How to Reduce Air Drag for a Vehicle?

Discussion in 'Off-Topic' started by 4beowulf7, Jul 27, 2015.

  1. 4beowulf7

    Thread Starter New Member

    Jul 25, 2015
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    Hello everyone!

    I was thinking about how to reduce air drag for a vehicle so that one gets better mileage.

    Here is the definition of the problem:
    A moving car faces air drag especially at high speed. The resistance of the air layers would try to slow down the car. In order to maintain the same speed, the driver has to press the gas pedal continuously. So, if the air drag can be reduced, the mileage would improve.

    So how can we reduce air drag?

    What if an on-board high-voltage (HV) generator is used?

    The HV generator charges the strategically located metal plates over the vehicle of interest. When the plates are positively charged, the air molecules in the vicinity of the plates are also positively charged (electrons pass to the plates leaving positively charged air molecules behind). Now the plates push the air molecules away so they can never hit the metal plates. Therefore, it is possible to reduce the air drag for a vehicle by using this technique.

    What do you think?

    Greetings
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Pure hogwash.

    Form drag cannot be eliminated by creating a vacuum around an object. If air molecules get moved in any way -- drag is the result. Any object that creates lift, by virtue of it's geometry, will also create induced drag as a result of creating lift. The two kinds of drag have different profiles as a function of airspeed.

    https://en.wikipedia.org/wiki/Drag_(physics)
     
    Last edited: Jul 27, 2015
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    But any force has an equal and opposite reaction, so the reaction tries to push the car back. The reaction force is known as .... drag.
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Yeah, what those guys said. My version of the wording is like this: in order for the car to move through the air, the air molecules must give way. Moving anything with mass (air molecules have mass), from one place to another (from in front of the car, to not in front of the car), requires work. Work = force * displacement. The faster the speed, the greater the force. The larger the car cross-sectional area*, the greater the displacement (of air molecules). The same amount of work is done, whether the mass of those air molecules is moved from point A (in front of the car) to point B (not in front of the car) by electrical forces or mechanical forces. So there is no gain to be had by introducing electronics to this basic physics problem; only loss, in system inefficiencies.

    *this is why large fast-moving vessels (bullet trains, jets, rockets, etc) are designed to be long and mostly cylindrical. The way to reduce drag is to reduce the cross-sectional area of air that must be displaced.
     
  5. Brownout

    Well-Known Member

    Jan 10, 2012
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    Just follow closly behind a big truck.
     
    JoeJester, #12 and strantor like this.
  6. #12

    Expert

    Nov 30, 2010
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    It doesn't even have to be unsafely close. I tried this when I had an MPG meter running. Under straight line conditions, an eighth of a mile is still in the sweet range. You're going to lose the draft in the curves, but that is the price of safety.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    This can yield a significant improvement in fuel mileage.
    I have performed long-term drafting experiments in both my 2010 Prius and my 2005 GMC pickup (5.3L V8).

    In my Prius, I drove from Houston TX to Meridian MS (overall uphill), drafting behind 18-wheelers the entire way, going however fast the fastest truck was going (mostly 60-65mph, sometimes 70-75mph).
    When I filled up in Meridian, my 1-tank mileage was 65MPG. EPA estimate for the Prius is 48MPG hwy. My result was 35% better than EPA estimate.
    On the way home (overall downhill) I did not delibarately draft behind trucks, drove 70-80MPH, and got 45MPG.

    My morning/afternoon commute to work in my GMC pickup is 45miles each way; 75% highway driving, and the other 25% is slower traffic - not stop-&-go, but slow down to 30mph, up to 45, maybe 60, and then back to 30mph.
    I typically drive 60-75mph with A/C on, and get about 17.5MPG.
    For two weeks during the spring when I didn't really need the A/C, I tried turning it off and drafting trucks. I was painfully slow on acceleration, and always behind a truck, and for those two weeks my average was 27.5MPG.
    That's an improvement of 57%!

    Now that it's 100 degrees outside I keep my A/C on full blast, and I don't draft trucks as often. But I do draft when convenient and occasionally get into the 20-21MPG tank-average range with my truck.
     
    tjohnson likes this.
  8. wayneh

    Expert

    Sep 9, 2010
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    When I was a poor college student driving my '67 Barracuda back and forth to school, I relied on drafting behind semis to save me a few bucks on my trip. This was back when gas was maybe $0.60/gallon.

    The easiest way to reduce air resistance is to buy a car designed to do that. Design engineers make many compromises. Minimizing drag is always important, but can be secondary to other concerns. The guys designing cars to win the solar challenge put air resistance at the top of the list. You can look up the drag coefficient of most cars. Look for one with a low Cd.

    About the only "active" drag reduction I can think of is the work folks have done on pulling air into the craft at one location and exhaling it somewhere else to achieve certain airflow effects. I'm not aware of any commercial application.
     
  9. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    What kind of car do you plan on using here ????
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    From a really old memory, 1935, a speed test was made with a sedan, & then sedan pulling a light teardrop shaped trailer. Trailer added
    20 MPH top speed.
     
  11. #12

    Expert

    Nov 30, 2010
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    Ah, butt vacuum. Close that shape with the trailer and lose the rear drag.:)
     
  12. alfacliff

    Well-Known Member

    Dec 13, 2013
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    to reduce drag, slow down.
     
  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Just use teleportation..
     
  14. Biff383

    Member

    Jun 6, 2012
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    You can sit on the hood and breathe deeply. DO NOT EXHALE UNTIL YOU REACH YOUR DESTINATION.
     
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