The tests will be identical, in pivot points, and lengths exposed to the airflow. The only variable will be the ambient wind effects, but that should be minimized by doing it on a long straight stretch of I-15, within a few minutes duration, early in the morning, so stable as the air gets here. I have a very accurate and consistent cruise control on the Toy, and it will be implemented.
The last time I did a similar test, was before cheap digital scales and car sun roofs were common, or at least I had them. The test involved just sticking out the side window similar lengths of round and streamlined tubing, at 45 mph. The difference was so dramatic, though without any precise documentation (just the strain on my elbow) that since then (35 years ago), I have sought to reduce needless drag any time I can. Big tires aren't needless, goes without saying.
Testing completed, sort of. It all looked good in the shop, with a big block of wood lashed down to the seat, and then a welded structure to pin the base of the test tubes. One unexpected thing, was that I could take the load off the load cell by partially closing the sun roof, then turn the cell on (it has an awkward button to do this, and it auto shuts off after a few seconds, plus the readout was at an angle and hard to read). Both tubes with 36" long, both pivoted at the same location at the end, and the load cell was hooked the same, about 6" up from the pivot point.
First the streamline tube: at 60 mph, I was first starting to realize that getting the load cell booted up, messing with the sun roof, and then craning my neck to see the digital readout, while talking on the cell phone and drinking coffee, left over little of my attention to my driving. No helper, other then dog in back. Just kidding about the cell phone...., but after getting into the rumble strips on the shoulder a few times, I seemed to get a reading of under 2 pounds. Thinking that must not be right, I felt the force manually, and to my surprise it was about 2 pounds. Not much at all, point being. With the round tube, I got about 9 pounds, but I stress that it was an intermittent reading, hard to see, and meanwhile I was back into the rumble strips. This fish de-lier has an irritating feature, if you turn it on with the load attached, it confuses it, you need to boot it up with no load, and apparently it was a bit much for my hand/eye coordination to do this at 80 mph, my second test. I quit while I was ahead, I have a CDL license to protect, and started thinking that what I was doing could be construed as inattentive driving by a state trooper with no aerodynamic interest or a sense of humor. Traffic was very light of course, no danger to anyone else, just me. The other thing, there is no real question that round tubing is a LOT draggier, thank you Wright Bros., who had a better testing setup then I did, 100 + years later!
Long story short, not wanting to spend any more time dicking around in the shop with the setup, and too cheap to buy a more appropriate scale, I went old school.
At 80 mph, holding on to the very end of the 36" streamline tube, I could quite easily hold it vertical in the slipstream, kind of amazing how little force it took actually. With the round tube, and still with pretty good hand/forearm strength from a lot of years swinging a hammer, no way could I hold it vertical. The best I could do was about 15 degrees off vertical, and that only with a lot of torquing on my wrist. So, no numbers worth anything, sorry about that, but the wrist-o-meter told me that the round tube is many times the drag of the streamline, it's not subtle at all, it was a dramatic difference. As I already have streamlined and covered gear, even my bungee/airshocks and cabane, I am obviously biased, and none of the "test" results surprised me at all. I take that back, I was not surprised on how draggy the round tube was, I WAS surprised by how low drag the streamline stuff was. That same streamline tubing, I had in the junk drawer from 40 years ago, either hang glider or ultralight vintage, is what I used to fair my cabane, and I'm not sure where I can get anymore.
