by gyroguy » Tue Aug 07, 2007 4:34 pm
There are other drag producers to consider that haven't been mentioned.
VENTS: Many tiny trailers have a 14" square or 9" square air vent on top of the trailer. This spoils the airflow over the trailer and causes vortices and turbulent air that spread out behind and at an angle toward the sides.
RACKS: A rack on top of the trailer produces drag much larger in proportion than the size of the roof rack tubing would suggest. Things get much worse if you actually tie anything on the rack.
ANTENNAS: A radio antenna also causes drag.
TIGHT CURVES: So does a small radius curve, like the one at the junction of hatch and roof on my trailer. Andrew is right, there would be airflow separation there. But as I said, the drawing was theoretical.
TIRES: On the sides, probably the biggest cause of drag is tires.
FENDERS: Rounded fenders can decrease tire aerodynamic drag somewhat. The old-fashioned rounded fenders that extend backward to a point would be best. But to be most effective, the fenders would need to be three times the tire diameter in length... not possible on a teardrop.
SMALL THINGS: Little things like doorknobs, clearance lights, and windows also add drag and produce vortices that create turbulent air and drag.
SMALLER THINGS: Littler things like rivet heads, edges of bent aluminum angle at the top and sides of the trailer, and piano hinges are great drag producers.
When you look at drag reduction, you have to look at ALL of the trailer.
Despite my efforts, the Crocodile Tear is aerodynamically a draggy little trailer. The one saving grace is frontal area -- 16 square feet -- which makes it possible for my small pickup truck to tow without overheating.
I'd be interested in seeing a discussion on reduction of rolling resistance of tires. My thought was to over-inflate the tires, but the benefits of reducing rolling resistance probably wouldn't compensate for the cost of uneven tire wear. Or would it, with higher fuel prices?
FYI, just completed a 3,500 mile trip with Crocodile Tear. I'll start a new topic, "3,500 miles in a TTT."
For build pix of Crocodile Tear, completed 10/26/06 -- Look at my album or new website <www.crocodiletear.com> (website has more info)