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What steps have you taken (/are planning to take) to improve your EV's aerodynamics?

  • A Belly pan

    Votes: 5 35.7%
  • A Purchased Body Kit

    Votes: 0 0.0%
  • Customised Body Work

    Votes: 4 28.6%
  • All of the Above

    Votes: 0 0.0%
  • None of the above

    Votes: 8 57.1%

Aerodynamics

8534 Views 56 Replies 8 Participants Last post by  Greenflight
Just wondering what people have done to improve the aerodynamics of their vehicles; belly pans, body kits, fiberglassing (Please elaberate). And whether or not these changes have made a noticible difference to range/performance.
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I'm not sure how useful a poll is going to be unless it's yes/no, as there are many components to enhancing aerodynamics that would make for a very convoluted poll tally.

In my case, I installed the factory GTI air dam and wheel arch flares, which are purported to lower the Cd by .4 alone. My car also has the grille blocked off by plastic inserts, and I replaced the open vents behind the front bumper with factory blanks. I've installed later model bumper mounts on the front that move the bumper closer to the body, and installed a factory valance between the bumper and the bottom of the grille which closes off the gap, lowering air circulation in that area.

Since the Pusher needs cooling air to enter the grille, I've fabricated custom mounts and cut down the rear air deflector from a 1980's Oldsmobile station wagon to catch a bit of the air coming off the rear of the roof and direct it down the slope of the rear hatch. No scientific data on that modification, but anything that smooths the air flow behind the car can't be bad.

Once, when this topic came up on the EVDL, it was suggested that installing factory fender liners from a Cabriolet could help reduce turbulence inside the wheel wells. I've obtained a set, but not yet installed them.

If I haven't already posted it here somewhere else, here's one possibility for improving front aerodynamics:



Looks a bit like Darth Vader or Dick Cheney, but it's cheap (foam insulation panels, duct tape and drywall screws), and it retains all of the factory safety equipment associated with the shock absorbing bumper, etc.

Finally, doing some research on a well-established platform might allow one to dig up images such as these:







You'll note that the Golf model involved is a European model, with the small metal bumpers and a "duckbill" spoiler under the front lip. It would be interesting to comare this with a typical U.S. issue DOT-approved shock absorber type bumper and no spoiler and/or a GTI set...
 

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Although the deflector is visible on several photos I have of the car, none show it very well. I drove the car today for the first time in six months, an afternoon jaunt into town to meet my sister and brother-in-law for coffee. I took the camera along to catch a shot of the car and the deflector, but it got late, and after a double shot of espresso, I was absolutely frying and couldn't stand still long enough to pull the car over at some picturesque location and frame up a photo. For that matter, I'm still buzzing from the caffeine five hours later...

Maybe tomorrow...

In the meantime, here's a shot of the tucked-in front bumper, trim valance, custom headlight guards and the GTI spoiler, just visible at the bottom...

 

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Don't know if anyone is still interested, but I did say that I'd post some pics of the rear deflector.

Here it is in a side view. I had my sheet metal guy fabricate some sheet aluminum brackets that fold under the hatch so that I didn't have to drill any holes on the exterior of the hatch:



(this view is of two Rabbits sitting side-by-side, the one in the foreground is powered by Biodiesel)

I didn't want a Rice-Racer picnic table sized fake wing apperance, so I made sure that it was pretty much tucked into the roofline of the car, and directed the airflow down over the hatch.

From the rear:



The Oldsmobile deflector ($10 at a wrecking yard) was much too wide for the VW, so I put it through the band saw, sculpting the ends to compliment the countours of the top of the roof at the sides. In this view, it looks fairly wide, but when you stand back a bit, it blends into the natural lines of the car.

A few holes to fill with Bondo, and a can of VW-matched touch up paint, some stainess steel fasteners, and I can at least pretend that it fills in some of the vacuum created behind a moving vehicle. Next time I have the backyard wind tunnel fired up, maybe I'll run some diagnostics...
 

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With 500 Kg of batteries where the back seat and fuel tank used to be, any lift generated by the deflector would be negligible.

What's laughable is all the asian import boy racers who put giant spoilers on the back of their Honda Civic and claim improvements in handling. Realistically, such attachments are eye candy only, as true aerodynamic ground effects don't really start to get generated until you are doing over 160 KpH.

