Thread: Boat tail easy
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Old 01-22-2023, 01:59 PM   #22 (permalink)
Caddylackn
EcoModding Apprentice
 
Join Date: Jun 2022
Location: Bremerton, WA
Posts: 104

Passat TDI Wagon - '97 VW Passat Wagon TDI
90 day: 55.81 mpg (US)

Blue - '21 Hyundai Sonata Blue
90 day: 53.79 mpg (US)
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The purpose of tapering all the sides is to reduce the total area of the back, low pressure zone area, that low pressure can "suck" the car to slow it down. If you can only get a 10% smaller back area by tapering the sides, then you are leaving a little drag reduction on the table, but saving a bunch of work. As you know, forming compound curves with cardboard or corrugated plastic sheets is very difficult.

There is a guy on youtube that built his boat tail out of foil back 2" styrofoam using different rear cross sections (large to small) and then skinning them with tapered pieces of the 2" foil back foam (shiny side out) then taping seams with the aluminum foil tape. Looked pretty decent and strong.

Since you don't want to permanently drill holes, look what you can use as a starting anchor point for your aero mods. Rear tow hooks and their mounting point?. Maybe some straps that start in the car, go under the hatch lid, then shut the lid on them. The rear license plate anchors. Bolt/ screw some structural members to these then screw the coroplast or cardboard to these so the whole thing won't blow off at once if the tape fails. Then gorilla tape the seams from the coroplast or cardboard to the body. Gorilla tape is very strong and won't blow off or come off from heat from the sun. You can use a heat gun to carefully remove the gorilla tape to minimize glue residue later. Duct tape sucks and will come off after a few weeks of sun beating on it and leave horrible glue smears.

Anyway, trial runs with your temporary aeromods should be on back roads with no one behind you. Then take it up to about 10 mph over your design traveling speed to make sure it won't blow off.

My cheesy aeromods are coroplast but are gorilla taped then truss head screwed to the sheet metal after the gorilla tape. I don't care about drilling holes in my car. I can always weld them shut, and the car needs painted anyway. My temp aero mods have become permanent. Some day, I will take all of the mods off to complete the A-B-A testing, then make them permanent with sheet metal or ABS sheet and welding.
__________________
97 Passat TDI Wagon
Bosio 520 DLC nozzles, chip tune
Mufflerectomy
306k miles
Scan Gauge II
full belly pan
26 gallon tank
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