Flying with Machine Guns? | Hacker News Reader

Flying with Machine Guns?

blog.wolfram.com

156 pointslelf68 comments

The article directly refers to Munroe's What-If article, and Munroe is pretty clear that he relies heavily on Wolfram Alpha for his calculations (see end of "Falling With Helium" [1])

So it's rather amusing to me that things are coming full circle, and that Worlfram's guys are now using Munroe's topic to demonstrate SystemModeler, another Wolfram product.

[1] https://what-if.xkcd.com/62/

The page you linked says that he normally uses Mathematica, and fell back to Wolfram|Alpha for that piece when it started locking up.

While researching this article, I managed to lock up my copy of Mathematica several times on balloon-related differential equations, and subsequently got my IP address banned from Wolfram|Alpha for making too many requests.

That was an example. If you have to be pedant, then here are his other references to it:

https://www.google.com/search?q=wolfram%20site%3Awhat-if.xkc...

Compare with his (currently) 2 references to Mathematica: https://www.google.com/search?q=mathematica+site%3Awhat-if.x...

Mathematica and Wolfram|Alpha are developed by the same company, if you weren't aware.

Oh, suuuuuure, some kind of magic mathematics company run by a reclusive genius who got a Ph.D. from Cal Tech when he was twenty, and/or college dropout and/or megalomanaic bald silicon valley mogul.

answer for those following along: all of the above :)

trivia about flying on helium balloons:

"In 1982, Larry Walters flew across Los Angeles in a lawn chair lifted by weather balloons, eventually reaching several miles in altitude. After passing through LAX airspace, he descended by shooting some of the balloons with a pellet gun."

In Brazil, a priest doing a gimmick to raise some funds to his church went on flying with helium balloons. He was drifted to the ocean by the wind and didn't know how to return. He did took a phone and a GPS device. But he didn't know how to use the GPS he took to tell people his location. He died.

source: http://en.wikipedia.org/wiki/Adelir_Ant%C3%B4nio_de_Carli

There's also the wonderful Australian romantic comedy film Danny Deckchair. Danny flies away from his problems in a deckchair-balloon aircraft.

http://www.imdb.com/title/tt0337960/

> "In 1982, Larry Walters flew across Los Angeles in a lawn chair lifted by weather balloons..."

I watched an old episode of MythBusters last night on YouTube where they tested exactly that, it was Season 1 Episode 3 - if anyone is interested.

Trivia: the rifle's momentum comes not only from (M_bullet x V_bullet), but also significantly from (M_gunpowder x V_gunpowder). The burnt gunpowder is often 1/3 to 1/2 the weight of the bullet, and traveling faster than the bullet.

XKCD did a whole article along with the math about this topic specifically. Great read.

https://what-if.xkcd.com/21/

https://what-if.xkcd.com/imgs/a/21/jetpack_speeding.png

Best part.

I've just realized that it's curious how the cop pulled him over. Pretty sure tanks aren't fast enough or durable enough to make pursuit, and unless he stops firing while changing lanes, he likely strafed the cop getting off the road.

Frankly, I think the scenario is just too unbelievable. Perhaps a souped-up SWAT van clad with ablative plating and 12 inch thick laminated windshields, but definitely not just some ordinary cruiser.

I dunno. The gun is not aimed downwards, and i suspect the bullet drop is fairly limited for some distance, allowing for the cruiser to potentially pull in underneath the stream. Whoever is driving said cruiser will have some big metal balls to pull it off.

Checking Wikipedia it seems the round drops 1 meter pr 400 meters of travel.

https://en.m.wikipedia.org/wiki/GAU-8_Avenger#Accuracy

> Perhaps a souped-up SWAT van clad with ablative plating and 12 inch thick laminated windshields

Well, the whole point of the GAU-8 is that it shoots through tanks, so...

Yes, absolutely. I could suspend my disbelief up until I saw the ordinary cruiser.

It is written on this article that the article was inspired by the XKCD post.

Ahh I didn't catch that at first look. I love when people break down absurd things like this in myth busters style.

that's the idea behind Project Orion (nuclear propulsion): http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propul...

Great reference! A thermonuclear explosion drive - not elegant, but damn would that be a sight to behold!

Bonus points for EMPing vast swaths of the launch region.

Not all nuclear detonations cause EMP. It requires a particular set of circumstances.

"but damn would that be a sight to behold"

I imagine it would be quite something to experience as well!

