The Wedge SE

The Wedge SE

Pinewood Derby Times
Volume 10, Issue 11
February 23, 2011

In this Edition:

- Editor's Notes

- Feature Article - Turbulators

- Humor

- Tip - Adding Brakes to Your Car

- Product Showcase - Free Decal Pack

- Car Showcase

- Q&A


Editor's Notes

Duplicolor Paint Formulation
Many times I have recommended to our readers that they avoid "enamel" paints. This type of paint takes a long time to cure (many days), and thus contributes to graphite fingerprints and paint on wheels. Instead, I recommend "acrylic lacquer" paints. This type of paint dries quickly (hours) and has a nice hard finish.

"Duplicolor" is a paint brand that I have often recommended as an acrylic lacquer paint. It can be found at most auto parts stores. However, Duplicolor has rebranded their products and has introduced an enamel product line. So, when buying Duplicolor you must be careful in your selection. According to Duplicolor, cans labeled as "Perfect Match" contain an acrylic lacquer formulation. Duplicolor also offers another family of acrylic lacquer paints that are identified as such on the label. The bottom line is when shopping for Duplicolor paint (or any brand for that matter), it pays to read the label.

Maximum Velocity Car Kits
If you are planning a race and are not required to use a specific kit type, our MV Basic Car Kit is just what you need. These attractively priced kits are equipped with:
  • Quality Block - Unlike the blocks provided by some organizations, our blocks are soft, northwestern pine blocks, cut precisely to 7 inches long, 1-3/4 inches wide, and 1-1/4 inches tall. These dimensions, as well as the axle slots accurately duplicate the dimensions of standard pinewood derby blocks from BSA and PineCar.

  • Simple Axle Preparation - Don't worry about filing off flaws, or losing hub caps. Our Speed Axles have no burrs or crimp marks, and install without hub caps. With or without polishing, they are ready to go. We supply five, so you have a spare.

  • Quality Wheels - Forget cheap, out of round wheels. We supply top- quality wheels to give great performance.

So, if your organization does not mandate a particular kit type, consider our Maximum Velocity Car Kits
Can We Help?
If we can help you in any way with your pinewood derby project, or if you have any feedback regarding this newsletter, please contact us at: info@maximum-velocity.com


Feature Article
Turbulators

When I first got involved in pinewood derby racing, I bought every speed tip booklet on the market (not very many at the time). One of the booklets I bought, "What Every Parent Should Know about Pinewood Derby Cars and More" by Thad Marvin, stood out because of its focus on aerodynamics (and its trivial treatment of other factors such as lubrication and weighting. Even though I was somewhat inexperienced, I was skeptical that aerodynamics was truly that significant.

One of the techniques touted in the booklet to improve aerodynamics was the implementation of turbulators. Probably like most of you, the word turbulator sounded like a made-up word to me. But I looked it up, and in a dictionary of technical terms, a turbulator is a device for improving air flow over a surface.

As air flows over a surface (such as an aircraft wing or propeller), the air wants to stick to the surface. As it leaves the rear of the wing, the air becomes turbulent, creating drag. However, if the air can be made turbulent before it reaches the rear of the wing, the drag is greatly reduced. So a ridge (a turbulator) is added to the wing to break up the airflow, creating turbulence before the rear of the wing. A similar concept is used on golf balls (the dimples).


Turbulator on a Model Helicopter Rotor
Source: www.rcgroups.com
(Note the ridge above the warning sticker)

Generally, turbulators are used where air speeds are high, and weight is low, such as on a glider wing or a propeller. So, given the lower speeds of a pinewood derby car, it seems questionable that tailing turbulence is strong enough to affect the speed of the car. But let's find out.

Experiment Setup
Instead of using a strip like on the helicopter rotor, I used the technique described in Thad Marvin's booklet. The turbulators are implemented as a row of pins along the high point of the car.



Turbulator Pins

I used a more traditional car-shaped body, as it would likely have more aerodynamic drag than a flat design. So, if turbulators help, they should provide more benefit on a fully bodied design than on a thin design.

The cars features were:
Ten heats were run with the turbulators. The pins were then pulled, and (to compensate for the weight of the pin) 0.015 ounces of weight were put into the underbody pocket (at the same relative location as the pins). Ten more heats were then run.

