View Single Post
Old 07-02-2008, 09:11 AM   #11 (permalink)
Shawn D.
Harebrained Idea Skeptic
Join Date: Jun 2008
Location: Alpharetta, GA
Posts: 211

The White Car - '84 Mercedes-Benz 300td
90 day: 28.84 mpg (US)

The Blue Car - '86 BMW 535i
Last 3: 23.86 mpg (US)
Thanks: 18
Thanked 13 Times in 9 Posts
Originally Posted by Bror Jace View Post
"drag increases exponentially with velocity"

That's the key. Spend lots of time at or above 100mph? Then washing and waxing becomes crucial. I'm always amazed when I look at older aircraft with exposed rivets, etc ... what a waste of efficiency!
Apparently, a number of you are disregarding what I said about pressure and friction drag on cars, maybe because I have no longstanding reputation here and haven't built up credibility. I really dislike pulling out this "hammer" because folks reflexively call it arrogant, but here it is: I'm an aerospace engineer and know what I'm talking about. There, I said it.

As I said before, pressure drag predominates on cars, not friction drag. Waxing does not become "crucial" for cars at any speed. In fact, having a rough surface enhances attachment on objects with low length/diameters, such as cars. Thus, waxing your car could make drag worse. In any case, the change is negligible.

As to the exposed rivets, it depends on the aircraft. It cost a great deal extra to manufacture it with a smooth surface, especially 40-60+ years ago. The P-38 was very smooth overall because the design led to thin boundary layers (i.e. no long fuselage), but the back end of a B-52 has many exposed fasteners/rivets, which isn't as important because the boundary layer was thick back there. Also, many combat aircraft were expected to have short operational lives due to attrition or obsolescence, so the extra $$$ was not always deemed worth it, especially when many had to be pumped out quickly.


Last edited by Shawn D.; 07-02-2008 at 09:20 AM..
  Reply With Quote