Abstract
The interactions of a car with its environment—gravity, the atmosphere, and the road surface—create forces which act on the car, usually opposing its motion. This chapter shows how these forces are related to the characteristics of the car under the designer’s control, such as its shape and weight, and to the effort required to move it: the tractive force . A magnitude will be calculated to give the reader an idea of the importance of each interaction. The calculations will use the characteristics of actual solar racing cars to make the numbers realistic.
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- 1.
Within specified design limits; absolute stability cannot be achieved.
- 2.
It is the relative motion that counts; you could also blow on a stationary car and create drag, as in a wind tunnel.
- 3.
Many fluids obey this relation between the surface shear force and the velocity gradient, air and water, for instance. Such fluids are called newtonian, after Sir Isaac Newton, who first proposed this linear model.
- 4.
The Reynolds number is important in other contexts. So, other reference lengths more appropriate for the context are defined for these cases.
- 5.
This apparently oversimplified scenario will still yield valid insights, believe it or not.
- 6.
Actually, we could equally well imagine the entire cylinder in a channel, but the drawing of a half cylinder takes up less space.
- 7.
There will even be back flow downstream of the separation point.
- 8.
These local zones of separated flow are called separation bubbles.
- 9.
Clarkson University’s 1995 Sunrayce car experienced this type of emergency at about 45 mph while running qualifying laps at the Indianapolis Raceway Park.
- 10.
In the first US cross-country solar car race, the solar cars were required to show that they could climb a 10 % (rise/run times 100) grade.
- 11.
This deformed shape is typical of the small, high pressure, rounded-cross section tires usually used by solar racers.
- 12.
Unless the relative wind blows from behind. This is an unusual situation and will be ignored.
- 13.
The effective mass is larger than the actual mass and accounts for the need to accelerate masses that translate as part of the body of the car, but also rotate about their own axes, such as the wheels. See Chapter 22.
- 14.
- 15.
The curves were normalized to their respective drag coefficients at zero yaw because the drag coefficient of the typical passenger car over the yaw angle range displayed was three to five times that of the solar racer.
- 16.
The results showed that the weighting factor could vary from about 1.04 (a 4 % correction) to more than 1.4 (a 40 % correction), depending upon the driving cycle and the vehicle’s drag characteristics.
- 17.
Other parameters: M e, 338 kg; μ 1, 0.004; μ 2, 0.0001 s/m, A D , 1.45 m2.
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Thacher, E. (2015). Interactions with the Atmosphere and Road. In: A Solar Car Primer. Springer, Cham. https://doi.org/10.1007/978-3-319-17494-5_2
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DOI: https://doi.org/10.1007/978-3-319-17494-5_2
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