Oct 032014
 

@NASCARRealTime, @TheOrangeCone and @CircleTrackNerd had an interesting dialog when the 2015 rules were announced. They were debating whether the track records that are now standing are going to be essentially locked into history. The debate ended with an appeal to me and Goody’s Headache Powder. TwitterConvo_TrackRecords

When the Gen-6 car was introduced in 2013, new track speed records were established at 19 of 32 qualifying sessions. Yes, that’s more tracks than we run, but the record at Martinsville, for example, was broken in the spring and again in the fall. Another way to look at it is that out of 20 tracks where there was an opportunity to break a track record (meaning we exclude Dega and Daytona because their records are pre-restrictor plate, plus rainouts) – it happened at 16 places.

Why? The primary change was the much lighter car – they took 150 lbs off relative to the Gen-5 car while maintaining the same engine power and increasing downforce.

That changes in 2015, as one of the new rules NASCAR announced is a 1.170″ tapered spacer that will reduce power by about 125 hp. Gene Stefanyshyn (senior vice president of innovation and racing development for NASCAR) expects this is only going to decrease speeds by no more than 3-4 mph in most instances.

That seems like a weird trade off, right? 125 hp = 3-4 mph? Well, that’s because the engine isn’t the only place they’re making changes. They’re going to decrease the spoiler size to six inches, which will take away about 300 lbs of downforce, but will also reduce the drag on the car.

Here’s the theory: racing on ovals is won and lost in the corners. The primary impact of horsepower (all other things held equal) is determining maximum straightaway speed. In the corners, you’re not (except for plate tracks) using all the horsepower you have – you’re more limited by your lateral grip, which is determined by downforce.

Any driver can mash the gas coming down the frontstretch. What makes a difference is how soon they get off the gas/onto the brakes coming into the corner and how soon they get onto the throttle coming out of the corner. Let’s say you have to slow to 180mph to make a corner. It makes a difference when you start braking if you’re going 210 mph vs. going 200 mph.

You may actually be able to take the corner faster if you aren’t slowing the car down quite so much. A number of the drivers and NASCAR officials have stated that slowing down the cars a little (and remember, we’re talking 3-4 mph) should give drivers more options in the corners and thus make for more exciting racing.

But What About the Records?

Yes. A lot of records were broken in 2013. But a number of those records have been broken this year. The overall trend of pole qualifying times is up. Even when a rules change or a track change decreases the qualifying time, the next year, it starts creeping back up. I plotted qualifying times for a couple tracks to show this. Everyone’s been talking about these records being broken as if the speeds were stuck and then suddenly they jumped up. Not at all.

TrackPoleSpeeds_Charlotte2

So here’s Charlotte.  There are year-to-year oscillations, but the overall qualifying times have ben nothing but increasing.  On average, over the last twenty years, they’ve increased by about 0.7 mph each year.  So let’s assume that speeds are down across the board by 3 mph. In four or five years, they will likely be right back where they were before. You see a big jump in the slope of the curve (how fast it’s getting larger) from Gen 1 to Gen 2, but after Gen 2, it’s been pretty consistent.

I put each of the car generations on the graph to see how much difference changing car models actually made, but the track condition also makes a huge difference. Let’s blow up the last twenty years.

TrackPoleSpeeds_CharlotteRecent2

So there was a big jump after the 1994 repave. Then remember 2005 when we all learned a new word: levigation? They diamond ground the track, which made it very rough. Pole speeds jumped and the fall race that year was an unmitigated disaster, with tires blowing left and right. They did a formal repave in 2006.

And if you really want to see what a different track surfaces make, take a look at Kansas.

TrackPoleSpeeds_Kansas

After the re-pave, the pole speed jumped from 176 mph to 191 mph. There’s almost no history to rely on, but the following year, the fall speed was 4.3 mph slower than the spring speed.

In addition to major changes in the track, you get year-to-year oscillations due to things like weather and the tires Goodyear provides. One of the goals for the new set up is to allow Goodyear to make grippier tires that wear out faster, which could have a big impact on qualifying and (more importantly) racing.

So are the track records safe?  Probably for a couple of years.  But I’m not betting for much beyond that. The guys designing the race cars are just too clever to let little things like rules keep them down. The impressive thing is going to be if they figure out how to make the cars faster while also making the engines more reliable and longer lasting.

A final note. In the end, we judge drivers on race wins and championships. Poles may help you win a race, but I guarantee you if you give a driver a choice between a win and a pole, they’re going to choose the win.

Aug 222014
 

TurbulentSmokeA persistent motorsports issue (and not only with stock cars) is the aerodynamic passing problem. You can’t pass without grip. Grip is a direct result of downforce. Downforce comes from two places: the weight of the car (mechanical grip) and the billions and billions of air molecules hitting the car (a.k.a aerogrip).