Experiment Results
With the turbulators, the car ran a 2.503 average time with a standard deviation of .003. Without the turbulators, the car ran 2.504 with a standard deviation of .002. The one thousandth second difference is less than the standard deviation, so it is not significant. The test was re-ran with a similar result.

Conclusion
Aerodynamics is a factor in pinewood derby racing, but it is a lesser factor. So make sure to take care of the "big ticket" items such as lubrication, weighting, wheel and axle prep, and alignment. Then minimize the aerodynamic affect, not by turbulators, but by building a low-profile car.(1)

(1) For more information on Aerodynamics, see:
Volume 3 Issue 9, "The Big Debates - Aerodynamics", and
Volume 5, Issue 9, "Wind Tunnel Testing".




Humor

A young executive is working late one evening. As he comes out of his office about 8 PM he sees the Big Boss standing by the shredder in the hallway, a piece of paper in his hand.

"Do you know how to work this thing?" the older man asks."My secretary's gone home and I don't know how to run it."

"Yes, sir," says the young executive, who turns on the machine, takes the paper from the other man, and feeds it in.

"Now," says his boss, "I just need the one copy."




Speed Tip
Adding Brakes to Your Car
by Peter Holzemer


You can't win no matter how fast your car is if it gets damaged at the stop section of the track. Our district track is a forty foot wood track with a three foot raised stop section terminated by a foam rubber stop bar across the end of the track. Unfortunately, the fastest cars slide through the stop section hitting the foam stop bar relatively hard. These fast cars either flip over the bar onto the hard floor, or hit the foam so hard that they bounce backwards through the stop section onto the track. Sometimes, the bounced cars collide with other slower moving cars, causing damage to all involved.

In our second year of racing, my son's car was the fastest in the first heat. His car slid through the stop section, hit the stop bar, and flipped onto the floor, bending a rear axle. Not realizing that the axle was bent we kept on racing and winning, only to have the car slow down in the finals. My son was fortunate enough to place third overall, but the other top cars were not so fortunate. Those cars also received damage from the foam stop bar, but ended up losing their top spots. After that experience, we decided a change was needed - brakes for the car.

The brake system is very simple, just two small strips of 80 grit black drywall sandpaper glued to the bottom of the car in front of and behind the rear axle. This sandpaper causes the car to slow down quickly when it reaches the raised stop section. The deceleration is enough to keep the cars from bouncing on the stop bar. Now, we add brakes to all our pack cars going to the district race. At this past year's event, none of our pack cars had a crash.




Product Showcase

Sampler Pack of Jackal Decals: Free with Shippable Order
Jackal Decals
Click Here for a Larger Photo
Jackal Decals
Click Here for a Larger Photo<

We think that Jackal Decals are a great way to enhance your pinewood derby car. To introduce you to these great decals, we have created a sampler pack of five decals.

Through March 8, 2011, you can add one of these Jackal Sampler Packs to your order at no charge. To take advantage of this limited time offer, Click Here.




Car Showcase

Some cars using our Tungsten Canopy.

Tungsten On Wood - Glen Stowers

I came into your store to buy a tungsten canopy and some tungsten putty in late May. As an adult, I was preparing for my first pinewood derby race in 30 years. I had looked forward to this for over a decade ... running designs around in my mind and making sketches of what I thought would work best. I entered a stock derby competition with a weight limit of 5.5 oz with a car I specifically designed for use with your tungsten weight products. The rest of the car was built from a stock BSA pinewood derby kit, from which I was allowed to modify the wheels. Not only did I win the speed competition, I also won the "Best Paint" category with my stained wood finish. I call it "Tungsten On Wood!" or "WOW!"

Not only did I beat every derby car in the stock category, I took my car over to the pro stock track and had an informal race with the fastest cars of the night (all gravity driven). The winning pro stock car was owned by a man who said his car had never been beaten in a single heat in years of racing. We raced twice... I beat him twice!

Purple Haze - David Keith

I helped a friend's son (Christian) design and build this car that bested 200 cars last Friday and Saturday. He also won his individual pack on Thursday. He was so excited! Thanks for all you do. Our cars would be nothing if it wasn't for your expertise and help.

