I’m just not believing that the windmill will do anything other than increase the drag of the car above the level of any power it produces. I’m going to call “cite” or “calcs” on anyone here proposing such.
No, but it has 14 k of d in a f p d.
This is true; the regenrative brake is a common feature on electric trains, not to mention hybrid vehicles.
However, in this case you are already trying to slow down the vehicle, so you actually want the drag such a device produces; you wouldn’t leave this braking mechanism on all the time just for the extra energy. If it’s on continuously, the laws of physics say it could never produce enough energy to offset the energy lost due to drag.
Now, if the windmill were designed such that it “popped up” only when the brake was applied, it would produce some useful energy. However I have to bet it wouldn’t be much, and doubt it would be worth having fellow motorists snicker at “that dork with the fan on top of his car”.
If that was directed at me, I was thinking about things like vortex generators (obligatory cite; pdf) that can be added to an automobile to decrease drag. I could imagine a small rotating device could acheive similar results.
Alternatively, I was also thinking about cooling airflow running through the radiator (if an analogy exists on an electric car). I could imagine a small rotating device in this flow not affecting the drag on the car.
Point is, with the interaction between the flow over windmill blades and around the car, I don’t think you can categorically state that all rotating devices of any size in any position around the car will always increase drag. In a free stream, yes. Around a car…not so obvious.
Well, it was directed at anyone, I guess.
I don’t state as such, but I don’t believe I’ve ever seen a practical example that could work. And I still have not.
It could work, just like that windmill boat cited above. The car has a turbine which is powered by the wind–not the percieved wind generated by the cars motion, but the actual wind. And that can drive the car even into the wind. The advantage would be that the car would drive more like a regular car than a car equipped with traditional sailboat-style sails.
Right. But a great deal of time, effort and money is spent on research into devices and techniques for improving airflow around automobiles. And from this, so far as I know, no one has ever come up with anything resembling a windmill.
Not sure if this counts as a rebuttal, but in the 70s there was a formula1 car that utilised a fan for massive downforce.
Kicked ass in the one race it took part in, and then was swiftly banned.
It’s not clear to me from that article if the turbine is intended to be used while the car is moving or only when the car is parked, to charge a storage device.
Good one. As you note, the job of the fan wasn’t to reduce drag, but rather to improve cornering.
Indeed. Thus the substantial qualifications in my original post.
When I drive my convertible with the top down, there is continuous airflow between the front seats from the back to the front. I could put a tiny windmill there, and any drag is (locally, at least) pushing the car in the forward direction. I’ve often wondered whether obstructing that airflow would help my mileage some minuscule amount, or if increases the car’s overall drag anyway. (Of course, I could just put my top down and get lot’s less drag, but we’re being theoretical here.)
Well, there is that pesky word, “Practical” that should be addressed.
In sailboat races where .01 KTS is critical, practical becomes something very small that can reap huge benefits… To bad the OP was about cars…
Even though it’s moving in the opposite direction to what you might expect, impeding it still might increase drag because at some point, something is scooping the airflow around and directing it the other way - if you block the reverse airflow, it would propagate back (by means of increased pressure or something) to the point where the airflow is being reversed, make that process less efficient and create greater drag. Probably not in any way that could be easily measured outside a laboratory though, but that’s only because the amount of energy you could hope to extract from the process would be minuscule.
Did not airplanes sometimes have little windmills attached to the fuselage connected to a generator to provide power on some of the early aircraft? They were however tiny compared to the size of the plane, I wonder how much drag vs power they did provide.
Such a system can only produce less power than is expended in pushing them along. One reason to still do this though is that it can provide an independent backup power source - as long as you’re moving forward (if you’re not moving forward, you have more pressing concerns than lack of electrical power)
Not just early aircraft either. I saw a made-for-TV film some years ago, a true-life story about a jet airliner that ran out of fuel at 30,000 feet thanks to getting a litres-to-gallons conversion the wrong way round, and the crew deployed an emergency windmill to provide electricity - while, of course, desperately plotting a glide path to an airport within reach. Fortunately they were over the continental USA and made it down without a scratch.
The key point here is emergency 
There is an emergency turbine that drops out on a loss of generation capacity. This allows restarts in case of an all engine flameout. As I recall, the guys flying the Gimli Glider were not happy about the extra drag and the impact on glide distance.
Si
Thanks for the link. Delete “continental USA”, insert “Canada”. When I saw the link, I thought there was something about dwarf-tossing coming up. 
keep your personal kinks to yourself 
Si