By on September 11, 2015

wind buffeting. Shutterstock user OmniGrace

Scott writes:

Hi Sajeev!

I have a 2015 Civic, but my question applies to lots of cars.

I live in Maine, which has lots of nice weather for driving around with the windows down. The buffeting, or “helicopter effect”, with the windows down is driving me batty! Also the “white noise” of the rushing wind is quite loud when the windows are open. I can adjust the windows to limit both issues somewhat, but is there anything else I can do?

Seems like they used to sell rectangular plexiglass air deflectors that mounted on a car’s A pillar. Is anything like that still available? Would stick-on side window deflectors help? I’m not keen on them because all of them I see are tinted, and visibility is already limited enough by the car’s thick A pillars. (True dat. – SM)

Sajeev answers:

Aeroelasticity is one of those fascinating sciences that scared me far, far away from a Mechanical Engineering degree. There’s even a software company hawking a solution toolbox to minimizing wind throb. I’m sure it’s only a million or so to get an R&D lab to work it out perfectly!

Cars have ways of reducing the air pressure concerns that lead to buffeting, wind throb, the helicopter effect or whatever you wanna call it. There are flapper ducts in the trunk that make it easier to close doors, circulate fresh air and maybe even to ensure the airbags inflate properly. Sunroofs have pop-up visors. Side view mirrors, headlights and fenders are sculpted to move air more efficiently/quietly around the body side. Everything is can be designed for good reason.

My first car, a 1965 Ford Galaxie 500 LTD, had a flow-through ventilation system; drawing in air from the kick panels (both sides), sucking it out behind the rear window. It rocked on those rare occasions when Houston had Maine-like weather. I never cracked open the windows unless I wanted the wind in my hair or to peep that sweet pillarless hardtop design. Ahhh, memories! 

So can you improve the factory’s built-in tech? Probably. I’ve had good luck reducing buffeting by tilting my moonroof after finding no correct combination of cracking open my windows. If your Civic has one. If not? Well, I’d have it installed nearby: what a great way to enjoy Maine summers and/or global warming!

If a moonroof is not helping, too expensive to retrofit, not your cup of tea…well you could…

Yeeeeesh, those are surprisingly unsightly! The tilting moonroof is the right answer.

What say you, Best and Brightest?

[Image: Shutterstock user OmniGrace]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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36 Comments on “Piston Slap: Buffeting Past the Helicopter Effect?...”

  • avatar

    I’d like to ask the B&B, has anyone used those “vent shields” or whatever you call them mounted to the window frames? How well did they work?

    • 0 avatar
      I've got a Jaaaaag

      I had them on my Saturn 15 years ago, they let you crack the window in the rain and keep the water out, which is useful if your AC is out or you smoke. Other than that for the buffeting, Every car I’ve ever owned has had a sunroof or moon roof and I always found having that opened fixed the problem.

  • avatar
    Arthur Dailey

    Just buy a car with vent windows.

    My Type IV VW shooting brake was the first car that I owned that did not have vent windows. Instead its windows had a ‘scalloped’ pattern allowing them to be opened just enough to allow some ventilation without creating any buffeting.

  • avatar

    ‘Also the “white noise” of the rushing wind is quite loud when the windows are open.”

    I *love* that! Free ambient music.

  • avatar

    Won’t help in an SUV, but in my truck this effect is completely gone as soon as I open the little sliding window in the back of the cab. This allows the air to flow through the cab and reduces the buffeting to next to nothing.

  • avatar

    In a 4 door, opening the diagonal windows fully and closing the other diagonal windows works for me. This channels air front to back without the buffeting.

    • 0 avatar

      Same here; although lowering the windows about a third seems to be the best compromise. Open them less, and you get more turbulance around the crack of the window; more, and you get more outside noise, and the airflow is less; so there is less cooling. Opening a sunroof apparently has the same effect.

      Most of the helicopter effect comes from opening the rear window, not the front ones. I am thinking the rear window opening sets up a turbulance pattern that resonates, causing the drumming. Those that have a vertical edge to the rear window seem to be worst; my 1990 Dodge Spirit and the wife’s Durango did it bad enough to hurt your ears; the Taurus barely does it all. Station wagon/SUV or sedan layout does not seem to make any difference.

