Aerodynamics

[vagen]

I have found the CD on a loyale wagon is rather bad ranging from a CD of .30 to .38 or more depending on how big the barn door you strapped to the roof is. My advice remains the same look for things that obviously stick out into the airstream. Roof racks are a big drag producer as are mud flaps. on some cars removing the outside mirrors actually hurts aerodynamics. Your plan for tuft testing is a great idea I would have a friend drive along side and video as you drive that way you can see what the air is doing in areas obscured from the drivers seat

Edited February 8, 2010 by vagen

[nipper]

The best method is to make up your own. You first need to take a baseline, a coast down test. YOu time how long it takes the car to coast from speed X to speed Y. It doesnt matter if the road has slope down hill, what matters is that you always use the same stretch of road, your tires are always inflated, the same wind conditions and you just change things one at a time. You time how long it takes the car to roll from 70 or 75 to 55. That will give you a very valid baseline. From there you can measure fairly accuratly what changes you make to the car and what effects it has.

 

nipper

[naru]

Oddly, so does your wagon. Prius is .25 cD. Your wagon is about .27 cD. Aerodynamically, you're really not that far off. You might just go to a taller set of tires and see what you get. Its effectively a taller set of gears. I'd find a set of steel pugs (they're lighter than the alloys) and put on some tall, thin tires with a hard tread compound. I bet that something like a 195/70R14 would do well.

 

Comparing drag coefficeints is meaningless w/o considering frontal areas.

A small brick has less aerodynamic drag than a large supersonic airplane despite having a much higher drag coefficeint.

[Scoobywagon]

Comparing drag coefficeints is meaningless w/o considering frontal areas.

A small brick has less aerodynamic drag than a large supersonic airplane despite having a much higher drag coefficeint.

 

I understand that. But it answers the original question.

[robm]

There is not a whole lot we can do about the frontal area. But we can play around a bit with the Cd. I agree, comparing between cars, CdA is what we need to compare, but when dealing with just the EA82 body, it is pretty much all the same area.

 

If we did want to compare between cars, we should also consider interior volume, too. How much stuff or people can we jam into a vehicle, compared to its CdA. A two seater with room for a bag of groceries might get phenomenal mileage (Smartfortwo, 50 MPG), but doesn't look near as good when compared to a Subaru wagon hauling 5 people and gear (25 MPG).

 

But the point of this thread is not comparison, it is improvement. Starting point: Sow's ear. Goal: the best bag we can make of it. We KNOW it won't make a "silk purse."

 

Nipper's coastdown test is probably the best idea. But there are so many variables there, too, like air temperature, wind, etc. Make only one change at a time, and make several runs. Ideally, do baseline runs every time, then add the aero mod and try again, to eliminate outside variables. (That could be tough to do with major changes to body shape).

[bheinen74]

There is not a whole lot we can do about the frontal area. But we can play around a bit with the Cd. I agree, comparing between cars, CdA is what we need to compare, but when dealing with just the EA82 body, it is pretty much all the same area.

 

If we did want to compare between cars, we should also consider interior volume, too. How much stuff or people can we jam into a vehicle, compared to its CdA. A two seater with room for a bag of groceries might get phenomenal mileage (Smartfortwo, 50 MPG), but doesn't look near as good when compared to a Subaru wagon hauling 5 people and gear (25 MPG).

 

But the point of this thread is not comparison, it is improvement. Starting point: Sow's ear. Goal: the best bag we can make of it. We KNOW it won't make a "silk purse."

 

Nipper's coastdown test is probably the best idea. But there are so many variables there, too, like air temperature, wind, etc. Make only one change at a time, and make several runs. Ideally, do baseline runs every time, then add the aero mod and try again, to eliminate outside variables. (That could be tough to do with major changes to body shape).

 

smart for 2 get 50mph?

DOES NOT get 50mpg

 

it is:

The smart fortwo is designed to achieve 33 city/41 highway mpg according to 2009 Environmental Protection Agency (EPA) standards, which involves measuring mpg while taking into account real-life driving conditions such as start/stop city traffic, air-conditioning, heating etc. According to information obtained on fueleconomy.gov, the smart fortwo is the most fuel-efficient non-hybrid gasoline-powered vehicle in the USA today. The gas tank of the smart fortwo is 8.7 gallons.

 

Fuel economy estimates were derived in accordance with EPA vehicle testing procedures for model year 2009 as specified in 40 C.***.R. pts. 86 and 600 (2007). These estimates are intended for comparison between other vehicles within the same class. Individual drivers’ actual mileage will vary depending on how they drive and maintain their vehicles.

 

found at http://www.smartusa.com/smart-car-faq.aspx

just needed to correct what is posted above.

 

It is a Unsmartfor2

heck a civic gets better mileage, AND it can haul 4 people. The smart is very dumb, unless you can argue better.

 

all that great not so great mileage while it gets terrific performance of The maximum speed is 90 mph, with a 0-60-mph time of 14.1 seconds. A five-speed automanual transmission drives the Fortwo's rear wheels and is shifted without a clutch pedal via a simple console-mounted stick (and column-mounted paddles on Passion models), and there is a fully automatic mode as well. With its 8.7-gallon tank, the Fortwo will return 33 mpg city, 41 mpg highway and 36 mpg combined.

the numbers really SUCK for a car weighing only 1800.

Now, someone who is SMARt can figure out that.

Edited February 9, 2010 by bheinen74

[robm]

I agree. The Smart isn't. That was kind of my point.

 

As for the MPG figure, I quoted a European test figure. I knew the US figures were lower. I also know that the US figures are often easy to beat, and that 50 MPG should be achievable, if you try hard.

 

Remember, the US "highway" mileage involves a lot of stop and go! It is not steady state, 60 MPH for hours on end on a flat highway.

