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What-If 0021: "Machine Gun Jetpack"

Posted: Tue Nov 20, 2012 11:47 am UTC
by Daimon
Link to the What-If

Clearly I have as much to say about this edition of "What If" as all my friends and family have to say about me.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 12:03 pm UTC
by Caffeine
I'm reminded of Yosemite Sam...

Edit: Like this! http://www.youtube.com/watch?feature=pl ... iwrg#t=22s

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 12:09 pm UTC
by peewee_RotA
Any chance this can be improved using MetalStorm?
http://www.metalstorm.com/content/view/64/109/

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 12:19 pm UTC
by peewee_RotA
Oh and if anyone else was wondering, here's a weapon that will fire 61 pound bullets:
http://en.wikipedia.org/wiki/BL_60_pounder_gun

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 12:34 pm UTC
by Klear
And then there's Project Orion.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 12:42 pm UTC
by Thorbard9
AK-47.
A-10 Warthog.
5" Artillery.
MetalStorm.
Nuclear Bombs.

Yep, that's a pretty terrifying arms race right there.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 12:58 pm UTC
by LittleMikey
The bit that intrigues me is the fact that the GAU-8 mounted on an A-10 produces so much recoil.

What I'd like to know is how much this can slow the plane down while it's flying. I'm guessing that the plane already lowers it's speed for a strafing run, but if the gun was fired in a sufficiently long burst would it be enough to cause the plane to loose so much speed it would stall? Or can the A-10 maintain flight even at very low speeds?

If anyone knows I'd be delighted to find out the answer!

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 1:01 pm UTC
by rmsgrey
By the time you're using rapid-fired nuclear bombs as propulsion, you're not really talking about a jetpack any more - at least not for people significantly smaller than the average skyscraper...

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 1:13 pm UTC
by project2051
How about a Schwerer Gustav?

Firing rate might be a problem though.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 1:30 pm UTC
by Vroomfundel
LittleMikey wrote:The bit that intrigues me is the fact that the GAU-8 mounted on an A-10 produces so much recoil.

What I'd like to know is how much this can slow the plane down while it's flying. I'm guessing that the plane already lowers it's speed for a strafing run, but if the gun was fired in a sufficiently long burst would it be enough to cause the plane to loose so much speed it would stall? Or can the A-10 maintain flight even at very low speeds?

If anyone knows I'd be delighted to find out the answer!


I think aviation experts are reluctant to give out any numbers about stall speeds as it depends on too many parameters. First of all, air density is crucial - the denser the air the less speed you need to maintain altitude. So, for close air support missions (for which A-10 is designed) stalling shouldn't be a problem. It also has "self-sustaining combustion section" which, I would guess, helps maintain the engines in operating condition during firing, although it's designed to prevent them from choking on the gases emitted when firing.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 1:38 pm UTC
by Klear
rmsgrey wrote:By the time you're using rapid-fired nuclear bombs as propulsion, you're not really talking about a jetpack any more - at least not for people significantly smaller than the average skyscraper...


Who cares? We need more power!

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 2:39 pm UTC
by atomfullerene
It's like the Kzinti lesson in reverse....the better a weapon is, the more efficient a reaction drive it makes...

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 2:46 pm UTC
by Beltayn
"An AK-47 clip holds 30 rounds.""

It's a magazine, not a clip.

-A magazine is an insertable container filled with rounds that can be removed, refilled, and re-used when it runs empty. An AK-47 and M-16 use magazines.
-A clip is a disposable attachment of several rounds together that simply gets ejected automatically when the last round is fired, following which you just insert a new one. There is nothing to remove or reuse. An M-1 Garand, such as was used in WW2, used clips. The clip being ejected was what made that distinctive CA-CHING noise when you ran out of ammo.

Also, there's some nominclature confusion in the article between "rounds" and "bullets". The two are not interchangable.
The bullet is just the projectile, the lead slug that is shot out of the rifle. The casing and charge, along with the bullet, all add up to being a round.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 2:48 pm UTC
by cellocgw
Vroomfundel wrote:
LittleMikey wrote:The bit that intrigues me is the fact that the GAU-8 mounted on an A-10 produces so much recoil.

