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## Flying a Cessna On Other Worlds: xkcd Gets Noticed By a Physics Professor148

Posted by Soulskill
from the make-sure-your-insurance-is-up-to-date dept.
djl4570 writes "xkcd's 'What If' series consists of humorous takes on highly implausible but oddly interesting hypothetical physics questions, like how to cook a steak with heat from atmospheric re-entry. The most recent entry dealt with flying a Cessna on other planets and moons in the solar system. Mars: 'The tricky thing is that with so little atmosphere, to get any lift, you have to go fast. You need to approach Mach 1 just to get off the ground, and once you get moving, you have so much inertia that it’s hard to change course—if you turn, your plane rotates, but keeps moving in the original direction.' Venus: 'Unfortunately, X-Plane is not capable of simulating the hellish environment near the surface of Venus. But physics calculations give us an idea of what flight there would be like. The upshot is: Your plane would fly pretty well, except it would be on fire the whole time, and then it would stop flying, and then stop being a plane.' There are also a bunch of illustrations for flightpaths on various moons (crashpaths might be more apt), which drew the attention of physics professor Rhett Allain, who explained the math in further detail and provided more accurate paths."
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## Flying a Cessna On Other Worlds: xkcd Gets Noticed By a Physics Professor

• #### Re:Wrong Professor is Wrong (Score:5, Informative)

on Saturday February 02, 2013 @05:41PM (#42773853)

Mach 1 is the speed of sound - in that medium.

• #### Re:Wrong Professor is Wrong (Score:5, Informative)

on Saturday February 02, 2013 @06:05PM (#42774001) Homepage
Correct. Also, it's important to point out that the Mach number of a vehicle is a local measure of vehicle speed. As the speed of sound varies with temperature, and thus altitude, you'll find that two vehicles having the same trace ground speed but that are flying different altitudes will be at different Mach numbers. Acoustics and aerodynamics are fun.
• #### Re:Not going anywhere... (Score:5, Informative)

on Saturday February 02, 2013 @06:32PM (#42774185)
Icebike is proving what I have previously pointed out about him. It is not important to him that he knows what he is talking about. Knowing what you are talking about is hard.
• #### Re:X-Plane (Score:2, Informative)

by Anonymous Coward on Saturday February 02, 2013 @06:33PM (#42774191)

http://www.x-plane.com

https://petitions.whitehouse.gov/petition/make-patent-trolls-pay-all-costs-associated-their-frivolous-lawsuits-if-they-lose/gWPpVYMt

Ed

• #### Re:Not going anywhere... (Score:4, Informative)

on Saturday February 02, 2013 @07:08PM (#42774449)

> I have to admit not ever reading xkcd, having more important things on my Kindle.

It publishes 3 strips a week, plus a what-if from time to time. It's not a book, or anything else which would compete with whatever's on your kindle for your attention, unless you're a very, very slow reader.

The bigger problem is that Friday's comic was number 1168, so if you've only just started reading now you have a lot of catching up to do. Then half way through you'll realise that if you hover the mouse over the picture some additional text pops up so you'll have to go all the way back and start again[1]. Then you need to read the blag to figure out what all the references to cancer are about.

Most of the comics can be fully enjoyed in 30 seconds or less, but some require a bit more effort...

The What-If's come out once a week and also require a bit more attention but there's only a handful of them so far.

[1] I don't know how to get hover text on my Samsung Galaxy S2... maybe kindle's can't get to it either?

• #### Re:Not going anywhere... (Score:5, Informative)

on Saturday February 02, 2013 @08:09PM (#42774757) Homepage
http://m.xkcd.org/ [xkcd.org] is a better version for mobile. The title below the comic has a clickable superscript (alt text) link that will display the alt text underneath.

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