tacoma aerocap ABA test
 

here is the ABA test on my Tacoma aerocap.

my truck is a 2002 Toyota Tacoma regular cab with a 2.4 4 cylinder engine 5 speed transmission with 206,000 miles on it. the truck has no mechanical problems, no check engine light, or any issues that i know of.

[IMG]http://i964.photobucket.com/albums/a...0/DSCF0893.jpg[/IMG]



it has the following modifications.

80% grill block
44 psi in tires
k&n drop in air filter
scangauge II
hot air intake
removed mud flaps
aerocap
smooth hub caps

i did the test on rt 192 west of Melbourne Florida. it is a 65 MPH speed limit road with some mild turns, one canal bridge with about a 5 ft rise over the water. other than that it is very straight flat 2 lane road. i used a 7.3 mile section and did 2 east and west runs for each portion of the test. i do not have cruise control so i used my gps to keep speed. i watched the average speed along with the actual speed and tried to keep the speed at 65 MPH and if i saw the average go up or down from 65 i would try to change my speed by a few tenths of a mph to keep the average at 65 mph. i think it was really accurate. i rarely was off more than 1 mph but i will include the average speed in each run

weather condition were taken from a weather station a few miles from the test road. i started the tests at 10:30 am with a temp of 62 degrees and winds out of the NE at 5 mph gusting to 7 mph and i finished the tests at 2pm with temps at 66 degrees with wind out of the NE at 6 mph gusting to 10 mph




A......west....................................eas t

run 1 27.8 mpg 65.0 average mph 25.6 mpg 64.9 average mph

run 2 27.7 mpg 64.9 average mph 25.8 mpg 65.0 average mph


A average 26.725 mpg





B......west...................................east

run 1 26.5 mpg 65.0 average mph 24.7 mpg 64.9 average mph

run 2 26.9 mpg 65.0 average mph 25.0 mpg 65.0 average mph


B average 25.775




A.....west.................................east

run 1 28.0 mpg 65.0 average mph 26.2 mpg 64.average mph

run 2 28.1 mpg 65.0 average mph 25.7 mpg 64.9 average mph


A average 27 mpg



all A average 26.863
B average 25.775


gain 1.088 mpg




when i had runs that i discarded due to problems with gps and truck interference i took some runs at different speeds just to see what i would get.

i did one run without the cap west at 75 mpg average 22.4 mpg
i did one run with the cap west at 75 mpg average 23.8mpg
i did one run with the cap east at 55 mpg average 30.2 mpg

sorry the results are so confusing all the spacing changed when it was posted

Nice work! Thanks for posting. Real data collection takes some serious time and effort. It looks like you should see some good results from your aerocap. Can you include a link to your build thread for the cap?

http://ecomodder.com/forum/showthrea...ghlight=tacoma

i did not start my own thread on my build but i posted some pics and stuff on this thread

Agreed. Thanks for putting in the effort.

Based on your numbers, that's a...

4.2% fuel economy improvement at 65 mph
6.3% fuel economy improvement at 75 mph

i was hoping for somewhere around 10% improvement but the numbers are the numbers.


anyone have any ideas on how i could modify my cap to see some better results? i guess next i should do the tuft test maybe the sharp edges on the corners are creating problems.

The sharp ones that the back are actually better than rounded, IIRC. The ones are the top could be rounded, but I doubt that they are hurting 10% worth.

How smooth is the transition between cab/cap?

How much does the cap weigh...what is the frame material?

Bajascoob FYI, see this thread for construction details: http://ecomodder.com/forum/showthrea...kup-11271.html

Tortoise beats hare
 

Thanks for sharing, and congrats on your progress.
I particularly liked your last line best! :)

Cheers
KB

I noticed that too. The difference in driving slower was greater than the aero mods. I can drive my car and get 55mpg. My wife takes it out on the highway and mileage drops below 40 mpg. But, the aero mods help every day with every driver at highway speeds.

I'd wonder about that area of the cap, and the cab/cap transition too. But I suspect you've already found the major gains from shape optimization at the back, and further improvement from tweaks may be relatively smaller.

Not trying to discourage you from doing more!

But I wonder if you'd be better off looking at cleaning up the underbody, in terms of effort vs. results.

here is a couple of pictures of the cap where it meets the cab


[IMG]http://i964.photobucket.com/albums/a...0/DSCF0899.jpg[/IMG]



[IMG]http://i964.photobucket.com/albums/a...0/DSCF0897.jpg[/IMG]

I would have thought you'd have better results. Yours fits much tighter to the cab than mine does.

