High-altitude Trip

[ceilidhdog]

Good day all. Just a brief note to report on a trip last weekend. We left Denver (5,280 feet) and drove to Saratoga, WY (7,200 feet), crossing the Snowy Range (8,500 feet) en route. I set the Eco Cruise at the speed limit (75 mph on the interstate, 65 mph elsewhere), and tried to stay at the posted speed limit whenever traffic or winding roads required turning the Eco CC off. The trip meter showed me 46.1 mpg for the trip to Wyoming, and 47.9 mpg for the trip home. When I got back to Denver, I filled the tank. It took 10.21 gallons for 480 miles driven... an average of 47.0 mpg. I'm one happy camper... but I'm still waiting for my check from Ford. :)

[hybridbear]

Incredible! Does something make the ICE more efficient at high altitudes?

[lolder]

The ICE is not more efficient, it's just less air resistance, same as for airplanes.

[SteveB_TX]

Tell that to my sister! She lives in Denver and bought a '13 Lexus ES300h just after I bought the MKZh. Her MPG is awful. She does not even get close to the 40 MPG Lexus advertises. Hmmm. Where have we heard that before? ;)

[ceilidhdog]

I don't know if the ICE is more efficient at higher altitudes. I agree that the thinner air might contribute to better mileage, but you'd think (at least I would) that going uphill might negate some of that. I don't know what it is, but as I said, I'm pleased.

[lolder]

Air resistance at highway speeds is about half the load. AT 5000 ft. altitude the air density is about 15 % less than sea level so you might expect a 7 1/2 % improvement in economy. The hills pretty much balance out unless the HVB gets full on descent. The potential energy gain from elevation is recouped 100 % on descent. If the ICE gets out of it's sweet spot on the high power side that might affect mileage.

With non-turbocharged piston aircraft the fastest cruise speed is obtained at about 7500 ft. where the maximum full throttle power is the same as the nominal maximum continuous cruise power; 75 %. Air miles per gallon increases with altitude. That's why jets fly high.

[GrySql]

Air resistance at highway speeds is about half the load. AT 5000 ft. altitude the air density is about 15 % less than sea level so you might expect a 7 1/2 % improvement in economy. The hills pretty much balance out unless the HVB gets full on descent. The potential energy gain from elevation is recouped 100 % on descent. If the ICE gets out of it's sweet spot on the high power side that might affect mileage.

With non-turbocharged piston aircraft the fastest cruise speed is obtained at about 7500 ft. where the maximum full throttle power is the same as the nominal maximum continuous cruise power; 75 %. Air miles per gallon increases with altitude. That's why jets fly high.

I love it when you go all aero engineering on us, fun to read... :)

[acdii]

Tell that to my sister! She lives in Denver and bought a '13 Lexus ES300h just after I bought the MKZh. Her MPG is awful. She does not even get close to the 40 MPG Lexus advertises. Hmmm. Where have we heard that before? ;)

Motorweek was gushing over the latest lexus CUV. I thought it was FUUUGLY! I don't see what the attraction is to a glorified Toyota.

[lolder]

I've operated aircraft from a 1/100 hp RC electric ultra micro "Champ" to over 100,000 lb thrust ( 3 engine ) Lockheed L-1011, 2500 hp Pratt & Whitney R-2800 on Convair 440s, 3750 hp Allison turboprops on Lockheed Electras and a lot of general aviation light aircraft. I'm probably a "carbon criminal" for burning about 2 million gallons of petroleum products as my share. The plane I flew the most for over 20 years the DC-9 carried 100 people 500 mph at 0.5 mpg. I don't think I'll be able to atone by burning a gallon an hour in my FFH.

Edited July 30, 2014 by lolder

[GrySql]

Your expertise and experiences are always interesting.

My career burnt a lot of fuel too, our old Fire trucks and Fire Boats had big engines that got terrible mileage and belched smoke.

All of our modern Los Angeles Fireboats still use a bit of fuel, there is no way to move big things without expending energy.

Like this one.

 

The OP's mileage was better than mine when I drove thru CO in May, except from the Eisenhower Tunnel to Denver, a nice downhill run.

Edited July 31, 2014 by GrySql

[mwr]

the DC-9 carried 100 people 500 mph at 0.5 mpg.

That's 50 mpg per person moved. Pretty good!

[corncobs]

That's 50 mpg per person moved. Pretty good!

Nice way to think about it!

 

Does anyone know the rate on a modern day aircraft?

 

That got me so curious that I had to answer my own question. A quick google search returned this.

 

http://en.m.wikipedia.org/wiki/Fuel_economy_in_aircraft#Fuel_consumption_factors

 

I had no idea but it's pretty impressive.

Edited July 31, 2014 by corncobs

[lolder]

The way to look at it is seat-miles/gal. The DC-9 would be 50. A FFH with four people at 50 mph and 50 mpg would be 200 sm/g. But the DC-9 is going 10 times the speed.

Edited July 31, 2014 by lolder

[acdii]

I'll bet after all the hours behind the plethora of gauges, dials and switches in the DC9 cockpit, MFT and the Hybrid stuff is too simple for you. :) Ever fly a Connie, or a Warbird? Hoping some time to get some seat time in a B-17 someday, missed out on a few times due to work schedules.

[lolder]

You can become much more unsafely distracted by the car displays. The only time you have to look outside a cockpit 100% is when you're taking off or landing. There are alarms for dangerous problems on takeoff. Watching the dash in our cars can be very distracting. That's why I advocate new owners to sit in their parking spaces and read the manuals for several hours and push all the buttons then. A 1/2 second of distraction in a car can be catastrophic. The proliferation of internet and other electronic connectivity is a bad trend. Touch screens are just as bad. Knobs and dials you don't have to look at.

[mwr]

You can become much more unsafely distracted by the car displays. The only time you have to look outside a cockpit 100% is when you're taking off or landing. There are alarms for dangerous problems on takeoff. Watching the dash in our cars can be very distracting. That's why I advocate new owners to sit in their parking spaces and read the manuals for several hours and push all the buttons then. A 1/2 second of distraction in a car can be catastrophic. The proliferation of internet and other electronic connectivity is a bad trend. Touch screens are just as bad. Knobs and dials you don't have to look at.

Absolutely agree. I've been a competent instrument pilot using GPS for most navigation and approaches. But the time I got a highly-rated Garmin car GPS, I found (1) it was very distracting and (2) it didn't do the few things I actually needed it to do, so I sent it back. I have no interest in car nav. If I drove to strange places a lot, it would be different, but I see no need for it at all and lots of drawbacks.

[acdii]

OTOH being a truck driver you MUST have an eye on all gauges as you drive. It is something that you train for. A glance to the right dash, air pressure, check, back to the road, glance right, trans temp, check, back to the road. Glance down, oil pressure good, etc. After a while it becomes second nature, and you get trained to do it by watching the road, you NEVER look directly in front of you but several cars ahead of you because most of the time that is where the problem begins. So if you are in traffic and keep a good safe distance, watching well ahead, then doing a dash glance is quite safe. You just have to train yourself to know what you are looking at and register it quickly.

 

It also helps to have good peripherals.