Racecars are designed to take advantage of aerodynamic downforce. Everything from their shape to the aerodynamic appendages added to the car are all optimized to produce downforce. You can play around with mechanical grip some by adjusting the weight on each corner of the car and trying to control how the weight changes as the car turns, brakes and accelerates. Aerodynamic grip is even more subtle.

And complicated.

Aerodynamicists think about fluid flow (fluid meaning liquid or gas) in terms of two extremes. Laminar flow is when the air (or water) moves predictably over a surface in nice, uniform sheets with relatively little variation from sheet to sheet.  In the diagram below explaining how a wing works (an airplane wing; turn your computer upside down if you want to see how a car wing works) the air is represented by nice, neat lines that very politely crowd each other as they work their way around the wing. Changes in pressure and velocity happen gradually.LaminarFlowOveraWing

The other extreme is turbulence – when the air (or water) flows in swirls that are not at all well behaved.  Turbulence is chaotic – large differences in pressure and velocity that change quickly. Turbulence is very difficult to describe mathematically because it’s just so darn complicated.

It’s easier to see experimentally. Pour some cream into your morning coffee and stir it with the back of your spoon. The spoon moves the cream out of the way, creating a gap. The cream swirls around the back of the spoon and fills the gap, forming a lovely swirling pattern.  You can see the same thing in the wake of boat – the water flows back in to fill the gap the front of the boat made. Smoke rising from a cigarette is turbulent as it mixes with the air.  Breaking waves are turbulent.

In turbulent flow, the air molecules end up going in all different directions.  If you’ve ever driven very close to the back of a semi on the expressway, you’ll feel your car buffeted from different directions – that’s the turbulence.

Laminar and turbulent flow are both evident in the aerodynamics of racecars. The front of the car is smooth and sloped.  The cross section of the car (what you’d get if you took a slide of the car perpendicular to the direction the car’s traveling) gets larger and larger as you get further from the front fascia. The car keeps pushing a bigger and bigger hole in the air.

Things change when you reach the B-post.  Now the car needs to push away less air because it’s sloping down. Its cross section is getting smaller. The air starts swirling in around the rear window, becoming turbulent. The wake of a racecar is similar to the wake of a boat. The water’s going in all directions, trying to fill the hole made by the front part of the boat.

A technique called computational fluid dynamics lets engineers visualize the airflow. The diagram here is from Ford Racing and shows the turbulence on the 2013 Ford Fusion.  This visualization shows you where there are big changes in the airflow.  You can see the giant wake behind the car. It’s strongest the closest to the rear of the car, but note that the wake extends almost two car lengths behind the car.

2013_FordFusion_CFDTopandSide

If you want to learn more about Ford’s CFD calculations and the role they play in designing racecars, check out their YouTube video - it’s worth a gander.

The wake creates drag on your car and slows it down just a little, but as the driver of said car, it’s not really a big concern. For the guy running behind me, however, my wake is a really big problem. Laminar air makes downforce. Turbulent air doesn’t.

And that’s the origin of the passing problem. A fast car catches up with the car ahead of it. As the trailing car research the leading car’s back end, the turbulence from the wake of the first car makes the flow over the front of the trailing car turbulent, which means the trailing car loses downforce or becomes ‘aeroloose’. And you can see from the CFD calculation that you don’t have to get so close for aeropush to become a problem.

Right after the Michigan race last week, NASCAR ran a big test (10 teams) to try out some options for possible rules changes for the 2015 season.  In case you think this is a simple problem to solve, they had two approaches: more downforce and less downforce.

On the increase downforce side, the first change was to a bigger splitter – nine inches tall.  The problem with increasing the splitter is that it unbalances the car. One of they key principles in racing is that you can only go as fast as your least grippy tire. Grip is proportional to downforce.  If you increase the rear downforce without making a commensurate change in the front downforce, you get a really tight car.  Lots of grip in the back, but the front tire – the ones that turn the car – don’t have enough grip.

Increasing the front splitter has its own challenges, so NASCAR turned to dive planes. Dive planes have been used for a long time on sports cars. They’re simply small, curved pieces of metal or carbon fiber composite. NASCAR used two dive planes – one above the other – and put one set on each side of the car.  The dive planes started at the front fascia and swoop upward, ending at the front fender. The pictures below are from the twitter feeds of @nateryan (top) and @2spotter (Joey Meier, bottom).
divePlane_NateRyan

DivePlane_Joey

The principle behind the dive plane is that it takes the turbulent air coming onto the front of the car and funnels it to make the flow more laminar.  More laminar flow should translate to more downforce.

NASCAR made the point that the dive planes may not be part of the final rules package; however, having the dive planes allowed them another little benefit – they could put pressure sensors on the dive planes and measure how the downforce changed for the different configurations.

