Has anyone measured the impact of wind on FE ? We seemed to get significantly better FE with a tail wind.

 

Not going to argue the results (though they do seem a bit extreme), but what I am curious about are your theories on why the first run was the best, and the second and third got progressively worse.

 

Not sure...

 

To be more scientific, the test should be conducted on the same road... same conditions... with the wind speed opposite. I can't help but think the mostly-level road has a little slant to it! Tests like this should also be done over longer distances to be more accurate. Unfortunately, you can't control the environment of this test (unless you have a wind tunnel!!!), so it's really hard to reproduce the EXACT same wind conditions over a longer distance.

I have a hard time believing 10 mph winds (+5 vs. -5) would make that much of a difference. I don't lose 11 mpg when I go from 55 mph to 65 mph (facing a 10 mph higher headwind).

 

since power required to overcome drag increases as the cube of the relative air speed you will never gain as much from a tail wind as you lose from a head wind.

 

I'm with Jeff here. Logic dictates that a longer test-run might minimize the 3 run-time MPG variations, AND be more representative of the MPG being achieved.
I just had a 65 MPG segment over 30 miles, but have never even had a 50 MPG tank (yet). So I'm not concluding that this one will hit 50 (let alone 60).
I also suspect that mostly level road may hav been favorable to the tailwind portion of your test.
What you are attempting to measure IS hard to definitively do, without being in a clsoed enviromnment. I think it's a great experiment though, and applaud your enthusiasm

 

It's a big impact. I have had trips that vary by as much as 8mpg based solely on wind direction. (IE, same route, different days, similar weather, but differing winds). Overall, unless I'm driving in one direction, I notice a marked increase in FE on calm days than windy days.

 

I have had trips from St. Louis to Chicago with a brisk wind either from the north or south and gotten 58 mpg with the tailwind and 43 against it!

 

I love it when someone actually injects a discussion of the applicable physics into these kinds of conversations. It's okay to have a few generalizations, but it's always best to get back to the basic physics to understand what's going on. The fluid dynamics of a car moving over roads are pretty much independent of the kind of propulsion used to make the car move, but overlooking them is a mistake.

 

the Power being referred to is irrelevant of the means of propulsion. Basically the amount of energy needed to be put into the system to maintain speed increases as the cube of the speed. This is irrelevant to what the object is or what is powering it.

its all about relative air speed, the lower the relative air speed the better off you are.

but if your driving 55 into a head wind of 20 your relative air speed is 75
conversely if you have a tail wind of 20 your relative air speed is 35

since we have that issue of drag increasing as the square and power required as the cube you can see how you will never be able to gain anywhere near the amount of energy into the system from a tail wind as you will lose from a head wind.

I am not sure that you were actually taking the post in the wrong way, but it seemed as though you are implying that the statement I previously made may not be applicable to a motor vehicle because somehow the fluid dynamics of the vehicle aren't linked to the amount of energy required to move the car, however I am probably just misreading your post. and my reply then will have been all for nothing.