July
6, 1998 Design News
Letters to the Editor
Readers state their views
Reverse drafting has its advantages
In the 4/20/98 issue of Design News, the news
article titled, "Being tailgated: not such a drag,
after all" made me chuckle. I find it amusing that
the researchers from USC must have never watched a NASCAR
race to see that the "good-ole boys" from
Down South had beaten them to the punch in discovering
the advantages of drafting.
Sometimes real-world testing/experience can be more
fruitful than academic study.
James R. Evans Jr.
Senior Software Engineer
Hypercom Inc.
Phoenix, AZ
You mean the guys at USC didn't know what any NASCAR
driver, pit crew, or fan has known for at least 35 years:
"drafting" makes both cars go faster? Incredible!
Let professor Dale Earnhart teach them NASCAR 101!
After all, this is a lot more fun than driving around
some old dusty lakebed.
J. Durham
I just finished reading Karen Auguston Field's article
with great interest. It reports on research that verifies
what NASCAR Winston Cup and Grand National racing teams
have known and practiced for many years.
In racing, the car in front "gets a push"
from the closely trailing car. This has the effect of
increasing speed and fuel mileage for the leading car.
Many teams regularly use this principle when team members
help each other gather momentum to pass a competitor.
This "reverse-drafting" effect is most usable
on the super-speedway tracks, where direction changes
are very gradual and speeds are nearly 200 mph even
in the turns.
Jim Hodson
Lockheed Martin Astronautics
USC responds:
Several letters took myself and student researchers
at USC to task for not realizing that the common occurrence
of "drafting"--as practiced for years by the
"good-ole boys" of NASCAR racing--vividly
demonstrates the drag advantage afforded two (or more)
cars running closely together.
The letter writers are correct about the importance
of drafting in NASCAR racing--I have a healthy respect
for what these drivers have learned over the years.
We have known of these results also. The motivation
for undertaking our research was to provide quantitative
information--that is, to answer the questions: precisely
how much drag saving can be achieved at various spacings,
and how is this drag saving apportioned between the
various vehicles?
Such quantitative information--necessary, for example,
to make estimates of possible fuel savings in close-following
configurations--is not available in the literature.
We undertook wind tunnel tests using two, three, and
four vehicles, and performed verifying field tests with
two vehicles.
What we discovered is that the average drag coefficient
for the two vehicles decreases continuously as the spacing
decreases. Both vehicles share in this drag saving.
This must be true; otherwise two NASCAR cars could not
run faster than a single car, as they indeed can. What
was surprising to us, as reported by Karen Field, is
that at a spacing of about 0.35 to 0.4 car lengths,
the drag of each vehicle is identical, and for spacings
closer than this the drag of the forward vehicle is
actually smaller that the drag of the trail vehicle.
This fact is certainly not common knowledge?
Fred Browand
USC
Weighs in on metric debate
Not all Americans hate metrics, but most of them either
don't care or don't understand. Witness some product
labels--A&P for at least one year had half-gallon
milk containers on their shelves, labeled 1/2 Gal (1.82
ml). I called their milk packager about this "ml"
business--no effect.
George Chaplenko
Edison, NJ
Airship design
I am sorry that it took so long for me to stumble across
your airship article on the Internet (Design News,
8/11/97 issue). Unfortunately, you neglected the Skyship
and Sentinel airships that were developed by Airship
Industries Ltd. and then Westinghouse Airships Inc.
A total of $188 million was expended by the U.S. Navy
on various airship R&D with the aforementioned companies,
in addition to approximately $250 million of private
capital. The airships that emerged as a result of this
expenditure are the most technologically sophisticated
ever built and their performance exceeds that of the
GZ22.
The web site http://globalskyships.com has further
details. Many employees from Airship Operations Inc.
(for whom I now work) have been involved with the successful
operations of different versions of the Skyship since
1985.
Gary Burns
Airship Operations Inc.
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Note: Opinions expressed are those of our readers and
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