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Flying a Cessna On Other Worlds: xkcd Gets Noticed By a Physics Professor
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."
It is a cessna engine, it doesn't run on air but on money.
i thought once I was found, but it was only a dream.
"plane would fly pretty well, except it would be on fire the whole time"
I think Boeing has a plane that meets part of the criteria already.
In the What-if it's explicitly stated that the gas tanks have been replaced with batteries and had an electric engine installed.
It would be an X-Plane!
Any sufficiently unpopular but cohesive argument is indistinguishable from trolling.
If your plane is on fire and not a plane anymore then you are having a bad problem. You will not fly on Venus today.
This is covered in the simulations as well. Is there something in particular preventing you from reading it?
This is covered in the simulations as well. Is there something in particular preventing you from reading it?
Although I am not the poster you asked this question of, I have to admit not ever reading xkcd, having more important things on my Kindle.
Having left my e-ink display in the car, I read through what-if and if nothing else, the penny exercise had me laughing out loud. Tough to force on a rocket scientist with humor less moist than a block of dry ice, but it happens.
Thanks to / for not posting a slashvertisement and giving me the giggles.
When the foot seeks the place of the head, the line is crossed. Know your place. Keep your place. Be a shoe.
Load liquid oxygen into the fuel tanks. Methane comes into the engine from the atmosphere. An engine with minor modifications might be made to operate.
http://michaelsmith.id.au
Mach 1 is the speed of sound - in that medium.
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Very first tile in illustration: rip out engine, install batteries and electric motor.
RTFA
Although I am not the poster you asked this question of, I have to admit not ever reading xkcd, having more important things on my Kindle
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As a rocket scientist, perhaps you might get a chuckle out of this xkcd: http://xkcd.com/1133/
This is helped somewhat by the higher density of the martian atmosphere, in relation to its pressure. The density is pushed up by the low temperature and the higher density of carbon dioxide. OTH Mars is quite windy so your vehicle will get blown around quite a bit which could create hazards.
http://michaelsmith.id.au
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.
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He used a simulator for Mars that accounts for things like the effects of density differences on prop thrust, son.
What exactly are you trying to prove by refusing to read the article?
Not to mention when he says that Venus' upper atmosphere is "room temperature" - duh! rooms on Venus would have a very different temperature from Earth's rooms! What and idiot.
sic transit gloria mundi
You can't hand-waive away physics.
Sense of humor, on the other hand, is commonly waived.
FTFA: The motor is electric, and the fuel tanks are replaced with Li-Ion batteries. But I'll give you style points attempting to stifle scientific hypothetical inquiry and outside-of-the-box thinking with cynical non-imaginativism. Keep it up and you might win the scientific curmudgeon of the year award!
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.
"His name was James Damore."
They also didn't point out that if attempting to fly in the Sun's atmosphere, you may last longer if you do it at night. :P
This space unintentionally left blank.
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You must be great at parties.
Dude, read the full article. Seriously.
> 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?
One of Einstein's what-ifs when something like this. Light moves at the same speed for all observers. So imagine a space ship travelling at near the speed of light relative to Observer A. Observer B is in the space ship and shines a laser straight up and back down off of a mirror. To Observer A the laser appears to move along the top of a triangle as the ship goes by at near light speed. Observer A sees the light travel a greater distance than Observer B. Both observers see light traveling at 299 792 458 m / s. So the only way this can be true is if time is moving slower for Observer B than A.
Feel free however to point that we don't know how to make a space ship go that fast. Point out the difficulty in actually observing such an event. Deride imagination.
Congratulations!
You seemed to forget the entire point of XKCD's what-if series is, in fact, taking childish daydreams and running with it. It's a bit odd, anyways, that a person who (begin rant) thinks a COTS laptop, in a shielded cabin in a magnetosphere-shielded environment using a tiny node size is every bit as radiation-hardened as a RAD750 with a 150nm node size to reduce susceptibility to smaller particles, with latchup-proof logic, parity-checked memory, etc etc. (end rant) is behaving as a physics expert to begin with.
Woosh!!!!! This low flying humor clearly gets no propulsion in all that hot air your blowing.
A fool throws a stone into a well and a thousand sages can not remove it.
Flight does not require propulsion when gravity is pulling you to the center of a planetary body. It only requires lift. The examples all clearly state that the plane is dropped from a great height.
A fool throws a stone into a well and a thousand sages can not remove it.
I really want that on a t-shirt... I'm a big guy, so it should work well on a 4X
Michael J. Ryan - tracker1.info
http://m.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.
If that professor wants to pick nits with xkcd, the path an object follows while falling in a vacuum isn't a parabola. Its an ellipse. In most cases, the ellipse intersects the surface of the body being orbited in what is typically referred to as a crash. But if one is considering dropping the object (with some forward velocity) above a small enough body, the distinction becomes important.
Have gnu, will travel.
It is explained that on one world, you burn then crash - as opposed to crash and burn - and why it would happen in that order. And, on another world, you would crash, but not burn, and why.
This little "what if" is a reasonable explanation of conditions on other worlds, as we understand them, and how they would affect flight in a particular type and model of aircraft.
If the story teller were addressing an international physics conference, he might sound a bit stupid with this presentation. As he is addressing an audience of nerds, with the intent of amusing and possibly educating them - he's done an excellent job.
"Windows is like the faint smell of piss in a subway: it's there, and there's nothing you can do about it." - Charlie Br
Wow, you mean he's wrong and the Cessna would fly awesome and not just fall to the ground?
Glad we had you here to set things right. I'm going to get started on my plan to fly to Mars!
If I have been able to see further than others, it is because I bought a pair of binoculars.
"And get propulsion from a prop in an atmosphere of .6 that on earth?"
There're two things to consider:
1) Of course you get prop: it's a rotating wing, isn't it? So as long as there's any atmosphere, you'll get propulsion. Maybe your question was not about "propulsion" but about "enough propulsion", which gets us into point two.
2) Who said that "enough propulsion" needs to be produced exclusively by the main rotor? In the experiment another quite porwerful prop source is included: gravity. You just take even a pig at 30 Km over the Martian surface and you'll see how it gains speed even without revolving its pig tail.
The thougth experiment was not about flying a Cessna in Mars (and other objects) but about *how* it would *try* to fly over there. See, for instance, in Jupiter it would crush, but it wouldn't crash.
Great idea! I'm also a big guy, but it might fit me best if I were to lay it out horizontally...):
Wow-- I just noticed this-- I got linked!
(at the pdf report linked at the words "...The acid's no fun, but it turns out the area right above the clouds is a great environment for an airplane" in the Venus section)
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030003716_2002108457.pdf
http://www.geoffreylandis.com
Like I said - in that medium. Except you wrote something wordier so you gathered more mods.
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This other what-if actually addresses this pretty well: http://what-if.xkcd.com/20/
I have developed a truly marvelous proof of this comment, which this signature is too narrow to contain.
The speed of light is constant and cannot be exceeded, therefore
By implication, we must have time dialation depending on frame of reference
We can work out how much we would expect that time dialation to be
We have a testable hypothesis that could potentially be disproven by experiment on board Concorde or another fast aircraft.
Nope, we could just fly it there. A C172, fully laden with fuel (or equivalent mass in batteries) weighs less than the Curiosity probe plus landing system, so we could just fly it there in a conventional rocket and release it into the atmosphere (possibly with a little entry shielding). You're taking this far too seriously ;)
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