Thursday, July 07, 2005

I Don't Know

Z asked me a question today that stumped me.
If the black box on an airplane is indestructible; why can't they make the whole plane out of the same material? He went on to say that he had heard this question posed on different occassions and the answer was that it would make the plane too heavy. Whew, Z answered this question himself!

Wrongo! His next question was about some new supersized airbus, that I hadn't heard of. He wants to know why a plane this big can carry an incredibly large load, yet they can't make a regular plane out of black box material?
Any answers out there?


At 7/07/2005 9:56 PM, Blogger Jason said...

I think it has to do with physics and aerodynamics, with a touch of economics thrown in. But the thing about plane crashes -- ulitmately if you have that kind of impact, pretty much everyone in the plane is going to be killed, even if the shell of the plane comes out intact.

At 7/07/2005 10:40 PM, Anonymous Sagepaper said...

Dad would love this question!

There is an experiment to show part of the answer. You need one or two undamaged, empty aluminum Coke cans. Have Z try to crush a can by pushing the two ends toward one another. He might or might not succeed. Have him then try to crush a can by squeezing the sides together, like an hourglass. There's a big difference!

Next, examine a small greeting card. The thick paper makes i very stiff. But imagine a 10 foot by 10 foot sheet of the same kind of paper. It wouldn't stand by itself on a table top.

You can make two things out of the same material, and have the smaller one tougher than the larger one. This has something to do with pounds per square inch, and something to do with tensil strength (I think Jason said it best when he said it had to do with physics).

For the weight of the plane issue, Jason is again right -- it has something to do with aerodynamics. The horizontal surface area of the wings determines how much weight can be lifted. An easier way of mentally experimenting with the weight issue, though, is to imagine two equally weighing chunks of lead. One is just a small ball. The other ball has been melted and hammered out to be a thin sheet of lead that is 10 feet by 10 feet. Which would make a better kite? Which would be harder to destroy in a bomb-blast?

In order to lift more weight, you need more surface area on the wings. You can't just make bigger wings of the same weight. The bigger wings will have to weigh more to be as strong.

So part of the extra weight capacity of larger wings is taken up by the wings themselves. To get a high enough additional cargo weight to be worth the money (Jason nailed the economics) you have to make HUGE wings. This is what they have done with the new Airbus.

Z's on to a brilliant revelation, though. In the examples above, I compared configurations of the same material. Different materials have different properties.

One of the advantages the former Soviet Union had over us was titanium submarines. Titanium was strictly for military use here until the fall of the Soviet Union. It is not found in abundance anywhere else in the world. We never had anything like enough of this metal to make a submarine. Now, there are titanium bikes and glasses frames. Titanium is very light weight (for bikes, and could be for aviation), flexible (for glasses frames, and a cloth sail is stronger than a wooden sail), and strong (it could withstand the pressures of greater depths than could our submarines, and could perhaps perform better on impact).

Why are there no titanium commercial airliners? I think Jason has the best answers: it would cost to much, and it would not save lives. Even if you built an aircraft that could instantly go from something like 500mph to 0mph (impact), without damage, people can't do that. We go splat.

At 7/07/2005 11:04 PM, Blogger Bridget Jones said...

I was gonna dive in here but sagepaper said it much better than I ever could.

You and Jason are awesome.

And kudos to Z for being so observant!


At 7/08/2005 1:01 AM, Blogger MonicaR said...

That was so fascinating Sagepaper. Thank you!!

At 7/08/2005 4:04 AM, Blogger SME said...

I'd always wondered that too! Thanks, Sagepaper!

At 7/08/2005 8:18 AM, Blogger Laura said...

I always assumed it was aerodynamics and economics. If you could make a plane out of that material, how much would it cost? But yeah, you guys pretty much nailed it imho.

At 7/08/2005 8:51 AM, Anonymous John said...


the black box is far from indestructable. It's been destroyed in many crashes. The black box, which is orange, and basically kevlar coated carbon fiber with the recording devices incased. There are actually 2 boxes in the plane, one in the tail, and one in the center. Commerical airplanes are made with redundancy for every system. That's why there's MILES of wires in a plane.

At 7/08/2005 10:27 AM, Blogger Notta Wallflower said...

How does he come up with his questions? Most kiddos don't know what a black box is - I'm impressed.

At 7/08/2005 5:42 PM, Blogger Wandering Coyote said...

Why not make the black box out of some floating material so we don't have to send divers down to the bottom of the ocean to find the darned thing, and it can be retrieved more quickly? Hm?

At 7/08/2005 7:24 PM, Blogger tshsmom said...

Thanks so much you guys!
I had a super-busy, frustrating day at work yesterday. My patience wasn't at its best last night. Z has been reading your comments today and thinks the blogworld "rocks"! I TOLD him I had a LOT of smart blog friends!

Jason-I'd already explained the inertia thing to Z, but he still wanted to know why we couldn't make a plane like this. When he saw your ECONOMICS comment, he said:"That makes sense!" Good practice for you, buddy. Your kids will be asking questions like this ANY day!

Sage-The idea of changing the shape of a material, thus changing it's qualities (and usefulness) really got Z to thinking. I'm sure he'll be coming up with more questions on this topic after he's mulled it over for a while.

John-Thanks for commenting; don't be a stranger! Z thinks kevlar is the next thing to a miracle, so your description of the black box and its locations got a big "holy crap" from him. Maybe you could explain to WC and the rest of us why they don't make them float?

Stay tuned, guys. This worked out so well that I'm sure I'll be picking your brains again in the future.
It really does "take a village to raise a child". Thanks for being our village!!!

At 7/08/2005 11:44 PM, Blogger greatwhitebear said...

Whew, glad you weren't counting on me... that made my brain hurt!

At 7/09/2005 12:19 PM, Blogger Squirl said...

Like GreatWhite, I didn't know the answer either, but I wanted to see what other folks said. Also wanted to let you know I dropped by.

At 7/09/2005 11:52 PM, Blogger MonicaR said...

MOM! Who is Ben and where can I see what the judge said about Richard Reid??!!

At 7/10/2005 9:20 AM, Blogger alix said...

GAH! looks like the tag on your link from my blog was certainly accurate! i most definitely did "learn something"

rock on with questions Z!

At 7/11/2005 4:31 PM, Blogger The Zombieslayer said...

If you used those materials, it simply would take way too much energy to fly it. Think of it in terms of driving a car that got 0.01 miles to the gallon. Airplanes are still one hundred times safer than cars for miles driven. However, trains are even safer and you don't have to deal with the TSA morons.


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