My differential (aerocap vs open bed) was right at 3 MPG.

Maybe I did better because the diesel retains efficiency at lower percentages of rated engine power.

10%
 

cc,if your bed had been longer,allowing the cover to drop all the way to the level of the rail/tailgate top you'd have it.It's the difference in wake size,between part way down,and all the way down that's getting you.
But it's still good and allows more utility within the bed.:thumbup:

Do you have a link to your build, or some bigger pictures..I started work on my F-250. Is yours a 7 or 8ft bed?

[QUOTE][My differential (aerocap vs open bed) was right at 3 MPG./QUOTE]

dave did you do a ABA test?

before the ABA test i thought i was getting around a 3 mpg gain also but i think i am just getting beter at hypermilling.

maybe i should put the tailgate down and build a removable extension on the tailgate that continues the back angle down so that the back flat spot is smaller. it would be nice if that would give me the extra 5.8% in MPG

extension
 

cc,you might be able to cobble together a proof of concept extension out of stuff laying around.If she delivers at the gas pump,then maybe it's worth the extra effort.

Bajascoob:

PM me an e-mail addy and I'll send some .jpgs.

Bed is 80" long.

Truck is not so much a build as the result of nine years of testing.

It looks like you were only able to reduce your trailing wake area by about 20-25%, so a 10% reduction in drag (for a slightly smaller % reduction in highway fuel economy) would not be surprising.

In an ideal world, you'd taper the sides inward for a larger reduction in rear area. In reality, that's difficult to execute with plywood, and it's nice to have the bedrails under your aero cap. In a very ideal world, you'd taper the sides of the bed inwards, too.

You can use the same template as you did for the side view, but line up the ground plane of the template with the center line of the truck. If your shape curves inward from both sides and from the top, you can get away with sharper shapes than the template suggests. How much sharper? I do not believe anyone here can tell you (except to recommend you imitate the EV1 and Honda IMAS), so you'd be flirting with flow seperation.

But back to reality. You have a classy looking cap, and I like the overhang. If you want further drag reduction, you'll need to find room for more reduction in trailing area. You've already plucked the low-hanging fruit in that department.

template overlay
 

I took your image from the other thread and overlaid the template. Not sure if it's the angle of the camera or not but it looks like your cap is a bit on the conservative side... better than too steep and getting separation.

Here's the image with a couple simple lines drawn in if you did a tailgate extension.
http://ecomodder.com/forum/attachmen...1&d=1267800945

Is the back open or closed?

Cheers
KB

the truck is slightly lower in the front in the picture if you look at the black bed liner under the cap compared to the template bottom. if the truck is perfectly flat the template matches up pretty close.

kamperbob the tailgate was closed during the tests. not sure if that is what you are asking. but the back of the cap has a piece of plywood on it.

i think i should do what metrompg said and move on to the under side of the truck. i think that my results showed that the big mpg loses as speed increased tells me that trucks have very bad aerodynamics and that if i clean up the bottom i should see less loses as speed increases.

since the test i have been more aware of wind conditions and yesterday i was driving from Tampa to Melbourne and i had a 10-15 mph tail wind and i was averaging over 30 mpg on the scangauge at 65 mph. which makes sense because i was getting around 30 mpg at 55mph on my tests

Good. I meant the cap not the tailgate. (I was wondering about possible reduced pressure *inside* the cap (vacuum effect) acting on large vertical surfaces, but if the cap was closed that should not be a factor.)

Cheers
KB

Thought that might be the case. The bed rail shows a bit of a downward angle in the image.

i just filled up my gas tank after doing my ABA test and the scangauge was not accurate on the fuel consumption on my truck. the scangauge though i used 13.6 gallons and i only used 12.96 gallons. so the scangauge was figuring the mpg 4.94% low (i just got it back from repair) i also thought the mpg's were a little low for my truck. so the actual mpg's for the test would be

A 28.045

B 27.048

A 28.333

gain 1.142

gain percentages still stay the same as metrompg stated

On another thread Aerohead suggested putting ballast in the car to simulate driver and passenger weight before determining the correct angle for a boattail from the template. As I recall, you said you need to haul things in your truck bed from time to time. I had this thought that it may be better to be conservative in your angles (as I think you are) than to get them just right and have it too steep as soon as you put a load in the bed of the truck.