Wind - how much affect

Wind is HUGE!

I can easily see a 10mpg drop/gain if it is windy enough and coming from the right directions. I think Bob has a great little program that shows how wind effects the Prius from different angles. I am off to a class or I'd find the link for ya.

 

I agree with F8L. You were near a worst-case scenario. The Prius MPG Simulator shows that a wind off your nose by about 30-35 degrees, rather than a straight-on headwind, causes the worst wind-related hit to fuel economy. The simulator shows a SE wind of 25 MPH reducing MPG from 43 to 27 MPG on an eastbound Prius at 70 MPH. You actually did well keeping it north of 30 MPG.

Even "moderate" wind can cause a hit coming from anywhere between your 9 o'clock and 3 o'clock. In your eastbound scenario, a 5 MPH SE wind would drop it to 38 MPG.

The calculations assume steady speed, level terrain, smooth dry pavement, and 50F temp.

 

Wind makes a huge difference to the energy required. I know this mostly from cycling, where the effects are more immediately felt. A brisk all-day headwind is not much fun, and is why most cross-country cyclists ride West to East.

 

Hi mein...,

Wind has a large effect on cars because a car is long and has a large broadside area. When the wind is straight head, the Coefficient of Drag is at its optimum, and the cross section area of the car is minimul. But as the wind goes off center, the cross section of the car increases to the relative wind direction. So if the wind is 45 degrees off access, and your going twice the speed of the wind relative to the ground, then the relative wind over the car is something like 15 degrees off the axis of the car. Take your car and look at it head on, now turn it 15 degrees and look at the increase in cross-section area. Additionally, the Coefficient of Drag gets worse, as there will be turbulence that is not designed for in the shape of the car, on the downind passenger rear of the car. The turbulence increases the aero cross section area even more.

So, Yes, wind is has a huge effect on highway driving. It may actually save gas to drive on 2-lane roads into the wind, and then at a greater angle to the wind, rather than on a diagonal course to the wind on a super highway when the wind is up around 35 mph. Lets asume a 30/60/90 triangle, where the main road is on the hypoteneus. The total length of the dog-leg route is then 1.366 as long as the hypoteneus route. If the dog-leg route gives you better than 1.366 times 27 mpg, or 36.9 mpg, less gas will be used. The two lane road will be slower too, which also saves gas.

In my daily commute, there is sometimes a steady diagonal wind during a warm day (late spring typically). With the power electric window controls in the Prius, I have dropped my fuel consumption up to 5 mpg at 60 mph by cracking the down-wind rear window ever so slightly (1/4 inch) with the AC ventilating external air. This injects air into the turbulent zone, and helps to trip it into laminar flow.

 

Sounds reasonable to me, all except the use of the word "affect" in the thread title. "Affect" is a verb.

[English lesson]

Wind will affect your mileage. <- verb

Wind will have an effect on your mileage. <- noun

The thread title should be "Wind - how much effect?"

[/English lesson]

 

Danial, I think the OP meant that the wind was a little light in its loafers.

As to the effect of wind on mileage, the power required to overcome wind resistance goes up by the cube of the speed. Twice as much wind speed requires eight times the power.

Tom

 

I am going to defend Daniel on this one. Words are like tools, and should be used with precision. When a wrong word is used, the reader can be mislead. Most of the time a good reader can reconstruct the writer's intentions, but not always, and a good writer wants to make the process easy for his readers.

Daniel wasn't snotty or petty in his comments. His information was calmly presented and of value. It was probably a simple typo on your part, but even so, Daniel's advice may help another less informed writer.

Tom

 

The term "affect" can also be a noun, as in "The man had a flat affect." meaning no variability in his apparent moods.

A headwind, or quartering wind from the bow, clobbers mileage.

That is all.