TFE blog

A Thousand Faster Thinkers

Posted by on Nov 2, 2012 in Current projects and Tech Notes | Comments Off on A Thousand Faster Thinkers

A Thousand Faster Thinkers

Think Fast – The Racer’s Why-To Guide to Winning achieved a major milestone today: One thousand books delivered! A thousand thanks to each of you who bought a copy.

I certainly wasn’t expecting this, but the feedback about Think Fast has been absolutely 100% positive. I have been honored and flattered by your comments about the book, and I hope to continue learning from them as well.

The content in Think Fast must be fairly solid if it has stood up to the scrutiny of so many racers. Also, I must have gone to print with it at the right time since I have only thought of one detail that I should have included. It’s an important safety related detail, so here it is:

Your brake bias bar clevises should have flats on one side that will contact the sides of the brake pedal when the bias bar rotates more than about 15°. That will keep one brake circuit functioning if the other one fails. This requirement is in most rule books, but many of the bias bar assemblies that I see don’t look like they would be very effective if one circuit fails.

I had several goals in mind when I wrote Think Fast:

  • Share what I have learned about race car engineering and driving at every level from autocross to the Indy 500
  • Show readers what to focus on and what to skimp on so that they can afford to do what it takes to run with the lead pack
  • Share the guidance that I have provided to a handful of Formula SAE teams with a wider audience
  • Inspire at least one racer to pursue a career in race car engineering, and to teach that person some of the specialized details that they will need on the job
  • Describe what it takes to create and implement a successful team-effort program in any field of endeavor, using the fundamental principles that racing teaches every competitor
  • Open new doors for myself as a motorsports engineer and racing mentor

As far as I know, every one of those goals has been met in spectacular fashion. Are you the one person that I inspired? If you are, I would be delighted to learn about your adventure.

If you would like to learn more about Think Fast, and perhaps order a copy for yourself, here is the place to go:

http://thinkfastbook.com/

Tripod Clocking

Posted by on Oct 6, 2012 in Current projects and Tech Notes | Comments Off on Tripod Clocking

Tripod Clocking

I’m a huge fan of tripod joints for high power applications. Tripods are one of the two common joint designs used on the ends of the halfshafts that connect the transmission to the drive wheels of a car with independent suspension. The other common joint type is a CV, or constant velocity joint. The reasons that I like tripods over CVs are that they are more efficient than CVs up to a joint angle of 8°, their service life in high-power applications is vastly greater, and they don’t need an exotic and annoying grease like Krytox in high power applications. Krytox is an amazing grease, but the only effective solvent for it is freon. Freon is not exactly a practical solvent. At Hall Racing, we went from having to do CV maintenance every day at the superspeedways to half-season inspection intervals with tripod joints. That made a giant difference in maintenance workload on the team.

When you are assembling tripod joints onto a halfshaft, you are faced with a choice. Since the coupling between the tripod and halfshaft is a spline, you can clock each tripod joint to any angle that the splines will line up. Should you align the two tripod joints on each halfshaft with each other, stagger them 60° apart, or just plug them on at a random angle?

Halfshaft assembly with aligned tripod clocking

 

Halfshaft assembly with 60° staggered tripod clocking

As it turns out, it does matter how the joints are clocked relative to each other, and that clocking depends on the driveline geometry and suspension alignment of your car. So, there is no one-size-fits-all answer to this question.

Many years ago, I performed a kinematic analysis of a tripod joint to find out what makes them tick, and if there were any oddities in the way they work. I learned some interesting things from that investigation:

  • A tripod joint produces an exact 1:1 drive ratio all the way around, regardless of joint angle, so it is a true constant velocity joint.
  • When the joint angle is not zero, the center of the tripod joint is offset from the housing axis. The joint center displacement increases with the joint angle.
  • As the car moves down the track, the tripod center precesses in a circle around the housing axis at an average of 3 times the shaft speed. I call that an average speed because it accelerates slightly for 30°, then decelerates slightly through the next 30°, and so on.

