Aerocap Performance (Why are we seeing wide variation in reported MPG savings?)

[Fubeca]

The crosswinds were not quite perpendicular to the road I was driving. I did run both directions and average the runs.

[bondo]

Originally Posted by round.boater

My butt-o-meter says ~15% is probably about right for my cap. I'll do A-B-A if anyone in Denver would help me lift the thing on and off. One of the big benefits for me is that I can take it up to 75 without watching the mpg's completely crater. (And FWIW, I'm still the slowest vehicle on the road where I do that)

Bondo, when are you going to design an underpanel that will bolt into the stock running board / step bar holes and fill the gap between the frame and the body?

Still waiting for someone to build a 50 mpg car that can tow 5000lbs and has room for me to sleep in the back...

You have been much more diligent than I on keeping a fuel log. Thanks!

Funny you say that about the side skirts. I have a scale clay model done of a design for some and plan on constructing a set this summer.

Glad you are enjoying the Aerolid,

Bondo

[ChazInMT]

Something which bears mentioning I think, or at least emphasized. The variations among "Pick-up" trucks are amazing. Since I've taken an interest in the aerodynamics of pickups (and really anything that moves through the air now, truth be told) I am amazed at the height differences, wheel/tire size differences, 4x4 vs 2wd, and cab/bed length differences. There is certainly no "One size fits all" remedy here for an aerocap advantage. I believe my extended cab 6.5 ft pickup really only has 15-17% room for improvement if I were to design the ultimate aerocap. I'm certain I have gotten better mileage with my cap. On my cross country 2500 mile trip I averaged about 16.2 mpg. Granted I was much more careful about my driving habits, I averaged 8 mph less on the whole. But I usually would have expected to see 14.5 mpg for an average. So that's a solid 10%, and with warmer temps, I'm hoping my average will climb to 17 mpg or better.

Also, as far as any fuel savings goes, at least an aerocap is a definite saving feature that has the potential to pay itself back over the life of it, there are very, very few accessories that people put on their vehicles which make this claim.

[KamperBob]

Originally Posted by Fubeca

The crosswinds were not quite perpendicular to the road I was driving. I did run both directions and average the runs.

If you can recall which direction the cross wind was coming from when that video was shot and give ballpark numbers for vehicle speed and wind speed then we could interpret the effective flow field. I'm suggesting the cross wind effected the upflow shown along side the aero cap. If you happened to shot both sides they could be compared.

Cheers
KB

[Fubeca]

Sorry for the confusion - there was little wind on the day of the video. I was speaking of the original ABA testing of my topper.

[KamperBob]

Originally Posted by Fubeca

Sorry for the confusion - there was little wind on the day of the video. I was speaking of the original ABA testing of my topper.

Gotcha. The updraft does not seem like a cross-wind anomaly then but a real effect in your application.

Thanks!
KB

[ChazInMT]

I think the updraft is caused by either an effect of the large low pressure area we create by having the downslope AeroCaps, or, it is just how it is with GM style pickup bodies. I have the same updraft on mine as evidenced by the water scum trails.

[KamperBob]

Originally Posted by ChazInMT

I think the updraft is caused by either an effect of the large low pressure area we create by having the downslope AeroCaps, or, it is just how it is with GM style pickup bodies. I have the same updraft on mine as evidenced by the water scum trails.

Or maybe the updraft is not caused by the cap at all. Come to think of it, rain water on my side windows (pushed around the A pillar) tends to crawl uphill. Given the amount of side taper maybe the cab itself is the cause. Any test data on side windows laying around?

Cheers
KB

[Big Dave]

Interesting you should mention side skirts. I made up a side skirt setup using an aluminum fabrication and rubber conveyor belt material. It worked OK as a complement to my air dam. I took it off for the winter. Eventually the snow will melt or so they tell me.

Word of advice. Don’t get too greedy on how close to the road you get. My side skirts were three inches above grade and they dragged some., eventually ripping the rubber. Maybe 4.5 or 5 inches would be more practical, but that far up may be losing the desired effect. I’m thinking about re-using the structure to support strakes.