Daytona Testing Notes: The Magic 200 MPH Mark — Not

 Aerodynamics, Daytona, Engines  No Responses »
Jan 132012
 

There is absolutely nothing magic about the 200-mph mark.

People have been treating the 200-mph number like it was handed down by a sacred oracle.

First off, a series of factors are required to make a car go airborne.  ONE of them is high speed.  Another is the car getting turned around at just the right angle.  It’s not like the minute a car goes faster than 200 mph, it is in imminent danger of becoming airborne.  The higher the speed, the higher the probability the car can leave the ground — IF other factors are also present.

Secondly, today’s car has very different aerodynamics than previous versions of the car.  NASCAR apparently feels confident that the 202-205 mph range does not raise the probability of a car becoming airborne significantly.  John Darby specifically said that NASCAR had wind tunnel testing data that led them to this conclusion.  NASCAR believes that the slight increased risk is small relative to other benefits (the most significant of which appear to be saving engine builders/tuners from having heart palpitations due to the engines turning very high sustained rpms).

If you can’t let go of thinking about 200 mph holding some mystical power, remember that 200 mph is really just 321.9 kilometers per hour.

Doesn’t sound so magical that way, does it?

 Posted by diandra at 7:46 pm

The Motorsports Science Minute Video: Radiators at Daytona

 Cooling, Daytona, Engines  3 Responses »
Jan 102012
 

Thursday marks the first time we’ve had an open test at Daytona in a couple of years.  With the myriad rules changes aimed at getting away from two-car drafting, the teams are going to need to make the most of these sessions — especially if NASCAR opts to make more changes before Daytona
 

Below, a short video explaining why radiators are such a big deal at Daytona this year.  As always, happy to answer questions you might have! Drop them in the comments and I’ll reply. Or send them to me @drdiandra on twitter.

 Posted by diandra at 4:11 pm

OPINION The Future of Motorsports Safety II: The Center for Motorsports Safety Research

 Dan Wheldon, IndyCar, Las Vegas Motor Speedway, Safety, Uncategorized  No Responses »
Dec 152011
 

The official Indycar report on Dan Wheldon’s death was released today.  The conclusions:  Wheldon died when his head/helmet hit a fencepost, but it took a combination of factors to bring about this awful tragedy.  They also noted that it wouldn’t have made any difference if the fenceposts were on the inside of the fence or the outside of the fence.  I pretty much said the same thing in my analysis of the incident.  Indycar, much to their credit, has released the entire 49 page report to the public, which comes to you here via pressdog.

The obvious question is “what do we do now”?

When I last spoke with Dean Sicking (the inventor of the SAFER barrier), I asked him who the primary groups were in the world who are doing motorsports safety research in the area of track barriers and fences.  There are a few, but most of them focus on human mechanics or medicine.  If you want to be specific, there is exactly one group in the country doing intensive research into motorsports track safety and that’s at the University of Nebraska.  Yes, I know that some sanctioning bodies have their own R&D divisions; however, they have limited staff and they also have the responsibility for doing things like certifying new products for use in their series.

Most research at Universities is funded by grants (usually from federal or state agencies, sometimes from private foundations) or contracts (usually from private industry and designed to accomplish a very specific objective, with deliverables.)

One of the primary issues with the catchfence is the vertical poles that support the wire mesh.  Initial reports argued that, if the poles had been outside the mesh, there wouldn’t have been a fatal accident.  This is not right.  Inside or outside, hitting one at high speed is going to be fatal.  I suggested before that a possible solution would be to somehow cantilever the fence so that the posts would be a few feet away from the mesh.  You’d need quite the system of wires, but I know it’s possible.

Let’s give Sicking and his group a grant to design a better catchfence.

Do you have  any idea how much money you would need to test such a catchfence?  When designing the SAFER barriers, Sicking told me that getting a driverless car to hit the barrier at a precise speed and angle was actually the most technically challenging part of the research.  Now we not only have to have a high-speed racecar hit the new catchfence, but we also have to have it in the air when it does so.

I suggest that the industry needs a Center for Motorsports Safety Research.  It would be a non-profit center operating independently of any sanctioning body, but it would work with the sanctioning bodies to prioritize research needs.   Representatives from the various sanctioning bodies, along with motorsports researchers, would form an advisory board that would try to anticipate safety issues, as opposed to how we deal with them now, which is reactively.

I think it’s important that this be an independent body and not beholden to NASCAR or IndyCar.  There would be a small research staff, with room for visiting researchers who can contribute particular specialization to specific problems.  I would (of course) put Dean Sicking in charge of it because he is one of the best engineers and most honorable persons I have even known.  He’s shown his ability to design for two very different cars at the same track already.   I’d also charge them with preparing educational materials for drivers at all levels to make them aware of state-of-the-art safety concerns and the equipment they need to be as safe as possible.

Who should fund this center?  The sanctioning bodies, the media who make money from broadcasting motorsports, the track owners, and you and me:  the race fans.

From Jayski’s track seating and attendance page, 3.6 million people attended NASCAR races last year.  Let’s add a safety surcharge of $2.00 per ticket is added on — and frankly, if you begrudge paying less than the cost of a beer to facilitate your part of this research, you shouldn’t call yourself a race fan.  That would be $7.2 million dollars right there for motorsports safety research.  Add on contributions from the media partners who broadcast motorsports, the occasional generous driver, and you have the start of a center.

As I said in my previous article, motorsports will never be entirely safe.   But that doesn’t mean we shouldn’t do everything we can to try to ensure that we never lose another driver again.

Kudos, Indycar for your transparency and commitment to learn as much as you can from this tragedy.

 

 Posted by diandra at 12:05 pm

The Future of Motorsports Safety I: Catchfences, Open Cockpits, High Banking and High Speeds

 Dan Wheldon, IndyCar, Las Vegas Motor Speedway, Safety  3 Responses »
Nov 142011
 

“This is a huge tragedy for IndyCar but I hope that out of this tragedy comes some good in terms of improving more in safety, like when Greg Moore died and Dale Earnhardt, and now Dan Wheldon. The innovations that come out from that in terms of improving driver safety need to be kicked up another notch. We hope that is what will happen.” –Paul Tracy

I’m a relatively new Indycar follower.  Part of dealing with a series of health crises over the last 18 months was getting rid of electronic baggage: relentlessly negative people, and those who confuse ‘snarky’ with cruel. That left some holes in motorsports content that were happily filled by new friends from the open-wheel world like PopOffValve, OilPressure and SpinDoctor500blog. They introduced me to a new world and a new group of drivers. I immediately picked out Dan Wheldon for his wit, his smile and his ability to communicate what so effectively during his Versus appearances. Over the last couple weeks, I’ve read many words of grief, tribute and, more recently, of thoughts about what happens next.

