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Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 11:58 am
by TEG
I am not sure if this was posted before, but the topic of funny headlight shape to direct airflow away from the mirrors (to reduce noise) has come up repeatedly...

Image

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 12:21 pm
by DaveEV
Nice - side mirrors are notorious for the drag they introduce as well - I wonder if moving air around the mirrors increases or decreases drag - or maybe the effect is negligible?

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 12:57 pm
by EricBayArea
That's a cool shot. Thanks for sharing.

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 12:58 pm
by palmermd
noise=drag...I'm sure the reason was drag and the noticeable benefit was noise reduction.

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 1:26 pm
by DaveEV
palmermd wrote:noise=drag...I'm sure the reason was drag and the noticeable benefit was noise reduction.
Yes, but moving air around also creates drag. There is no free lunch here. Otherwise you'd see more cars with this feature.

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 1:42 pm
by palmermd
drees wrote: Yes, but moving air around also creates drag. There is no free lunch here. Otherwise you'd see more cars with this feature.
Yes, but doing it gently is less disruptive than doing it abruptly hence less drag and less noise. Otherwise all cars with the same frontal area would have the same drag.

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 2:25 pm
by davewill
drees wrote:
palmermd wrote:noise=drag...I'm sure the reason was drag and the noticeable benefit was noise reduction.
Yes, but moving air around also creates drag. There is no free lunch here. Otherwise you'd see more cars with this feature.
I have. I've noticed several cars recently with bubble headlights. None quite as prominent as the LEAF, but obvious enough.

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 3:42 pm
by kevin672
palmermd wrote:noise=drag...I'm sure the reason was drag and the noticeable benefit was noise reduction.
I think Nissan has said that the reason was the noise. The car is otherwise so quiet that the noise from the wind over the mirrors was a problem and Nissan's solution was to use the headlights to direct airflow away from the mirrors.

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 5:21 pm
by GeekEV
palmermd wrote:Yes, but doing it gently is less disruptive than doing it abruptly hence less drag and less noise. Otherwise all cars with the same frontal area would have the same drag.
I wonder how much of a difference this makes on drag. I recently read (Car & Driver I think, but I forget exactly where) that side mirrors account for 7% of the a car's drag. I'm sure that's a generic statement and varies from car to car, but that's not a trivial amount. If this helps helps with drag in addition to noise, that'd be huge.

Re: Wind tunnel picture of headlight / mirror airflow

Posted: Wed Nov 16, 2011 9:08 pm
by aqn
palmermd wrote:noise=drag...I'm sure the reason was drag and the noticeable benefit was noise reduction.
kevin672 wrote:I think Nissan has said that the reason was the noise. The car is otherwise so quiet that the noise from the wind over the mirrors was a problem and Nissan's solution was to use the headlights to direct airflow away from the mirrors.
The "host" at the "Drive Nissan LEAF" event I attended in late 2010 said the same thing. At the time, I thought to myself, "And, of course, the battery is built by bachelor Norwegian farmers so you know it's good for you." Now, all I need to do is to find proof that the pic above is not a Photochop job! :D