Headlamps and MPGs

Headlamps and MPGs

While driving on the Golden Gate Bridge this week, I remarked to my wife that all cars now have unique Headlamps and that this only came about 30 years ago.  Before that headlamps were either round or square and mounted flush with the grills of the vehicles at 90 degrees to the road.  The old round and square headlamps caused air flow to be interrupted and increased the coefficient of drag of the vehicle.

The photo below of a 1980 Honda Accord shows this

  

By 1985 Honda was hiding the headlamps in a retractable housing

Then came the molded plastic headlamps in 1990 and the beginning of more aerodynamic fronts to vehicles

 Now that we have reached 2016  the fronts are far more aerodynamic and streamlined

Folks back in the 1930s also produced streamlined vehilces.  The Tatra pictured below is one such vehicle.  Read up on it in the wiki link as well

https://en.wikipedia.org/wiki/Tatra_77

The poor Tatra tried to make the most out of the old round Headlamps.  Interestingly the Tatra had a coefficient of drag of 0.24.  The Hummer H2 which is like moving a brick through air has a coefficient of drag of 0.57.  The amount of power needed to break through air at the same speed is directly proportional to the coefficient of drag.  If 24 BHP were needed to break through the air for the Tatra at speed X then 57 BHP would be needed for the Hummer to break through the air at speed X.

https://en.wikipedia.org/wiki/Automobile_drag_coefficient

The Tatra of eighty years ago had the same coefficient of drag as the Tesla Model S.

If Tatra had the opportunity to use headlights from 2016 rather than what was available eighty years ago the Tatra not the Tesla would be the talk of the town and Hand Ledwinka not Elon Musk would be on every Greenies’ lips.  Interesting the first three letters in Ledwinka are LED and we are now moving rapidly to adopting LED headlamps for vehicles.

By my estimate the 800 million vehicles on the roads of planet earth that have molded headlamps save 25 gallons each a year compared to if they had the old fashioned flat round or square headlamps.  Each gallon of gasoline emits approximately 25 pounds of CO2 (well to wheels).  Therefore molded headlamps save 500 billion pounds of CO2 emissions per year or 250 million short tons a year of CO2 emissions.  This is approximately equal to the amount of CO2 that 1.4 billion humans breathe out.  I love the style of the new headlamps and there should be a headlamp exhibit at the Museum of Modern Art.