As a reminder, this blog focuses on analyzing and understanding the science and engineering of racing. Opinions are welcome, but they have to be substantiated by fact and stated respectfully. No ad hominem attacks.

A Brief History of Barriers

The original purpose of barriers around tracks was keeping cars separated from spectators.  In addition to concrete walls to prevent the cars from driving off track, debris-spewing accidents necessitated fencing to contain airborne objects.  Most fencing was standard-issue chain-link, which is cheap, plentiful, easy to put up and surprisingly strong.

Solving one problem (as so often happens) generated another:  while very effective at keeping spectators safe, drivers could be (and were) seriously injured hitting these rudimentary structures.  The problem became worse as speeds rose – the kinetic energy of an object increases with the square of its speed.  This means a car going 180 mph has nine times more kinetic energy than the same car going 60 mph.  When a car comes to a stop, all of its kinetic energy has to be dissipated – transformed into heat via skidding or friction between the brake rotors and the brake pads, for example.  The longer the car takes to come to a stop, the less force experienced by the driver.

Concrete walls are simply too unyielding.  Springy walls might seem like the answer, but bouncing a car back into the paths of other cars creates other problems.  The SAFER (Steel And Foam Energy Reducing) barriers were a huge technical advance because they dissipated the car’s energy via flexing hollow steel square tubing and smushing foam between the tubing and the concrete wall. The SAFER barriers have been one of the most visible technical achievements associated with motorsports.

Chain-link fabric

Photo from: http://www.chainlinkfence-yihang.com/Engineering-Drawings.html

Catchfences pose a slightly different set of problems.  They should have the same properties as the walls, but they can’t block the view.   In addition to sight, one of the best parts of seeing a race in person is the sound and – if you’re close enough – feeling the wind generated by the cars zooming by. Chain link fence is a good compromise between visibility and protection.

Chain-link fabric is like an elastic metal mesh. It can give in two ways: gentle forces cause the mesh to deform.  The diamonds stretch out of shape, but when the force is removed, the fabric springs back to its original shape. The fence can also deform by stretching the wires that make up the mesh. A large-enough force will break the wire, leaving a hole in the fabric.

How much the mesh can stretch depends on how it is supported.  If the frame is too big – meaning that there’s a very large area of mesh between supports — the mesh will stretch too much. Vertical poles are used periodically to provide additional strength.  How the poles are attached to the mesh is critical, because the attachments allow the load to be shared between the fabric and the poles.  The larger the forces, the more robust the links between the poles and the mesh must be.

Photo from: http://jonesinforspeed.blogspot.com/2008_07_01_archive.html

Race track fencing is stouter in just about every way.  The mesh is made of larger-gauge wire with higher tensile strength.  The links between the poles and the fabric are stronger:  In the picture at right, steel cables run horizontally through the mesh and are fixed to the vertical poles using some massive turnbuckle-like fixtures.

Different tracks have different installations.  Some have metal tubing running horizontally as reinforcement.  One of the pictures below has larger-holed mesh that is attacked to the poles at every possible point.

The SAFER barrier represented a paradigm shift in barriers:  a entirely different principle of operation.  Catchfence improvements have primarily been via stronger mesh, stronger or a greater number of poles, or better links between the poles and the mesh.  But it’s basically the same fundamental design.

The chain-link fence has been institutionalized in motorsports, with governing bodies developing specific standards for debris fencing.  These standard tests allow us to compare different types and installations of fences.  In the FIA test, a 760-kg  (1675 lb) test mass is shot into a fence at a speed of 65 km/h (40 mph) at heights of 1.6 m and 2.5 m (5.25 and 8.2 feet respectively).  While 40 mph seems very slow, they’re taking just about the entire mass of an Indy car and concentrating it in a relatively small sphere.  A real car would impact over a much larger area and spread out the force.

Photo from http://www.geobrugg.com/contento/security/English/Home/Debrisfences/CrashTests/tabid/3874/language/en-US/Default.aspx

The photo at left shows the fence working perfectly in terms of what’s being tested:   The mesh deforms (a lot!) without breaking.  Load is transferred to the poles, with the poles nearest the impact bending.  The emphasis, however, is pretty strictly on containment.

With that background, let’s examine some of the theories that have been advanced and see how the science stacks up.

The “It’s Obvious What Went Wrong” Theory

I got a chuckle out of Dean Sicking, inventor of the SAFER barriers and Director of the Midwest Roadside Safety Facility, when I started our conversation by asking him how many people contacted him after the crash and asked him to make a definitive conclusion about the cause of the crash solely the basis of the television video.

Motorsports accidents rarely have a single cause. It is almost always a confluence of events that add up to disaster. Even Sicking, with many years of experience, can’t look at a videotape and positively identify a cause.   A formal investigation is in progress.  Sicking (who is not part of that investigation) noted that the investigators will use every bit of data they have access to:  accelerometers in the cars that measure the forces the cars experience and earpiece accelerometers (which all Indycar drivers wear) that provide data about the forces the driver feels (because the two forces are rarely identical).  They will have that information from every driver and car on the track.  The team will investigate all of the safety apparel (HANS, firesuits, helments, etc.), in-car video, photos, broadcast video and all of the information from race control.   This is a very complicated situation given the number of cars involved and it’s going to take some time to unwind.

The one think Sicking is willing to say definitively is that “It’s too soon to blame the fence”.  He has some ideas on how the current catchfence design could be improved – but he politely declined to share those given that he hasn’t had an opportunity to test any of them yet.

The “Inside-Outside” Theory

Photo from: http://markjrebilas.com/blog/?p=6338. Check his website - there are some really great pictures.

