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Old 04-12-2011, 07:49 PM   #99 (permalink)
aerohead
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windshield

Quote:
Originally Posted by winkosmosis View Post
Common sense? Take a cardboard folder, hold it at a 15 degree angle and move it through the air and note the resistance you feel. Then angle it to 45 degrees and fold it so that the frontal area is the same. Is the resistance more or less or the same??

Then look at the real world examples. Car windshields- you've never noticed that economy cars have very slanted windshields? Prius? Heck, look at your own picture of the Beetle in the wind/water tunnel. The fact that air piles up and forms a "bubble" proves that flow is not as easy as if the windshield were sloped back. Look at the fan and ask yourself why the blades are curved instead of flat.

I know you are into rear end aerodynamics. Did you ever ask yourself why airflow is better able to stay attached the shallower the rear surface angles are? It's because it takes less energy for the pressurized air to expand toward the surface and flow along it.

Just visualize-- use the spatial common sense that mother nature built into your brain which allows you predict where a ball will land depending on how hard and at what angle you throw it.

But if common sense and visualization isn't enough for you here is an article that talks about hood and windshield angles:

In This Chapter the Modifications That Were Carried Out To




Note that even though the language suggests that a strongly inclined windshield doesn't "contribute to local drag reduction", their strong incline is less than 30 degrees from horizontal, much less than the OP's. I believe that's even a shallower angle than the cab forward Honda Civic's.

They say that a steeper hood angle doesn't help drag once it's good enough that flow stays attached, so it seems to me like the bubble that forms when the transition is too severe is the problem.

BTW, that article also has a section on arched roofs, where they explain that even though an arched roof increases frontal area, it can reduce total drag.
inclined windshields are low cost.They do not reside on low drag cars.No low drag car has a simple inclined windshield.
If the objective of the car maker is to channel a lot of air over the roof,then the incline is beneficial.
You know that Honda and Toyota cars which use this also have speed limiters to throttle top speed .
You may also be aware that when Bugatti,Lamborghini,and Imperator use this windshield they build a lot of induced drag into the car to keep them earthbound.
* Riley's Tri-Magnum wasn't fast enough to be in jeopardy
* Toyota's first minivan had limited speed
* Mercedes A-class isn't at risk
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The greatest economy cars all have compound windshields
* M-B C-111 III
* ARVW
* Honda P-100
* Renault Vesta II
* GM Ultralite
* GM Impact/EV-1-2
* GM Solaraycer
* Dymaxion Car
* 1935-1/2 DeSoto Airflow experimental
* Jean Andreau Peugeot 402
* 1927/8 Chrysler Jaray prototype'
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Roof camber can only help if normal roof height is maintained and frontal area is maintained.
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Can you please explain 'pressurized air'?
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