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05/22/2001
Sandwiches, Wind and SUVs
Last week I mentioned a golf match, the Sandwich Islands Big
Match, in Honolulu with my friend Dan. In the March 12, 2001
issue of Chemical and Engineering News (C&EN) I found the
reason the Hawaiian Islands were initially called the Sandwich
Isles. They were named after the Fourth Earl of Sandwich, who
was also the First Lord of the Admiralty and who sponsored
Captain James Cook''s expeditions in the Pacific. Cook stumbled
upon Hawaii, where he was greeted like a god, particularly on
the Big Island of Hawaii. Unfortunately, according to a lecturer
on our cruise to Hawaii, after leaving the Big Island, Cook ran
into some difficulty and decided to return to the place that had
treated him so warmly. What he didn''t know was that this time
he was approaching the site from the wrong direction. This
direction of approach meant to the natives that he was a fake and
actually a bad god. They therefore followed their customary
welcoming of a bad god by cutting Cook up into small pieces to
be distributed amongst the warriors who had participated in this
quaint welcoming rite! The officer now in charge of Cook''s
expedition decided it was unacceptable to return to England
without any evidence of Cook''s demise. Lacking a complete
corpse, he did manage to negotiate the return of some bits of
Cook from the natives for show and tell back in the mother
country!
According to the C&EN article, the current 11th Earl of
Sandwich, John Montagu, and his son Orlando have started a
sandwich-making and delivery business. They plan to deliver
fancy sandwiches in London''s financial district. It seems only
fitting that they do so since it was the same Fourth Earl of
Sandwich who gets credit for inventing the sandwich. He
decided that the quickest, least messy and least disruptive way to
eat a meal was to place a beef slice between two slices of bread.
While in the Sandwich Isles myself, I saw an article in the
Honolulu Advertiser titled "Danes open giant windmill park".
I''ve written earlier about the Danes and their expertise in wind
turbines. Those in the wind business decry the use of the term
"windmill" to describe modern energy-producing machines. The
news item described the operation of the Middelgrunden
"windmill" park at the entrance to Copenhagen''s harbor. This
wind park was scheduled to start delivering power on May 6.
The size of these wind turbines is impressive, to say the least.
They stand 211 feet tall and the three-blade rotors are 250 feet in
diameter! You may recall that, in an earlier column, I admitted
my embarrassment when I misidentified a huge "sculpture" near
our hotel in Copenhagen as a piece of modern art. It was one of
these rotors. The Middelgrunden park contains 20 wind turbines
and delivers 40 megawatts (40 million watts) of electricity.
Advanced mathematics tells me that''s 2 megawatts per turbine,
making these turbines the among the most powerful, if not the
most powerful wind machines on earth. The Middelgrunden
park will supply enough energy to power over 30,000 homes or 3
percent of the electricity usage in Copenhagen.
According to the Advertiser article, the price of the electricity
emanating from the wind turbines is a measly 4 cents a kilowatt-
hour. Californians would die for electricity at that price today!
By 2030, the Danes expect that half of their electrical needs will
be supplied by the wind; today it is 10 percent. From the
business standpoint, wind is a profitable market for the Danes.
They are shipping their wind technology worldwide; in 1999
$1.5 billion in sales. The ownership of the Middelgrunden park
is interesting. The park is co-owned by the Copenhagen''s
electric power company and the 8,500 members of the
Middelgrunden Wind Turbine Cooperative. Some 90 percent of
the members of the cooperative are individuals who just want to
encourage the production of "green" energy.
Energy is quite a hot topic these days, I heard something on the
news about how many millions of barrels of oil could be saved if
SUVs were mandated to have the same gas mileage as ordinary
cars. You may recall that last week I described the unusual
situation where we were forced to change our seats on a plane
that carried us home to New Jersey from Los Angeles. I asked
my friend Dan in Honolulu why we had to be reseated. Dan is an
excellent pilot, at least on his flight simulator, and he did have an
answer. When the weight is not evenly distributed along the
length of the airplane you have to calculate the center of gravity.
If the weight is concentrated too far forward or aft of the center
of gravity, the aircraft will demonstrate "negative dynamic
stability". If this unbalanced plane is disturbed from level flight,
negative dynamic stability means that the plane will be difficult
to control and unsafe to fly. Am I glad we changed our seats!
Thank you, Dan, for the explanation.