A popular theory making the rounds is that the fence at Las Vegas Motor Speedway is unsafe because the vertical support poles are on the inside of the fencing (facing the track).  The support poles in the picture at left are on the outside (facing away from the track).  In a coincidence perfect for the black helicopter crowd, SMI tracks (like Las Vegas) have the vertical supports inside the fencing, while ISC tracks have supports outside the fencing.  Sicking doesn’t think the location of the poles inside vs. outside makes a significant difference.  A number of people have advanced the theory that the poles on the inside ‘shred’ the car and that moving them to the outside of the wire mesh would provide a much smoother surface.

I think the picture they have in their minds is of a car traveling along parallel to the fence and hitting the posts as it goes by.  If that were the case, then it would be true that having the posts on the outside would be better; however, it’s highly unlikely a car would travel that way.

Most crashes don’t happen parallel to the fence – the car hits with some component of velocity perpendicular to the fence, which makes avoiding hitting a pole virtually impossible given the spacing between the poles.

Sicking says the problem is not whether the poles are inside or outside the mesh, but that they are so close that it is almost impossible for a flying car to hit the fence without hitting one (or more) poles.

The “Close the Cockpit” Theory

It is hard to find any evidence countering the assertion that an open-wheel driver is much more susceptible to injury from a cockpit-first barrier or catchfence hit than a stock car driver.  Indy cars have a roll hoop, but it’s a fairly minimal structure and, if compromised, leaves nothing to protect the driver’s head.   If you want evidence in support of closed cockpits, consider the two extremely violent crashes experienced by Audi LMP (closed-cockpit) cars at this year’s 24 Hours of LeMans.  Both drivers walked away.

While acknowledging that open-cockpit cars are an integral part of Indycar tradition, I don’t think you can escape the conclusion that maintaining that tradition increases the risk to the drivers.  Whether that’s an acceptable risk or not, it seems to me, is up to the drivers.

The “Hockey Rink” Theory

Hockey rinks use a clear wall to protect fans from flying hockey pucks (and sometimes from players being slammed against the boards).  The Lexan polycarbonate is strong enough to withstand the force of the hockey puck and still allows clear sight lines for the fans.  Lexan is used for bullet-proof windows and similar demanding applications. Lexan is also used (and recently mis-used) in the windshields of NASCAR stockcars.

When thinking about forces, the mass of the object, its speed and the time of the hit (how long the two objects are in contact) are important.  The record speed for a hockey puck (which weighs about 5.5-6 oz.) is about 106 mph.  Race cars, on the other hand, weigh a whole lot more (1600 and 3250 lbs in round numbers for Indycars and stock cars) and travel even faster.  I’ve compared on the plot below the kinetic energies (KEs) of a NASCAR stock car, an Indy open-wheel car and a hockey puck.  Some values are shown in the table for comparison:

Comparing the kinetic energy of a hockey puck with race cars.

Object Mass (kg) Weight (lb) Speed (m/s) Speed (mph) Kinetic Energy (J)
Hockey Puck 0.17  0.375 47.4 106 191
IndyCar Car 710 1560 98.4 220 3,433,733
NASCAR Stock Car 1477 3250 80.5  180 4,782,648

(The hockey puck is that flat purple line on the graph.)

Even if we consider that the time of the hit for the hockey puck could be, say, 100 times shorter than that for the cars, we’re still talking about factors of hundreds or more in terms of the force the wall would have to sustain.  Lexan is simply not up to the job.  You could try a composite – a combination of two materials that produces properties superior to either. For example, you could reinforce Lexan with steel cable — or even carbon nanotubes; however, you would still need an unrealistic thicknesses of material and it would be very expensive to encircle an entire mile-plus-long track with it.  Economically and practically, this isn’t a reasonable solution.

The “Just Keep the Car on the Ground” Theory

This seems like a very simple approach:  The best way to prevent car-catchfence collisions is to keep the cars from hitting above the SAFER barriers, which means keeping them from leaving the ground.  The new car is designed to decrease the wheel-locking problem that contributes to propeling cars into the air; however, Sicking suggests that the rear wing angle needs to be investigated as another contributor to the problem.

“Angle of attack” refers to the angle between a wing and the oncoming air. In a racecar, the angle of attack determines downforce and drag.  Sicking says that the way the wing is run now – pretty close to flat – provides huge downforce and very little drag.  The problem, he suggests, is that when the car gets a little bit off the ground, the angle of attack of the rear wing actually encourages the car to continue rising.  Increasing the angle decreases downforce and adds drag, which prevents the drivers from running wide open the whole way and discourages the car from lifting. Sicking suggests that increasing the horsepower would also help.

It seems to me there’s a safety issue anytime a driver doesn’t have throttle response. Have you ever been in a rental car trying to enter the expressway (or pass a truck) and you’ve got your foot all the way down on the gas but the car just isn’t going any faster? Not a good feeling.  Throttle response gives a driver additional control and additional control is always a good thing.

The “Pack Mentality” Theory

Cars moving at high speeds give drivers very little time to react. Cars moving in close proximity to each other also decrease the margin of error allowed the driver.

The phrase you hear on the Indycar TV broadcasts is “A football field per second” (which is about 204 mph).  Those of us who aren’t race car drivers may not appreciate how fast that is.  Since most of us don’t have access to a 200-mph car and a track, Sicking sugests heading out to your local high school football field.  Park a car at one end and, when you reach the other end, turn around imagine that (one second later) that car is right on top of you.

When cars are moving together at similar speeds, there isn’t actually much danger because their relative speeds are  very small; however, the minute one car slows down, the relative speed jumps and the drivers have to responds.  From SportsScience to accident reconstruction experts, there is overwhelming evidence that racecar drivers have extremely good reaction times. But even a 99th-percentile reaction time won’t keep you from hitting something if you’re too close to it.

The “We’ll Try Harder and Make Racing Safe so that We Never Lose Another Driver” Theory

Dave Moody touched on this on his Sirius Speedway radio program – he asked whether the Indycar drivers should have been expected to get back in their cars and race after a fatal accident. He suggested that maybe the sport is more humane today and we don’t expect people to ‘buck up’ in the face of tragedy like they did ‘back in the day’.