The ‘prime rules package’ that was tested consisted of the larger spoiler, a lower rear differential gear, and decreased horsepower.  They tested 850hp, 800 hp and 750hp.  The second test package was actually a lower downforce package, in which they went with a smaller spoiler and they removed an underbody piece that had been new this year.  The estimate is that these changes decreased the overall downforce by 28-30%.

And (of course) the drivers were not very enthusiastic about the prime rules package. They liked the lower downforce better. Reporting from the track suggested that the prime rules package gave rise to in-line racing, while the lower downforce package got drivers really excited about possibilities for passing.

Unfortunately, there’s no time for another test because NASCAR really needs to have the 2015 rules finalized pretty darn quick so the teams have time to prepare for next season.  Right now, a bunch of NASCAR engineers are sitting back at the R&D Center, trying to make sense of the gigabytes of data they collected during the test. I’m sort of glad I’m not the one who has to make this decision!!

I didn’t mention one of the big changes in this blog post – the ability for the driver to modify the trackbar position from inside the car, but I will comment on that in the near future.

Jul 252014
 

One of my favorite memories from Nebraska was coming home from the I-80 Speedway  covered in a dusting of red clay. (Planting in that clay was another question entirely.) But there’s something about dirt tracks you just don’t get at the asphalt ones.

It’s great that NASCAR is bringing a little of that spirit to the Truck Series.  Wednesday’s Mudsummer Classic race at Eldora Speedway was a great show. A dirt track challenges drivers and their crew chiefs who are mostly used to asphalt and an occasional foray into concrete.  A lot changes when you trade surfaces: Set ups, driving approaches, pit strategy and, perhaps most significantly, tires.

Some people made a lot of noise about Goodyear and their ability to produce a tire that would stand up to dirt-track racing, but Goodyear has a long history of equipping cars for the dirt. The tire they developed for NASCAR’s first foray into dirt in 40 years (in 2013) was based on rhwie standard 10-inch wide dirt modified tire. They started testing with that tire with Tony Stewart and the Dillon brothers (that sounds like a gang from the Wild West, doesn’t it?)  at Eldora back in October 2012.   They modified the tire based on that test, making it a wider (11 inches) to help with grip. Trucks, being on the order of a thousand pounds heavier than a typical modified, require greater force to turn.

In addition to the individual tire construction, Goodyear also provided some built-in stagger.  Put a red Solo cup on its side and give it a push. It automatically rolls in a circle because the drinking end has a larger circumference (distance around) than the bottom. The same strategy is used for race vehicles that only turn one direction.  At the 2013 race (I’ve been unable to find the specs for this year), the left-side tires had a circumference of 85.8 inches compared to 88.5 inches on the right.  Teams got four sets of tires for the event.

Goodyear_Wrangler_G23DirtTireRegardless of whether they were left- or right-side tires, the tires used at Eldora have two primary differences compared to the standard truck tire used at the other races.

The first is that dirt-track tires have treads. The Goodyear Wranglers employed for the Eldora race use the G23 tread pattern (shown at left). The treads serve the same purpose they serve on rain tires – they provide a path for loose dirt to move out of the way so that the rubber can grip the track. The edges of the blocks provide bite. The tread compound used is a softer compound, which again improves grip on the dirt surface.

The second difference is that the tires used at Eldora are bias-ply tires, not the radial tires that are standard in NASCAR.  Let’s back up a little and remember a little tire anatomy 101.  The diagram at right is from the Michelin website (the people who led the way in popularizing radial tires way back, just a little after WWII).

Tire_Anatomy_new

The part we’re interested in for the sake of this discussion is the plies.  Plies are a type of fabric made up of layers of rigid cords embedded in rubber. The body plies run from the outer bead to the inner bead. The reinforcing fibers (cords) have been made from materials like cotton, rayon, polyester, steel, fiberglass and aramids like Kevlar.

If you ask Goodyear which materials they use in their race tires, they will neither confirm or deny any particular material or combination of materials they use — which should give you an idea how important the cords are in terms of giving the tire desirable properties..

tirecords_wikipediaIf everything works the way it should, you will never see tire cords. When a driver hears during a race that the tires that were just removed had cord showing, they know there’s either a problem with the setup or with their driving. The cords are there for strength and stability. A tire’s grip comes from the tread – not the cords.

The plies have directionality, depending on how cords are arranged.  They are usually parallel to each other – it you look carefully at the picture to the left, you can see the rows of cording.  Whether a tire is radial or bias-ply depends on the way the cords point.

