Aerodynamics Fundamentals: Aerodynamic Force Effects on the Engine
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Aerodynamic Force Effects on the Engine
05.17
| 00:00 | In the last module, we spoke about how aerodynamic forces affect the tyres, but it doesn't stop there. |
| 00:05 | They also have an effect on the engine and brakes. |
| 00:08 | Now, as we discussed, downforce, or FZ, can increase the amount of grip available, which will of course increase the amount of longitudinal acceleration and deceleration that a vehicle can sustain. |
| 00:21 | This will increase the load on the braking system of the car, as it must be able to provide additional force to enable that maximum deceleration. |
| 00:30 | The car will also decelerate in a shorter time frame for a given speed differential, which will decrease the amount of time that the brakes have to reject heat. |
| 00:39 | As the downforce increases the cornering speeds, we don't typically need to brake to as low a speed, however we're also entering the final corner before any straight at a higher speed, so generally speaking, we'll be faster everywhere. |
| 00:53 | This increases the amount of energy that the car will be able to generate as it decelerates. |
| 00:59 | So essentially, if we double the speed we're going, the energy doesn't double, it quadruples. |
| 01:04 | This means that even a modest increase in speed is going to put a lot more energy into the braking system, so again our brakes have to be more robust to thermal loads. |
| 01:14 | The engines in high downforce cars are also under more demanding requirements than low downforce cars, courtesy of the increased lateral and longitudinal loadings. |
| 01:24 | Oiling systems in particular can suffer from starvation and sump scavenging issues as the loadings increase, and this is one of the reasons why high downforce cars will almost exclusively run dry sump systems. |
| 01:36 | To get an idea of the cornering forces we expect to see, a stock road car can achieve around 0.8 to 1g through a corner, whereas a race car on slicks with no aero might be able to achieve 1.5g. |
| 01:49 | Add aero to a club level race car and we're pushing towards 2g, and if we go to the extreme end of the scale, modern F1 cars can corner in excess of 5g. |
| 01:59 | From a thermal perspective, in many ways engines are easier to manage on high downforce cars because the average speeds are higher, so more cooling flows are available and the time on wide open throttle per lap will generally decrease, again courtesy of higher cornering speeds. |
| 02:16 | However the main thing we need to discuss when it comes to the aerodynamic force effects on the engine and brakes is the effect of Fx, also known as the F2.2. |
| 02:24 | This is defined as the resistive force applied to any body moving through real -world airflow, and is essentially the force trying to slow our car. |
| 02:34 | Think of it a bit like a parachute, or as per my earlier example, when you stick your hand up vertically out of the car window and the force pushes it back. |
| 02:43 | Different bodywork and aerodynamic shapes will create different amounts of drag, and we generally consider drag to be a negative effect. |
| 02:50 | Drag will slow down your acceleration, determine your top speed, and slow down your acceleration. |
| 02:54 | And it will make your braking faster. |
| 02:57 | Drag is also typically generated as a consequence of downforce production. |
| 03:01 | It's rare to make a bunch more downforce on a car without increasing the drag of that car. |
| 03:06 | So it's all a balancing act. |
| 03:08 | We want to make enough downforce to corner quickly, but not too much drag that we're too slow on the straights. |
| 03:14 | In terms of what the ideal number is for downforce to drag ratio, commonly known as efficiency, there is no fixed value, and it is very situationally dependent. |
| 03:24 | Having more power will allow us to run more drag, but exactly how much is highly dependent on a lot of factors. |
| 03:32 | Different categories, cars, and tracks will demand different target downforce and drag levels. |
| 03:37 | We'll be discussing this more in an upcoming lesson. |
| 03:40 | So we'll leave it here for now. |
| 03:42 | There is one other factor to consider, and that's raceability. |
| 03:45 | So what do I mean by that? Sometimes we'll need to set up a car to deliver passing opportunities for wheel-to -wheel racing instead of ultimate lap time. |
| 03:54 | If we can't pass in a straight line, and we are easily passed down the straight, we won't perform very well in the race, even if our single lap pace is solid. |
| 04:02 | For categories with no park-for-may, which is when cars aren't allowed to be touched, or have a setup change between qualifying and race, the solution is simple. |
| 04:10 | Run a high downforce, high drag setup in qualifying, and then run lower drag and downforce for the race. |
| 04:16 | If park-for-may is in place, and no adjustments can be made, we'll need to choose what we favor more. |
| 04:23 | Track position? Through better qualifying. |
| 04:24 | Or top speed for passing. |
| 04:27 | Typically for a race, I'd personally favor the latter. |
| 04:30 | The best way to set our targets here is to look at top speeds in practice. |
| 04:35 | If we're significantly lower on top speed than other cars, then we may need to decrease our drag level. |
| 04:41 | Before we finish up with this module, let's summarize the main points. |
| 04:45 | Aerodynamic forces affect not only a car's tires, but also their engine and brakes, increasing the demand on these systems. |
| 04:52 | Downforce enhances grip. |
| 04:54 | Leading to higher speeds and increased braking load. |
| 04:57 | But also generates drag, which slows acceleration and top speed. |
| 05:02 | Balancing downforce and drag is crucial, with the ideal ratio depending on specific track conditions, car categories, and racing strategies, often requiring on -track testing to optimize performance. |