I have a slightly different take: ‘Back in the day’, more drivers died. People steeled themselves because it was more likely than not that someone would die during a season. Racing has become so much safer, and we’ve had so many fewer accidents that perhaps we have forgotten that this is still inherently dangerous. Getting in a racecar is a calculated risk. When you look back at the old days — tire testing by having drivers run through nails and tacks at high speed — you marvel at the risks drivers willingly accepted.  We’ve minimized many of those risks, and a lot of lives have been saved as a result.  But there is still a risk that what happened on that tragic Sunday at Las Vegas will happen again. I worry that younger drivers – especially those who have never lost a colleague in an on-track incident – feel an unwarrented invincibility (for themselves and others) that leads to less than prudent moves on the track.  But even with everyone on their best behavior,  the motorsports sanctioning bodies could implement every innovation we have and that could still not be enough.

Racing is not 100% safe.  It never will be.

The “We Owe it to Dan” Theory

At the risk of saying this the wrong way, one of the side effects of the reduced number of serious accidents is that we don’t have a lot of data on those types of accidents.  Understanding how to prevent accidents like this requires that we understand the accidents.  Many others have put it more eloquently:  We owe it to Dan — and all the other drivers — to learn from this tragedy and to make changes.   Those changes will not ensure that no driver ever dies on a racetrack, but everything we do will decrease the number of drivers who do make that ultimate sacrifice.

In the second part of this series, I’ll explain how we could do that.

 Posted by diandra at 2:58 pm

Ray Evernham on Carbon Monoxide

 Daytona, Edwards Carl  No Responses »
Jul 022011
 

Ray Evernham was one of the first people who realized the carbon monoxide (CO) has an effect on driver that could be affecting his performance.

“(I could tell immediately) …by the way Jeff answers me on the radio, whether the carbon monoxide is getting to him.  He becomes a smartass. But the more I got to know him and the more I learned about carbon monoxide, the more I realized what was happening.”

I usually talk about the development of the catalyst in talks I give. I was very embarrassed to have put this PPT slide up at Notre Dame with priests in the audience.

 

 Posted by diandra at 8:20 pm

How Likely are You to Win the TNT Million Dollar Challenge?

 Daytona, math, Probability  No Responses »
Jun 292011
 

TNT is offering a million dollars to anyone who picks the top ten drivers – in order – at any of the six races they broadcast.  You have up until 25% of the race has been run to lock in your selections, which means up to mile 100 at Daytona this weekend.   How likely are you to win?

You have a 1 in 43 chance of picking the first driver correctly.  There are now 42 drivers left and you have a 1 in 42 chance of picking the second driver correctly.  When you calculate the probability of doing two things, you multiply the probabilities.  It makes sense that there ought to be less probability of picking two numbers in a row than of picking one, right?  So the odds of picking two drivers in the right order is 1 in (43 x 42) or 1 in 1,806.

Continuing this pattern…

# picked in right order

 Calculation Chances are …
1 1 in 43 1 in 43
2 1 in (43 x 42) 1 in 1806
3 1 in (43 x 42 x 41) 1 in 74,046
4 1 in (43 x 42 x 41 x 40) 1 in 2,961,840
5 1 in (43 x 42 x 41 x 40 x 39) 1 in 115,511,760
6 1 in (43 x 42 x 41 x 40 x 39 x 38) 1 in 4,389,446,880
7 1 in (43 x 42 x 41 x 40 x 39 x 38 x 37) 1 in 162,409,534,560
8 1 in (43 x 42 x 41 x 40 x 39 x 38 x 37 x 36) 1 in 5,846,743,244,160
9 1 in (43 x 42 x 41 x 40 x 39 x 38 x 37 x 36 x 35) 1 in 204,636,013,545,600
10 1 in (43 x 42 x 41 x 40 x 39 x 38 x 37 x 36 x 35 x 34) 1 in 6,957,624,460,550,400

That’s one in 6.9 quadrillion to get all ten in the right order.

Is Picking Them in Order Harder?

What if TNT had just said you had to get all ten, in no particular order?

If you look at ten numbers, there are ten ways of picking the first number, nine of picking the second, etc. That multiplies out to there being (10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1=) 3,628,000 different ways of organizing ten numbers in every which way possible.

If TNT had decided that you only needed to get the drivers right, but not the order, your chances would increase to a whopping 1 in 1,917,334,783.

But there aren’t Really 43 Drivers Capable of Placing in the Top Ten…

OK, in reality, the odds are a little better.  The calculation above assumes that the finish is a totally random event and we know that it’s not because there are 7-9 start and parkers.  Realistically, you’re picking from maybe 35 cars (8 S&Ps), so the odds for getting all ten in the right order if you’re only picking from 35 drivers are 1 in 818,441,006,423,040. or 1 in about 818 trillion.

But there aren’t Even Really 35 Drivers Capable of Placing in the Top Ten…

Yeah, the husband tried to make the argument that you’re really only choosing from about 17 or maybe 20 drivers.  Five words:  Regan Smith and Trevor Bayne.

Just for comparison…

Odds of being struck by lightning are 1 in 576,000.
Odds of being killed by lightning are about 1 in 2,320,000
Odds of a meteor landing on your house: 1 in 182,138,880,000,000

So you’ve got a better chance of a meteor landing on your house than winning that million dollars.

Often for promotions like this (free televisions if it snows 10 inches on New Year’s Day!!), a company will take out an insurance policy.  They’ll pay some amount of money to hedge against paying more.  The people at the insurance company who figure out how much to charge them use these types of calculations to figure out the risk.  I’m guessing TNT wouldn’t want to pay much of a premium because the odds are clearly in their favor.  But it’s a great promotion.

Does this mean you shouldn’t play?  Heck no – TNT isn’t charging you to enter, so get your best guess together and see if you can beat the odds.

RANDOM NOTES

Look at this cool project from Clemson and DuPont to take middle and high school teachers to the racetrack and teach them about science!  Way to go, Tigers.

The probability of becoming a saint is estimated at about one in 20 million, but if you’re Jacques Villeneuve, the odds rise to one in a flying pig.

Gratuitous link to The NASCAR Insiders just because their Wednesday Q&A is always worth checking out – it is a blog I always learn something from!

Daytona this weekend – read all about drafting vs. bump drafting, why you’re likely to see two but not three cars drafting together, why NASCAR limits radiator pressure to try to keep the two-car draft to a minimum, and why drivers shift to the right to get air to the engine if they’re turning left.  Or take a look at the Science of Speed video on drag and drafting.