The first tires appeared in the mid-1800s and were simple pieces of solid rubber. They provided a bumpy, uncomfortable ride. The pneumatic tire was introduced in the mid 1800′s, but a tire made soley of rubber didn’t last very long, nor allow you to go very fast. Tires needed to be stronger and more resistant to road hazards. The idea of using cords in tire plies to increase strength was introduced in the early 1900s. A number of plies was used – two to four was common – to reinforce the rubber in the tread.w

The first tires were bias ply tires, which literally means that the cords in different plies were oriented in alternating directions running between 35-60 degrees with respect to the bead, which increases the strength of the tire, as shown in the diagram below, at right.

radialvsbiasply

In a radial tire, the cords go straight across the tire, as shown in the left picture. The cords are 90 degrees with respect to the direction you’re going. The radial tire was patented in 1915 and, as I mentioned earlier, Michelin really pushed the development of the radial tire starting in 1946.  Radial tires didn’t offer as smooth a ride as bias-ply tires; however, the gasoline crisis of the 1970′s made people value their improved gas mileage (which happens because they have less friction.) Almost all passenger car tires at this point are radials.  Because the radial cords go in one direction, the tire isn’t as strong, which is why radial tires have an additional belt package. Belts made of steel, polyester or Kevlar-type polymers are inserted over the plies and under the tread. Those belts greatly increase the strength of the tire..

Bias-ply tires create more friction and thus more heat and more wear.  A bias ply tire is inherently round, which means that the contact patch is smaller. Extra rubber has to be built up at the shoulders to provide a flat surface. Importantly, the sidewall and the tread on a bias-ply tire are one piece, which means that they move in concert with each other.  As a result, a bias-ply tire will give more in a turn because of the lateral force. The separate belt package in the radial separates the sidewall (the plies) from the tread (the belts) so the sidewall can flex, leaving the tread to hug the ground. Bias ply tires give more and allow better grip on an irregular surface like dirt. Radials would make the racing a lot harder — and not just for the drivers who don’t have much prior experience on dirt!

Many lower level series, as well as weekend racers, use bias-ply tires for another very important reason: they’re (in general) cheaper than radial race tires. This doesn’t mean they’re cheap, but it does help cut costs a little, which means more money to put toward going faster.

 

Jul 112014
 

Doug Yates was  guest on Dave Moody’s SiriusXM Speedway last week. He brought up a conversion you hear a lot in the week before Daytona and Talladega.  Every 25 horsepower in the engine translates to about a 1 second decrease in lap times. Dave did the math: Removing the plates would increase the engine by 450 horsepower. Four hundred and fifty more horsepower equates to 18 seconds off the lap time, assuming all other things equal.  That last part was a very important qualification. It will come back to haunt us in a moment.

David Gilliland got the pole at Daytona with a lap speed of 45.153 seconds, translating to a speed of 199.322 miles per hour. Using the above argument, his lap time would decrease to 27.153 seconds.  That translates to a speed of 331.456 mph.In 2004, Rusty Wallace ran 228 mph at Talladega in an unrestricted engine. That’s almost 100 mph slower than our theoretical max speed. Let’s ignore the concerns that NASCAR racecars tend to get aerodynamically unstable if they turn around at high speeds and think only about straight line speed.

So let’s look at what limits how fast a car can go.  We’re considering two major forces: the force the engine makes, which propels the car forward, and the drag force, which pushes the car backward.

 

DragandForceActingonCars

It’s exactly like a tug of war. Which ever is pulling harder, that’s the direct the car is going to go. (That’s because force is, as your physical teacher no doubt repeated over and over, a vector.DragandForceVectorSumsAt most tracks, if you want to pass someone, you step on the gas, the engine produces more force and you accelerate.  Daytona and Talladega are unique in that engine power is limited to about 450 hp. The pedals on the floor the whole way around. You’re perennially in the last situation, in which the car moves at a constant (a terminal) speed, which is the fastest speed you can get. The engine is doing all it can.

So here’s the catch – the reason why the phrase “all other things equal” causes problems.  All other things are not equal. Specifically, drag. Drag is simply the force of the air molecules pushing on the car, but that force increases quadratically, just like downforce. If the car goes twice as fast, you get four time (two squared) the drag.  It’s not fair: you have to work four times harder to get twice as fast. But that’s physics for you.

The argument above relied on the assumption that the drag remained constant – and it definitely doesn’t. It gets worse, because power depends on velocity cubed. So to go twice as fast, you have to overcome four times as much drag and you need eight times (2x2x2) the power.

You can estimate the terminal velocity of a racecar using some simple physics. The terminal velocity is the ratio of the power (P) to the drag (D):

EQ_TerminalVelocityPowerDrag

The maximum drag you can have is proportional to the terminal velocity squared:

EQ_terminalvelocityvsPower

Which means that the terminal velocity ends up depending on the cube root of the power!

