quest for 30 mpg
- Thread starter wulimaster
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That is the same umich study. I recognize the photos of those responsible.
Two reasons.
1. The fact that in my own testing the results don't match up to the results of their testing.
2. Air forced past a car at high speeds is not the same as moving a car through still air. In the wind tunnel you have deflected air colliding with the high speed directional air stream which passes the car creating one kind of turbulance. With a car moving through the still air you have the deflected air meeting with still air which creates a different kind of turbulance. Since the two turbulances are not the same I cannot say the results from one necessarily correlate 1:1 with the other.
I also don't like the fact that drag and wind resistance are used interchangable. I tend to think they should be distinct. Drag would be the force of the vacuum acting on the rear of the car while wind resistance would be the friction caused by the high pressure wave at the frontal area of the car.
Think of the difference between a spitzer bullet with and without a boattail. Tailgate down is the boattail.
Anyone know of a coastdown test being done on a truck with and without a tailgate? How about a J1321 style test? I would settle for someone from this forum with a newer truck with the mpg digital calculator try resetting the calculater with the cruise set at 55, 50, 65, 70mph doing the test on a windless day on the same stretch of empty highway with the tailgate up and down. Any takers?
I do these tests all the time with my wifes excursion and that is how I knew my new tires cost me 2 mpg at 65 mpg.
What??? Do you know something that every aerodynamicist (including Orville and Wilbur Wright thru WWII enginneers with Mitsubishi Messersmidth(sp) Grumman, through Lockheed, Boeing and every automotive aerodynamicist ever employed) doesnt know? If so, tell them so every automaker and aerospace firm can stop building these huge wind tunnels! Formula One and Nascar can save all this money on needless wind tunnel tests.
Can you tell me why they are considered equivalent?
I didn't know the Wrights had a wind tunnel?
In a wind tunnel, the ground stands still relative to the car. On the road, the ground moves relative to the car. In a tunnel, the pressure wave created by the car reflects back down on the car. On the road, it propagates away, like the waves around a slow moving boat.
It would be neat to borrow a wind tunnel for a day, though.
It would be neat to borrow a wind tunnel for a day, though.
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