      This buffeting seems to be an unintended consequence of aero design; the airflow around the greenhouses of older cars was such a mess that opening a window made little difference; with today’s mostly smooth airflow, it breaks up the airflow.

      The early aero cars of the 1980s also had a lot of buffering around the rear view mirrors. The mirrors were faired into the A pillar; and air would flow out of the high pressure area along the cowl and create turbulance around the mirrors. You can actually see the turbulance in the traces the water droplets make on the windows of my Taurus during a rainstorm; it causes a drumming sound on the window glass.

      Around the mid-1990s the mirrors were moved outward by mounting them on a stalk to get them out of that airflow. The stalks themselves are moved below the base of the windshield to reduce the noise down to nearly nothing (except maybe in crosswinds.)

      And that is where most of your wind noise comes from; I don’t think the above fairings would make that much of a difference.

  • avatar

    You need to open the two rear windows down just about 4″ or so if you aren’t already doing that.

    With the rear windows closed, there’s too much wind buffeting.

    That said, I do have a moonroof on my 2008 Honda Civic. It’s actually the window I open the most – I use it down to 50 degrees. A bit of heater for my feet and a bit of cold air over my hair is magic for me. Side windows stay closed – when they are open, too much wind when it’s not that warm outside. If you do not have a moonroof, perhaps trade in for one with a moonroof? I live in Maine, like you.

    • 0 avatar

      Even opening 2″ should work will. The buffeting is caused from air pressure building up in the car and then escaping; lowering the rear windows gives this air pressure a place to escape.

    • 0 avatar

      My dd is a ’91 Acura Integra 4 door. No combination of windows and/or sunroof fully and/or partially open will produce any wind throb.

      It often amazes me that newer vehicles seem to be prone to this problem.

      That said, having the windows open is quite noisy. (Tire and engine noise is fairly bad anyway.) The best combination of massive airflow and low buffeting/wind noise is one REAR window open and the sunroof. Beautiful on warm summer evenings.

      • 0 avatar

        Your Acura plays into my theory that cars that have a slanted rear edge to their rear window frames do not drum; my Taurus does not either. My guess is that the slanted edge does not allow air pressure to build up in the rear of the greenhouse like a vertical edge does.

        Both the wife’s Durango and my ’90 Dodge Spirit had vertical rear window edges, and both drum very loudly.

  • avatar
    Car Ramrod

    Related question– what is the point of the pop-up wind deflector on a sunroof? I assume it’s intended to reduce turbulence, but it increases wind noise significantly– is there any harm in pinning it down somehow?

    • 0 avatar

      It significantly reduces aerodynamic throb when you have the moonroof open and nothing else. It also keeps leaves out.

      It basically trades “THUMP THUMP THUMP” for a steadier state wind noise. There’s papers on car throb!

      • 0 avatar

        Note my comment below. While I agree it helps, the built-in deflector on my Saturn Vue was totally ineffective against that thump. On the other hand, in my Fiat 500 it comes across more as a flutter and is less annoying. Another factor is that in the VUE, the roof slid down and into the vehicle, between the roof and the headliner, while in the Fiat, it slides up and back, tilting up slightly at the rear. I prefer the Fiat’s version for the small car, but don’t know how effective this is for a larger vehicle. Will have to try it out on a Renegade some day, as it’s about the same size as the old Vue, but with the Fiat-style lifting glass instead.

        • 0 avatar

          There are better and worse designs out there, certainly. But that’s the theory behind them: reduce booming, deflect leaves, and try not to whistle too much.

          EDIT: of course, active air extractors would solve some of this, but at quite the price…. All you have to do is disrupt the Helmholtz effect.

          Or admit most customers just want their windows up so they can hear Katy Perry with their AC at exactly 74.25 degrees F.

  • avatar

    Today’s cars are made almost air-tight in order to limit road noise. Since nearly everybody keeps their car closed up with either heater or AC turned on, quiet became a real priority. The drawback is that when you have a car sealed so tightly, air cannot move into and out of the cabin smoothly. Windows down means you get noise and you can adjust those windows to help move the noise and the buffeting somewhat–but you simply cannot eliminate the noise. For me, in a four-door car or SUV, the best choice is to lower the back windows by ⅓ to ½. I don’t think this is possible for a 2-door car. However, this doesn’t address the buffeting from the sun/moonroof. That’s another issue entirely.

