02 03 Pinewood Derby Stories and Photos from Maximum Velocity 04 05 15 16 19 20 21 22 23 24 25 26 27 28 31 32 33


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.

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:
- Five ounces with a one inch balance point
- standard wheelbase
- three wheels on ground, set to rail ride
- RA Racer Wheels (less aerodynamic drag than full width wheels
- Awana Speed Axles
- Krytox 100 Lube

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.


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.


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".

From Pinewood Derby Times Volume 10, Issue 11

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