
Flying with Machine Guns? - lelf
http://blog.wolfram.com/2014/12/05/flying-with-machine-guns/
======
AceJohnny2
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/](https://what-if.xkcd.com/62/)

~~~
mintplant
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._

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

~~~
logicallee
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 :)

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damoncali
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.

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winslow
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/21/)

~~~
digi_owl
[https://what-if.xkcd.com/imgs/a/21/jetpack_speeding.png](https://what-
if.xkcd.com/imgs/a/21/jetpack_speeding.png)

Best part.

~~~
HCIdivision17
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.

~~~
digi_owl
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](https://en.m.wikipedia.org/wiki/GAU-8_Avenger#Accuracy)

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bra-ket
that's the idea behind Project Orion (nuclear propulsion):
[http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propul...](http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29)

~~~
nickpinkston
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.

~~~
arethuza
"but damn would that be a sight to behold"

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

~~~
rtkwe
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.

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lutorm
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.

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

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acadien
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.

~~~
CurtMonash
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.

~~~
marktangotango
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.

~~~
CurtMonash
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).

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

~~~
bitwize
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).

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cmsmith
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.

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unchocked
Relevant video at 0:24
[https://www.youtube.com/watch?v=FRp3S8OOeZc](https://www.youtube.com/watch?v=FRp3S8OOeZc)

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lmm
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?

~~~
maxerickson
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.

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

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

~~~
Gracana
"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](http://en.wikipedia.org/wiki/GAU-8_Avenger)

~~~
digi_owl
And then thanks to a certain XKCD what if article: [https://what-
if.xkcd.com/21/](https://what-if.xkcd.com/21/)

We learn about a certain russian gun: [https://en.wikipedia.org/wiki/Gryazev-
Shipunov_GSh-6-30](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....](https://play.google.com/store/apps/details?id=com.halfbrick.jetpackjoyride)

~~~
TheLoneWolfling
> 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.

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prestonbriggs
An alternative video:
[https://www.youtube.com/watch?v=uKOrpyO0z48](https://www.youtube.com/watch?v=uKOrpyO0z48)

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

~~~
ajuc
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](https://www.youtube.com/watch?v=C6rfXFyssbE#t=695)

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

~~~
darsham
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](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!

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

