Note from Darin (admin): this installment is part of a series posted by Phil (aerohead) about the effectiveness of various aero mods - usually with quotations and citations to source data.
See the Aero mods data index here.
End note.
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More debris! This is a follow-on to stuff Darin and others have already posted. I'm only going to touch on things I have numbers for. I'm guilty of minimizing the importance of interference-drag earlier, and since re-visiting my articles and numbers-crunching on CRX data, I'm gonna be a camp-follower for those who are ferreting out the significance of "excrescenses" ( sp?).
All the modern Btu-stretchers are mirror-free designs for instance and if the big-boys are sweating after details like this, then it's okay for me to look there too. I've included my Bonneville numbers but don't take it as a jab at mirror deletion. So lets get to it.
Interference-Drag
1963, Kelley & Holcombe, GM, "....very efficient body shapes can be greatly increased in drag by the application of small projections."
1975, Car and Driver Project Aerovan: side-mirror deletion reduces drag 6-percent. Roof spoilers (as mentioned in installment on aftbodies/spoilers) increase drag 15-52 percent with 2-6 mpg loss.
1981, CAR and Driver, April: Ford Escort mods: at 60-mph, 12-cubic foot rooftop cargo carrier costs 6-mpg (19%), hood open and locked at 12-inches (300mm) costs 2-mpg (7.1%), open side windows cost 1.0-mpg (2.7%).
1982, Volkswagen AG, wind tunnel, 1982 VW Scirocco (all at 55-mph):
empty luggage rack = 13-percent increase
lowered side windows = 4.6-percent
mud-flaps = 7-percent
auxiliary fog-lamps = 2-percent
radio antenna = 1-percent.
1986, Subaru XT, wind tunnel development: side mirrors moved out 80mm from body, side glass made flush, door handle made flush, all mods together = 3-percent drag reduction.
1988,Texas Tech University Aero Lab: pickup truck roof "eruption" responsible for 20-percent of truck's drag (note: the motor industry refers to pickup trucks as a two-door sedan sans trunklid ).
July 1991, Bonneville International Speedway, Wendover, Utah, U.S.A., the Phil Knox, 1984 CRX 1.3 streamliner: windshield-wiper and driver side mirror deletion demonstrate no improvement in top speed. A cardboard and duct-tape cowl fillet over the wiper area demonstrates a 0.28-mph improvement to top speed. A cardboard and duct-tape 30-degree rear spoiler at boattail causes a 2-mph speed penalty.
August, 2003, the Phil Knox Dodge D-100, without hood, doors, and truck bed overheats in a matter of a few miles at 60-mph, and cannot operate long enough for mpg testing. With the bed removed mileage drops 2-mpg at 60-mph (a drag increase from Cd0.50 to Cd 0.62 is estimated).
1999,VW 1-Liter Car (Cd 0.15 and 257mpg) has no side mirrors.
1999, GM Program For New Generation Vehicle (PNGV) car, with Cd 0.163 has no side mirrors. Interference drag of body cut lines, wheel covers, styling features raise drag by only 0.007.
General note about side-view mirrors: the air velocity at the cowl area can be accelerated to 25-30 percent higher velocitiy do to airstream deformation, and consequently, the actual drag of a mirror in that location will register higher due to the local velocity. My '64 Ghia had fender-mount mirror, out ahead of the windshield to keep it in slower air. Looks like mirror deletion and camera/view-screen is way of the future.