Aerodynamics
Richard Roake
Most vehicles can be broken down into a few elements that make or break the design. In this case we have drag that needs to be offset by the thrust, lift that needs to be offset by downforce so the car stays on the ground, and the weight of the car that determines what sort of thrust is required to get the acceleration you require to accelerate in x amount of time to a given speed while still being bounded by the two previous requirements.
When you break out the 3 requirements above, drag quickly becomes your obsession, followed by thrust and mass. A simple way to understand this is what is called Flat-Plate Drag Area (FPA) which can be used to make a comparrison between different vehicles, be it a car, an aircraft or a boat. Rather than comparing different shapes and sizes of vehicles we can simply compare how efficient they are compared with each other at given speeds. The flat plate area is measured in square feet and can be imagined as a large (or small) flat object moving forwards through the air. The smaller the area the lower the drag and the more efficient the vehicle moves through the air (or water in some cases below).
To put all this into perspective, the list below compares various vehicles at their maximum speeds with their drag areas.
| Vehicle | Speed (mph) | Horse Power | FPA (ft^2) |
| Thrust SSC | 763 | 103,277 | 34.32 |
| Bloodhound SSC | 1,050 | 125.038 | 18.46 |
| Bugatti Veyron | 253 | 1,001 | 9.13 |
| 2006 Hummer H2 GT | 140 | 566 | 29.92 |
| Top Fuel Hydroplane | 260 | 7,000 | 52.92 |
| UIM F1 Hydroplane | 140 | 425 | 20.85 |
| Spitfire F MK24 | 454 | 2,120 | 6.97 |
| P-51D Mustang | 387 | 1,335 | 3.07 |
| F-22 Raptor | 1,129 | 154,861 | 75.63 |
| Jetblack | 253 | 957 | 8.50 |
| at 1,000mph | 1,000 | 81, 323 | 12.00 |
Having done some initial CFD work to confirm our initial design concepts validity, we feel comfortable in the fact that the CFD solutions are a bit better than out initial assumptions. The video below shows a top view of the way Jetblack interacts with the oncoming air and what is happening behind the car as it travels forward.
The different colours represent different pressures - Red is high pressure through to Blue which is low pressure