It's been a little while, but hopefully someone out there is still interested in the results of the test runs of my Little Deuce Scoop. I tried a few different things: scoops open, scoops closed, different axles, scoops covered (canopy), and paddle wheels. All test runs were completed using the same lane and staging technique (dfw touching, rear wheels spread to axle head and centered on lane strip) on my 40' wood track (not aluminum, but one of the nicest I've seen).
To close the scoops I covered the outlets in the wheel wells with masking tape, allowing airflow into the cavity but not to the wheels.
To create a canopy I put masking tape across the front of the scoop intakes to try to mimic how the car would be shaped without scoops and block air from flowing into the cavity at all.
To make the paddle wheels I changed from Max V kit wheels to the Pinecar spoke style to take advantage of the thicker tread. I used a small forstner bit to remove a scallop of material every 1/4" or so around the wheel. I am now prepared for the next off-road pinewood derby.
The paddle wheels pick up speed much more quickly in unweighted blow tests than standard wheels, so the form appears to catch air as intended. They also ROAR down the track. This set of wheels is amazingly loud. My wife probably won't let me race cars in the bedroom anymore.
Test Runs: I lubricated every 16 heats - running 8 with the scoops open, then 8 closed, relube, 8 closed, 8 open, relube, etc in an effort to even out advantages of fresh lube. After 64 heats I tried switching axles hoping to improve the alignment. It didn't work. More on that in a minute. The times did slow after that change, likely from rushed/incomplete axle prep on the second set. I put the original axles back on at the very end and the times improved again.
Results: This thing is all over the place! At some point I began to wish that I had also been tracking stability for each heat. Sometimes it ran as smooth as could be - others it was trying to rattle itself off the track. I don't normally have alignment issues creating wiggle in my cars. I felt that it did tend to rattle less with the scoops closed - without the data I can't be sure. It obviously was pushing air through the scoops to the wheels. There are sparkling graphite swirls in the tubes. I wonder if it was pushing enough air under the wheels to lose stability - like hydroplaning without water (I'm sure there's some fancy engineering term for floating on air). Interestingly, this car (when it runs smoothly) can compete with the best cars in my collection despite its bulk and conservative center of mass. It has sparked many more design ideas. Throw them on the pile, I guess. Hopefully I'll get to at least one this year. I'm a bit burned out from walking the length of my track to fetch my car 164 times.
Axle A, Scoops Open: ave 3.022, min 3.012, max 3.040 (32 heats)
Axle A, Scoops Closed: ave 3.023, min 3.007, max 3.048 (32 heats)
Axle B, Scoops Open: ave 3.033, min 3.024, max 3.044 (16 heats)
Axle B, Scoops Closed: ave 3.035, min 3.028, max 3.050 (16 heats)
Axle B, Scoop Canopy: ave 3.034, min 3.028, max 3.046 (16 heats)
Paddle wheels, Scoops Open: ave 3.197, min 3.157, max 3.271 (24 heats)
Paddle wheels, Scoops Closed: ave 3.200, min 3.162, max 3.233 (16 heats)
Reprise Axle A, Scoops Open: ave 3.027, min 3.009, max 3.054 (12 heats)
My statistics knowledge is a bit rusty. The online calculators I tried suggest that the variances in these times aren't statistically significant. Could the design be better? Absolutely. Is one thousandth of a second worth the effort that went into this build? Not for me. But the fun of devising solutions and overcoming challenges was.
Just do your best and we'll always have fun. Rockets are who we are! Go Rockets!