The fact that the joint center is offset when there is a non-zero joint angle is a source of vibration. That vibration can be minimized by clocking the two joints on each halfshaft optimally. The optimal clocking will offset the two ends of the halfshaft in opposite directions, so that they will precess out of phase with each other, and the center of gravity of the halfshaft assembly won’t move much.

If the tripod clocking results in the two joint ends being offset in the same direction, it can produce a vibration that is severe enough to halt a test day at a high speed track. This happened to us at Hall Racing in 1994 at the Phoenix International Raceway mile oval. That was our first oval track test day with the new Reynard 94I, which was our first Indycar with tripod joints on the halfshafts. That’s the day that we discovered that on oval tracks, the tripod clocking had to be different on the left and right sides of the car, because the right side had negative camber and the left side had positive camber.

Here is the way to clock your tripod joints optimally:

If the two tripod joint angles on a halfshaft are in the same direction, then the tripod clocking should be staggered 60° in order to offset the two joint centers out of phase with each other. An example of driveline geometry that produces both joint angles in the same direction is a car with the diff center slightly below the axle center, negative camber, and a small or zero fore-aft offset between the axle center and the diff center. Here is a rear view illustration of that driveline geometry:

Driveline geometry with both halfshaft angles in the same direction

If the two tripod joint angles on a halfshaft are opposite to each other, then the tripod joint clocking should be aligned. That will offset the two joint centers out of phase with each other in order to minimize the movement of the CG of the assembly for minimum vibration. An example of driveline geometry that produces opposite joint angles is a car with the diff center above the axle center and negative camber. Another example is a car with a large fore-aft offset between the diff and the axle center. Still another example is a car with the diff center a long way below the axle center. Here is a rear view illustration of that:

Driveline geometry with opposite tripod joint angle directions

So, now you know how to clock your tripod joints when assembling them.  I’ll bet that you didn’t think you would learn that today, did you?

Crude Tactics

Posted by on Oct 3, 2012 in Current projects and Tech Notes | Comments Off on Crude Tactics

Crude Tactics

My second article for NASA‘s Speed News online magazine enabled me to score several points in one go. While you are reading the October 2012 issue, pay special attention to page 82. This was an opportunity to highlight Lee Sicilio’s Bonneville land speed racing program in the process of describing what oil dot flow visualization can do for you. It was a big hit all around. It’s an opportunity for you to learn a lot in the process of making a mess. Enjoy!

Big win for Scratcher

Posted by on Sep 25, 2012 in Current projects and Tech Notes | Comments Off on Big win for Scratcher

Big win for Scratcher

Paul Costas is making the most of the “Think Fast” approach to racing. He unearthed a partially completed GT-1 Camaro project and bought it for pennies on the dollar, completed it in a very cost-effective manner, spent real money only on hardware that offered a near-certain performance payoff, and modified and developed the car in a very logical process. He has created a very inexpensive but scary-fast dominant track day car in the process. Early on, the bodywork of the car seemed to have a mind of its own, which resulted in some injuries and the car’s name: Scratcher. The best part of this car is the fact that it has a passenger seat, so he can share the thrills.

His latest escapade included stomping the Time Trial Unlimited class by big margins both days at the North American Road Racing Association competition at Texas World Speedway. Major congrats to Paul and the team who helped with this most excellent achievement! The team members are Nicholas Valentin, Ron Miller, Gary Robertson, Anna Comigore Costas, Louis Gigliotti, and Yours Truly. Paul regularly returns the favor for me by guiding me in the right direction as the Witchdoctor of Strategery for ThinkFast Engineering.

It’s a “WE” deal

Posted by on Aug 20, 2012 in Current projects and Tech Notes, ThinkFast Engineering | 9 comments

It’s a “WE” deal

Lee Sicilio’s outlook on racing is “This is a WE deal, not a ME deal”. He is eager to grant the credit for his spectacular successes to the major contributors who helped him get there. This approach is both commendably noble and very smart. The key team members that he has attracted with this approach are quite possibly the best in the sport, and their loyalty is absolutely the best in the sport. Spectacularly stunning is not adequate to describe just how good these guys are.