 

 Posted by diandra at 11:49 am  Tagged with: , , , , , ,

The Math of Fuel Mileage

 Engines, Fuel Mileage, Kansas, Pocono  5 Responses »
Jun 102011
 

The gas needed to do one lap at a one-mile track fits in this quart bottle

I guess when you have people feeding you all the numbers you need through your earpiece, you think they’re easy to come by.  That’s the only explanation I can figure out for the snarky comments by television commentators about crews not being “smart enough” to figure out how much gas to put in the car so that it doesn’t run out before the end of the race.  There have been a lot of fuel mileage races the last few weeks.  Pocono is traditionally also highly likely to be a fuel mileage race, so let’s clarify how easy (or hard) it is to not run out of fuel.

Average mileage under green is about 4 miles per gallon.  At a one-mile track, than means one lap (one mile) requires one quarter of a gallon, which is one quart.  A car running out of gas coming out of turn four is short by probably a cup of fuel.   On the one hand, it’s amazing that it takes a whole quart of gas to do one lap.  On the other hand, the fuel cell holds 18 or 19 gallons.  Let’s say they get 18.5 gallons in the fuel cell – that’s 74 quarts, so you’re talking being off by 1/74th of a tank, which is a pretty narrow margin of error.

For comparison, a passenger car getting 32 mpg would need only a half a cup of gas to do a lap at Phoenix.  Although much more fuel efficient, the television ratings would likely be much lower.

There are some other considerations.  Here are two that are hard to quantify:

  • The pickups on the fuel cell can’t pull all the gas out of the tank, no matter how much swerving the driver does.  There’s likely to be some fuel in the fuel cell that just doesn’t make it to the engine.  It is a small fraction of the fuel cell, but  if we’re talking about 8 ounces of fuel being the difference between making it and not, small amounts matter a lot.
  • The driver’s ability to save fuel varies, depending on the driver and if he’s racing hard or if he’s able to set his own pace.  If he’s racing hard with another driver, he’ll likely get less than the expected fuel mileage.  If he’s skilled (getting off the throttle earlier going into the corner and getting onto the throttle later coming out of the corner), he might save a lap or two or three worth of gas.  It’s the same principle as you and I not stomping on the gas or the brake to be more fuel efficient.  When the crew chief asks the driver how much gas he’s saved, the only thing the driver can do is guess.  The more experienced the driver, the better feel he is likely to have for how much gas he saved.

One of the biggest challenges for the crew chief is calculating the actual gas mileage.  Let’s say you or I are calculating the fuel mileage of our car.  We go to the gas station and fill up the car.   The next time we stop for gas, we figure out how many gallons it takes to fill the tank back up and how far we drove.  For example:

I fill up my tank.  300 miles later, I stop for gas again and find that I need 10 gallons to fill up the tank.  It took me 10 gallons to drive 300 miles, which means my gas mileage is 30 miles per gallon.

OK, that’s not perfectly accurate because what does “fill up” mean?  Some people top off the tank and others stop as soon as they sense it is close to full.  There’s some variation in the fuel pumps as to where the pump shuts off automatically.  300 miles on the expressway is different than 300 miles in town.  If you want a meaningful number that characterizes your own gas mileage, you need to measure it consistently over a period of time and use an average.  Of course, that’s not possible in NASCAR.

But at least you and I get a decent measurement of how much gas we put in the car.  NASCAR teams don’t get to measure how many gallons of fuel goes into the car: They get to measure how many pounds of fuel went into the car.

A NASCAR fuel can holds about 12 gallons of fuel.  Gas weighs about 6 lbs per gallon, so the full gas can holds 76 lbs of gas.  The can itself is about 20-25 lbs, so round numbers, 95-100 lbs total. (Thanks to the NASCAR Insiders for the numbers.  I am writing this from a neuroscience retreat and don’t have my notes handy.)

Before each pit stop, the team weighs each one of the gas cans.  Let’s say one of them weighs 96 lbs.  The car comes in to pit, they add fuel and then weigh each gas can again.  Let’s say that the can weighs 36 lbs after a stop.  The change in weight is 96 lbs – 36 lbs = 60 lbs.  At 6 lbs per gallon, you can infer that the can is missing 10 gallons.

Note that I very carefully said ‘the gas can is missing 10 gallons’ because we have no assurance that all 10 gallons went into the car.  You’ve seen gasoline spill out everywhere when the gasman pulls the dry break away from the fuel cell inlet.  That happens even more with the new dry breaks because they are a little trickier to put in place and pull out than the old gas cans were.

The crew chief looks down and makes a mental estimate of how much fuel is spilled, converts the masses from the cans into gallons and comes up with a number for how much fuel he thinks is in the car.  From that, he estimates how many laps they can run.  If you want to see a frustrated crew chief, look for the gas man with the raised eyebrows and the shrugging shoulders.  He thinks he got it full… but he’s not sure.  That’s actually sometimes worse than the one who knows he didn’t get it full.  Sometimes it’s better to know the answer, even if it’s bad, than to be unsure.  The scales in the pits have at least one decimal place, and my friend Josh (a member of the ex-Elliott crew chief club) suggests that the better teams have almost certainly moved to scales with two decimal places.

Do the decimal places really matter?  Turns out they do.  Sunoco provides NASCAR teams with the exact density of the gas on race day, and they provide it to two decimal places.  So instead of 6.00 lbs/gallon, they’ll tell you 5.94 or 6.06 lbs/gallon.  If you weigh 60 lbs of gas, that’s 1o gallons @6.00 lbs/gal vs. 10.6 gallons @6.06 lbs/gal.  Remember that on a one mile track, one lap requires 0.25 gallons.  That 0.6 gallons difference is more than two laps on a one-mile track.

One more thing that’s different this year.  Here’s your word to impress people with this week:  Hygroscopic (hi-grow-skop-ick).  It means very attractive to water.  Ethanol – and 15% of the NASCAR fuel is ethanol – is highly hygroscopic.  If you turn your back on ethanol for even a moment, you turn back and there it is sucking up water.  We use ethanol in the lab to clean things and we actually have to use acetone afterward to get rid of the water the ethanol leaves.