From inside the ship you wouldn't really know that you were being propelled using nuclear bombs. Between the pusher plate and the ship are extensive shocks that would be designed to smooth out the pulsing power of the bombs into a smooth acceleration. Anything else wouldn't work very well and induce loads of stresses up the ship.

Great way to use up all those nukes we have lying around.

My first thought was a space propulsion drive based on machine guns, much like ion propulsion. If humanity decided to get rid of all firearms (ha!), we could probably send them to space and drive a few spacecraft cheaply, easily and for a very long time (there are a lot more bullets than nuclear weapons)

Thermonuclear propulsion, as cool as it is, would be very powerful but uncontrolled acceleration, whereas a firearms-based drive could be controlled a lot more.

It would be fun if someone did a comparison on how long, fast and far nuclear versus bullet drives would get us in space.

My first reaction was that bullets don't work in space due to the lack of oxygen, but quick ducking proved me wrong. Related interesting article: http://www.livescience.com/18588-shoot-gun-space.html

Some space propulsion engines work in this kind of "batch" fashion. http://en.wikipedia.org/wiki/Pulsed_inductive_thruster

Or we could just take all the bullets apart, use powder for fuel and casting melted bullet casings into rocket engines :).

Most bullet cases are made out of brass. I'm no rocket scientist, but brass cases would make a horrible rocket engine material.

The only reason cases don't catastrophically fail when you fire a gun is because of the bolt/chamber providing support.

Brass IS pretty good about stretching quite a bit before a catastrophic failure. This property is what allows case fire-forming (http://en.wikipedia.org/wiki/Fire_forming). It's also a pretty awesome safety feature.

Cases are so bad by themselves about containing the force of expanding gas, that ammunition fires aren't nearly as dangerous as you might expect them to be. (https://www.youtube.com/watch?v=3SlOXowwC4c) It's a long video, but if I recall correctly, it demonstrates that a rifle cartridge fired without a chamber doesn't have the energy to penetrate cardboard at like an 11 inch range.

I had a box of cartridges in a fire - they didn't go more than a few inches. The cartridge fragmented, like a firecracker with no net momentum to the bullet in any particular direction.

Didn't know that. Thanks for information!

He seems to make it unnecessarily complicated. Average thrust (momentum flux) is m_bullet x v_muzzle x fire rate, which needs to be higher than m_rocket x g for it to work.

The point here is to advertise Mathematica, not to solve a problem.

Reminds me of that Neal Stephenson book, Anathema, that had a space ship that was propelled by setting off nuclear bombs just outside its hull.

He didn't make that up. As crazy as it sounds, NASA considered exactly that idea in the 1950s: http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi....

Well it was the 50s. Both sides of the cold war tried to come up with various uses of nuclear power. From civilian cars to military strategic bombers. Never mind using nukes to dig harbors...

https://en.wikipedia.org/wiki/Project_Chariot

And would it surprise anyone that a champion of this project was Edward Teller?

Don't disparage the idea. It's by far the most efficient high-thrust rocket engine we could build with any technology we know exist.

My favorite is Project Pluto:

http://en.wikipedia.org/wiki/Project_Pluto

Which is nuclear ramjet, which has the small side-effect of spewing large amounts of radiation as it flies.

There were some crazy conventional technologies also. One scientist, as a joke, did a calculation about the effects of adding mercury to rocket fuel. It wouldn't react with the fuel, but it would add a lot of weight which would make the thrust more efficiently move the rocket forward.

This was tested, found to be true, and thankfully never put to use in any actual rockets.

(For confirmation, track down Ignition!.)

You mean, a convenient feature.

For everyone who's scrolling through this thinking, "Hey, this is pretty morbid," you ought to read http://www.infinityplus.co.uk/stories/colderwar.htm which kicks that feeling up to 11.

Pluto missiles also appear in Missile Gap, also by Charlie Stross - ballistic missiles have stopped working for quite an interesting reason....

NB A Colder War also gives me the creeps - largely for the point about what certain entities actually do with the souls they eat...

I know exactly which line you're talking about, and it's probably one of my favorite lines in literature.

I swear there is something in the water on the British Isles...

Niven & Pournelle's Footfall also had an Orion-type ship. It was a desperation tactic on the part of the overmatched Earthlings, but it worked.

Ha! Great reference, iirc the humans put a pusher plate under a battle ship (uss missouri?), launched into orbit and pummeled the aliens. I also recall something about fighter craft and 16 inch cannons. Great read.

I recall mainly the jury-rigged pipes that a character based on one of Niven/Pournelle's friends kept working at the cost of his own heroic death. Apparently they asked him what the fate of his character should be, and he picked death.