    The sunroof creates a huge hole right in the aerodynamic slipstream of the vehicle. Typically, it’s located where the roof is still rising slightly, so it’s guaranteed to catch more air than the side windows. But worse, this is also a location where you get that surface effect where the airflow ‘clings’ to the shape of the car, as compared to those side windows. What happens is that you get a huge gulp of air that increases pressure within the car, and the car has no way to let it out again except through the same big hole. End result? The ‘helicopter effect’. Depending on the size of the cabin, it can be a fairly rapid fluttering or it can become a pretty deep “thump, thump, thump” as I experienced in my ’02 Saturn Vue (over 100 cubic feet of interior space). The best means I discovered to eliminate this effect was to lower the back windows a mere inch or two to let those big gulps of air back out. But as you claim, this is not the solution you’re looking for.

    The roof is your big culprit here and what you need is one of those air deflectors in front of it. A number of types are available, but the stick-on type is really the better choice as it eliminates the risk of developing a water leak in the future. That little dam right at the front of the opening as the roof is opened does help to deflect some of the air over your head, but actually increases the noise level because it is almost never aerodynamically shaped. The plexiglass (acrylic) ones mounted a little ahead of the opening doesn’t disrupt their airflow as sharply and can significantly reduce the noise–but you still need to vent the air coming into the cabin or the helicopter will continue to flutter over your head.

  • avatar

    What works best for me to get a stiff breeze in my ’08 civic (no sunroof) without any thump is lowering the front and rear window about 4-5 inches on the passenger side of the car (when I’m driving). It worked better in my ’99 Accord than it does in the Civic, and I’m guessing that has to do with the more extreme rake of the windshield in the Civic. But it puts a good stiff breeze at my back, with no thump, and not that much noise.

  • avatar

    I believe this is just the interior cavity acting as a Helmnoltz chamber (in simplified terms, pressure waves entering through an open window or sunroof are reflected back in a way such that they are self-amplifying) and is usually best addressed by opening another window slightly. I find that cracking a rear window works best.

  • avatar

    I actually like white noise. It helps me to doze off.

  • avatar

    Worst buffeting I’ve ever heard by far? Gen 1 Highlander with rear windows open half way.

  • avatar

    Generally driving with just the back windows down is what causes you to think you’re piloting a UH-1 “Huey”.

    Having a sun/moonroof with a wind delfector does help, at least in my car. If I have any doubt, I reach up and pull it down to hear what a difference it makes.

    On my car, if I want a nice flow-thru airflow, I crack open the roof and lower the rear passenger side glass about 3″. Not overly loud, but nice. However, when the weather’s just right, I just open all windows and cruise. A bit loud, but usually there’s nothing much of interest to listen to on the radio anyway.

  • avatar

    Is s/he driving a coupe? Kinda hard to open the back windows in that case.

  • avatar
    30-mile fetch

    I always wondered what those trunk vents were for! Love your posts, Sajeev.

    • 0 avatar

      All cars/trucks need to have some way for air to escape, if not when you slammed the door you would pop a window out. Actually the air just compresses but it makes closing the door a touch harder. In all the vehicles I’ve had with sunroofs you could see this effect because the sunroof would raise a tiny bit when you slammed the door. This was especially true in vehicles with large rear hatches, as that moved alot of air.

      As for the buffeting – like others I’ve found lowering another window a few inches usually does the trick. Sunroofs that have a tilt feature are another way around the problem, a slight crack open allows for really good airflow. Back in the day I remember on my Honda’s you could slide a level to let fresh air in and just crack the sunroof to get a nice breeze in the car. That is the thing I miss most about not having a sunroof… because it worked really good in the evening when it was cool enough to not need the A/C but not so cold you had to put the heater on. Granted living in FL the heater was almost NEVER needed.