EQ_TerminalVelocityPowerCubeRoot

If the power of an engine doubles, the terminal velocity only increases by the cube root of two, which is 1.26. If we take 200 mph as a nice round terminal velocity for a restricted engine, removing the plates and doubling the engine power to 900 hp would only increase the terminal velocity for the unrestricted engine to 252 mph.  That’s pretty surprising – you double the engine power and you only get 50 mph more.  Such is the power of cube roots.

If nature were linear, it would be a whole lot less interesting.

Many thanks to my friends Josh Browne and Andy Randolph, both excellent engineers and always willing to let me bounce ideas off them and verify that I’m not crazy.  Not, at least, when it comes to physics.

Jul 082014
 

Given all the rain at Daytona this weekend, there was plenty of time to think about auxiliary NASCAR issues.  Regular readers know that I’m a huge fan of the racing-reference.info website because they have a trove of data just waiting to be analyzed.  The spouse asked about payouts and whether it really made much of a difference for a team to get back on the track, so I plotted up some data.

I’m showing below for the Nationwide and Sprint Cup Series, the winnings as a function of position. The line is not monotonic (decreasing with each point) because of all the contingency plans, sponsor deals, etc, but the data work pretty well in terms of overall trends. I’ve plotted both races in 2014 – July (red) and February (green).

BSPEED_DaytonaWinningsNWide

Two things surprised me here:  first,  how quickly the prize money goes down and second, how small the money is in the first place, especially relative to the Sprint Cup.  You’re talking about $20,000 for finishing in the upper 30s in the July race and $40,000 in the February race. If you consider how expensive it is to just build a racecar, much less hire a driver and people for the track, that’s not a whole lot of money.

If you look at the drop off, it’s huge for the first five places. From 1st to 2nd in February, we’re talking a drop of almost $30,000. When you get out to 21st compared to 22nd, it’s less than a thousand dollars.

I thought the difference in prize money between February and July was interesting as well.  It’s even more pronounced in the Sprint Cup, as shown below.BSPEED_DaytonaWinningsThe first thing to notice is the huge difference in purse from the 500 to the 400.  The money for first place is four times as much for winning in February versus July. From first to second for the Daytona 500, you’re talking $357,000, but for the July race, it’s “only” $134,000.  If you come in dead last in February, you take home $292k, whereas last weekend, poor A.J. Allmendinger went home with a little under $70k for finishing 43rd.

That outlier at position 32 for the 500 is Paul Menard. I double checked the data at my other favorite source of racing information, jayski.com, and they have the same information. (UPDATE: as @nuggie99 points out in the comments, there was that $200,000 bonus for leading at halfway.) I have no explanation for why he’d make $200,000 more than the guys who finished immediately in front of and behind him.

For both series, though, you can see why it makes sense for teams that aren’t running all the races, or teams with limited resources, to disproportionately focus attention on the restrictor plate races. With the wild card nature of the races, getting a top five can make a huge difference in the money you take home – and thus your ability to build a more competitive team.

 

 

Jun 242014
 

This weekend, we learned that the real weather challenge for the NASCAR Nationwide Series isn’t rain. It’s not enough rain. It wasn’t raining hard enough to put on rain tires, but it wasn’t quite dry enough to safely race on slicks. (I’ve written before about why racing in the rain is hard.) But they managed to pull it off, put on a great show and @Brendan62 finally got that long-sought-after win.

When the teams switched to rain tires, the crew chiefs had to remind the drivers that their tach readings for maintaining pit road speed would be different .  I’ve written quite a bit about tach readings and speed limits:

If you know the  gear ratios in the transmission and the rear end, you can convert the engine speed (in revolutions per minute) to the rotation rate at the wheels.  How far the car moves each revolution of the axle depends on the distance around: the bigger the tire, the further the car moves. This is why your odometer and speedometer get screwed up if you don’t use the right size tire on your car.  You can check this out yourself using two tumblers with different sizes.  If you lie them on their sides and start at the same place, they roll them each one revolution, the larger tumbler will have gone further.

Rain tires have thicker tread and a larger circumference. The car moves further along with each rotation of the tires. If you don’t compensate for this in your tach readings for pit road speed, you’ll end up with a speeding penalty, even though you would have been fine at the same tach readings with the slicks on.

I couldn’t find the difference in the circumferences, but remember that teams are always pushing to get as close to the pit road speed limit as possible, so even a relatively small change in the relationship between speed and circumference can put you at the tail end of the longest line.

Jun 132014
 

You are hurtling down the frontstretch at Michigan, your speed approaching 215 mph.  Your seat moves up and down as you hit the seams, but your focus is squarely on getting into Turn 1 losing as little speed as possible.  You squeeze the brakes and feel yourself moving forward, only to realize that you’re still moving too quickly. As the car starts to head toward the wall, you panic and squeeze the brake even harder.

