Number 620
Date Aug. 7th 2009
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Wings is the 620th xkcd comic.



Titan is the largest moon of Saturn. It has a dense atmosphere of mainly nitrogen. The surface gravity at the equator is 1.352 m/s2 or 0.14 g, that is 0.14 times the equatorial surface gravity of Earth. The atmosphere density (i.e. mass per volume) is 50% higher than on Earth.

A lower gravity will obviously mean flying requires less effort. A higher density atmosphere will also mean flying requires less effort, as for instance helicopters have great difficulty landing on Mt. Everest because at these altitudes, the air is extremely thin, meaning the helicopter's wings have to turn faster to create the same amount of lift.

With an atmospheric density 50% higher than on earth, in other words the density is 1,5 times that on earth. Flying will then require (1/1.5) times the effort = 2/3 or approximately 0.6667. Multiply that by 0.14 and the outcome is 0.09. According to these data and not considering other factors (such as the extra weight of a space suit and/or breathing equipment) flying on Icarus would require 0.09 times the effort it would require on earth Earth.

The construction with ropes, pulleys and counterweightEdit

If a person is attached to a mass such as a stack of bricks 0,81 times their own weight, using a pulley, then their own effective weight is only 0,09 times their original weight. This would mean that if 0,09 times their own weight in lift is generated, that person would lift of the ground. This means that person could fly with 0,09 the effort, again only if other factors are not considered. For instance as soon as that person would fly in such a manner (as is likely) that the rope to which he is attached is no longer hanging 90 degrees vertical, the effective lift generated by the stack of bricks on the other end, will become smaller. In other words, the further away from his original position the person flies (even if he would fly in small circles around his original position straight under the pulley)the more effort it will take. And that is not even considering the fact that, as the person flies away in such a manner that the distance between him and the pulley above him increases, he will effectively pull on the rope, rendering the whole construction with pulley and counterweight contraproductive, and greatly increasing the effort required to keep flying.

Greek mythologyEdit

In Greek mythology, Icarus built wings from feathers and wax, to be able to escape from crete. He then ignored warnings not to fly too close to the sun and when the wax melted, he crashed to in the sea and drowned. Icarus is sometimes seen as a (mythological) pioneer in conquering the skies, as well as a symbol of 'hubris' (arrogant overconfidence) or failed ambition.

Mouseover textEdit

"Please do not try any of this and die or get arrested."

See alsoEdit

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