Care to show how it contains both?

As far as I know, the relationship is linear only at a very slow speed where there is no turbulance, so for all practical purposes, it's the equation with the second power of speed that counts.

 

yes you r. u been drinkin apple pie down in Georgia again<SMILE>. what would be more appropiate would be the amount of beehives i would be able to carry in such a rig and the total cost of transport per hive per mile.

 

This test mule is a 91F250 with extreme rust. I have committed the vehicle totally to scientific experimentation. It will eventually be consumed by testing. This is serious fun. Look at the car I drive. You guys are making me dust off books, i haven't looked at in 30 years. And I just want to get riveting.

 

aurgathor, do you know how i can find the formula's used for airfoil shapes?

 

"Theory of Wing Sections" by Abbott and von Doenhoff has the airfoil cross sections of many common NACA airfoils.

There is also a program called XFoil that can give you CAD files of cross sections. Do a Google search for it and see if anything comes up. If not, I might be able to get a copy of it.

 

thanks
this site gives the x-y points for the NACA four digit series
http://www.pagendarm.de/trapp/programming/java/profiles/NACA4.html

 

Body drops specifically only benefits aerodynamics and therefore fuel economy when it decrease the profile of the vehicle by closing the gap between the suspension and the frame/body. This is the most extreme but quantified body drop I've seen http://ecomodder.com/forum/showthread.php?t=85 The numbers for the body drop .08 meaning that it probably achieved 11% better fuel economy just for the body drop. There are other ways to minimize drag without a body drop like the standard grill block, a more extensive mod like a full under tray or just slapping a larger front dam on the vehicle. The dam is probably the easiest for stock vehicles if it only goes down to the lowest suspension part, below that it's only going to add more drag. An under tray would be more useful for a lifted truck if you could make it fit the style of your truck. Most guys with lifted trucks seem more than willing to remove the front valence and let all their suspension parts hang out for the world to see.

Wings add drag to create more downforce for better handling. Most decklid wings simply add drag for looks but more specifically rally or maybe road race cars use wings to boost handling. It's bad for top speed and bad for FE.

I dunno about measuring proper distances for turning a truck into a tear drop shape because that would require measurements and geometry of the specific vehicle. Less frontal area is best and smoothing out all of the blunt spots and filling any empty areas is my best advice. Plus a curved shape like in the front and back could really improve the flow, as I've only read.

But you can use:
http://www.geocities.com/CapeCanaver...79/evcalc.html for aero drag, wind drag, and rolling resistance drag. That is, if you're willing to look up your vehicle's drag coefficient, frontal area, curb weight, and multiply your gearing by your axle ratio or guess it all. You'll have to excuse the EV references and remove the weight added by batteries, motor, etc before you can properly calculate your rolling resistance. I don't know the equation for aero drag but this calculator appears reasonable for estimates.

Don't forget that taller/shorter tires affect the odometer/speedometer accuracy. Wider tires add rolling resistance and some more air drag. If you swap to higher axle ratio or even higher tranny gearing to match taller tires you may not notice as much error or FE difference. I've noticed many people do this so it's probably more common knowledge than I let on. Using GPS for speed and distance has been mentioned in various places as better for accuracy. I wonder if GPS calculates accurately for inclines or underpasses though. It would seem that satellites are powerful enough and have more accuracy than your speedo but I'm not as educated on this topic, sorry but it's only a suggestion.

You could probably compare aero findings on http://ecomodder.com/forum/ or http://www.gassavers.org/ . They're nerdy enough to be accurate without as much talk about conspiracy theorys. Plus they have aero modding in which they do measure the effects by A-B-A testing maintaining same speed, monitoring weather conditions, and using a scangauge.

The biggest gains in FE is still goes to driving techniques. The big ones for the average driver is for shorter trips(less mileage overall), lower average speeds eg less than 55 mph with 55 mph being the maximum top speed, and maintaining a steady speed. At least that is what everyone who knows anything says .

