[jamesont]

Re: Drafting with the Prius

Out of curiosity, a few months ago, I tried a few mild attempts at drafting with my Prius. I noticed a 1 to 2 mpg increase when I did it while following tractor trailers at 65 to 70 mph. I did not tailgate, but did try to stay close. If the road was straight, and there was no wind, there was a spot behind the truck where this would work. Others, who have followed really close, have reported bigger increases, but that is too dangerous.
I also noticed the same increase in mpg by driving next to the trucks. There seems to be a spot on each side of the truck, near the back. Under the same conditions, no wind and straight road, it worked just as well and was much safer!

From a flow dynamics point of view, the drafting gets exponentially better as you get closer. If you can get right in behind him you can actually be "pulled" by the significant pressure drop from the eddies in the wind flow, ie, less then regular air pressure. Unfortunatly this is dangerious. That's why I want a computerized cruise that uses radar to bounce off the vehicle in front of me so the computer can react to changes in the trucks speed, braking as required automatically. Since humans have a reaction time of 1/2 to 3/4 of a second and a computer is reletively instantanious. I see this happeneing with computer controlled autopilot and radar adaptive cruise control.

I know from experience in speed skating that drafting someone can make a HUGE difference in power output required to maintain speed. From short little trials on a very long stretch of plain road on the Mass Pike I can get in behind a semi and only barely touch the accelerator in my honda civic to maintain around 75.

 

[jamesont]

The low pressure behind the semi will actually increase the drag on the semi, by interrupting that low pressure zone by putting your car in it, you are actually reducing his drag so thereby increasing his milage.

The benefits favor both.

Now we just need some computers to do it.

From speed skating, whether the leader or follower or in the middle of a pack, it is always advantagious to skate in a pack then alone.

 

[jamesont]

Something like this:

http://www.dfrc.nasa.gov/gallery/photo/ALT/Medium/ECN-6887.jpg