 

Under those circumstances, the old diesel Smartfortwos are capable of much higher figures. Real nuts were getting close to 100 MPG (Imperial, about 6/5 more than US). The car still doesn't have enough room in it for a big suitcase.

 

And this is not the point of this thread.

[bheinen74]

cool.

would it be possible, for sheetmetal front clip from a XT6 to be fitted to a wagon chassis up front, hood, fenders, bumper, lights. Is that doable?

If so, then I think we have a winner.

[robm]

The XT clip would get rid of the big bluff radiator on the front of the Loyale body. Would probably help. Is the windshield the same angle on the XT as the Loyale? Low angle windshields are good.

 

Another bad spot would be the transition from windshield to roof. Some kind of fairing there might help. A roof rack could be used to support it. Kind of like the ones the semis use to fair in the area between cab and trailer, except this would try to bring the flow back down to the roof. Duct tape and flexy plastic? Maybe well-carved styrofoam?

 

Does the wing on the back do anything except keep the mud off the rear window? (Does it do anything at all?) If it helps pressurize the zone behind the car, it would help.

 

If you want to get really extreme, cut the cargo area roof down and make it into a Kamm back. It would look really cool, that is for sure. But it might turn into a 2 seater....

 

How about a nose piece between the headlights, to get rid of that bluff body? A lot of the rad is below that, under the bumper, so it might not screw up the cooling too badly. More styrofoam. Easier to manipulate than welding a whole front clip on the car. If it helps, then fair in the lights, too, with clear plastic.

 

This is where the bits of wool taped to the body come in.

[4WDFrenzy]

I think that I am going to try to make a rear bumper diffuser and maybe some sort of under body panel for under the engine. Also I want to find(which may be impossible) an RX front airdam. Another thing is to try and fab a roof mounted spoiler for the rear, similar to the style that can be found on the mid to late '90s Legacy wagons or maybe one for an Impreza wagon. Something that doesn't stick up into the windstream, but would still help divert airflow passing over the top of the vehicle and direct it downward to pressurize the low pressure zone immediately behind the car.

 

-Patrick

[nipper]

I agree. The Smart isn't. That was kind of my point.

 

As for the MPG figure, I quoted a European test figure. I knew the US figures were lower. I also know that the US figures are often easy to beat, and that 50 MPG should be achievable, if you try hard.

 

Remember, the US "highway" mileage involves a lot of stop and go! It is not steady state, 60 MPH for hours on end on a flat highway.

 

Under those circumstances, the old diesel Smartfortwos are capable of much higher figures. Real nuts were getting close to 100 MPG (Imperial, about 6/5 more than US). The car still doesn't have enough room in it for a big suitcase.

 

And this is not the point of this thread.

 

Sorry but you are mistaken. Euro test cycle is very different from US EPA test cycle, to reflect the different driving styles of the two countries. Also there is a difference between fuels of the two countries. It is an apple and oranges comparison. Also you can not quote a test rating number then compare it to real world driving. And there are plenty of places in the USA where you can drive steady state at a given speed limit.

 

Smarts were never really meant for highway driving (Though i have seen one or two). Aerdynamics of cars doesnt really start to come into play untill over 35mph (maybe 40).

 

For real world testing air temp only has a minor affect on the coast down test. I would worry more about wind affecting the test then anything else.

 

nipper

[Uberoo]

The best method is to make up your own. You first need to take a baseline, a coast down test. YOu time how long it takes the car to coast from speed X to speed Y. It doesnt matter if the road has slope down hill, what matters is that you always use the same stretch of road, your tires are always inflated, the same wind conditions and you just change things one at a time. You time how long it takes the car to roll from 70 or 75 to 55. That will give you a very valid baseline. From there you can measure fairly accuratly what changes you make to the car and what effects it has.

 

nipper

 

coast down doesn't really mean much.My 89 Dodge W250(barn door with solid axles hanging down) coasts down hills hills faster than than any car Ive owned just because it has the sheer mass to smash its way through the air.Where as all of my cars on the same hill slow down much faster because even though they are more aerodynamic they don't have the momentum.

 

however off the top of my head I have two cheap/easy things you could do to an EA82 wagon.1 the turn signals in the bumper are indented a small amount creating a tiny cave(think old dodge charger grill and you get the picture).So if you mount the lights flush with the bumper and seal the edges of the lights it should help somewhat.

2nd one is counter intuitive, as a wagon or SUV rips a hole though air a HUGE vacuum is created behind it.If you draft a larger vehicle you are riding along in that vacuum of air and the larger vehicle is slightly pulling you.Here is where it gets counter intuitive.If you add one of those rear spoiler type things that have a sharp rake to them so that they clean your rear window.If you add of those to the rear of your wagon it will increase your CDa slightly but will improve your MPG a fair bit because you wont be dragging around such a huge vacuum of air behind the car.

[vagen]

If you add one of those rear spoiler type things that have a sharp rake to them so that they clean your rear window.If you add of those to the rear of your wagon it will increase your CDa slightly but will improve your MPG a fair bit because you wont be dragging around such a huge vacuum of air behind the car.

 

That actually works Back when I was a Datsun owner I saw a guy with one of those on his 510 and on the track he was about 10mph faster than me and I had more power.

[robm]

Coast down tests are only useful to compare between the same car with and without some neat new feature added to reduce its aerodynamic drag. It is not valid as a comparison between two different vehicles. However it is a good point that the load in the car must be the same for both tests, although this may not be significant if the coast-down is done on the flat, and not down hill.

 

If MPG goes up, CdA must have come down. That wing really makes that much difference? Why didn't all the wagons come with it? I woulld love to see coast-down tests to prove this one.