I wish that I could show you every detail of the design and build quality that Ryan Fain put into “Twilight Zone”, which is Lee’s newly constructed land speed racing car. The sheet metal is 100% original steel from a 1969 Dodge Charger, with an aftermarket Daytona nose and rear wing that are faithful to the original parts. That’s the end of the original content. Everything inside that classic skin is pure Ryan Fain brilliance. Ryan is a genuine artist whose medium is high speed steel. From his base at Brink Racecraft in Irving, TX, the chassis, suspension, and everything else inside Twilight Zone was designed and built by Ryan with unbelievable quality. For example, Ryan fabricated the hood scoop entirely by hand, in steel. The car was built to the Blown Altered Coupe rules established by the Southern California Timing Association. Here’s a quick photo of Ryan through the windows:

Ryan through the car

 

Twilight Zone at the Bonneville starting line

Lee has set numerous Bonneville class records in another ’69 Charger Daytona, and his new one was built to a higher-performing, more ambitious rule set with significantly more speed potential. Lee is the kind of guy who is so dedicated to land speed racing that he has the logo signifying his membership in the Bonneville 200 mph club tattooed on his arm. The primary purpose of the new car is to carry him to membership in the 300 mph chapter, no doubt to be followed by that “3 Club” tattoo on the other arm.

Lee Sicilio in his office

Randy Hughes is the team Crew Chief, making it all happen. He’s also the paint and body artist, so the smooth shine is all his. The highly competent but low stress environment within the team is a credit to his leadership style. The fact that everything that was needed was right where it should be, and everything that was in the trailer had a good reason to be there, shows how organized he is.

The other side of Scott Clark

Scott Clark is the team’s engine tuner / electronics engineer / data acquisition system developer / performance analyst, and boy does he ever know a lot about what’s going on! I didn’t get a photo of his face, but this angle displays his attitude and enjoyment of the festivities just as well. He is an absolute jewel, so I don’t want to make him too famous! The depth of his knowledge of the inner workings of ultra-high performance automotive engines is unmatched by anyone else I have ever met.

Ray and David Barton developed the twin-turbo 498 ci Mopar Elephant motor that ran like a clock the whole time. This engine was one of many monster-power engines they have created over the years for a multitude of champions.

It says a lot that Twilight Zone has no sponsor logos, only credits for the key team members. Although my name is on the trunk lid, my contribution was miniscule compared to everyone else’s.

A trunk lid covered with team member credits

So how did the first outing of this brand new car go? The class record for A/BGALT was 257.201 mph. Here are the time slips for the first two full-length passes that the car ever ran:

Record-breaking time slips

The team took a very cautious, incremental approach to testing the performance limits of the car, and because the car is so new, neither of those runs were anywhere near the full potential of the car. For example, the 267 mph pass was done at less than 3/4 throttle all the way down the track, and Lee didn’t even use 5th gear! There is a LOT of speed left in the car as it sits, and a lot of development remaining to be done. Despite that, the average of those two runs produced a new class record of 273.514 mph, besting the previous record by 16.313 mph.

Congratulations to the whole team for a spectacularly successful first outing! It’s a very good feeling to know that there is a lot more easy speed to be had, and that the car is rock-solid stable at speeds beyond the limit of nearly everything else on the planet.

Prepper for Salt

Posted by on Aug 8, 2012 in Current projects and Tech Notes | Comments Off on Prepper for Salt

Prepper for Salt

I’ve done Indy and Oshkosh as an on-the-job engineer, and I still want to do Bonneville and Reno. Well, next week I’ll get my first taste of the salt at the Bonneville Speed Week event! I’m excited about that as I ever get about anything.

In addition to supporting a ThinkFast Engineering customer, I will also be marketing TFE to competitors who are searching for aero performance, aero stability, or both. Here is the flyer that I will leave with prospective customers:

 Wish me luck!

Weight Matters

Posted by on Aug 8, 2012 in Current projects and Tech Notes | Comments Off on Weight Matters

Weight Matters

If you are in the mood to learn how to make your own setup pad on a thin budget, and to learn some of the many things that you can do with it, here is an article I wrote for NASA’s excellent new e-zine called Speed News:

http://www.snmagcurrent.com/publication/?i=120245

Flip forward to page 54 and dig in, then read through it all for a great look into the world of the National Auto Sport Association. I’m honored to have the opportunity to write for Speed News, and this article will hopefully be the first of many. Enjoy!