What I'd like to know is how much this can slow the plane down while it's flying. I'm guessing that the plane already lowers it's speed for a strafing run, but if the gun was fired in a sufficiently long burst would it be enough to cause the plane to loose so much speed it would stall? Or can the A-10 maintain flight even at very low speeds?

If anyone knows I'd be delighted to find out the answer!


I think aviation experts are reluctant to give out any numbers about stall speeds as it depends on too many parameters. First of all, air density is crucial - the denser the air the less speed you need to maintain altitude. So, for close air support missions (for which A-10 is designed) stalling shouldn't be a problem. It also has "self-sustaining combustion section" which, I would guess, helps maintain the engines in operating condition during firing, although it's designed to prevent them from choking on the gases emitted when firing.


Well, wikipedia quotes 120 kt design stall speed. You should be able to calculate the "initial speed" vs. "length of firing burst" from the info Randall provided. :mrgreen:

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 3:02 pm UTC
by OK Whatever
As a full-time professional technical consultant for the firearms industry, I applaud the author for making essentially no glaring technical errors (other than the clip/magazine mistake), as would be rampant with typical journalists.

I also would suggest a system that jettisons depleted machine guns, like "up goer five."

Perhaps even using different stages, with first stage optimized for pure thrust, and later stages optimized for lighter weight.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 3:11 pm UTC
by kurukkan
Metagun.

Registered to say this.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 3:28 pm UTC
by JReynolds
Interesting. In the excellent book Ragamuffin by Tobias Bucknell, the main characters have to escape from some baddies using exactly this method (it's even shown on the cover art). It helps that they're in zero g. They could even shoot at the bad guys and keep accelerating.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 3:40 pm UTC
by peewee_RotA
JReynolds wrote:Interesting. In the excellent book Ragamuffin by Tobias Bucknell, the main characters have to escape from some baddies using exactly this method (it's even shown on the cover art). It helps that they're in zero g. They could even shoot at the bad guys and keep accelerating.


lol

Image


This has been explored in video games as well. There are laser jumps in halflife (1), megaman 9 has a level where you move around in gravity by firing the buster. I'm sure there's more examples but I know that this is something I try routinely in FPS's to try to get higher jumps. Although rocket jumping is more common, every so often you get lucky with kickback.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 3:45 pm UTC
by AvatarIII
Beltayn wrote:"An AK-47 clip holds 30 rounds.""

It's a magazine, not a clip.


I blame Doom, the ammo you pick up in doom is called a clip and it looks like a magazine.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 3:45 pm UTC
by Klear
JReynolds wrote:Interesting. In the excellent book Ragamuffin by Tobias Bucknell, the main characters have to escape from some baddies using exactly this method (it's even shown on the cover art). It helps that they're in zero g. They could even shoot at the bad guys and keep accelerating.


I believe this is a (perhaps often forgotten) reason why you often have lasers and such in sci-fi settings - so you don't have to deal with the recoil in zero g.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 3:56 pm UTC
by rmsgrey
Klear wrote:
JReynolds wrote:Interesting. In the excellent book Ragamuffin by Tobias Bucknell, the main characters have to escape from some baddies using exactly this method (it's even shown on the cover art). It helps that they're in zero g. They could even shoot at the bad guys and keep accelerating.


I believe this is a (perhaps often forgotten) reason why you often have lasers and such in sci-fi settings - so you don't have to deal with the recoil in zero g.


Not that that would work - photons have momentum too.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 4:07 pm UTC
by MrT2
LittleMikey wrote:The bit that intrigues me is the fact that the GAU-8 mounted on an A-10 produces so much recoil.

What I'd like to know is how much this can slow the plane down while it's flying. I'm guessing that the plane already lowers it's speed for a strafing run, but if the gun was fired in a sufficiently long burst would it be enough to cause the plane to loose so much speed it would stall? Or can the A-10 maintain flight even at very low speeds?

If anyone knows I'd be delighted to find out the answer!

I don't know any relevant figures, but the A-10 does automatically go to full throttle power while the gun is firing. Additionally as it will be aiming at ground targets, the angle of attack will be negative, which helps pick the speed back up once it stops firing.