The car snaps loose and the next thing you feel… is an engineer’s hand on your shoulder.  You turn around to see her barely suppressing a smile.

“Let’s try that again. Maybe you want to brake earlier this time, huh?”

The latest racing simulators are far more involved than your steering-wheel-feedback-enabled video game. When you hear drivers talk about using simulators to familiarize themselves with new tracks, you are only hearing about the surface layer.

Ford opened a new Racing Technology Center in Concord NC just about a month ago.  The old Ford facility used to be called “The Shack” because of it’s size. The new facility, which is across the street from Roush Fenway Racing, is 33,000 square feet. One of the main features is a driving simulator similar to the ones that F1 uses.  Five screens provide a 180-degree view for the driver. The cockpit is the front half of a NASCAR Sprint Cup car that is set on a full-motion platform.  The platform duplicates the exact motions you would feel in the car – bumps, slips, sways, yaw.

Let’s move away from the driver for a moment, because he (or she) is a relatively recent addition. All race teams use vehicle dynamics simulations: computer programs that predict lap times for specific setups. A crew chief changes the setup on the computer – camber, cross weight, track bar, etc. – and can see in advance whether the changes make the lap time better or worse.

DriverintheLoop2

Simulation programs have to be validated, meaning you have to make sure they correspond with reality. Every team also has (or rents time on)  K&C and seven-post rigs.  (K&C stands for Kinematics and Compliance – I’ll be getting into those in upcoming posts.) These machines attempt to quantify how the car responds to external changes, like turning, bumps, etc.

Engineers thus went back and forth between theory (the simulations) and experiment, developing a model of the car, testing it against how the car behaved, and then refining their model.  (Unsurprisingly, this is exactly how scientific research on things like alternative energy sources and cancer works.)

This is a great model for the Google driverless car. But that’s not how racing works. Racing requires a living, breathing, thinking (hopefully) human being in the seat who has to constantly take in information, process that information and act on it.

And that’s where racing simulators are moving. The buzzword is “Driver in the Loop”, which means that you’re creating a model that includes the driver.  This is not an easy step. Drivers are very different in terms of their preferences for set-up, what they’re comfortable driving, how loose they’re willing to be early in a run to make the car faster later, etc.

The simulator in the new Ford Tech Center is a sled-type simulator. Less advanced models have hydraulic pistons that raise and lower the cockpit to simulate bumps and change attitude.  The sled can actually duplicate all six types of motion: three linear motions (up/down, left/right, front/back) and three rotational degrees of freedom (yaw, roll and pitch).  This motion platform was developed by a British company called Ansible Motion and the picture below is from their website. You can see the sled rails at the back, and the 180+degree surround on which the images of the track are displayed. The steering wheel provides feedback to the driver and even the seatbelts are cued in so that when you brake, the seatbelt tightens just as it would in a real car. Ansible is the same vendor that worked on McLaren’s F1 simulator. The Ford folks claim that this design has a much faster response time, meaning that the time between when you turn the steering wheel and when you feel the result, is shorter and more like real life.

AnsibleMotionPlatform

 

 

At present, they’ve got ten tracks in the library for the new simulator – eventually they will have all the NASCAR tracks and, since the Tech Center is meant to support all of Ford’s motorsport activities, they will be able to change out the cockpit to, say, a Daytona Prototype, and including tracks like Sebring.

So far, I’ve made it sound like they’re just one-upping iRacing, but a prime feature of the center is that there is a whole room associated with the simulator that is filled with engineers who are watching both the driver and the racecar input/output data.  The driver is being assimilated into the simulations. This is why it’s called “Driver-in-the-Loop” simulation.
DriverintheLoop

 

On the one hand, the driver will help validate all the models.  If there’s a bump on Pit Road at a track that gives a driver trouble, he or she will recognize when it’s not in the model of the track used by the simulator. (And since tracks change significantly, the models have to change to keep up with reality.)

While we’re talking tracks, let’s point out that the track models aren’t made by someone sent out with a tape measure. Tracks are laser scanned to a resolution of a few millimeters. Every dip and bump is recorded and used in modeling the tracks. Laser scanning not only collects three-dimensional location information, it looks at the quality of the reflection.  Laser scanning can differentiate between a white painted line and a yellow painted line, between two different lanes of asphalt, or even skid marks. When you’re traveling at top speed, any surface irregularity becomes important because all it takes is for the car to be throw a little out of equilibrium and you’re in the wall.

