Plus full body fenders helpfull or not
plus fender skirts ( assumeing you can get the wheel to not rub on them)
http://www.maximum-velocity.com/pinewoo ... mes-v13i1/
1. Fenders done right help.
2. Doing them right for maximum benefit is an absolute pain in the [censored]. And its not just shaping the fenders - they complicate many aspects of the build and exposes a bunch of fragile parts that a cubby could easily break during the build process. For this reason, we did not put fenders on my clan's cub scout cars even though I'm convinced they help. (The cars I built with fenders are league cars).
I really enjoy this kind of testing - very interesting.MaxV wrote:Here is the results of an experiment I did showing that there is a very small benefit to fenders:
Speed is particularly sensitive the CoM placement. How much, and in what direction, did the CoM change when exchanging ballast for fenders? This would be measured most sensitively by the measured weight under the front and rear wheels for each operating configuration.
A small observational sample size, where outliers have been trimmed, is not technically random and the sample standard deviation will tend to underestimate the true uncertainty. Also, the test statistic is the differences in the averages of two populations, which may not be statistically independent. All this means that the observed 0.005 difference might not be a statistically significant difference. (Might you post the raw data, including outliers, for analysis? )
- Master Pine Head
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Since learning to do fenders correctly, our times have improved a bit. It just depends how competitive your racing is. We have a couple of very good builders in our pack, we were the only ones that used fenders, both my boys won by small margins. The fenders helped make that difference.
I think it is better to error on your fenders being too small than too big for sure.
It was pretty obvious that the car was faster. The timer said .01 faster when all four were on, but I would attribute some (guessing up to half) of that to other break-in benefits. I think it is a LOT tougher doing comparisons on graphite lubed cars. With an oil lubed car, you could run a few dozen heats and put the fenders on/off repeatedly and not have to worry near as much about what is changing in your lube.
These fenders only weighed 1.2 grams total, even after sealing/painting them, so the affect on COM, etc., was not measurable. Now these weren't the first fenders I have ever worked on, so I knew about clearance near the body on the bottom, etc. They were also offset from the body and somewhat angled to match the angle (cant) of the particular wheel and not waste material.
There were more lessons learned. I wasn't confident that the taped on fenders would be able to withstand a Scout race handling, stop section, etc. So we took off the tape and glued them on. The glued on fenders had clearance issues (even with a little spacer to substitute for the tape) that the taped on ones didn't. The clearance did look a little precarious once you set the car down and there is weight on the wheels. Without a track however, we could have easily screwed the car up.
I think the long debate over the car being faster with fenders should have ended a while ago (yes, just look at the adult league cars), but I wouldn't suggest them to a novice builder without track access and time to test.