In my case, the Pusher generates much more lift on the rear of the EV when it's providing power. I can and do feel the steering get a little bit lighter when I'm accelerating hard, but nothing that would cause the car to become unstable. I do have a fabulous amount of custom suspension work on the car, and it is rock solid on the road and in turns.

Oh, and high speed? "High speed" for this car is 100 KpH. If I was worried about the rear wheels coming off the ground due to the few pounds of lift that the deflector might generate, I'd put a couple of bricks in the boot.
 

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How good are E-meters and that kind of thing at measuring your effeciency?
The E-Meter patent was purchased by Xantrex and has been renamed "Link 10" (Here's a link to a descriptive page about it from Energy Outfitters). If you were to use the method described by veperformance above, the Link 10 could be very useful, especially if you purchased it with the RS232 option, which provides a data port from which you can compile data at one second intervals. Running this data through Excel, it's possible to make some very useful graphs:


Chart of power usage while using the Pusher trailer: Following the blue line, we see significant discharge currents at the beginning of the trip, which represents surface street driving and acceleration when entering the Interstate highway. About 09:25, the Pusher trailer assumed the majority of the load while operating at a steady speed on the highway, and some amount of regenerative braking replenishes the power used earlier. Large upward spikes in this line of the chart represent regenerative braking used to decelerate the vehicle at stop signals and when exiting freeway off ramps. At 09:52, I exited the freeway and drove the remainder of the trip on rural roads with some traffic stops along the way.

This chart represents about 50 miles of driving. Note that the number of ampere-hours consumed from the battery pack (yellow line) totals about -20Ah.

You could generate similar charts while running a known course at a fixed speed and see the results of any changes you make fairly easily. A one second capture duration for the data would help insure accuracy. I'm no Excel whiz, but I'm sure the program is capable of some powerful equation processing that could average the data, making the results even more useful.

I've always monitored efficiency by reading from a dedicated kilowatt hour meter and writing down the number of kilowatt hours consumed by the car and cross referencing that to the miles covered. While not an instantaneous result of efficiency, and subject to many variables, over the course of several weeks or months, a very reliable result can be obtained.

Overall,the Link 10/E-Meter is very useful. I own three of them, and wouldn't run my car or my renewable energy power systems without them, or something similar.
 

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In my case, I have ducted air from the grille of the car with blower assist.

The controller in my car handles only 10 amperes of current, so heat dissipation is negligible there.

Cooling for the motor is collected from an opening in the grille, which is accomplished via a custom-made aluminum box with a removable tray that holds a 4x6" sheet of blue polyester filter media to collect dirt and bugs. The output of this filter box feeds a 4", 12 volt DC squirrel cage blower, which in turn feeds the motor shroud from the brush end. Spent cooling air is exhausted from the shaft end of the motor.

The blower is connected to a PWM speed controller, and runs at about 1/4 speed anytime the ignition switch is on. When motor temperature gets up to about 75 degrees C, a temperature sensor signals the PWM controller to feed 100% duty cycle to the blower motor, bringing it up to full speed.

The combination of positive air flow from the motion of the car and the blower running at low speed seems to be more than enough to keep the motor at a low temperature on city streets. The blower usually only runs 100% at highway speeds, and usually throttles back to 25% by the time I have exited the freeway and driven home to park (based on my previously living in the city).
 

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OK Sharkey, fill me in here. HOW does your car's controller only handle 10A?
Simple: Shunt Wound Motor. The controller's only load is the field coils in the traction motor. A single TO-3 high current/high voltage transistor handles the current. It's mounted on a small aluminum plate, enclosed within the larger controller enclosure. No heat sinks, cooling fans or atmospheric radiation necessary.

The armature in the motor of my car is connected directly to the battery pack through a high current contactor. The fields receive 100% PWM duty cycle from the controller when the motor is idling (and during full regen), and the field is weakened (lower PWM cycle) for acceleration.

Matt:

I was looking for a decent image showing my filter box and ducting, but don't think I have one, perhaps I can go out and snap one tomorrow when it's not storming. Only one battery under the hood, a 26 Ah gel cell for 12 volt accessories. Lots of room to view and move under there.
 
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