The Wackiest Ship in
the Army, or, Of Airplanes and
Buildings
The
first clause of the above headline is the title of a 1965-66 TV series
loosely based upon actual events, revolving around a two-masted schooner
presented to the U.S.
by New Zealand
early in World War Two.
One
episode I saw at my buddy Doug’s house featured the shoot-down of a
Japanese Zero by one of the protagonists (Jack Warden) using a Thompson submachine gun. Since a Thompson uses a .45 caliber
ACP pistol round, and we were all very familiar with firearms (a necessary
skill for growing up in the Bushwick section of Brooklyn), we began
thinking that Hollywood had done it again, putting something on the
screen which had no basis in reality.
I
mean, shoot down an airplane with a pistol?
Nah.
Actually
yeah, depending upon how close you get.
I did the ballistics calculations on a 230 grain (about half an
ounce) bullet exiting the muzzle at 850 feet per second (about 580 mph).
Re-doing
the calculations now, I find it has a muzzle energy of about 370
foot-pounds, and about 183 foot pounds by the time the bullet has slowed
down to about 600 feet per second (maybe one or two hundred yards
downrange). Try dropping a 180
pound weight, which has a contact area about the size of the tip of your
thumb, on to a thin aluminum sheet from a foot away and you’ll
discover it will punch right through it.
Since
a Thompson’s rate of fire is between 600 and 800 rounds per minute,
it’s punching through the aluminum (positing the shooter’s
ability to hold on target) at least 10 times in a one second burst,
tearing up all kinds of systems under the skin as it does so.
The
math behind all this is the Physics definition of kinetic energy, or how
hard something hits, which is half of an object’s mass times the
square of its velocity, and that leads me to the second clause of the
headline to this piece.
A
couple of weeks back, the New York Times (I
just gotta do that with the typeface) published an article explaining
that the TSA was going to look at anti-terror rules for small jets and
boats, but in the body of the story, they referred to a Cessna, saying it
weighed about as much as a small SUV.
The
implication of the story was that a single engine lightplane could be a
terror threat. That is,
today’s general reader knows very little about business jets, and
next to nothing about Very Light Jets, which are currently only in
development, and would naturally think of a single engine lightplane with
regard to the Cessna reference, particularly since it didn’t
specify a business jet.
Since
I fly single engine lightplanes I looked at this as another story by the
unknowing about the (to them) unwanted.
I
wrote a letter to the editor doing the math to point out that the reason
the Cory
Lidle crash had the same effect as the unfortunate who
intentionally flew a Cessna into a hi-rise
in Florida shortly after 9/11, was that
such aircraft simply cannot hit hard enough to do much to a building.
That
is, taking two objects of the same mass
if one travels twice as fast as the other, it will hit four times
as hard; three times as fast, nine times as hard; four times as fast;
sixteen times as hard, etc.
The
math works out like this:
A
business jet weighs 5 times as much as a Cessna 172, and travels about 5
times as fast, so it’d hit something 5x25 or 125 times as hard as the 172.
A
commercial airliner weighs between 100 and 150 times as much as a 172,
and can travel up to 6 times as fast, so it can hit as hard as 150x36 or
5,400 times as hard as a 172. This
means it also can hit about 43 times as hard as a business jet.
Let’s
look at this in another way.
43
business jets or 5,400 single engine lightplanes would have to fly into a
building at exactly the same time to have the effect of a single
commercial airliner impact, and even at that, the 9/11 impacts
didn’t bring down the twin towers.
The
fires, however, did.
Medieval
blacksmiths softened iron over coal or charcoal fires with bellows, and
wood (8,000-10,000 BTU per pound) is a lousy source of concentrated heat
energy when compared to petroleum products (18,000-24,000 BTU per pound
or about 124,000 BTU per gallon for gasoline).
Your
car’s gas tank might hold between 12 and 25 gallons of
gasoline. A 172 with long-range
tanks could bring as much as 50 gallons of avgas to a building impact.
A
business jet could bring between 500 and 5000 gallons of kerosene to such
a scene, while in the case of a commercial airliner we’re talking
between 12,000 and 24,000 gallons.
To put these numbers in some sort of perspective, the fuel tanker
trucks you see delivering gasoline to your gas station typically carry about
3000 gallons of fuel, maybe 150 cars’ or an eighth of an
airliner’s worth.
Rust
or iron oxide, by the way, is the slow burn of the iron in steel by
oxygen in the air. Get a hot
enough fire going, and steel will not simply soften or melt, but some of
it will, (contrary to Rosie O’Donnell’s monumentally ignorant
proclamation as to the impossibility of such) burn.
I
guess the point of this piece has been that while having opinions is
necessary, one needs to have facts upon which to base those
opinions.
That
is, there are medical opinions, legal opinions, engineering opinions, and
just plain ignorant opinions.
We
live in such an information-rich age that it’s easy to mistake
consensus for fact, and easier still to form opinion based upon the
common perceptions or beliefs of one’s peer groups. What should be so obvious as to not
need stating is that the danger here is that such beliefs or perceptions
may have little or nothing to do with fact.
This
gets me back to one of my recurring themes; what defines a
professional. Actually, what
I’m aiming towards here is that you keep in mind the fact that
neither legislators nor
journalists have any special qualifications which should have you take
their words as gospel.
Quite
the contrary, in fact.
The
dirty word “lobbyist” can be nothing more than someone who
can be on call to educate the ignorant that they don’t do or say something really stupid.
