Thursday, October 25, 2012

Accidentally on purpose or vice versa

photo courtesy of the Discovery Channel

Earlier this month the Discovery Channel presented "Plane Crash," which was about, you guessed it, a plane crash.

But this wasn't a real plane crash, but a controlled demonstration plane crash. An old Boeing 727 was equipped with surprisingly primitive radio controls and directed into a Mexican desert.  The point, then, was not to determine why the plane went down, but to see what happens inside a plane when it collides with the ground "accidentally."

The plane was packed with some crash-test mannequins, many cameras, and other recording devices. Engineers, test pilots, and other specialists were on hand to set up the event and then analyze the results.   Eventually the data will purportedly be presented to the public so that aircraft designers and scientists can glean information about how to improve crash safety.

The show, "Curiosity," paid an undisclosed amount of money to arrange and film the event. It was promoted as a scientific first and goldmine of information, ranking somewhere between discovery of the Higgs boson and seeing what happens when you mix vinegar and baking soda to make sodium acetate and bubbles of carbon dioxide.

(This reaction is actually more interesting than a full scale test of Newtonian physics. )

Aside from the improvisational air of the show -- the 727 was flown with a model airplane controller -- the event was  surprisingly not surprising.  After the crew parachuted out of the plane's rear exist the plane was guided to the ground at a gentle glide and low speed so that the onboard instruments would not be destroyed. The team also wanted to avoid a fire after the crash.

The show was entertaining, but the odds of an American dying in a domestic air crash are somewhere between 1 in 6 million to 11 million.  In other words, dying in an aviation disaster should be close to the bottom of your risk list. 

Experimentally, what happened was pretty much exactly what you would expect. The front landing gear crumpled, which pulled the nose under the fuselage,  the other two wheels detached as designed and "dummies" in the plane who weren't wearing seat belts were subject to greater forces that those belted in.

The one anomaly was that the engines continued to operate after the crash, which is kind of odd. But it was not pursued. 

Otherwise, most of the results seem as if they could be obtained through first principles. That is, if you know the mass and speed of an object, then calculating its momentum is a simple matter of multiplication.

Likewise, if you have information about the plane's design, predicting what would happen after it exceeded its envelope should also not be too difficult. 

Moreover, there are unfortunately many real plane crashes to study. What Curiosity demonstrated was what damage would result from intentionally crashing a perfectly operating plane into an unpopulated desert.

Which is kind of cool to watch over and over, but of what value is that?  Also, if the experimenters did not want a fire, they could have limited the amount of jet fuel.  Otherwise, they discovered that overhead wiring comes loose impeding rapid exit, and that sitting in a brace position wearing a seat belt is safest. 

That's one data point. And an unusual one at that. The chances of this recurring seem remote.

 To be more useful, a large number of identical  planes would have to be crashed at the same place at the same speed and rate of descent. However, what would be the point? Why not crash scale models, or use computer simulations?

Because those would be relatively dull to watch.

 And this crash was for entertainment more than science. Just like the vinegar and baking soda "volcanoes" that appear frequently at science fairs.

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