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wyatt · 06-15-2011, 05:45 PM

AIR TABS COAST DOWN
My friend and I played hookey from working on his front yard one night and took his van out to get some data. We didn't have much time to do data acquisition, so we only got a total of 5 bi-directional runs, 3 with Air-Tabs, 2 without, so it's not much data. We already knew from previous testing that the Air Tabs do alter flow patterns at the back of the van, bringing the flow more inward all around, so it gave us some confidence that we may see results. I ran the numbers, but don't have much confidence in them, since it's such a small data set and the lines are all over each other.
I assumed the rolling resistance would not change between runs, so I just set it the same, and solved for Cd.

JUST THE VAN
Direction A - RED (Cd~0.53)
Direction B - ORANGE (Cd~0.74)
VAN + AIR TABS
Direction A - BLUE (Cd~0.55) [~-2% Highway Fuel Economy]
Direction B - GREEN (Cd~0.80) [~-4% Highway Fuel Economy]

I think if we wanted a higher confidence we would need to do a larger set of coast downs in an area with less variations in directions (you can clearly see the Direction A vs. Direction B at their tail end, so the numbers above are split out). If the numbers are correct, and the AirTabs add drag, the difference seen here would equate to between 2% and 4% highway fuel economy.

AIR TABS WAKE TESTING
I attached a picture of the Van Wake Test Demonstration Instrument (VWTDI, my friend is a big VW Diesel fan). We did all flow tests at 40 miles per hour on calm days. My friend drove, and I rode in the back and watched what was happening through the rear window, then I took notes while he was setting up for the next run. Horizontal and vertical markings are on 6" centers, and the tufts on the "wing" are at 3" centers.

Differences in flow were seen with the use of Air Tabs. Flow came in at a sharper angle, but as can be seen above, that did not translate into drastic improvements in the coefficient of drag. Handling and stability were not tested.

I am guessing that since we have the Air Tabs we will be doing more testing with them placed in different configurations, but no guarantees.

Comments and questions are welcome!

Wyatt

06-15-2011, 05:45 PM	#1 (permalink)
wyatt EcoModder Join Date: Jul 2008 Location: North Central Alabama Posts: 572 Big Salsa - '04 Toyota Sienna LE Silver - '10 Toyota Prius III Thanks: 110 Thanked 123 Times in 71 Posts	Air Tabs AIR TABS COAST DOWN My friend and I played hookey from working on his front yard one night and took his van out to get some data. We didn't have much time to do data acquisition, so we only got a total of 5 bi-directional runs, 3 with Air-Tabs, 2 without, so it's not much data. We already knew from previous testing that the Air Tabs do alter flow patterns at the back of the van, bringing the flow more inward all around, so it gave us some confidence that we may see results. I ran the numbers, but don't have much confidence in them, since it's such a small data set and the lines are all over each other. I assumed the rolling resistance would not change between runs, so I just set it the same, and solved for Cd. JUST THE VAN Direction A - RED (Cd~0.53) Direction B - ORANGE (Cd~0.74) VAN + AIR TABS Direction A - BLUE (Cd~0.55) [~-2% Highway Fuel Economy] Direction B - GREEN (Cd~0.80) [~-4% Highway Fuel Economy] I think if we wanted a higher confidence we would need to do a larger set of coast downs in an area with less variations in directions (you can clearly see the Direction A vs. Direction B at their tail end, so the numbers above are split out). If the numbers are correct, and the AirTabs add drag, the difference seen here would equate to between 2% and 4% highway fuel economy. AIR TABS WAKE TESTING I attached a picture of the Van Wake Test Demonstration Instrument (VWTDI, my friend is a big VW Diesel fan). We did all flow tests at 40 miles per hour on calm days. My friend drove, and I rode in the back and watched what was happening through the rear window, then I took notes while he was setting up for the next run. Horizontal and vertical markings are on 6" centers, and the tufts on the "wing" are at 3" centers. Differences in flow were seen with the use of Air Tabs. Flow came in at a sharper angle, but as can be seen above, that did not translate into drastic improvements in the coefficient of drag. Handling and stability were not tested. I am guessing that since we have the Air Tabs we will be doing more testing with them placed in different configurations, but no guarantees. Comments and questions are welcome! Wyatt Attached Thumbnails __________________