Solo Heat

Posted by on Aug 6, 2012 in Current projects and Tech Notes, RB6 Formula Ford | 2 comments

Solo Heat

When a tire is slipping on the pavement as a result of hard cornering, braking, or accelerating, that slipping heats the tread rubber. A tire generates the most grip when that heating is uniform across the width of the tread because every point on the tread generates the same force on the ground. That heating is a good thing because racing tread rubber generates the most grip at a temperature that is higher than ambient. Of course there can be too much of a good thing, too. Autocross tires are designed to perform best at a lower temperature than track racing tires because an autocross run is over before a pace lap is halfway around the track.

The common method of measuring tire temperature is a needle probe pyrometer that is stuck into the tread as soon as the car stops. Normally, 3 temperature measurements are taken on each tire: inside, middle, and outside. Comparing the three temperatures across a tire provides guidance for optimizing tire pressure and camber settings, and comparing temperatures from front to rear is an indication of cornering balance. The upsides of a tire pyrometer are that it’s relatively inexpensive and easy to use. The downsides are that tire temperatures change rapidly, the measurements only reflect the time-weighted average conditions over the most recent segment of the track, and the temps can only be measured after the car is stopped in a safe place.

Of course there is a fancier way to measure tire temps: a series of non-contact infrared temperature sensors mounted on the car, with the sensor outputs recorded by a data logger. The upside of this technique is near-continuous, real time measurement of the tread surface temperature. That’s what matters the most, and it’s what the photo above shows. Freddie has one front and one rear tire instrumented with 3 sensors across each tire tread. The sensors are fastened to a square steel tube mount that is bolted to the upright, so steering and suspension travel don’t affect the relative positions of the sensors and wheel. The mounts are symmetric, so they can go on either side of the car. They are on the left front and left rear at the moment. Now we get to find out what’s really going on!

If you plan to use these sensors, here are a couple of notes: 1) The field of view is quite a bit larger than the data sheet shows. My first autocross with the sensors on 2 weeks ago resulted in bad data because the holes in the mount were sized to clear the advertised cone angle, but part of what the sensor saw was the mount. 2) The internal processor in the sensor only updates the output signal at about 3 Hz, so even though the logging rate was 100 Hz, the data has large stair steps. Of course the signal updates among the sensors are not synchronized, so the data for each sensor steps up or down independently of the timing of the other sensors.

This weekend, I ran another autocross at El Toro with much larger holes in the mounts, and got good data. There are a lot of real surprises in the data, and we all get to see them.

But first, here’s a look at the course that was generated by logged GPS data:

Here’s the video. The cross is at the start line and the map is color coded with speed. My maximum speed was 66 mph and minimum was 29 mph. The run time was 57.296 sec. Since there were more long left hand corners, the sensors would have provided more valuable data if they were mounted on the right side, but there was no way to know that before hand. I don’t have all four tires instrumented because each sensor plus wiring harness extension costs $220.

While I’m in the process of re-learning my driving skills, I’m running used Hoosier R35A compound road racing tires, so my maximum cornering acceleration was only 1.4 g. That’s because the tires weren’t up to their operating temperature for road course running. I’ve seen 1.9 g on flat road course pavement on hot R35As. Others have reported similar grip while autocrossing on R25Bs. When it makes sense, I’ll buy a set of Hoosier R25B compound autocross tires.

A really interesting thing I saw in the temp data was on the way to the start line for my first run:

Sunny/shady tire temps

The sunny side of each tire was 30°F warmer than the shady side. Now take a look at the data in the shut down area after my first run:

Sun/shade post run

5° of that solar heating was still there after the run! I predict that I have just started a new fashion trend in the grid, so I’ll name it: the Solar Roll.