Two issues with hygroscopicity:  First, you’re getting water in the fuel and water isn’t combustible.  You put the same volume of liquid in the cylinder and you get less power because some of the molecules turn into steam instead of combusting.  So you need more rotations to get the same power and thus you’re using fuel at a different rate.

Second, water has a different density than the hydrocarbon fuel molecules (or the ethanol), so the amount of gas you’re getting in the car is different that what you think.   Density changes with temperature, so if you think about a race like Kansas, where it was really hot, or like Charlotte, when the temperature varied quite a bit from start to finish, you might experience meaningful changes in the density over the course of a race.  Even if you did all the calculations successfully, you might still be surprised because one of the inputs was off. Also, when the temperature rises, more water can be absorbed by the ethanol.  The water molecules hang out in the gas, pretending they belong there.  But when it cools down, the water can separate from the fuel, so it’s possible to have liquid in the tank, but not have a lot of fuel.  This is a tremendous unknown that the teams have no experience with and it may account for why there have been so many fuel mileage surprises.

A lot of factors go into correctly calculating fuel mileage.  I think if you really want to get it right, you’d want to use a model that involves calculus.  And I bet there are at least a couple teams doing that.  You can make little widgets for things like fuel consumption or gear ratios and rpm using something as simple as Excel.  I know NASCAR likes to portray itself as simple, but let’s give the folks sitting with all the computers up on the pit box their due.

A few misc notes:

  • Happy to hear that Chad Johnston is getting a shot at crew chief for the 56 team.  Chad was the engineer for Elliott Sadler’s team when I was following them around for the Physics of NASCAR book.  Chad is a talented guy who reminds me a little of Rodney Childers – not self-promoting, doesn’t talk when he doesn’t have anything to say, but when he has something to say, make sure you listen.
  • I wish the story about what happened to the Second Chance Motorsports Nationwide crew at Chicago got just a small fraction of the attention Richard Childress/Kyle Busch did.  It’s sad, but there are so many people trying to get into NASCAR that there will always be some people who will work for someone who doesn’t have a history of treating people right.
  • BTW – I’m tired of hearing about RC/KyBu… you can stop now.
  • Here are a couple neuroscience tidbits I learned this week.  Perhaps the most useful thing was that if you get eight hours of sleep, but it’s not continuous (think new moms), your reflexes and ability to think are comparable to someone seriously sleep deprived.  The least useful (but perhaps most interesting) piece of information was that rodents lack the ability to vomit.  If you want to test whether a drug induces nausea, you use ferrets because they barf pretty readily.  Moral of the story:  If you’re going out drinking, take the rat as your bar buddy and let the ferret be the designated driver.  (The second moral is that if you went into physics because you have a queasy stomach, watching that talk right before lunch was maybe not the best thing to do.)
  • Where have I been?  Well, the last year or so I’ve been dealing with some really, really serious medical issues and it’s been all I can do to get through the day.  Blogging was one of the many things in my life that just seemed to require too much energy to manage.  I’m starting to feel better now – sometimes I would go so far as to say “inspired” – so I’m hoping my comeback will keep.  Thanks to the many online buddies who have kept me in their thoughts and brightened my days.  You don’t know how much you have been appreciated.
 Posted by diandra at 4:00 pm  Tagged with: , , , ,

turning left, shifting right: why drivers move to the right to get air to the engine

 Aerodynamics, Cooling, Daytona, Engines  5 Responses »
Feb 222011
 

Jack asks:

I’m curious as to why the rear cars are offsetting to the right, when offsetting to the left would let the rear driver see what is happening ahead of them and keep the radiator in cooler air, since the exhaust on these cars is on the right. I know that all those drivers and crew chiefs are smarter than I am, so I must be missing something.

Thanks for the question, Jack. Give yourself a little more credit: you bring up some really good points that I bet a lot of people didn’t see.

Drafting at Daytona has become more important than ever, with the two-car draft being the most effective means of getting speed. The problem is that this mode of drafting completely blocks the front grille, and that limits how much air gets in to cool the engine.  The trailing car has to back off to let air into the grill when the engine gets warm.

Jack noticed that everyone was shifting to the right.  I think it’s a matter of simple geometry and the fact that NASCAR is chiral.  Chiral means simply that something twists one way.  All of your DNA twists in one direction.  NASCAR drivers turn (with two exceptions a year) right left.  (Note:  Thanks to the commenter.  What WAS I thinking there?)

Below, I’ve drawn two cars trailing each other in line on the left, the trailing car shifted to the right (middle) and the trailing car shifted to the left (right).

When cars turn left, a natural gap opens up on the right-hand side between the cars.  Moving to the right takes advantage of the gap and makes it slightly larger.  If the trailing car moves to the left, I don’t think it’s going to get as much air.  So despite the possibility of being able to see better, going to the left doesn’t look as effective to me as shifting to the right is if the goal is to get the most air into the engine.

Thanks for asking the question, Jack!  I always read the comments, so if you have a question you’d like answered, please leave it in the comments for me.

 

 

 Posted by diandra at 7:21 pm

Popping Off: Breaking the Two-Car Draft by Heating up the Engines

 Cooling, Daytona, Engines  2 Responses »
Feb 162011
 

Any closed vessel that is subjected to high temperature will experience increasing pressure.  When that pressure gets high enough, we change from calling it a pressure vessel to a bomb because if(when) it explodes, the vessel itself becomes a collection of high-speed projectiles.  For safety, we don’t heat closed containers if there’s a chance they will reach high enough pressure for them to explode.  A pressure cooker, for example, has a relief valve that at one time was as simple as a rubber stopper tightly fitted into the lid.  The rubber stopper fit in the hole securely enough to handle up to some cutoff pressure, then popped out when that pressure was exceeded.  (This is not an ideal safety mechanism because the flying stopper can injure someone, as can the blast of steam that dislodged the stopper.)

A more practical version is a valve that automatically opens when the pressure exceeds some cut-off value.  The open valve allows excess steam (and sometimes water) to escape.  As soon as the pressure is below the cut off, the valve closes again.  In addition to being safer, it eliminate the time-wasting step of looking for the stopper.