Edit: a bigger issue than recoil stalling with large calibre weapons on jet aircraft is compressor stalling of the engine, caused by propellant gases from the munitions entering the engine - so it's quite likely that the length of bursts allowed is limited by the gas produced before the recoil has a substantial effect on airspeed.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 4:39 pm UTC
by gmalivuk
rmsgrey wrote:
Klear wrote:I believe this is a (perhaps often forgotten) reason why you often have lasers and such in sci-fi settings - so you don't have to deal with the recoil in zero g.
Not that that would work - photons have momentum too.
Yes, it will still work, in the sense that there's not enough recoil to need to "deal with" with a photon weapon. You'd need a 17GW laser weapon to produce the recoil calculated for an AK-47. For the same amount of recoil, meanwhile, the AK only puts out a bit over 20kW (which would produce 68 micronewtons of thrust from the laser weapon).

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 4:54 pm UTC
by rmsgrey
gmalivuk wrote:
rmsgrey wrote:
Klear wrote:I believe this is a (perhaps often forgotten) reason why you often have lasers and such in sci-fi settings - so you don't have to deal with the recoil in zero g.
Not that that would work - photons have momentum too.
Yes, it will still work, in the sense that there's not enough recoil to need to "deal with" with a photon weapon. You'd need a 17GW laser weapon to produce the recoil calculated for an AK-47.

What's the power-level required to burn a 1mm diameter hole through someone in a tenth of a second?

The standard SyFy blaster does at least equivalent damage to a conventional firearm - so a 9mm hole might be more accurate - the goal being to incapacitate or kill the target, not to give them a localised sunburn...

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 5:16 pm UTC
by gmalivuk
rmsgrey wrote:What's the power-level required to burn a 1mm diameter hole through someone in a tenth of a second?
Less than 17GW.

Atomic Rockets says 1J pulses in 5 microsecond intervals is ideal against soft tissue, so 200kW average. Which produces about 2/3 of a millinewton.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 5:27 pm UTC
by Whizbang
The damage from a bullet is not always from the size of the entry point. Bullets often bounce around inside the body, ripping organs to shreds. A "through and through" is usually not very serious, unless it is through an organ. A laser would always be a through and through, and so require more accuracy. You'd always have to hit the heart, lungs, or head. A gut shot would be messy, and probably lead to death eventually, but would give the victim plenty of time (assuming they tolerate the pain) to shoot back at you.

Bullets, FTW.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 5:33 pm UTC
by rmsgrey
gmalivuk wrote:
rmsgrey wrote:What's the power-level required to burn a 1mm diameter hole through someone in a tenth of a second?
Less than 17GW.

Atomic Rockets says 1J pulses in 5 microsecond intervals is ideal against soft tissue, so 200kW average. Which produces about 2/3 of a millinewton.


Okay, so realistic laser weapons (intended for use against unarmored targets) would produce a bit less than one microgee of thrust for a human wielder. That sounds like manageable recoil :)

Meanwhile, back at the article, I'm not sure why the cop pulled Cueball over either - speeding, reckless endangerment, aggravated property damage, manslaughter, possession of an illegal weapon...

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 5:43 pm UTC
by J Thomas
rmsgrey wrote:Meanwhile, back at the article, I'm not sure why the cop pulled Cueball over either - speeding, reckless endangerment, aggravated property damage, manslaughter, possession of an illegal weapon...


I wonder if he chased the car down from behind with his siren on. Pretty gutsy if so, since the slightest little hill would leave him only a thin smear of blood and tissue coating a bunch of bullets.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 5:50 pm UTC
by Beltayn
Whizbang wrote:The damage from a bullet is not always from the size of the entry point. Bullets often bounce around inside the body, ripping organs to shreds. A "through and through" is usually not very serious, unless it is through an organ. A laser would always be a through and through, and so require more accuracy. You'd always have to hit the heart, lungs, or head. A gut shot would be messy, and probably lead to death eventually, but would give the victim plenty of time (assuming they tolerate the pain) to shoot back at you.

Bullets, FTW.


