane Stress element, with the traction/compression stresses (σx and σy) alongside shear stresses (τxy).
Figure 7 - Orthotropic carbon fiber tissue, with its fibers perpendicular with each other. The most commom commercial carbon fiber of the world.
Figure 8 - Carbon fiber failure due to compression stress. Here we can see that delamination (due to buckling) is taking a huge role at the failure of the structure
Figure 9 - Carbon-fiber sandwich with aluminum honeycomb. This is a very resistant structure and very lightweight also, resistant to stresses at many directions.
Because of this feature of different strength and stiffness at different directions, the designer can make the structure stiff and resistance to a certain load in a certain direction, and at other direction there is no need to make the structure to have the same resistance and stiffness. Then, depending of the loads that are acting at the bodywork, the structure engineer can make an optimization of the directions of the carbon fiber sheets and the number of sheets needed to support such loads, making the structure even lighter! In addition to, with Carbon Fiber you can make complex shapes of bodywork in a very simple way: just using molds.
Figure 10 - Carbon fiber modelling process.
This is when Carbon Fiber started to be the standard of Motorsport, but also increased the costs to develop a car. Carbon fiber was not cheap, and the tooling and autoclave costs were very high (much higher than ordinary tooling to make metal structures). Also, the need of computation increased, then, the need of staff of engineers and computers just increased very much. This explains why nowadays it is difficult to.have a team at Formula One and a team in top categories of motorsport.
After 1982, Ground effect was banned and new solutions arrived. There was a need to increase the efficience of front and rear wings, to increase downforce at this wings to compensate the loss of downforce due to ground effect. Researching at wind tunnel, Mclaren engineers realised that if the back of the car was narrowed, the efficience of the flow at the rear wing increased and the downforce increased also. This narrowing of the back of the car was called "Coca-Cola bottle shape".
Figure 11 - Coca-Cola bottle shape at the back of the car. This configuration of aerodynamics is still used since it was developed in 1983.
Figure 12 - The first car with "Coca-Cola" bottle shape - Mclaren MP4/1C (1983).
This Coca-Cola bottle shape is standard nowadays at motorsport (Formula cars, as seen at Figure 11). There is always a need to narrow the back of the car the most possible just to the rear wing to have a clean (less disturbed) and effective flow.
This need of creating a effective flow into rear wing was also an objective pursuit by the aeronautical industry. The T-tail configuration is used at Aircrafts to avoid the disturbed flow of wing and fuselage. With this clean and almost undisturbed flow, the horizontal tail can be smaller than conventional horizontal tail. The option for T-tail depends of other dedicated studies (analysis of the horizontal tail flow at stall conditions, interference of jet engine flow at horizontal tail, etc), but the main advantage is to make the horizontal tail free of disturbance of wing and fuselage.
Figure 13 - Conventional Tail (left) vs T-tail configuration (right)
Figure 14 - Embraer KC-390, with its T-tail configuration. We can see that the horizontal tail is high enough to avoid fuselage and wing disturbed flow at cruise configuration (low angle of attack configuration).
At last, after the ban of skirts and ground effect at Formula 1, at other categories, there was a development of undertray (tunnel) element, which generated downforce at bodywork due to venturi effect (Figure 15). The effect of such a tunnel on the air is similar to a diffuser. The air enters the diffuser in a low-pressure, high-velocity state after accelerating under the car. By gradually increasing the cross-sectional area of the diffuser, the air gradually slows down and returns to its original free-stream speed and pressure. The diffuser's aim is to decelerate the air without it separating from the tunnel walls, which would cause a stall, reducing the downforce and inducing a large drag force. By installing an inverted wing close to the diffuser exit it is possible to create a low-pressure area, which essentially sucks the air from the diffuser. The diffuser and wing combination permits a higher air-mass-flow rate through the diffuser, thus resulting in higher downforce. Sharp edges on the vertical tunnel walls generate vortices from entrained air and help confine the air through the diffuser and reduce the chance it will separate. This effect will be adopted into Formula one at 2022, after 30 years using flat bottom at the cars, in order to generate downforce with less air disturbance generated.
Figure 15 - Undertray tunnels in different type of racecars.
Figure 16 - Undertray tunnels in a Indycar.
Figure 17 - Undertray layout (venturi tunnels) at 2022 F1 concept vs 2021 F1 floor concept.
Since then, the aerodynamics of the cars did not suffer a great revolution. The fight for downforce is nowadays into details and how much the teams works into the flow of the car to divert from tyres, cancelling undesired vortices and to understand the regulations of each category to work at the refinement of the aerodynamics. Each piece of bodywork has a little effect on aerodynamics that, when added, generated a great effect at the car. That is why the aerodynamics of a motorsport car looks very complicated nowadays, because it is difficult to extract a huge amount of downforce at nowadays motorsport regulations. Then, you need these small devices to extract the maximum possible of your car, in order to organize the flow around it to generate the maximum downforce with the less drag possible.
Figure 18 - Aerodynamics of modern Formula one car. Take a look at aerodynamic devices at front wing which generates vortices to control the flow over the car and the aerodynamic devices that deflects the flow from the front tire. These kind of devices are playing a big difference in modern motorsport cars.
In addition to, aeroelastics also is playing a huge role in modern aerodynamics. The deflection and deformation of the structures can generate positive advantages under certain conditions. For example, the rear wing twist back into high speeds, making the angle of attack of the rear wing diminish and generate less drag, which is beneficial at straight acceleration. Of course that there is regulations that limits the deflection and deformation, but whithin the limits, the teams works with those deformations to maximize car performance under certain circunstances. This aeroelastic effects was also very studied in aeronautical engineering.
Figure 19 - Aeroelastic effects in a rear wing of a Formula 1 car (picture by Giorgio Piola).
Nowadays, we can state that aeronautical engineering is very deep into motorsport. Depending of the category, the aerodynamics is the most important factor in motorsport performance at track. At the next few years, research at aeronautical engineering can also play a role at motorsport, like: morphing, load alleviation system, natural laminar flow due to flow ionization, etc. About these new technologies, I will talk about later, on a new and dedicated post. These technologies could be incorporated also in motorsport, generating gains into car performance at races.
Figure 20 - Morphing on a wing. With a flexible structure and a servo-motor, the shape of airfoil (wing cross section) and the shape of the 3D wing can change due to position of servo-motors. This could shape the airfoil into its best shape for each flight or race phase. There are many prototypes of aircraft with this kind of structure (in phases of study), but at motorsport it was not tested yet.
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