tacoma aerocap ABA test

[RobertSmalls]

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.

[mjboks]

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.

[KamperBob]

Is the back open or closed?

Cheers
KB

[ccrider]

Originally Posted by mjboks

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.

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

[KamperBob]

Originally Posted by ccrider

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.

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

[mjboks]

Originally Posted by ccrider

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.

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

[ccrider]

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

[COcyclist]

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.