h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

An engineer at Lucas Aerospace (long time ago, this story) once told me that, aeroplane part manufacture being such an exacting science (safety and all that), the toughness of aircraft windscreens in measured by those in the know in sledgehammer-seconds , being what it takes to withstand an average bloke wielding an average sledgehammer at an average strike rate for n seconds.

The same engineer told me that in practice the toughness of, say, a typical jet fighter windscreen, is fact measured in sledghammer-HOURS. For comparison, he said, you should understand that bulletproof glass has a toughness of about 1.5 sledgehammer-seconds.

So it may be patented, but the only reason the holders of the patent can make any money is that the aerospace industry is conspiring to prevent the protection-desiring public from getting any.

Were you also aware that airplane canopies are tested by shooting chickens at their windows with a pneumatic cannon? The chicken hits the canopy at almost mach 2. I know, it surprised me too!

Were you also aware that airplane canopies are tested by shooting chickens at their windows with a pneumatic cannon? The chicken hits the canopy at almost mach 2. I know, it surprised me too!

Then there's the story about how British Rail borrowed a chicken cannon off Rolls Royce (the aircraft engine manufacturer, not the cars) to see how a new high speed train would stand up to a bird strike.

The chicken supposedly went straight through the cab, halfway down the locomotive and embedded itself somewhere in the engine block. When the engineers doing the test rang Rolls Royce to find out what they might have set up wrong, they were asked (so the story goes) "did you remember to defrost the chicken first?"

Then again, privatised it may be, but the recent safety record of the inheritors of the British Rail mantle hasn't exactly been exemplary, has it ...

I don't mean to be picky, but I don't recall chickens being used to test aircraft canopies. They are, however, used to test jet engines.

The test involves running the engine at full speed on a test bed and firing chickens into the intake to simulate a bird strike. I think the engine casing must contain all the debris generated from the strike to pass the test.

The part about BR borrowing the rig is unfortunately probably all too true.

An interesting story I heard whilst at university involved 'bulletproof' glass - Remember the famous scene in the film Robin Hood Prince of Thieves where the camera films an arrow flying directly towards it? It was filmed using a plate of the latest laminated bulletproof glass in front of the camera to prevent the arrow smashing the equipment.

To test the glass prior to filming it was shot at using a Magnum handgun. The glass passed the test and was fitted to the camera. Time for filming and the first arrow shot at it passes straight through the glass destroying several thousand pounds worth of equipment.

Ooops thinks the glass manufacturers and sends the glass to the same university department where I studied for analysis. It was found that where the bullet was stopped immediately, the compression in the wooden arrow shaft from the impact created a hammer-drill action that broke each laminate in turn and passed through the glass intact.

Hopefully we won't see a spate of bow-and-arrow armed bank robbers!

the urban legends reference pages deal with the myth of the chicken cannon at the following link...


http://www.snopes.com/science/cannon.htm