Based on physical appearance, he surely was also the prototype for the question-asker in "What Can You Say About Chocolate-Covered Manhole Covers?" That basically obscure story was big in my life because it's one of the things that introduced me to Roger Zelazny (it referenced his Agnostic's Prayer).

If I remember currectly, the Fthip dropships used a similar (but cleaner) pulse technology. They even claimed to have taught us the trick...

There is a game that puts this into concept called Jetpack Joyride (made by creators of Fruit Ninja): https://appsto.re/us/TybrB.i.

My physics class actually did a lab report to find the relationship between the # of bullets and distance propelled in the air with the game. While it was nowhere near as accurate as this simulation, it was definitely interesting to see the results.

An automatic-fire weapon in Cave Story also allows you to fly by firing it downward (though there is a separate jet pack item available as well).

This analysis and the xkcd one linked below both neglect the concept of staging - which could get you higher. As a first order try you could replace the human on the bed of guns with a smaller bed of guns supporting a squirrel - now you're twice as high! Of course at that point there is nothing stopping you from reaching the moon except for your gun budget and how much unobtanium you can get for the bed connecting structure.

Relevant video at 0:24 https://www.youtube.com/watch?v=FRp3S8OOeZc

Come now, everyone knows you use asparagus staging for this kind of thing. What happens when you start jettisoning empty machine guns as you go?

The ammunition mass is a more effective way of increasing your stored energy than extra rifles, so it is at least addressed implicitly in the section that examines the ammo to carry (1 gun with 2 bullets obviously beats 2 guns with single bullets, I guess more complicated situations would follow).

You always want to fly with the minimum number of guns necessary to provide your desired thrust and then as much ammo in addition to that.

Yeah, but the optimal amount of thrust need decreases as your mass decreases.

There is a jet aircraft, the A-10, with a gun so powerful that it provides more thrust than the jet engines.

"The average recoil force of the GAU-8/A is 10,000 pounds-force (45 kN), which is slightly more than the output of one of the A-10's two TF34 engines (9,065 lbf / 40.3 kN each). While this recoil force is significant, in practice a cannon fire burst only slows the aircraft a few miles per hour in level flight"

Source: http://en.wikipedia.org/wiki/GAU-8_Avenger

And then thanks to a certain XKCD what if article: https://what-if.xkcd.com/21/

We learn about a certain russian gun: https://en.wikipedia.org/wiki/Gryazev-Shipunov_GSh-6-30

That can apparently produce 40G of recoil force...

Towards the end of it all, it is starting to look like the premise of a certain mobile game: https://play.google.com/store/apps/details?id=com.halfbrick....

> The airframe vibration led to fatigue cracks in fuel tanks, numerous radio and avionics failures, the necessity of using runways with floodlights for night flights (as the landing lights would often be destroyed), tearing or jamming of the forward landing gear doors (leading to at least three crash landings), cracking of the reflector gunsight, an accidental jettisoning of the cockpit canopy and at least one case of the instrument panel falling off in flight.

It also used to produce so much oxygen-free gas that the engines would flame-out. The engines were modified to deal with it. Its in the same wikipedia article.

Some guys used exactly this effect to land the A-10C on an aircraft carrier in a flight simulator: https://www.youtube.com/watch?v=fteYkPabLTA Very entertaining.

An alternative video: https://www.youtube.com/watch?v=uKOrpyO0z48

I think someone could have a hit building a flappy-bird clone off this concept.

In the game Jetpack Joyride, you start with a "machine gun jetpack". http://jetpackjoyride.wikia.com/wiki/Machine_Gun_Jetpack

I was thinking of a sort of violent version of _Up_, in which Carl launches his house by shooting an assortment of machine guns attached to the bottom his house to propel it upwards instead of using balloons.

There's this old split-screen real-time worms clone called liero, it has rifle weapon that allows this in-game.

They play with reload times set to 0, so this is a little extreme, but just to give an idea:

https://www.youtube.com/watch?v=C6rfXFyssbE#t=695

This game is great BTW, very playable, strange that nobody did html5 online clone.

He's playing against the ridiculously bad AI in that video. Here's the more impressive "mortars only" style in the LieroX remake:

https://www.youtube.com/watch?v=kx3ivYFY4ig#t=67

I had a couple of years at uni where we played this on LAN in one of the computer labs during every lunch break. We even made some maps!

Maybe not html5, but teeworlds is a free clone with modern graphics and network play.

Ooooooh, give me about a week and your wish will be my command.

I'm going to file this under: I've always wanted to know this, but never knew I did.

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