Here are the 3 front tire temp sensors and lateral acceleration from my best run:

Front Temps Run 3

Color codes: Yellow = Inside front, Gold = Middle front, Red = Outside front, Gray = Lateral acceleration, right turn is positive.

The middle of the tire was only 70°F hotter at the end of the run that at the start, and it only warmed up that much because of the long braking zone and the long right hander at the end. For this run, the static camber was -0.5° and the pre-run pressure was 16.5 psi. If the pressure were set optimally, the middle temperature would be right between the inside and outside temps while cornering to the right. Since it’s higher than that average, the optimum pressure is lower than 16.5. How much lower? More runs at lower pressures will answer that question. If the camber were set optimally, the inside and outside temps would be the same. Since the outside temp was lower, I have too much negative camber. That’s a surprise since I’m only running -0.5°. So, I’ll run less negative camber next time, and I’ll keep adjusting camber and pressure until the three temps across each tire are the same while cornering with the sensors on the outside tires.

It’s interesting that the inside front tire either does nothing or gets cooler while cornering. In this case, the left front tire is the inside tire while turning left, which is negative on the graph above. That’s an indication of how lightly it’s loaded due to weight transfer. From this, it’s easy to conclude that the primary influence of the inside front tire is to tune the loads on the other tires, and it doesn’t contribute much if anything to cornering grip. I believe that this is why Ackermann steering is such a numb adjustment on cars that don’t produce massive aero downforce. It takes a huge change in Ackermann to produce a noticeable difference on most cars.

Here is the front tire temp data again, with longitudinal acceleration shown in green:

Front temps and Longitudinal Acceleration

The front inside and middle temps responded to braking at 81°F per second! Those rapid spikes were a result of near-locked brakes. The front outside temp didn’t follow suit unless the car was also turning right while braking. That’s another indication that Freddie has too much static negative camber.

I locked the left front a couple of times during earlier runs, and the front temps instantly shot past the 300°F measurement range of the sensor. I have seen data from other cars that showed the same result due to massive wheelspin.

The rear tire temps were very similar to the fronts in most respects:

Rear Tire Temps and Lateral Acceleration

Color codes: Light blue = Inside rear, Medium blue = Middle rear, Dark blue = Outside rear, Gray = Lateral acceleration, right turn is positive

For this run, the rear static camber was -0.5° and the pre-run pressure was 18.5 psi. Again, the data shows that Freddie had a bit too much negative camber and a lot too much tire pressure. More experimentation is in order here!

That’s OK by me, because my policy is to never run exactly the same setup twice: Every time the car comes to a stop, I change one thing, sometimes two or more if they are in unrelated areas. That makes every run or outing a development opportunity. Also, during every road course outing, I will adjust at least one bar and the brake bias while under way.

It’s interesting that the rear inside temp didn’t respond to left turns at all. It would seem that the primary influence of the inside rear tire is very similar to that of the inside front, but with the additional burden of resisting acceleration wheelspin since FF rules require an open differential.

Again, here are the rear temps with longitudinal acceleration shown in green:

Rear Tire Temps and Longitudinal Acceleration

Aside from a very small wheelspin spike at the start, the rear temps didn’t respond strongly to longitudinal acceleration or braking. It makes sense that the wheelspin spike went away very quickly since the surface heat was soaked up radially through the thickness of the tread rubber, which was much cooler.

Because the front temps did respond to braking and there was no evidence of a locked rear tire, the brake bias was front-heavy.

Comparing front to rear temps shows a happy story:

Front to Rear Tire Temp Comparison

Since the temps stayed nearly the same through the full run with the exception of the hard braking zones, the cornering balance of the car looked reasonably close to balanced. It felt loose in steady state cornering, which could be real or it could be a false perception on my part.

Just for your amusement, here is what the tire temps looked like during a spin:

Tire Temps During a Spin

Ummm, yes I meant to do that, just for your education. See how generous I am?

Despite that spin, I’m happy to report that my driving skill has advanced to the level of basic competence, meaning that I’m not horribly embarrassed and completely disgusted with myself every time I get out of the car. I managed to drive two runs that weren’t complete disasters, and I had fun doing it. There is a very long way to go before I’m competitive again, but I finally have a reasonable baseline to build on.

