(Note – this post was modified on 7/8/15 to update some information.)
This has been a pretty frustrating weekend for NASCAR fans thanks to Mother Nature. After repeated attempts to dry the track, NASCAR finally postponed the race at 1 a.m. CST. Jet dryers dry the track by heating the surface and evaporating the water. The cool weather increased the time it took to dry the track, so even after three hours of drying, there were still problems with weepers.
Weepers were the bane of today’s race–or attempt at a race–as well. Casey Mears’ crash and Denny Hamlin’s assertion that his scrape with the wall was because of a slick spot on the track raised questions about the track condition in turns 3 and 4.
Weepers exist because asphalt is porous, sort of like floral foam. When rain hits asphalt, it doesn’t sit on the surface: It seeps down through the track. Asphalt tracks aren’t asphalt all the way through: The track starts with the native dirt, on top of which are placed layers of finely ground rocks and stones.
If there is enough rain, water collects below the track. If there isn’t enough downward drainage, there is nowhere for the water to go but back up through the track. If the water comes up in a banked turn, it runs or ‘weeps’ down the track. Track personnel often make cuts in the track with the intent of allowing the water to drain through the created troughs underneath the surface, instead of coming to the surface.
There are two long-term solutions. The first is to make it easier for the water to drain downward, say by creating reservoirs or other drainage structures and then making it easier for the water to go there than for it to go up through the track. The second is to make the track more resistant to collecting water in the first place. Developing “better” asphalt is not a simple task. The asphalt has to be extremely strong, it can’t crack easily (including from weathering) and now we’re going to demand that it’s waterproof as well. The folks who re-paved Indy used polymerized asphalt (think asphalt with a rubbery binder) in the joints and made the asphalt as dense as possible by heavily compacting it.
The problem with weepers is that the water just keeps coming up from the track because it has nowhere else to go. The jet dryers have to work on those areas until enough water has drained. Around 1 a.m. (Central time), the track folks decided it was a better idea to wait until morning and make sure that there were no more weepers.
Track (and asphalt) design is one of the underserved areas of racing. Who designs tracks? People like Bruton Smith and Rusty Wallace make decisions about how long the track is and the degree of banking, but what about the actual engineering? Who decides on the type of asphalt structure or the water drainage below the track? I hope the folks who are repaving, or considering repaving, are paying attention not only to the surface, but to what is below the surface as well.
I had the pleasure of interviewing Gary Eaker (who developed the AeroDyn wind tunnel) for my book, The Physics of NASCAR. Among the things I didn’t have room for in the book was an interesting conversation in which Gary talked about the fun an engineer might have designing a track where surface conditions could be varied at will–say, heaters embedded in the track that could be used to change the track temperature (and thus the grip) in particular areas. Perhaps there is a way to help the drying process from underneath as well using embedded heaters or more sophisticated drainage structures. Here in Lincoln, Nebraska, we have a couple pedestrian overpasses that are heated to prevent them from getting icy. I wonder if something similar might be possible for racetracks.
Mikey oils the track
I work in a vacuum. Literally. The nanoparticles we make require that we remove as much air as possible from the deposition chamber before we start. O-rings–rubber loops that look like Os–are one mechanism for creating air–or fluid–-tight seals. O-rings are made from elastometers like Viton. O-rings have to be very flexible because they seal by deforming when compressed. You’ll find o-rings in a lot of places, like kitchen faucets. In the KF couplings we use in the lab, two shaped pieces of metal press together an o-ring. Tightening a clamp forms the seal.
You’d like to be able to make connections very quickly, and that’s where connectors like the Adel Wiggins (shown below) come in.
These connectors are used for air and space vehicles, but you’ll also find them on NASCAR cars. The Adel Wiggins coupling consists of two pieces, each having o-rings, a sleeve and a clamp. The sleeve slips over the o-rings and forms a seal when the clamp is tightened. These types of connectors are used often for oil lines and apparently, one of the clamps on the 55 car didn’t get tightened quite enough, which is why Michael Waltrip started the race by dumping oil on the track.
Viton o-rings are impermeable to oil and gas. The Adel Wiggins seals are good to about 125 psi and 425 F. O-ring seals tend not to work when they get very warm (or very cold, as Richard Feynman showed in regards to the space shuttle Challenger). In the engine, the seals are made of metals. But that’s another blog. By tomorrow morning, the disconnected oil line will be just a foggy memory when they finally finish this race. I’ll be pretty foggy myself having stayed up late. I hope I at least got the DVR programmed correctly so that I can watch the outcome when I get home tonight.