What does this have to do with SUVs and energy? I''m glad you
asked. Curtis Rist, in the April issue of Discover magazine,
discusses the center of gravity of SUVs. The situation is not
good. Witness the article''s title, "Roll Over, Newton", and the
subtitle "The design of Sport Utility Vehicles is enough to make
the father of physics turn over in his grave". Any owner of an
SUV should read this article. I must admit to a personal bias. I
drive a little VW Jetta, hate SUVs with a passion and think they
never should have been allowed on the road in the first place. So
much for objectivity. Back to science and technology.
Isaac Newton''s first law of motion applied to a moving vehicle
says that inertia will keep a car''s center of gravity moving in a
straight line unless some force changes its speed or direction.
Let''s say you''re driving in a straight line and decide to do a bit of
drag racing. You accelerate so strongly that the weight shifts
almost entirely to the rear tires and you may even find the front
wheels lift off the ground. Then brake suddenly and the weight
shifts to the front tires and the rear ones may lift off the ground.
A vehicle with a high center of gravity and a short wheelbase
(distance between front and back tires) can be made to lurch
backward and forward enough to do a somersault end over end.
A frontal end-over-end somersault is admittedly a pretty rare
event. But the lateral somersault, the rollover, is not. Over 60
percent of fatalities in accidents involving SUV occupants occur
in rollovers compare to 23 percent for occupants of cars. The
center of gravity plays a key role. I should have noted that the
center of gravity is the point at which an object''s mass is at
equilibrium. Put more simply, if you put a hook on a vehicle at
its center of gravity and picked up the vehicle, it would be
perfectly balanced in all directions, front to rear, side to side and
top to bottom. The height of the center of gravity off the ground
is the key to how stable a vehicle will be on the road. Let''s take
a spin in your SUV. This time, instead of going straight, let''s
make a left turn. The center of gravity wants to keep moving
straight (inertia) and the weight shifts to the two right tires,
particularly the right front tire. If you''re going a bit too fast,
the left tires will lift off the road. They may only be off the road
a fraction of an inch and you probably don''t even notice that you''re
riding a bicycle on two wheels. Now you''re really vulnerable to
any disturbance such as a wind gust, a pothole, soft shoulder or
the like. Any of these can roll you over.
How likely is a vehicle to flip? You already know the answer.
You know that it''s harder to tip over a thin flat sheet of metal
than to tip over that sheet of metal rolled into a cylinder standing
on its end. Similarly, the tendency toward tipping is related to
the height of the center of gravity divided by the distance
between the two front wheels, called the track width. A typical
car has a center of gravity about 20 inches above the ground and
a typical SUV about 5 or 6 inches higher. The track widths aren''t
too much different, maybe 2 or 3 inches smaller for the SUV.
This doesn''t sound like much difference. However, the ratio
translates into an SUV being at least three times more likely to
tip over than a car in a single vehicle accident.
You proponents of your SUV will say, quite properly, "Hey, I''m
only going to tip over if I''m not driving carefully." And, with
your added height, you say that you can see the road and traffic
conditions more clearly than I can in my Jetta. But did you know
that you have to be a better driver than I am? This is something I
hadn''t thought about before reading the Discover article. It has
to do with the perception of speed. Rist points out that your
perceived speed, as opposed to your actual speed, depends on
how high you are off the ground. Taking the extreme example of
an airplane, when you look out the window it seems as though
you''re not moving very fast, even though you''re going 500 miles
an hour. On the other hand, if you''re driving a road-hugging
racecar you think you''re moving at a rapid clip even if you''re
going only 30 miles an hour.
Ron Noel, a professor of psychology at Renssalaer Polytechnic
Institute, has carried out studies in this field and says you judge
your speed by what he calls "optic flow". I deduce that optic
flow is how fast things you think things are whizzing by you.
Noel developed a model for this effect in an SUV and a car. The
SUV seats are typically about 20 inches higher than in a car. As
a result, he concludes that a driver of an SUV driving at 60 mph
feels as though he or she is going the same speed as a driver of a
car who''s doing 40 mph! Result - the SUV driver tends to drive
faster than normal on turns and the rollover chances are
increased. He''s got to be a better driver - and no cell phones!
The article contains some other interesting points. For example,
antilock brakes actually can increase the chances of a rollover.
The antilock brakes are fine in a straight stop but applying them
in a turn is a problem. Pulsing of the brakes in a turn can result
in an on-and-off force that might flip an SUV that''s already
leaning that way. The article also discusses the physics of a
rollover and, again, it''s better to roll over in a car.
Save energy and sell your SUV! Meanwhile, I''m off to the store
in my little Jetta.
Allen F. Bortrum
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