The cooling system on a car is a prime example of a closed system that is heated to high temperature.  Water is pumped through holes in the engine block, where it collects heat.  The now-hot water moves out of the engine and into the radiator, where the heat is transferred from the water to air surrounding the radiator.  The cooled water returns to the engine to pick up more heat.  A Sisyphusian task, indeed.

A radiator is a twist of metal tubing onto which is fastened thousands and thousands of fins that help cool the water that circulates through it.   A typical stock car radiator (like the one at left) might have 20 fins per inch (compared to 10 fins per inch on a typical car radiator).  The more fins per inch, the more surface area available for exchanging heat between the radiator water and the outside air; however, air has to pass through the radiator, so if there are too many fpi, the air flow is decreased and that lessens the cooling.

The water can only carry away so much heat on each trip, so the water temperature gets hotter and hotter as long as the engine keeps producing heat.  The water increases in pressure as the temperature increases.  (See Equation, Clapyron for more on that.)   Water, of course, boils at 212 degrees Fahrenheit, and that would seem to set a limit on how hot you can run an engine; however, there’s a caveat.  Water boils at 212 F only at atmospheric pressure.  As the graph below shows, the higher the pressure, the hotter the water can get before it boils.  Atmospheric pressure is right about 14.7 psi, and that’s where the 212 degree Fahrenheit number applies.  But if you can get the pressure of the system up to about 45-48 psi, the water won’t boil until 275-280 F.  If you can maintain a high pressure in your radiator, you can prevent the water from turning into steam.  Water is much better at carrying away heat than steam is.  Water also flows much better.  Most radiators have a pop-off valve that blows when the pressure gets too high.  A typical radiator cap on a car would be about 15 psi, which actually means 15 psi above atmosphere.  Atmosphere is 14.7 psi, so you’re looking at about 29.7 psi in absolute terms.  This is why your radiator cap has all of those warnings about not removing it while the car is hot:  when the system is vented (opened to atmosphere), the super-hot water will turn into super-hot steam and gush from the opening.

A pop-off valve serves as a ‘weak link’: it has to blow before anything else in the system blows.  Most radiator caps on passenger cars are spring loaded:  When the pressure gets too high, the cap lifts off its seat, opening the system and allowing the hot water to escape into a reservoir.  As soon as the pressure is back down, the radiator cap goes back to being closed.

In a NASCAR car, the pop-off valves open and route the escaping steam and/or water through a tube that passes up near the right-hand side of the car’s windshield.  When you see a car “pushing water”, the maximum pressure has been exceeded and the pop-off valve opened.

For the last couple of years, most of the top NASCAR engine shops have focused on strengthening radiators.  It’s not difficult to get a pop-off valve set to 100 psi.  The problem is that if the pop-off valve isn’t the weak leak in the system, something else breaks.  It’s much more expensive to replace a radiator than a valve – so the size of the pop-off valve is really limited by the strength of the radiator.   A stronger radiator allows a higher pressure to be maintained.  Tim Brewer said that teams were pressurizing their systems to 80 psi (which would be 94.7 psi on my graph were it to extend to the right.)

Two-car drafting produces very high speeds, and that makes NASCAR nervous.  Cutting down the restrictor plate (which they did today) slows down the cars, but NASCAR doesn’t want to change the plate more that 1/64th of an inch or two because the change in plate size significantly affects how air enters the engine.  Teams have been designing engines around a particular plate size, although you would think that by now, they’d know to test not only the announced size, but plates one or two sizes up and down.

The limiting factor on how long two cars can stay in a draft is temperature.  The air intake of the trailing car is blocked when it is drafting, and the water temperature increases.  Two cars could go twenty laps or more before they had to separate.  NASCAR’s plan to limit the two-car draft started with a mandated pop-off valve.  NASCAR requires all teams to use a 33-psi pop-off valve, which corresponds to (33+14.7=47.7 psi) in my graph above.  All the work teams did to manage an 80 psi pressurized system is now out the window.  They also decreased the size of the opening through which air enters the car to cool the engine.  Less air reaching the radiator means less heat transferred from the water and a warmer engine.

Now if someone only could come up with a pop-off valve for drivers…

*****

EXTRA:  Wondering about the different between a tapered spacer and a restrictor plate?  Check out this video, which illustrates very visually how a fluid flows differently through an orifice (the plate) and a nozzle (the spacer).  They’re using both on the Nationwide cars now.  The way the air enters the engine really makes a difference in the combustion dynamics.  Making a smaller spacer would have created too big a perturbation.  The holes in the new space are actually larger, but the plate will help decrease the overall flow.

 Posted by diandra at 7:23 pm  Tagged with: , , , , ,

Why Two and Not Three Cars in a Draft?

 Aerodynamics, Daytona, Drag  13 Responses »
Feb 132011
 

The most talked-about feature of the racing at the ‘new’ Daytona is the two-car hookup.  Just in time for Valentine’s Day, drivers are finding that the term ‘drafting partner’ is more accurate than ever before.  Why two and not three-, four- and larger packs that used to be characteristic of Daytona?

Drafting 101

Anytime you move forward, you are working against something.  To walk through a swimming pool, you have to push  water molecules out of your way.  To drive through air, you have to push the air molecules out of the way.  The faster you go, the more air molecules you have to push out of the way in a given time.

Aerodynamic Forces on Cars

I’m going to focus on just the forces acting along the length of the car, ignoring sideforces.  The key to my drawings is that the length of the arrows and their color indicates speed.  Long green arrows indicate fast moving air, while red short arrows indicate slow moving, denser air.   Some air gets under the car, while most of it goes up and around.

We are interested in two primary features:  The front of the car acts like a wedge, pushing air out of the car’s way.  The air molecules resist this motion, creating a force that pushes in the direction opposite the car’s motion.  As the air passes over the car, it becomes turbulent at the back end, creating a partial vacuum at the rear of the car.  The physical phenomena at the front and the rear of the car are different, but they have the same effect:  they slow the car down.  We can get rid of the little arrows and just represent the force of the air as arrows pushing against the front of the car and pulling backward on the rear of the car.

If the two cars are far apart, each car experiences forces on the front and the rear of the car.  When they get close enough to each other, they appear as essentially a single object.  The trailing car is traveling in the aerodynamic shadow of the first car, so it doesn’t get the huge blast of air on its hood.  The trailing car prevents the air from getting as turbulent at the rear of the first car, so the force sucking back the first car is reduced.  (To learn more, or at least see much better drawings than mine, see the Science of SPEED video.)