In addition to the track, the driver can also provide feedback about whether the “car” responds the way it does in real life. But at the same time the driver is evaluating the simulator elements, the engineers are evaluating the driver. They can start to look at things like how a particular driver’s comfort level may dictate a different line for them relative to another driver. They can run repeated tests to find out how constant a driver is. Do they brake the same way going into Turn 1 at Charlotte every time? Or are they hyper aware of something like tire fall off and able to tailor their braking to the condition of the car?  This type of research has great potential to improve communication between the team and the driver.

Skeptics will worry that we’re getting uncomfortably close to a situation in which we have a bunch of engineers sitting around driving the racecar via remote control and the driver is no more than a warm body executing commands as he’s told. The beautiful thing about human beings is that you can’t model a human being. Having done research in both physics and science education, there’s a huge difference between measuring electrons and measuring people. You kick an electron twenty times and it will pretty much do the same thing each time. You kick a person twenty times and (aside from the danger of being kicked back), you’ll get at least ten responses depending on the person’s mood.

It’ll be interesting to see whether tools like this can help the Ford teams (especially Roush Fenway Racing) catch up to Chevy.

May 282014
 

Everyone’s favorite “planet” killer had a spare hour because COSMOS was pre-empted Sunday by the Coca Cola 600.  Astrophysicist Neil deGrasse Tyson edified us with some “NASCAR physics”.

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There were 43 drivers who had no problem taking the corners at more than 165 mph without skidding into the “embankment” and a couple million viewers who knew instinctively that these were not correct statements.

CarTurning

Some basic physics. A car going around a racetrack in a circle is no different from a ball on a string being swung in a circle. In both cases, the reason the object makes a circle is because there is a force that point toward the center of the circle at all times. For the ball, it’s the string. For the car, the tires generate that force through friction between the tires and the track. The car tries to slide away from the center and the tires keep it from doing that.

The amount of force the tires generate is proportional to the force pushing down on the car. If you slide a tire across a parking lot, it takes you a certain amount of force.  If someone sits on the tire, you need more force to pull it. The force the tires generate is given by:

FismuN There are two forces pushing down on a racecar: the weight of the car (which provides mechanical grip) and the aerodynamic downforce (which provides aero-grip). Let’s ignore the downforce for a moment because it gives car more turning power and lets it reach higher speeds, so it only helps the argument.

If you look at a flat track, all of the frictional force is in the direction you want it to go – toward the center of the turn.

CaronFlatTrack

 

I’m showing three forces: The track exerts a force on the car equal to the car’s weight. The frictional force is toward the center of the turn, as required.

In most situations, the coefficient of static friction (the μs) is less than one, which means that you get less frictional force than the weight of the car. For regular tires on asphalt, for example, you only get 70-80% of the force pushing down.  On ice, you get maybe 10-20% of the force. Racing tires are different. They take advantage of some really interesting physics, which is that of adhesive friction (versus abrasive friction, which is what we all learn about in school).  Rubber is a truly amazing material. While the actual coefficients of friction for specific race tires are closely guarded, you can use 1.2-1.3 as a good approximation.  The 165 mph number Tyson came up with is a result, I believe, of having used the coefficient of friction for regular tires, not race tires.

Now throw in banking.

BankedTrack

The directions of the forces change. Except gravity, which (on Earth) always points straight down.

The track always pushes perpendicular to its surface, so now part of the force from the track is pushing up and part is pushing toward the center – the banking helps the car turn.  The higher the banking, the more help you get turning.  If the track had a banking angle of 45 degrees, half the track force would be pushing up and half would be helping the car turn.

If you’re paying attention, you’ll notice that the frictional force (which always acts parallel to the track surface) also changes direction. In fact, the amount of frictional force in the direction you need to turn actually decreases a little; however, you get such an advantage from the banking that it compensates for the loss due to the frictional force.  (Of course – otherwise, no one would bank tracks.)

The calculations (without aero) are pretty straightforward and standard in many intro physics courses.  Hyperphysics is my go-to reference for basic physics when I don’t have a textbook handy.  You can follow them through the whole calculation to get the equation that shows the maximum velocity is determined by the radius of the track (r), the static coefficient of friction between the track and the tires (μs), and the banking angle of the track, θ and the acceleration due to gravity (g).

vmax

The parameters are easy to look up. g has a value of 32.2 feet per second per second (ft/s2), the turn radii at Charlotte vary (

At Charlotte, the turn radii are 685 feet (turns 1/2) and 625 feet (turns 3/4)  and the banking angle is 24 °.  Hyperphysics even gives you boxes and lets you plug numbers in on their site, so you can play around to see how the maximum velocity changes with the parameters.

The important thing here is the difference in friction between race car tires and regular tires. Race car tires are made of a different composition of rubber. They get much hotter than passenger car tires and the surface layer of the tire actually melts a little bit. Rubber gives additional grip in a way I like to describe as what happens if you step on a piece of chewing gum on a hot day. The chewing gum sticks to your foot and prevents you from moving – a slightly different type of friction.

