12% MPG Improvement from Flying in Formation
 

Found this article on how airlines could save 12% in fuel by flying airplanes in formation. See article here:

Taking Cues from Birds to Green the Airline Industry | Triple Pundit

Now, I know, cars wouldn't have an extreme "upwash" like airplanes do - but it made me wonder how close you'd have to drive to a car in front of you to get similar improvements. Mercedes' "distronic" cruise control that keeps a constant distance could be modified to draft people closer than anyone would want to do manually.

Just imagine: Special high-speed drafting lanes could emerge for vehicles with this system! Who needs high speed rail, if you can have high speed automobile trains? (And before anyone answers that last one - yes, I know trains are more efficient, bla-bla-bla - t'was more a rhetorical question...)

I think for cars, significant differences can be obtained at just over 1 second of following time by following something as small as a full-size truck/suv. *NOTE: possibly illegal in some jurisdictions* But I am happy to follow at about 1 to 1.3 seconds and can feel considerable improvements in the ride when behind such vehicles - especially in a head wind.

and good grief...3-5 miles?!? It really is hard to put your head around just how big the wake is from a commercial airliner--especially for being so aerodynamic.

About the article:
It's hard to give credibility to the author when he doesn't know the plural for "vortex". The description of the wake (one up, one down) is outrageously wrong.
The concept of formation flying is well known. Another aircraft's wake is an extremely dangerous, if attractive, place to fly in. It'll take years before airliners do it.

About cars:
Indeed. Already I'd love to have an instrument giving me the time separation to the car in front - it'd be a good start to measuring safety margins when drafting.

Credibility should lie with the authors of the study - graduate students who probably do know what they're talking about and could probably say the plural form of "vortex" if they thought about it long enough.

And as the vorteces leave the wingtips and begin to dissipate, there is one side flowing "up"-the wing side and one "down"-the fuselage side. At 3-5 miles, I suppose they're weak enough to not interrupt the flight characteristics significantly. If you notice, the third plane flies in the middle of two planes ahead, so both of the "up" sides of their trailing vorteces are in the middle of the chase plane's flight pattern - probably yielding the better stability they're talking about.

formation
 

Hucho's book has a number of tables from windtunnel studies conducted for stock car racing,convoy driving,formation driving,etc..One of the premises for my trailer project is borrowed from the NASCAR two-car draft.You ( everyone ) need this book!

OTOH, there's a school of thought which disagrees with the idea that adopting a loan word from Latin means that we should also adopt its Latin plural form - something we don't do with any other language, as a general rule.

Not a rhetorical question to General Motors and a consortium set up in the 90's to study the issue:

http://www.skytran.net/16Calculators...%20Platoon.gif

20% is a conservative number of course.

http://path.berkeley.edu/%7Ebougler/...s/buickcar.gif

Info:

Smart Cars and Automated Highways

http://www.path.berkeley.edu/nahsc/p...l_Overview.pdf

EDN Access--12.18.97 Take your hands off that car!

Bénédicte Bougler - Jobs

The plural form is vortices btw.

Just one interesting thing to note about driving in convoy. Take 2 identical vehicles traveling in a convoy. As the distance varies between the vehicles, so does their Cd. At some point, as the trailing vehicle gets close enough, the Cd of the leading vehicle eventually gets lower than the trailing vehicle. Which means the leading vehicle can benefit more from drafting then the trailing vehicle. This makes total sense as we know most passenger vehicles need more aero help in the back than the front.

http://ecomodder.com/forum/attachmen...1&d=1250595765

I do not think so. The Cd of the drafter may be higher, but his airspeed is now much lower, too.

If you remember the drag equation, the Cd is power one, but the airspeed is power two. In other words, reducing air speed by 29% [one over square root of 2 is 71%] or halving your Cd have the same effect.
(assuming you can do both reductions independently).

Note, also, that the (awful) vehicle shapes depicted in the figure will tend to produce higher drafting benefits than better streamlined vehicles. It'd be pretty pointless drafting an aerocivic, for example ;-)