Aerodynamics is mostly an advanced topic since most of the aerodynamic knowledge is held by companies that do not share this knowledge with their consumers or educate them on the effects of aerodynamics. Why should they? It's not like we're asking them about it. For example the average vehicle's rolling resistance to air drag is almost equal at 55mph. Under that number it is mostly rolling resistance that adds weight, beyond that and it's all air drag. Plus it becomes more complicated when you add in wind drag.

 

Allch Chcar
about measuring proper distances for turning a truck into a tear drop shape because that would require measurements and geometry of the specific vehicle. Less frontal area is best and smoothing out all of the blunt spots and filling any empty areas is my best advice.
http://www.pagendarm.de/trapp/programming/java/profiles/NACA4.html
this site is interesting because it is interactive and you expand the cord and thickness to fit the application.
my theory is that shape is more important than frontal area. So if the frontal area of the truck is 120% more, the drag coefficient be lowered enough to more than compensate for the increase in area? That is the basis for my experiment. the truck 18' longx 80"widex74" high. or approx. 41 sq.ft frontal area(differential hits the air below bumper)airfoil to enclose the truck is 8'widex74"highx 35feet long or 49.3sqft a 20% increase in frontal area. But the Cd in the book for a foil section this shape is .02 that would be 20 times less than a truck. so when you put ends on that section you lose a lot but still a big gain even with all the extra area seeing fiction. the result I am hoping for is it wouldn't look a truck but it is bigger than a truck and it will haul more than a truck on less fuel.

 

I concur with your statements. Though it is difficult to tell if you are quoting me or rephrasing what I said in the first three sentences. I made a grammatical error when I stated back instead of the top of the truck bed.

Less frontal area is always best in aerodynamics. But in modding preexisting vehicles you often sacrifice a slightly larger frontal area for greater aero efficiency gains. Basically if you cut the coefficient of drag by a greater percentage than the increase in frontal area you gain better fuel economy in the end.

I believe the great emphasis on reducing the Cd is because the frontal area on a vehicle may already be error in estimation based on a sloppy measurement of the front like it was a flat board. But it's not, it has many holes and gaps that would make measuring the entire frontal area very complicated. So everyone is big on Cd but since you recognize the frontal area to Cd, you're alot better off to figure out the truth of the benefits.

Plus some aero mods actually turn the front of the vehicle into a board with tapered ends. But that hypothesis only applies to the frontal half of the vehicle. Which is only half of the whole dynamic approach .

I'd point to this a source of greater Cd is always best even if you add a little frontal area: http://forum.ecomodder.com/showthread.php?t=290 . The teardrop might be the best and most talked about shape but the box fish is a naturally inspired vehicle shape: http://www.worldcarfans.com/2050607.004 . That last one is probably more akin to the kamback they use in the Toyota Prius. The kamback itself is the alternative to the "boattail" like design you would use to make a tear drop. It is claimed that a kamback like the boxfish's tail is better than an elongated tail. Boattails have lower Cd but the kamback has less total surface area. Something at least worthy of note.

 

I'll try this quote button. Aflat board with a window would probably be less drag force then the same size truck because all the intakes, protrutions and trubulence. I might chop the design off at the trailer hitch.

 

Exactly. You obviously weren't asking me. But yeah I may not have been clear on the frontal area vs Cd. On paper you will only note the decrease in Cd. But in reallity adding surface area to your vehicle that still lowers you Cd will not be as effective as you think. Glad we had this conversation I probably changed my math several times in my head. But you got the right idea.

Recommending chopping the tail drop off at the tail gate is what I was shooting for. Since you have a trailor hitch...yeah you got it.

So long as percent decrease in Cd is less than the percent increase in frontal area and the cost of added weight, your mods will all be beneficial.

You can probably use chloroplast for the upper parts of your design and put aluminum sheet where heat might build up especially in the undertray. But I haven't gotten that far in my modding. I just put a grill block up yesterday using aluminum sheet normally used between the foundation and wood structure of a house. It's normally for redirecting termites now it just redirects air. How long have you been learning aerodynamics?

 

You could go all nascar-like and tape up all of the front openings...great downforce...it'll just suck for cooling.