This. Most of the damage from a ballistic impact on tissue is caused by either fragmentation bouncing around inside the chest cavity within the rib cage and shredding the organs, or the shock of the exit wound.

As any medic or doctor would tell you, the Human body is both astonishingly fragile, and at the same time astonishingly resilient.
In the military, they teach us that a hit anywhere except directly through the brain stem (known in marksmanship as the "T box") is potentially survivable. The main killer is not the punctures or tissue/organ damage, but rather bleeding out.

Additionally, ballistic exit wounds are often a lot worse than the entry wounds. As the projectile enters the tissue, basically causes a bow wave of force that blows out the back of the body.

A laser weapon would not have any of these advantages. It would leave a nice, perfect burn incision that would likely cause little damage unless it severed a major artery or hit the brain stem.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 5:51 pm UTC
by rmsgrey
Whizbang wrote:The damage from a bullet is not always from the size of the entry point. Bullets often bounce around inside the body, ripping organs to shreds. A "through and through" is usually not very serious, unless it is through an organ. A laser would always be a through and through, and so require more accuracy. You'd always have to hit the heart, lungs, or head. A gut shot would be messy, and probably lead to death eventually, but would give the victim plenty of time (assuming they tolerate the pain) to shoot back at you.

Bullets, FTW.


Hitting just one lung would generally be non-lethal - the lethality of a lung-shot comes from all the blood and other fluids getting into in the wrong places (and out of the right places) - you can survive pretty much indefinitely with just one lung.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 6:14 pm UTC
by gmalivuk
Plus the laser will neatly cauterize the wound, which is kind of the opposite of killing through bleedout.

I'm not suggesting that laser weapons would actually be useful, but they wouldn't cause significant recoil, photon momentum notwithstanding.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 6:37 pm UTC
by Klear
What if the laser doesn't fire pulses (think phasers in Star Trek) and is capable of slicing the target in half, though? ;)

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 6:41 pm UTC
by neremanth
Presumably if you were good enough at aiming you could blind someone with a laser gun - that'd have to severely reduce their capacity to continue firing at you. Or would that take long enough that they'd be able to turn/move their head out of the beam before the damage was done?

(I suppose there'd also be the freak possibility that you might instead correct any pre-existing shortsightedness...)

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 6:52 pm UTC
by ahammel
Lasers would also be presumably be better weapons in a space combat setting where if you get a hole of any size in your space car or your space clothes you are having a bad problem and it may be a bad thing that you are in space today.

Recoil is presumably a worse problem in free-fall/vacuum as well.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 6:52 pm UTC
by gmalivuk
Klear wrote:What if the laser doesn't fire pulses
Then it will be even less effective, because the gas from vaporizing the material will get in the way of the beam.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 6:56 pm UTC
by gmalivuk
Considering 1W lasers have serious accidental blinding potential, I'd say it happens too fast to close your eyes or move out of the beam. But of course going without eye protection into a fight where you know people will be shooting lasers is a seriously stupid thing to do.

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 7:10 pm UTC
by Radical_Initiator
gmalivuk wrote:Considering 1W lasers have serious accidental blinding potential, I'd say it happens too fast to close your eyes or move out of the beam. But of course going without eye protection into a fight where you know people will be shooting lasers is a seriously stupid thing to do.


Would make for an interesting warning panel on your laser: "Eye protection is required at all times laser is in use, especially military engagements."

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 7:12 pm UTC
by charonme
The GAU8 is not mounted on the A10 plane. The plane is built around the gun :)

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 7:22 pm UTC
by Klear
gmalivuk wrote:
Klear wrote:What if the laser doesn't fire pulses
Then it will be even less effective, because the gas from vaporizing the material will get in the way of the beam.


Ok, have several pulse laser next to each other, so that they'd in effect make a long hole capable of severing limbs... or some other shape capable of taking chunks of meat off your enemies. Or would that make the recoil no longer negligible?

Re: What-If 0021: Machine Gun Jetpack

Posted: Tue Nov 20, 2012 7:28 pm UTC
by gmalivuk
Just multiply the recoil per laser by the number of lasers to get the total recoil.