Mechanical Engineering Magazine

LETTERS & COMMENTS

To the Editor: Our beloved Mechani-
cal Engineering magazine took a step
backward in the October 2013 issue with
the article, “Stepping on the Water.”
I recall a letter to the editor a year
or so back which commented on what
appeared to be a direction of reduced
engineering rigor in the articles found in
the magazine. I have seen improvement
since then.

It was with a sense of disappointment that I read the explanation provided by the authors to the right of the schematic of the fingers on page 39. There is simply not the space here to express my exasperation with the disjointed and inconsistent explanation of this physically observable phenomenon. It certainly would not receive a passing mark if submitted for grade by a student in an undergraduate fluids class.

I was a professor of mechanical engineering at West Point for 10-plus years—spent a good deal of that time teaching fluids, thermodynamics, and heat transfer. I read this magazine cover to cover each time I receive it.

I have never sent an article to the editor before this. I suppose I just could not sit still after trying to make sense of the explanation provided by the authors of the schematic in the article.

I have great respect for Dr. Bejan.
I can only conclude he did not spend
enough time proofing the work.

Eric B. Zimmerman, P.E., ASME Fellow, Burke, Va.

To the Editor: In “Stepping on the Water,” (October 2013), the authors assert that “… all of us learn to swim with cupped hands.” Their claim is patently false.

For at least the past half-century, those of us who have been competitive swimmers have been coached to keep our hands flat with our fingers slightly spread when we swim because it is the configuration that provides the maximum amount of water resistance against our hands when we pull.

Back in the 1960s, our coaches would
have us stand in shallow water and do
sequential arm pulls with cupped hands,
hands flat with fingers together, and hands
flat with fingers slightly spread so that we
could feel the difference. It was easy for us
to tell that the most resistance came from
pulling with the hand flat with the fingers
slightly spread.

Moreover, this principle appeared in
print in many of the swimming books of
the time. For example, in the 1961 Sports
Illustrated Book of Swimming, legend-
ary coach Matt Mann II, advises that “…
the hand should be flat, not cupped.” In
James E. Counsilman’s 1968 book, The
Science of Swimming, he writes: “In hand
positioning for the pull it is fundamental
that the hand be flat, not cupped. … The
cupping of the hand does reduce the
pull considerably … . ” In addition, he
notes that “Research in the area of fluid
mechanics indicates that it may be pos-
sible that a hand with the fingers spread
slightly may produce a bit more pull than
a closed-finger hand.”
In short, not cupping one’s hand and
swimming with a flat hand with one’s fin-
gers slightly spread are not profound no-
tions to competitive swimmers. We were
coached to do that from an early age.

David A. Levinson, Palo Alto, Calif.

Note: The author, an ASME Fellow, has placed in the top ten finishers in 210 U.S.

Masters Swimming events since 1975.

To the Editor: As an educator, I could not help but notice Richard Benson’s reference to PID controllers (Workforce Development, August 2013). As an engineer, I hope that someday very soon, we abandon Proportional + Integral + Derivative (PID) control algorithms altogether.

Instead, I hope that we embrace a slight
modification of PID that produces stunning
improvements in performance: faster
response times with zero overshoot.
A PID system integrates a signal that it
has just differentiated. We get remarkably
better performance by simply feeding
back a second but different proportional
OCTOBER 2013

One reader takes us to task for an incomprehensible chart. Another says that when it comes to beginning swimmers, we're all wet. And a third makes the case for a new kind of control algorithm.