Quote of the Day
The majority of men are bundles of beginnings.
— Ralph Waldo Emerson. I understand this saying well as I have three brothers, and I am the father of two sons.
My youngest son and his wife are going to have a baby girl in November – my first grandchild. Since they live in Montana, I will soon be doing some long-distance traveling. As I am famously cheap, I usually drive the 1000+ mile distance to visit them. I have started to think about flying there because the drive to their home is 16 hours of extreme boredom.
As I looked at the cost of airline tickets versus driving, I became curious as to how much fuel would be used to fly me to a Montana airport like Bozeman or Butte. I was surprised to learn that airliners can be quite fuel efficient compared to cars. This post contains my analysis.
The car fuel economy data available from the US Department of Energy. There is fuel economy data available on hundreds of cars – I limited my view to data from Honda and Subaru, my two favorite brands.
This post assumes that all the airliner seats are occupied. Appendix A shows the load factors of various airlines. I will also ignore any energy differences that exist between gasoline and jet fuel – I am only looking at volume of fuel.
Equation 1 shows how to convert between kg per km and L per 100 km using the density of aviation fuel (0.81 gm/cm3). I should note that the Wikipedia page on airliner fuel usage also provides a "mileage" in terms of fuel volume, but it looks like each manufacturer used a different density value. I decided to use an average fuel density that I applied to all aircraft.
Airliner Fuel Economy Data
Figure 2 shows how are converted the airliner data from kg/km to L per 100 km.
Figure 3 shows my table of long-haul and turbo-prop airliner fuel usage, which range from 2.31 to 6.11 L per 100 km per seat.
Automobile Fuel Economy
The fuel economy data was given in an Excel workbook, so I just did my unit conversion work using a pivot table and a calculated field. Figure 4 shows a screenshot of my pivot table of Honda and Subaru highway-driving, fuel economy data, which has a range from 5.88 to 10.23 liters per 100 km.
I found that fully loaded long-haul and turbo-prop airliners have a fuel economy between 2.31 to 6.11 liters per 100 km per seat. My favorite brands of automobiles had fuel economies of between 5.88 to 10.23 liters per 100 km. So many fully loaded airliners use substantially less fuel per km than a car carrying a single passenger.
Appendix A: Airliner Occupancy Levels
Figure 5 shows the load factor (i.e. percentage of seats occupied) by airlines for various years – it looks like most airlines operate at ~85%. I know that most of my flights are fully occupied, i.e. load factor =100%.