Blue Racer - Terry Duke

While buying supplies through Maximum Velocity for our second year of building Pinewood Derby cars, my son and I ran across the new "Vaccinator" kit. We both thought it looked pretty cool, and from what we learned of speed tips last year, we also thought it looked fast, so we chose to use that as a model for our design this year.

Since we've only been building PWD cars for two years, we don't have the tools or experience to completely mimic the Vaccinator, but we chose to follow the principals of making it thin, carving the sides around the front wheels, and using Tungsten for our first time.

The only weight on the vehicle is the Tungsten Canopy. After using lead last year, the switch to tungsten was immediately obvious and significant design improvement. We had a lot of fun building our cars, and Maximum Velocity has been a huge help providing our tools, designs, and weights to improve our competitive abilities and improve our father/son experience.

Blue Light Special - Ron

Here is our winning car: stock axle spacing, stock axles - polished of course - stock BSA wheels, a Tungsten Canopy mounted sideways to maximize the center of mass at approximately 9/10 of an inch in front of the rear axle. The car won 12 out of 12 races so we are off to districts.


Share your car with our readers!
Do you have a car you would like to 'show off' to our readers? If so, send us a photo of your car along with a brief description of any special features. Also, please include your full name. If selected, we will include the photo and description in this newsletter.Please e-mail photos to:
info@maximum-velocity.com.

Photos must be sent by e-mail in JPG format (minimum size of 640x480, maximum size of 1280 x 960). Please shoot photos from the front left of the car, similar to the orientation of this car:



Send only one photo per car, unless an additional photo is needed to adequately show a feature. Also, only one car per subscriber per year please. Thanks!



Q&A

What is the difference in the standard wheelbase and the extended wheelbase? Is one faster? Is the extended wheelbase legal?

An extended wheelbase car has the axles mounted as far forward and backward as possible. This allows the added weight to be placed further back on the car, and also tends to allow the car to go straighter. Click Here for a wheelbase comparison.

Generally, extended wheelbase cars are faster than standard wheelbase cars.

Many groups allow extended wheelbase cars, while others do not. So, certainly check your local rules for whether they are legal.

I am not sure that I drilled my holes deep enough. Do you recommend re-drilling or should I just hammer/press the axles in the rest of the way? Can you please suggest the best method for installing the axles in the holes to ensure they go in straight?

Drill the holes deep enough so that you do not pound them in. Generally, 3/4 of an inch in depth is plenty.

Then, press the axle into the hole as far as you can with your fingers. Then put the axle head on our Axle Install Support tool. Hold onto the car and press down with a slow but steady pressure. Make sure to use a gap gauge to set the wheel to car body spacing.

Wheels that are turned on the outside have a smaller circumference. So a car with a larger diameter wheels will go farther per revolution than a car with smaller diameter wheels - correct?

True, a smaller wheel will have to spin more times over the same course. So, the tradeoff is between accuracy and RPM. A trued wheel has to spin a little faster. But generally it is better to have a true wheel than an out of round wheel (which will start, and spin slower).

Comparing a raw wheel (1.185) and a wheel trued to 1.170, the difference in revolutions over a 28 foot run is about 1.2 (91.4 for a raw wheel, 90.2 for a trued wheel). So the trued wheel has to spin just a tiny bit faster. Since the wheel is true, it can easily spin faster.


Do You Have Questions that Need Answers?
Do you have a pinewood derby-related question? If so, send your question to: info@maximum-velocity.com. We answer all questions by e-mail, but not every question will appear in the Q&A section of the newsletter.



Back Issues

Are you a new subscriber, or have you missed some of the previous newsletters? Don't miss out! All of the issues for Volume 5 through Volume 10 are posted on our web site and can be found using our Newsletter Index.

Issues from Volumes 1 to 4 are available in four formatted documents, ready for immediate download. To find out more, Click Here.





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Randy Davis, Editor, Pinewood Derby Times
E-Mail: info@maximum-velocity.com


Copyright ©2010, Randy Davis. All rights reserved. Please do not reprint or place this newsletter on your web site without explicit permission. However, if you like this newsletter we grant permission, and encourage you to e-mail it to a friend.

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