Drafting 102

Every television program explains the very basic aspects of drafting, but we need to go a little deeper to understand what’s different now.

The most important change in the car has been the improved match up between the rear and front bumpers with the new car.  To get the maximum benefit from drafting, you really want the two objects to look like one, which means that they need to be as closely matched as possible.   Compare the  diagrams to the right.  In the top diagram, two different shaped objects will have turbulence between them because of the height difference.  (If the heights were reversed, there would be extra front drag.)

The second diagram shows two shapes that are the same size, but not very close to each other.  They are so far apart that both experience the front drag and the rear turbulence.

The lowest diagram shows two objects of the same size fit right up against each other.  The air travels over the two objects as if they were one.  The better the back end of the first car and the front end of the rear car fit, the more of an advantage you will get from drafting.  I apologize for my terribly drawing.  Graphics has never been one of my strong points.

With the old car, cars could usually add 5-10 mph by drafting.  We’re seeing much larger increases now – qualifying speeds are running 185 mph, while we’re seeing 205+ mph in the draft.  This tells me that the cars fit together aerodynamically significantly better than the old cars did.

Why the Two-Car Draft Works Better than Before

The new car was introduced in 2007 and although the splitter has changed, that’s likely not the big effect.  Drivers report that the repaving has really changed the character of the track.  It’s got more grip, but the biggest effect is probably the smoothness.  The key to good drafting is maintaining the relative positions of the two cars:  they have to be close.   Now the third dimension becomes important.  The figure at left is meant to be a top view of two cars driving to the right, so we’re looking at the path of air around the sides of the cars.

On the top figure, the two cars are in perfect alignment, so the air can flow past them smoothly.  If the trailing car stays the same distance behind the leading car, but slips slightly to the right, you’ve introduced edges.  The top part of the trailing car (in red) now is having to push air aside.  On the right sides of the cars, the misalignment of the trailing car means that there is a rear edge, and that means turbulence.

The old Daytona was bumpy.  Those bumps made the cars move up and down relative to each other (which would decrease drafting effects).  The bumpiness also made it harder for the drivers to control the cars, which made it more difficult to keep the cars aligned and close to each other.  The new, smoother track seems to allow the drivers to keep the cars tucked up.  The pull of the draft is so significant that we’re hearing drivers say that they have to ride the brakes.  This is mostly unheard of -usually, crew chiefs have to remind the drivers to pump the brakes before hitting pit road because the brakes get very cold since the only place they were used was on pit road.  Jaime McMurray had a brake rotor fail during practice and trashed his primary car when he blew a tire running over a piece of the broken rotor.  That’s a surprising thing to happen at Daytona.

Hot Engines

One piece of evidence supporting the hypothesis that the cars are staying together better is rising engine temperatures.  Air hitting the front of the car does produce drag; however, it also provides the air that goes into the car and cools the water in the radiator.  If you draft too long, the trailing car’s engine starts to overheat.  If you move to the side to try to expose the intake vents, you increase the drag and decrease the effectiveness of drafting.

One rumor is that NASCAR is going to require pop-off valves that would decrease the maximum temperatures the engines could reach.  (How that works is a separate article.)  This would decrease how long two cars could draft before they would have to separate or switch positions so that their engines didn’t overheat.

Why Two and Not Three

Go get three oranges from the kitchen.  Try to juggle two of them.  Not super easy, but not impossible.  Now juggle three.

The reason we’re seeing two-car drafts and not three is that it is very hard just to keep two cars in position with each other without hitting each other or overheating.  You’re asking the drivers to keep their minds focused on a lot of things, all while driving 200+ mph.

When two cars hook up, they take off.  A third car would have to be right there in position, ready to latch on. All three drivers would have to focus on keeping the pack together.  That’s far different than the old version of drafting, where becoming and staying part of the pack was easy… and fast.  It’s additionally complicated because the old version drafting didn’t require the trailing driver to use his brakes.  We’re seeing a lot more sudden drafting breakups as drivers realize they are overheating.  Do you want to try to get precisely positioned behind someone at 200 mph who is dragging his brakes?  The probability of getting two things to function together precisely is low.  Add a third and it becomes very, very difficult to do.

The Fix?

Speeds reached 206 mph during the Shootout, which makes aerodynamicists nervous because a sideways racecar going 200+ mph has a strong proclivity to unexpectedly start doing an airplane impersonation.  The usual head-first, tail-last position is just fine at high speeds – there is no reason that a stockcar can’t race at 230 mph or more; however, if the car gets turned sideways at that speed, it can become airborne, even when its roof flaps deploy.  There’s not a magic “take-off” speed below which it is safe because it’s a combination of the speed and the angle the car makes with the direction it is traveling.  We would be fine racing at 210 mph, provided that no one gets turned sideways.  The consequences are uncomfortably large if a car does get airborne. Everyone remembers what happened when Carl Edwards got airborne at Talladega and no one wants to take a chance on that happening next Sunday.  Most prognosticators are predicting that NASCAR will make a change after qualifying.

One quick fix (which has been used before) is to decrease the restrictor-plate size.  This probably isn’t practical because the change in size to compensate for the higher speeds would have to be larger than NASCAR would prefer to make.  The engines are tuned to work with a specific plate size, and changing the plate significantly could disproportionately affect one engine shop relative to others.  This change would address the speeds, but it wouldn’t do anything about having only two-car drafts, which seems to be a problem if you believe twitter to be a representative sample.

The fairly simple fix is to limit the time two cars can be hooked up by making it easier for the radiator to overheat.  If you force the radiator to start leaking steam at a lower temperature, the drivers can’t draft in pairs for as long as they can now.  This is pretty simple to implement and the primary consequence will be sleepless nights for the engine tuners.

Mother Nature will help as well:  the race will be during the day and temperatures will be higher, so there won’t be as much grip on the track.  That should slow down the speeds as well, but it won’t change the preference for two-car drafting.

Etc.

Did you catch what Craig Ferguson said about NASCAR drivers and their understanding of science on the Late, Late Show?  It’s in the first third of this clip.

 

 

 Posted by diandra at 12:50 pm
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