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[DJ]

Why armor an actual human when you could just send in a remote-controlled combat drone? Not needing room for an operator gives you a lot more freedom when designing it. In case enemy is capable of jamming or even hijacking the signal, go with fully autonomous AI instead of remote operators. There's no way that could go wrong

[Sergarr]

This is not the route military technology will evolve in. The future of infantry hardware is detection and concealment aids, not ways to make an individual soldier attract higher-caliber gunfire.

Yeah say that to people who have to storm buildings.

[Magistrum]

Then I say that the future of military is no soldiers at all, why the heck don't we just build small automatons, like for everything.

[GiglameshDespair]

Then I say that the future of military is no soldiers at all, why the heck don't we just build small automatons, like for everything.

Some people are not overly fond of autonomous killing machines wandering around, not to mention the practical difficulties of keeping them armed, maintained, fuelled, or stairs.

[NullForceOmega]

The other problem with heavy PA is that it diminishes the role of the soldier, he can no longer engage in urban warfare as his mass is too high to enter the vast majority of buildings and his dimensions to large to maneuver well.  The point of PA should be to expand the role of infantry, not restrict it, we have tanks, IFVs, attack choppers and numerous other options for heavy weapons usage.

[Jopax]

Yeah, I don't see powered armour really being successful, atleast not on Earth. Having a fully enclosed and armoured suit for a single person isn't really practical, especially since the tradeoffs are so high. Having it in an enviroment that already requires a fully enclosed suit is a bit more feasible since you're throwing resources into a suit anyways, might as well make it hardy enough to survive a couple of uses.

What I do see developing is exoskeletons, like the kinds we've seen in Elysium or Stalker. Where the focus isn't so much on protection, which is mostly the same as a regular trooper, but increasing the carrying capacity, strength and endurance of the wearer. A combination of spring systems and actual motors would be the best I think to minimize the energy required and maximize the operational time.

[NullForceOmega]

No, full environmentally sealed PA most certainly does have a place on Earth's battlefields, it just has no reason to be a tank.

[Jopax]

In certain situations yes. But think about it.

However armoured you make it, you can't make it completely immune to the kinds of weapons infantry has access to these days. So you're better off having fully enclosed regularly armoured suits (so todays chemical warfare equipment and regular infantry armour in essence) that are cheap and easily fieldable than having a single very expensive system that can get killed just as easily.

And that's the problem with PA, it sits in that middle ground of protection and investment that doesn't offer the protection of an AFV yet is almost as expensive to manufacture because of the required tech. So you either invest little for minimal protection for everyone, or you invest a lot for maximum protection of several. The middle ground is just not a feasible thing right now and I can't see it becoming one anytime soon. Because as much as protection tech develops, weapons tech is always either in lockstep or a few steps ahead of it.

[NullForceOmega]

The US Army has been actively developing PA since the 1970s.  If they feel that the investment is worthwhile enough that they have been actively working on it for forty years, it must be viable enough for their purposes.

[DJ]

I can see exoskeletons at least being useful in urban environments. They could carry heavier weapons than a normal soldier, and deploy them on rooftops.

[Morrigi]

The idea with the power armor that the U.S. is developing seems to be to keep it small and light enough to prevent it from causing serious mobility problems in confined spaces, yet tough enough to be able to protect against anything short of .50 BMG. It will be ideal for urban assault and special forces raids, if they ever get it to work.

[wierd]

Honestly weird, there is no valid reason to try to keep the operator on their feet under that kind of kinetic force, what the armor has to do is keep the soldier alive, not turn him into a one-man Abrams.  All the plating a suit of viable PA needs to do is disperse the force, just like a Kevlar vest only heavier, that way you have still made the soldier functionally invulnerable to small arms and allow him/her to survive against heavier weapons.  It is not unimaginable that such a system could come in at under five hundred pounds, including power supply (depending on your willingness to spend money.)  We don't actually have a need for Glitterboys, just T-51.

You are very much underestimating how heavy a T-51 is going to be.

To stop small arms fire, you need either steel plate that is about a quarter inch thick, or some kind of hybrid plate with ceramic.

There is an equation for this, from this source document

5-3.4.2.1.2.  Steel.   

The projectile velocity at which a given
type and thickness of steel plate can prevent
perforation is commonly referred to as the limit
velocity.  Equation 5-3 is a manipulation of
the limit velocity equation for steel to give
plate thickness.  Note that the thickness
reported by Equation 5-3 is what is necessary
to stop complete perforation (the projectile
passing completely through the plate and
emerging with zero velocity).   

