AeroWorker

MPG Testing Uphill Both Ways

Dawn broke bright and clear on the morning of Friday April 10th while I was getting ready for my two day trip to Monahans, TX from our home in Radium Springs, NM. I had the boat tail mounted on the truck as well as the Herdon Aerolid and I only has last minute items to pack. It took 3.6 gallons to top off the tank in Las Cruces, before I got on the road for Texas.

Conditions were not bad for my trip but I was running into road construction north of El Paso, TX so I exited and took Trans Mountain Road which deposited me on the east side of El Paso. It was 70 F in El Paso and I pulled some good numbers as I made my way back to I-10. I seen 25.5 mpg at 60 mph, 24.5 at 65 mph, 23 mpg at 70 mph, and 21 mpg at 75 mph.

I had decided previously to gas up in Fabens because the speed limit changes to 80 mph just west of there. It turned out to be 12 miles to the change in speed limit. The truck had pulled 20.78 mpg over the 80.5 mile drive from Las Cruces.

After 12 miles of driving 75 mph I begin to do 80 mph on the road to Van Horn, TX. I had chosen this fueling stop because the highway changes directions from generally SW to NW at Van Horn. After driving 89.2 miles I reached Van Horn where I refueled needing 4.691 gallons of gasoline. This turned out to be my best run at 19.0 mpg. While that number doesn't sound that good you need to factor in that I drove 15 miles at 75 mph and 74 miles at 80 mph. Doing the math yields an average speed of 79.15 into a 4 mph headwind out of the NE. My effective road speed as far as the air was concerned was 83.5 mph. I had climbed 176 ft from 3,754 ft to 3,950 ft in Van Horn.

On the way to Pecos I recorded a 19.2 mpg figure at 75 mph on level ground. I had two sources to know when I was on level ground. I had installed a trailer level on the passenger door I could observe while driving and I would also watch the GPS elevation read out while looking for level highway. If the GPS only moved around a fixed elevation of only a couple feet while driving I knew my status and could pull a number.

In Wicket, TX on the outskirts on Monahans, TX I stopped for fuel. The truck required 6.642 gallons for a composite average of 19.01 mpg over 118.7 miles. Because I was bucking a direct head wind and even more grade changes I slowed down on some sections of this highway. I-10 changes to I-20 to travel to Monahans. Doing 80 mph around curves side by side with semi trucks is not for the faint of heart like me.

My plan was refuel before I left the Monahans for home and to treat all this run as trash mileage. I arrived at the park around 3 PM MDT and met Phil Knox who was waiting for me at the park. We went to our camp site and removed my boat tail for the driving over the next two days. I was going to sleep in the Aerolid camper shell. The boat tail/stinger blocks the tailgate, and access to the bed. I had brought shortened saw horses to put the stinger on. I also used the stinger for storage.

We went to Odessa, TX to eat dinner and take in a movie that night. We got to a late showing of the movie Sniper which we both liked very much. We got to the site and turned in late. I did not sleep that well on the first night in my new digs. Saturday morning broke clear and we went to breakfast in Monahans. Thence back to the park to hang out until lunch.

After lunch we headed out to Pecos to check out a museum there. Having Phil with me to take notes we naturally did some mpg testing of the truck at 80 mph. With the Aerolid only the truck managed 17.2 mpg on a two way run on level ground. My 19.2 mpg number with the stinger gives us a good comparison to discuss. The improved performance amounts to a 10.41667%. This amounts to reduction in needed RHP from 56.4 RHP to 50.5 RHP to do 80 mph on level ground.

We had dinner at a Sonic in Monahans before returning to the park for the night. Our neighboring campers were there for the astronomy as were we. I set up my 102 mm Mak and showed everyone the Sun before it set. We observed Venus and Jupiter. It was windy which made observing difficult at times. I helped our neighbors find Comet Lovejoy low in the NW. Lack of sleep was ganging up on us so we turned in early. We wanted to get up at 2 AM to observe Saturn but the winds were still gusting hard so we sleep on through the night.

In the morning we got up around sunrise. After some morning coffee, and performing our ablutions, we packed our gear, and set off our separate ways. Phil was headed back to Denton, TX.

My trash mileage refueling in Monahans turned up 16.13 mpg figure for 252.7 miles using 15.622 gallons. Then I set off for Van Horn starting at 2,628 ft to climb 1,322 ft to 3,950 at my next fueling stop. While not a great mpg run this is where I reached my goal of 20 mpg at 80 mph. The winds were out of the SES at 7-8 mph. I was traveling SWS at 3,879 ft and it was 70 F. This means my truck was only needing 48.5 RHP to do 111 ft per second. I have a table that says it can take up to 30 RHP to overcome rolling resistance at 80 mph which could mean the truck was only using 18.5 RHP to overcome other forces.

At Van Horn it took 6.92 gallons for 125.2 miles netting me a 18.09 mpg average. The winds were switching around and I had some real grades to climb from Van Horn. I slowed down to 75 mph then just before Fabens I ran into rain. The conditions showed up at the pump in a 17.26 mpg return.

Driving through El Paso can be good for your mpg returns. Firstly you have to slow down to 65 mph or less, then there is something called the "Corridor Effect" which can happen in traffic all moving the same direction. In Cruces I netted my second highest return of 20.06 mpg.

I had traveled a total of 575.5 miles using 30.941 gallons of gas for a net average of 18.6 mpg. My mythical tail winds for my trip had never materialized or had only showed up briefly so I could set my 20 mpg at 80 mph record. I think this record is a sure thing with a belly pan.

I learned some things on this trip. I learned just how difficult real world mpg testing is really. Hence my title "MPG Testing Uphill Both Ways". It seems nature can conspire to give you head winds and turn them around into head winds going the other way. My data from all my gasoline logs shows the vehicle with aerodynamic appliances has averaged 18.5618 mpg over 8,223 miles using 443 gallons of gasoline.

The truck naked only got 14.525 mpg over 2,907 miles using 200 gallons of gas. To be fair I subtracted the gas from the first 1,000 break in miles and this brought the average for the truck up to 16.677 mpg over 1,797 miles using 108 gallons of gas. But then again this was in warm weather and I got the Aerolid installed on November 15th when winter started. I have only been driving about six weeks in warmer weather. More time and warmer weather will tell the story whatever that story is. So far my MPG testing has really been up hill both ways.

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