12% MPG Improvement from Flying in Formation

[superchow]

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...)

[2003protege]

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.

[2003protege]

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.

[raquatrac]

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.

[2003protege]

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.

[aerohead]

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!

[jamesqf]

Originally Posted by raquatrac

It's hard to give credibility to the author when he doesn't know the plural for "vortex".

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.

[MetroMPG]

Originally Posted by superchow

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...)

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

The most celebrated demonstration of traffic automation took place last August on a stretch of California freeway near San Diego. The experiment was conducted by the National Automated Highway System Consortium (NAHSC), a public/private partnership authorized by Congress in the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 to perform long-term research on automated highway systems (AHS) for approximately seven-and-a-half years. In late 1994, the U.S. Department of Transportation (DOT) awarded the contract for this work to the NAHSC, which comprised Bechtel, Delco, Caltrans, Carnegie Mellon University, General Motors, Lockheed Martin, Parsons Brinkerhoff, PATH, and Raytheon. GM's James Rillings served as the NAHSC program manager.

Furthermore, "with platoon spacing set at a half a car length, cars can draft off each other, reducing drag by half." This arrangement, Shladover added, could result in a 20-percent boost in fuel economy and similar-size cut in emissions.

20% is a conservative number of course.



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

[tasdrouille]

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.

[raquatrac]

Originally Posted by tasdrouille

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.

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 ;-)