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Balsa Crankbaits Action? or inaction?
23 replies to this topic
Posted 19 February 2008 - 04:27 PM
I think you are perfectly right with your balloons examples. And the airplane example is the same example as a submarine. The difference is that in the case of a submarine, the pressure is applied from outside to the wall, while in an airplane flying high in the sky the pressure is from inside out. Both submarine and airplane preserve the pressure that humans are used to. This is not exactly right, since you sometimes feel your ears sore in an airplane. But your ears would feel a very light change in the pressure of the surrounding air.
Something similar happens with crankbaits deep under the water.
What I was saying is that from 8 or 6 atm to 1 atm (the pressure at sea level) there is a much higher difference compared to the difference from 1 atm. to 0 atm (maximum lack of pressure that you could obtain in a jar, using some vacuum devices). I think you could not get 0 atm with usual vacuum devices.
Moreover, a crankbait's topcoat can withstand high pressure mainly because it leans on the wood (the deeper the crankbait is supposed to run, the strongest the wood should be), while with your test (pressure from inside out) the topcoat would lean on nothing.
Posted 19 February 2008 - 04:31 PM
I kind of get what you are trying to say Senkoman85. The plane and the sub are equally good for your analogy.
When the human body dives, as you explained, the body is compressed. The air in the lungs is compressed. This is equivalent to a soft, flat sided balsa body. The body pressures balance out when the pressure inside equals the pressure outside.
In a sub, the pressure inside essentially stays at one atmosphere. The enormous pressure on the outside is absorbed by the structure of the hard shell.
In a plane, again, the presure stays essentially at one atmosphere, the enormous pressure on the INSIDE is held in by the rigid structure of the hard shell.
Both these analogies are the equivalent of the hollow hard plastic body. Eventually, a depth will be reached where the pressure loads will be greater than the rigid structure resisting them and the body will implode.
In reality, on aircraft, they reduce the internal pressure to the equivalent of 10,000 ft. This is why your ears Plaster of Paris as they regulate the pressure and you feel tired and occasionally gasp for an extra breath for no apparent reason. By introducing this pressure drop, the difference between the inside pressure and the outside vacuum is reduced and thus the loads on the airframe are reduced.
Also, a submariner does not have to worry about the bends, he does not have to control his rate of ascent, as he is working at a constant pressure of 1 atmosphere. If a regular diver rises too fast. Certain gasses start to come out of the blood as bubbles. Exactly the same way as a bottle of coke starts to fizz when you open the cap. The sudden reduction in pressure causes the dissolved carbon dioxide to come out of the solution as gas.
Posted 20 February 2008 - 01:23 AM
Vman, I did not know that the pressure in an airplane is the one which you normally have at 10 000 ft. That explains the problems with the ears.
Your explanation is very logical.
Posted 20 February 2008 - 02:47 AM
You guys explain this so logically, even I can understand it. Thanks pete