That represents a safe condition for most
applications, although there are times
when ensuring that there is no rear face
spalling is necessary.  In those cases, add two
bullet diameters to the plate thickness
determined from Equation 5-3. 

Note that Equation 5-3 is only valid for
calibers of 0.50 (12.7 mm) or less.  For
larger calibers, refer to UFC 3-340-01.
   
If the plate thickness is less than that given
in Equation 5-3, the bullet will pass
through the plate with a residual velocity,
which can be predicted using Equation 5-4. 
That residual velocity could then be applied to
another material layer. 

In doing so, it is commonly assumed (conservatively)
that the bullet retains all of its mass. 
In that equation, impact velocity can initially
(conservatively) be taken to be muzzle velocity. 
Where the equation is used to evaluate multiple
protective layers, the residual velocity
would be used as the impact velocity in equations
 5-3 or 5-4 or in other similar equations
for other materials.

And here is the "Appendix A" they are referring to.



For an example of a real world product intended to help people survive small arms fire, here's a commercial offering.
http://shop.tacticalshit.com/10x12-armor-plate-steel-defender-new

It is a 10in by 12in, by .24in steel plate with a brinell hardness of 500.  It weighs 7.5lbs, give or take. With this type of steel plate, we can extrapolate how much a suit of power armor will weigh, with JUST the plate. (Not counting the actuators, the weight of the hydraulic fluid and pumps, the weight of the fuelcell and electronics-- or all that other stuff that makes it into power armor and not just steel plate armor.)

I will do a very rough estimation of a human's volume, expanded 1/4 inch in thickness as a shell in my preferred CAD software, apply a suitable material to the resulting shell, and get the calculated mass.

I am assuming an ellipsoid volume of 5.5ft (tall) by 1.5ft(wide) by 1ft(thick) as the basic volume of a typical human body. I am then going to extrapolate a 1/4in thick steel shell, and measure the mass in the software.

I get the following result.



This gives us a rough mass of the needed steel plate of approximately 333.75kg, which is 735.7928lbs

This is actually CONSERVATIVE, because wolfram gives an average volume of a human body of 66.4L, which works out to 0.0664 cubic meters.  As you can see from the CAD software, the volume I worked with, when extrapolated with the .25in thick plate, is only .042 cubic meters.  That means the actual plate weight will be LARGER than this rough estimate!

So, I will say again, for the power armor to be useful as power armor, it is going to weigh a shit ton. With the weight of the occupant, fuel, actuators, and all that shit, we are talking over 1000lbs for the ensemble-- easy.

That's assuming it is made of steel, of course.
 

[NullForceOmega]

And all of that is based on flat penetration and disregards sloping, deflection angles or other principle elements of design, which reduce the overall thickness and mass of armor that needs to be utilized, and as you yourself said, it assumes all steel construction, which is obviously unworkable, and so it would clearly involve composites and synthetics.  All you're doing here is trying to brute-force the equation and in so doing you are totally ignoring the design.  For an example, construct a box made of steel a foot thick and fire a cannon at its' nice flat side, it'll cave right?  Now turn it into a properly constructed tank, and suddenly, lol, bounce.

[wierd]

Nope, that equation has a theta value for angle of incident.

The problem with ceramic armors is that they are ablative. That means the ceramic chips off under stress. Ballistic ceramic plate armor will disintigrate under repeated bullet impacts. That means that using it as a composite will only net you so much weight reduction before adding more ceramic becomes a design liability.

And, like I pointed out, this comes in BEFORE you have the hydraulic systems installed. The fluid in the hydrualic system has weight, as do the compression cylinders.

The brute force math that you derided was just to get a ballpark rough estimate of the mass required. It far exceeds your 500lb value for assemblage with occupant.

To get that, you need to have an empty assemblage weight of around 300lbs, give or take. What you will find is that the fuel cell itself required to operate the device is easily going to weigh 100lbs just by itself, and the hydraulics needed another 200lbs. You cant have armor plates that weigh 0lbs. (Most fuel cells use platinum as the catalytic element, which is a very heavy material-- and the hydraulics have to be made from very thick steel to handle the compressive torque forces applied)

Again, your estimates for what a T-51 will weigh are WAAAAAAY off.

[NullForceOmega]

I never included occupant in my estimate, the estimate is for armor and components only.  And furthermore, hydraulics were the very first thing the Army tried, and they summarily dismissed the concept, so were much more likely to be looking at high-torque servomotors.  And yes, I see it's inclusion of angle of incident, but I certainly don't see yours.