As I understand it, the gas crisis of the mid 70’s saw everyone shifting from making/buying cars that were either as big or as powerful as possible and getting sometimes single digit gas mileage to much more fuel efficient vehicles. But while cars got smaller and lighter and engines got handicapped for the sake of efficiency, it seemed that cars of this period were some of the least aerodynamic vehicles since the dawn of automobiles, especially compared to the bubble cars of the 40s and 50s. This seems counter productive.
In: Engineering
Terrible answers.
There are two main forms of drag particularly when it comes to things like a car.
1. Air resistance that is caused by the cross sectional area of an object that is being exposed to airflow.
2. Skin friction that is caused by the shape itself (i.e. a square vs a circle).
The first option is significantly more impactful than the second hence why cars from the era, and even into the 90s and 2000s tend to be significantly smaller than cars now or in the 50s and 60s.
**The explanation only gets longer from here.**
Option 2 is also significantly more difficult to manufacture. Steel likes being bent in simple shapes. Making complex aerodynamic shapes is really rather difficult, compared to say making a box with rounded corners.
Simply rounding off the corners of a square goes a long way to reducing flow separation and is significantly more easy to manufacture. It’s the operating principle behind the truck tails.
***Why is it more difficult to manufacture aerodynamic shapes?***
Because when you bend metal you aren’t moving the material into a perfect bend, you are stretching the outside of the bend, while compressing the inside of the bend which leaves a surface that is either measurably, or visibly, warped in the location of the bend.
Other commenters have suggested that early CAD programs made it more difficult to have complex shapes. Maybe that did play some sort of role, but I’ve dealt with complex casting drawings in my career that were drawn in the 50s, 60s, 70s, and 80s that were done by hand that are just as complex as drawings I make now.
***Why make body panels out of metal then, why not something like plastic that can be molded to any shape?***
Well it’s been tried plenty of times before and it is definitely a workable solution, at least from the engineering sense.
However, from the aesthetic design perspective, plastic, or other non-ferrous materials have been problematic because they don’t expand and contract at the same rate as the steel that inevitably makes up the frames of cars.
Also depending on the era, plastics might have had poor structural properties, and even worse UV resistance.
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