[dtbaker]

I am wondering if anyone has 'real life' results showing the effect of closing off the front grill and/or adding a full or partial length bellypan for improved aerodynamics.

Since my average use is 'suburban' with average speed probably around 35, with fairly frequent stops at intersections and lights, I am wondering if it will have any noticeable effect....

[gottdi]

At minimum you might consider the belly pan. Should be pretty easy to do. On what kind of car do you want to close the grill? Plastic front end? Metal? Usually the grill will be closed if you plan on doing plenty of high speed driving. Your driving should pose no real issues.

Pete : )

[gottdi]

Well I took a look at your little EV. Looks like that vehicle might have a pretty flat underbelly anyway. How bad is the undersides of one of those little cars? Might find some sort of aluminum or something you can form to shape and rivet in place to close off the grill. The put on the grill cover to hide the ugly rivets.

Pete : )

[dtbaker]

Originally Posted by gottdi

Well I took a look at your little EV. Looks like that vehicle might have a pretty flat underbelly anyway.

The front (under the motor) is pretty 'lumpy' and probably has a fair amount of turbulence even at low speeds. I am probably going to do that section no matter what just so I can protect my motor from the occasional water splash, mud, snow, etc.

The front 'grill' used to funnel air thru the radiator, and looks like a nice 'smile' with my white battery cases showing thru, but I m wondering if sealing it over would help the airflow enough to make a discernible difference in efficiency at 35mph. On a bicycle I kow that aero effect starts adding up at speeds over 20mph, but on the absolute horsepower scale its pretty small... noticible on a bike where you only have 1/3 hp, but pretty small percentage on a car using 10-15hp on a flat road just from the frontal area.

The mid section IS pretty smooth, but the the tail behind my battery box could act as a fair 'parachute' the way the rear bumper scoops down. I left bolt threads sticking down from my battery box thinking that I would use them to fit a pan to....

In my case, both front and rear bumpers are un-painted ABS. I bought a sheet of black ABS with a belly-pan in mind. Its easily heat formable, gluable, and heat-weldable.... Attaching should be easy, I am just wondering if anyone had a real-life numbers to show effect.

[gottdi]

At speeds under 50 you really don't need to do any of those things. Covers for water and mud protection is a good idea and should be done. Just be sure you still get proper cooling for your motor. I would not bother with the grill unless you plan on driving at higher speeds.

Pete : )

[mattW]

I disagree, I think a grill block and belly pan will make a significant (~5%) improvement in range. Even if aero is only a third of your losses at 35mph, something in the order of 20% of the drag in an ICE car is due to cooling. A perfect sealed bay would get 7% better efficiency at those speeds, I think 5% is probably doable.

Darin from ecomodder.com does some pretty extensive testing on his ICE metro and he found the following:

2.3% = gain from outside mirror changes
2.3% =gain from partial boat tail prototype
2.2% =gain from undertray

Edit: also tested

2.8% =gain from wheel skirts*
2.9% =gain from grille block*

* winter testing - denser air - also I tested at 95 km/h, whereas the ones above were between 88-90 km/h.

So 5% sounds about right for a grill block+undertray albeit at slightly higher speeds

[esoneson]

I suggest that you check our ecomodder.com.
The guys there know every trick in the book about how to reduce coefficient of drag. And you will be surprised at how much energy you can save with a few simple things like blocking off the grill and belly pans.
Also, even if you think that the belly of your vehicle is 'relatively' smooth, you should consider covering with aluminum (as suggested above) or some other covering, just check out some of those guys results.
What I am saying is, that it WILL make a difference, especially at highway speeds.

Eric

[dtbaker]

Originally Posted by mattW

Darin from ecomodder.com does some pretty extensive testing on his ICE metro and he found the following:

very interesting.... I am thinking that perhaps I need to develop a better test and measurement method so I can more accurately report effects in my case.

There is a stretch of road nearby about 3 miles long with no lights or intersections and do an out-back at a steady speed.... what would be suggestions on the most accurate way to measure actual kWhr consumption accurately?

I have been using the energy IN from my wall with the kill-a-watt meter divided by trip odometer. This is start-stop at my house, and would be thrown off by getting there and back. Also not exactly the same charge cycle probably.

Is there a cheap meter I could attach to accurately measure kWhr actually consumed during a set test course?

[tj4fa]

I would recommend closing off the grille and belly for rain/water purposes except maybe for any air ducting to the motor bay/controller that you might need to keep things cool.