Every package should be set up to allow the vehicle to travel through air as efficiently as possible.
The importance of aerodynamic soundness depends on the type of vehicle. Sports cars need high airflow and downforce improve top speed, handling and engine/brake cooling. Trucks, however, usually have drastically compromised aerodynamics because of their large frontal surface area and underbody structure.
The two most important aerodynamic factors are the drag coefficient (Cd) and total drag. Analogous to the coefficient of friction from AP physics, the drag coefficient (Cd) is an intrinsic property that measures the "slipperiness" of a particular shape, regardless of its size. The total drag is the product of this coefficient and the cross sectional area of the vehicle. This product is a force, which describes the amount of force needed to propel the vehicle.
Airplanes obtain "lift" when the air pressure below the wings exceeds air pressure above the wings. At high speeds, this phenomenon starts to influence the handling and balance of cars too. Spoilers are often applied to maintain consistent down force on the front and read tires, improving traction as well.
Vehicles also need air intake systems to perform several different functions. Engine cooling requires substantial air flow for the cooling modules to work. Cars and trucks usually have very pronounced breathing apertures for this purpose. It is also common for cars to have openings for airflow to cool the brakes. The HVAC (heating, ventilation, and air conditioning) system takes in air from the base of the windshield (aka cowl/plenum), called the cowl screen. Spanning between the a-pillars, the plenum chamber filters the incoming air.
Below are illustrations from H-Point depicting good and poor aerodynamics.
This car's small front reduces drag. The gently contoured roof line, sharp rear-end cutoff, and fared-in rear wheels also contribute to a low drag coefficient.
It doesn't take an aerospace engineer to notice the inefficiencies of a Hummer. The body is large in all dimensions, causing it to push through a lot of air. The sharp changes throughout the body's exterior and the exposed underbody components will create additional drag.
Thanks for reading!
Did you know that aerodynamics is a subset of fluid dynamics? So an interesting side note. I had a neighbor that was complaining about how often her windshield gets cracked. Then it was pointed out that her windshield is closer to a 90 degree angle verses a 45 degree angle, which does not allow rocks to bounce off as easily. What angle are you thinking for your car?
ReplyDeleteThat's an interesting point. Since air and fluids are "shapeless" it makes sense that . A lower windshield creates a smaller front profile, but if the angle is too aggressive then it can distort the driver's view. A 25 degree windshield installation angle is the maximum to avoid this. My car will have a windshield angle very close to the maximum.
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