Physics classes rarely teach students about materials that aren’t pretty well-behaved solids. Stretchy, squishy materials like rubber or any type of liquid introduces a lot of complications. I had been teaching physics for 15 years before I learned  you could have a coefficient of friction greater than one.  So it’s not too surprising Tyson didn’t know it either.

However, as my friend James Riordan points out, theory always has to be checked against experiment. And that’s part of what’s so annoying about this. All you had to do was watch the race to know this upper limit was incorrect.  A huge number of media outlets re-tweeted these ‘facts’, or featured the tweets as they exclaimed how wonderful it was that an astrophysicist was explaining NASCAR to its fans.  Sorry folks – NASCAR fans are smarter than they are given credit for.  There’s a level of complication and sophistication to the sport that people who have never paid attention to it simply don’t appreciate.  Sure, NASCAR isn’t F1 – but there aren’t many of the high-level teams that don’t have at least a few Ph.D. level aerodynamicists and mechnical or chemial engineers on the payroll. It’s a must if you want to be competitive.

 

May 272014
 

Okay. COSMOS was pre-empted Sunday in favor of the Coca Cola 600 and COSMOS host, astrophysicist Neil deGrasse Tyson, decided to edify us with some NASCAR physics.

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I bet 90% of NASCAR fans immediately know there’s something wrong here. In fact, all you had to do was watch the broadcast.  I’ll write a longer post, but here it is in brief.

The calculation for a car rounding a banked track with friction is pretty straightforward. There are a lot of angles in it, but if you work through it, it does make sense.  Check out hyperphysics for the details. The important thing here is that the maximum velocity is determined by the radius of the track, the coefficient of friction between the track and the tires, and the banking of the track.

banked

 

where r is the radius of the track, θ is the banking angle and μs is the coefficient of static friction. I know, it looks complicated, but stay with me.  The next paragraph is just the important stuff.

At Charlotte, the turn radii are 685/625 feet (the two turns are different, depending on whether you’re going into the dogleg or the backstretch) and the banking angle is 24 °.  Hyperphysics even lets you plug in numbers on their site, so I could very quickly determine that 165 mph is what you would get if you assumed a normal coefficient of friction between a regular tire and an asphalt track (around 0.75).  The reality is that NASCAR tires have a much higher coefficient of friction, which is why they easily exceed 165 mph and have no problem staying away from the “embankment” – whatever the heck that is.

Details to follow, but I wanted to get this up because I’m getting flooded with questions.

 

 

May 092014
 

OK, so ‘monozone’ is just a fancy way of saying it’s the old tire.  It’s all in the branding, isn’t it?

Goodyear has been experimenting with multi-zone tires since last year.  Multizone tires attempt to get the best of both worlds by combining a harder compound on the inner 2-3 inches of the tire (for wear resistance) and a softer compound across the rest of the tire (for grip).  I went over the reasons for the need for a tougher inner shoulder to the tire and why the new camber rules in a good amount of detail previously.

Multizone tires were a hit last year in Atlanta, but not as praised much in Kansas.  Likewise, this year the tires made for great racing in Texas, but the Richmond race featured a lot of tire wear and some unhappy drivers.

Goodyear tested a multizone tire at Kansas Speedway on April 14th this year. They weren’t happy with the results and have opted to go with a monozone tire at the race.  They used a combination of information in the historical record regarding previous compounds used at Kansas, along with lab testing to develop a new monozone right-side tire.  The compound is slightly different than the grip-centric compound that had been used on the multizone tires.  The same left-side tire will be used as has been used previously.

Given that Goodyear starts making tires for Daytona back in October, it’s pretty impressive that they were able to generate the tires for the race in a little under a month.

The problem seems to be excessive wear on the inside edges of the tires. I covered the reasons for this previously, but those reasons are exacerbated when you’re at a track with a lot of grip.  This means that the problems are more likely to rear their heads at grippy tracks (i.e. newly paved tracks) and during night races because the cooler temperatures result in more grip.  The other factor is high loads on tires, especially transient (i.e. short-time) loads.

Larry MacReynolds pointed out this morning on SiriusXM NASCAR radio that the teams have the car suspensions set up to be be rather stiff.  In the corners, there isn’t much springy in the car except the tire – the tire becomes the only point with any give. That puts a lot of stress on the tire.  Corner speeds have also been much higher this year – and that’s were much of the load comes about.

The one common thread I’ve heard is that there is a very small window between ‘fine’ and ‘oops’ – the tires are good for a long time and then they just go.  This is a problem because you don’t get much predictability – there’s no way they can run enough testing during practice to know that they can go 54, but not 55 laps before the time starts wearing enough to get into the danger zone.

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