Defining the scope

The scope sets the limitations on how we should go about achieving our goals, and how much our goals can or can't be stretched or changed. This requires that we have goals to apply such limitations to...

With our small team and lack of sufficient previous data, it was obvious that designing, manufacturing, and testing a full aerodynamic package (front, mid, and rear of car) within 12 months was not going to be achievable. The team has previously managed this twice (albeit with more members), but the end results were lacking performance to justify the cost and effort, and both validation and documentation were almost non-existent. No surprise then that the team had to start from scratch each time, until ultimately the plug was pulled on aerodynamics at the end of 2018 for the next 5 years. 

That's where this year's goals and scope come in. This time, we're looking beyond the 1-year cycle. We want genuine real-world performance and, most importantly, we want to set up a foundation to build upon each year. This means that for 2024, development of testing methods and simulation software are focus areas, and will dictate every choice made. It's from this idea that our individual SMART goals and KPIs for the aero team naturally spawned. The build-up to this sustainable ongoing development was organised into a 5-year plan for the aerodynamics team, summarised with goals for the end of the period:

Goals:

• Have the aerodynamics team big enough and experienced enough to be able to develop full aerodynamics packages on a 24-month design/optimisation cycle, with justified performance vs resources and development time trade-off, and sufficient data and documentation to allow and feed continual improvement 

• Solid understanding of both steady-state and dynamic suspension and VD behaviour to enable informed decisions on maximising performance beyond just steady-state downforce and drag in ideal scenarios and conditions

• All significant performance-altering aspects of the CFD model should be identified, and either semi-permanently validated (pending "large" aero changes to the car), or have a defined recurring validation test plan 

General timeline and methods to achieve the goals:

• Spend two years (first 24-month design cycle) focussing on just a simple ground-effect side-floor design to provide experience in CAD/CFD, and allow a focus on experimental testing of airflow behaviour, kept within a manageable scope and cost. This will feed into initial development and tuning of the CFD setups for precision, accuracy, and relevance/usefulness, while allowing a build-up of experience in understanding how different surface designs affect and utilise the surrounding flow field. This will also be the time to determine a selection of vehicle scenarios for the CFD setups that are most representative of full-lap performance, and are most efficient at picking up conditional sensitivities. The low force magnitudes resulting from a simple side-floor design also mean the influence on suspension (and more generally, vehicle dynamics) doesn't need to be considered during this phase.

• Spend two years (second 24-month design cycle) adding a rear diffuser and side-mounted wing design to add an additional 50%-100% downforce. These increased forces will allow a similar learning experience to occur, but this time focussing on vehicle dynamics and suspension interaction for validation of suspension/VD simulation, lap simulator, and verification of data collection methods and the ability to correlate suspension data with aero pressure data. Experience with larger-scale aerofoil manufacture/mounting and managing the build processes of multiple parts is also an important outcome. Keeping the aero surfaces concentrated toward the centre of the car will continue to keep mounting requirements simple. At this stage, pure on-track performance of the vehicle is still not a priority in its own right. 

• Spend the second half of the fourth year (end of second 24-month design cycle) setting the goals and scope for a full aero package, while considering manufacture and mounting planning as these will now be significant processes. Begin surface design, continuing in the fifth year, and have a simple but efficient and insensitive full-aero package by the end of the fifth year that can be easily optimised and built upon with reasonable confidence over subsequent years. Consideration will be needed at this point as to whether the team chooses a sprung or unsprung aero mounting method. After the first full package design and testing, on-track performance will become the priority and dominate the scope and goals. 

While performance goals aren't the focus of the first two years, it's a good idea to still have a target based on what should theoretically be possible.

Providing there isn't too much drag up high, making a decent amount of downforce with a central floor will hopefully bring the centre of pressure into the ballpark of our lap-sim's optimum front/rear aero balance of 70% rear. 

Some quick research and reconnaissance of other teams suggest a well-designed but simple floor should be capable of around Cl*A = -1.0 to -1.2 (ideal/CFD values). We set a target of -1.2 accordingly, for a straight-airflow case at 80kph. For reference, if our car attained this during the skidpan driving scenario, we would be making 6-7 kg of downforce. At our Vmax of ~110 kph, it would be 65-70 kg, but a more realistic maximum speed for autocross is 85kph and thus just under 20kg of downforce per floor, which should be easy enough to design simple mounting for. We expect that a Cd*A of no higher than 0.7 should also be achievable, and therefore targeted. If we meet the above downforce and drag goals, and assume a worst-case manufacturing scenario of high weight (5kg total) and standardised cost event price ($1000), we are still making an estimated 11 point gain (2.1%) over all competition events assuming perfect performance at all times. Not an important consideration given the goals for this year, but good to know we're unlikely to be limiting the car's score at competition if we choose to run with the side-floors.