  • avatar
    30-mile fetch

    Lowering the rear window varying amounts when the fronts are down pretty much eliminates buffeting on our newer cars. Never lower just one rear window with all others up unless you want to turn your inner ears inside out.

    If driving solo, I will sometimes roll down only the passenger side windows so I can still hear my music. Doing this with the heat cranked up in autumn is a nice way to roll.

    Crosswinds are more difficult to deal with, I just roll them all up.

  • avatar

    I owned one car that zero buffeting with the sunroof in vent, or removed (wasn’t a power roof).

    First generation Ford Probe. Best aero design for a sunroof — ever.

    Sunroof flipped to vent, and you can have either side window down, at any variation of opening. You could control how the air flowed in the cabin, but no buffetting.

    If you opened the sunroof to the vent position, had the windows rolled up, it pulled the air through the ventilation system perfectly, fresh air curled in above and went to the back, and the warm air from the vents on a cool day pulled through more effectively, and up and out through the top of the roof. God I loved that – and water never, ever entered back in when it was in the up and vented position.

    Take the roof out and store in the hatch, same thing – windows all the way up – not only no buffeting but surprisingly quiet. Vary with the windows rolled down, you felt a significant pressure change if you lowered the windows a bit (and noise of course increased) but no issues.

    I’ve never owned, driven, or rented a car that came close.

  • avatar
    Jeff S

    The window deflectors work well if you want to open your window slightly giving you a little air without a strong breeze or too much noise. Additionally window deflectors are good if you want to crack you windows in the heat without letting rain in. I have window deflectors on all my vehicles. Weather Tech sells window deflectors to fit your specific vehicle’s windows exactly in tint or no tint. Weather Tech deflectors are made in Germany and are of a high quality. Weather Tech also makes excellent all weather floor mats and you can get them to fit your specific vehicle. I have a set of Weather Techs in my 99 S-10 for over 7 years with very little wear on them.

  • avatar

    Back in the day my friend’s mom had a then new Jaguar. Forgot the year but the first Jags to get kind of square and a digital information center. Anyway, the buffeting with the sunroof fully open was painful. So bad that the roof stopped part way open; just at the point before the noise began. You had to hit the switch again to get it to go the rest of the way. What a nice Lucas inspired British fix!

  • avatar

    Hi, everyone, I am the Scott who posed the question. Thanks for all the insight. I find the best position for my windows is to raise the fronts about 3″ and lower the backs the same. I’m rather sensitive to the white noise because I have tinnitus that gets louder in tandem with the noise level around me.

  • avatar

    On motorcycles with windshields, pressure equalization (in conjunction with lower air deflectors) is helpful in reducing wind buffeting. Some windshields come with air vents, or one can simply leave an intentional gap between the headlight and the windshield. Anything to reduce the negative pressure which “pulls” in turbulent air.

    I suppose a similar effect is possible in a car by opening the dash vents and cranking up the blower, but it would probably take a full Mythbusters episode to prove it.

  • avatar

    I run with sunroof open or vented as much as possible, with or without driver’s window down — it’s wind-buffeting, not a helicopter effect per se, that bothers me.

    I do get the “Huey” effect if I have the rear seat down and the roof open in any position. I noticed the same thing in a dealer loaner CR-V I had (when I was having a detail and oil change done on successive days with my Accord); the noise stopped when I closed the roof to about the two-thirds-open position. Next time I have a CUV or other vehicle with a large opening to the rear, plus a sunroof, I’ll try cracking a back window to see if it helps! :-)

  • avatar

    When I was in high school, my older sister would roll down all the windows in her ’57 Pontiac Chief and crank up the radio. Compared to Elvis and the 4bbl V8, the wind noise was a minor irritant. It was fun waving back to all the pedestrians waving at us, though.

  • avatar

    You are absolutely right, there’s nothing more annoying than the ‘helicopter effect’ on a roadster while trying to relish a top down cruise. I had to endure this bogey for some time until I decided to go for an external wind deflector. Thanks to the Windblox windblocker now I need not shout my jugular out to get myself heard.

    • 0 avatar

      Windblox windblocker is definitely one of the best draught-stops in the market. I too have one affixed on my ride and now my cabin is devoid of all gust gremlins.

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