Update: More data! This is a graph of front middle temperature versus lateral acceleration. The outer bounds of lateral acceleration show a clear trend of increasing grip with increasing temperature. That’s not a surprise at all since the R35A compound is intended for road racing. An autocross run doesn’t last long enough to get the tire up into its designed operating temperature range.

Here is longitudinal acceleration vs front middle temp. Because there was only one straight-line braking zone, there isn’t enough data to show a clear trend.

Production

Posted by on Jul 19, 2012 in Current projects and Tech Notes | Comments Off on Production

Production

I admire quiet brilliance. It is what I strive to produce as the end result of every project.

While pondering my fundamental motivations for doing the things that I enjoy, I remembered a great example of this ideal result. Its brilliance appears effortless. It could be truly effortless, or it could be the result of an infinitely diligent effort that turned a common rock into a flawless gem. Either way, the end result is so powerful that its excellence is self evident. Take a couple of minutes to enjoy this, then come back.

It’s my favorite moment from Fiddler on the Roof. That may seem to be an odd example of an ideal result for a motorsports-oriented blog, but I think it’s a great one because it’s a perfect example of quiet brilliance. While there are many ideal results of racing projects that I could point to, it’s usually very difficult to notice that excellence through the fog of confetti and champagne spray.

ThinkFast Engineering is in business to provide the foundation of victory for other racers. Auto racing is a highly technical sport compared to most, so it takes a deep knowledge base and innovative approaches to problem solving to earn your way to the top step of the podium. It is entirely understandable that most racers don’t want to become their own engineers in order to achieve success on the track. That explains the popularity of spec car racing. It also provides a market for services like TFE to provide the technical expertise necessary to achieve success in open-development racing venues. While it’s not too difficult to learn enough about race cars to campaign one very effectively, racing is one of the fields of endeavor where there is no such thing as good enough. Every single aspect of your entire racing enterprise can and should be improved every day. If there is a better way to do something, go for it starting right now. Contacting TFE is a great start, and we will work together to produce the results you want.

Inhaling coolness

Posted by on Jul 6, 2012 in Current projects and Tech Notes | 1 comment

Inhaling coolness

The power that an engine produces varies with the temperature and pressure of the air going in. Lower temperature and higher pressure result in more power. The pressure increase from a ram air intake hardly makes any difference in power output below 150 mph or so, and the drag that it creates wipes out some of the power gain unless it is located and shaped really well. That leaves temperature and the pressure drop through the air filter as the two things that are worth doing something about.

The AIM EVO4 data logger in Freddie records the inlet air temp sensor output and the data logger internal temperature. The logger is located low in the car, forward of the dash bulkhead. Because it is in the shade, the data logger temp is a reasonable substitute for ambient air temp. I ran the March driver school without any ducting to the air filter because of time constraints, so the engine mostly inhaled air that had been heated by the radiator. Like that, the inlet air temp stabilized at 42°F above ambient. That cost me about 7.2% of the power that the engine could produce if it were breathing in ambient air. That’s a big loss! Fortunately, the school wasn’t about going fast.

I calculated that power loss by simplifying the math to: Power is proportional to absolute air temperature. Air temp in degrees Fahrenheit + 460 = absolute air temperature.

For the Buttonwillow race in May, I installed a nicely made fiberglass inlet duct from Motorsports Composites that connected the inlet in the roll hoop fairing to the air filter. My fairing is distorted at the bottom of the inlet opening, so there is a 1/4″ gap that allowed some of the heated air from the radiator to get inside the duct. Like that, the inlet air temp was 6°F above ambient. So, the duct was a huge improvement, but there was still a 1.1% power loss due to that temperature increase.

For the Fontana race in June, I covered the inlet duct with an absurdly thin gold mylar insulation film and taped the duct to the roll hoop fairing with yellow racer tape. The tape sealed the gap, so there was no more leakage from the engine bay into the inlet duct. Like that, the data showed that the inlet air temp and the ambient air temp were the same. Victory! It doesn’t get any better than that. So, tape those gaps!