Today’s plan: drive west and stop
at every SuperCharger on I-90 in Minnesota and South Dakota. Okay, so, there
was a bit more to today than that but not much.
Since we started from a full
battery in La Crosse, WI, LJ made a speed run across the Wisconsin border and the
eastern part of Minnesota. The skies
were a beautiful blue with only a couple tiny white clouds off on the
horizon. Winds were steady at 15 mph
from the northwest with gusts to 25 mph.
Between the strong winds and the blistering pace, our average energy
usage for this first led was an astounding 431 Wh/mi. If you remember back to previous posts,
“typical” driving conditions are supposed to be 300 Wh/mi and our first two
days we averaged 361 Wh/mi.
The next leg of the trip used
even more power. I was averaging more than 450 Wh/mi cruising at highway speeds
when I started to get worried about the ever-closing gap between the Projected
Range and the distance to the next SuperCharger. I drafted behind an 18-wheeler for about 10
minutes as we approached the stop in Worthingon, MN, which brought it down to
the 441 Wh/mi shown in the photo below.
 |
| Day 3: winds were howling on this leg |
******
Today’s physics lesson starts with
the word draft (transitive
verb): to stay close behind (another racer) so as to take advantage of the
reduced air pressure created by the leading racer.
Draft is a key verb for Tesla
energy efficiency. Out here on the wide
open roads, drafting behind an 18-wheeler is critical for minimizing the time
spent at charging stops. The physics is
pretty simple: the truck pushes most of the air out of the way, which means
less energy expended by our car. Per the
Wikipedia
article on drafting, following within 100 feet of an 18 wheeler can lead to
an 11% increase in mpg efficiency for a gasoline-powered car.
The first photo above shows the
stats from the second leg of the trip.
(The Trip A is supposed to be a daily update but we didn’t reset it
until 100 miles into the trip today.) The
wind was howling across the plains, leading to the high usage of 441
Wh/mi. For the next leg of the trip (Mitchell
to Murdo), I drafted behind a truck going 74 mph for about half the trip. As he was leaving the highway, I fell in
behind another one going just a bit faster.
I managed to drop the average energy usage down to 327 Wh/mi for that
leg of the trip. While some of the
efficiency increase was due to the wind dying down, the instantaneous power
change that occurred when I got out from behind the truck showed that drafting
was clearly making a difference.
 |
| Day 3: why drafting matters |
******
The one touristy thing we did
today was to stop by the World’s Only Corn Palace in Mitchell, SD. Since we already had to leave the interstate
to use the Mitchell SuperCharger, it was just a short detour to see the
palace. After a dinner and charging stop
in Murdo, SD, we headed to Kadoka for the night.
 |
| The World's Only Corn Palace in Mitchell, SD |
We crossed into the Mountain time
zone somewhere in the middle of South Dakota, which means we stopped reasonably
early for the night as compared to the last two nights. Probably a good thing, given how long
tomorrow will be. A key error in our
original trip planning was that we didn’t think about how few hours of daylight
there are in a day when we’re this far north in November. We had planned to do the Badlands on Tuesday
night until we realized that we would be driving through them in the dark. So tomorrow we check out the Badlands and the
Black Hills as we continue on our way west.
Day 3 stats:
562.7 miles in about 11.5 h for
an average speed of ~49 mi/h overall (including stops)
4 SuperChargers stops:
- · Albert Lea, MN
- · Worthington, MN
- · Mitchell, SD
- · Murdo, SD
Overall
trip: 1915.4
miles miles in 3 days, which means we’re more than halfway to Palo Alto
 |
| Day 3: Kadoka, SD |
No comments:
Post a Comment