From: ke4zv!gary@gatech.edu (Gary Coffman)
Newsgroups: sci.military
Subject: Re: Power Armor
Message-ID: 1991Aug5.222335.20925@cbnews.cb.att.com
Date: 5 Aug 91 22:23:35 GMT
Sender: military@cbnews.cb.att.com (william.a.thacker)
Organization: Gannett Technologies Group
Approved: military@att.att.com

From: ke4zv!gary@gatech.edu (Gary Coffman)

In article (1991Jul30.025031.28980@cbnews.cb.att.com)
fcrary@headcrash.Berkeley.EDU (Frank Crary) writes:
>
>
>From: fcrary@headcrash.Berkeley.EDU (Frank Crary)
>In article <1991Jul29.214711.16876@cbnews.cb.att.com> ke4zv!gary@gatech.edu
(Gary Coffman) writes:
>
>Too noisey for what? I think we are, again, talking to cross purposes. All
>I am trying to get out of "power armor" is IFV-level armored protection for
>the infantry. That way, they can hold terrian in exactly the way infantry
>has done for years, only much more safely and effectively.
>For my purposes, it is not vital for the suit to be quiet. I doubt the motors
>and other moving parts can be made all that quiet, even is the power source
>was...
>Personally, I see very little subtlty in a steel-encased infantry man.
Indeed we are still at cross purposes. I'm looking at a replacement for the NBC suit that restores a soldier's mobility, stealth, comfort, and sensory capabilities to normal or super normal levels. I'm willing to throw in a little armor for protection against small arms fire and shell fragments as well if it doesn't increase the mass of the suit unacceptably.

Modern DC brushless motors are available off the shelf in 5 hp that are only 1.5 inches thick and 3 inches in diameter. They develop maximum torque at stall so don't require gearboxes. They are virtually silent in operation. Synthetic joints coated with a material like teflon can make joint movement nearly noiseless. The real source of noise is banging one part of the suit against another. A possible solution to this problem is a thin coat of padding worn over the armor. A uniform for the suit if you will. Or more realistically, simply coat the armor with a thin layer of synthetic rubber like material. Hopefully one that is non-flamable. With synthetic materials like kevlar available, the suit would not necessarily have any appreciable amount of steel in it. Any needed structural members could be made of graphite epoxy composites. This would give the suit near immunity to magnetic proxmity mines.

>>This brings us back to electrical power provided by batteries or fuel
>>cells. In their present incarnation, batteries to operate for more than
>>24 hours are out of the question. Fuel cells are a better candidate, but
>>are a little farther away from practical use.
>
>In a recient report to the National Space Council, 1 kW-hr/kg was suggested
>as a goal (if a somewhat optomistic one) for fuel cells to achieve by 2010.
>Modern batteries run less than 100 W-hr/kg. Assuming my 5000 W estimate is
>good, this would result it 120 kg of 2010, state-of-the-art fuel cells for
>a 24-hour lifetime. I don't see this as very viable when compared to 25kg
>for a similar energy/power IC engine. If the noise bothers you, just use a
>turbine instead. The M-1 does. Based on the less effiecint fuel use, I'd
>still guess that this would weigh less that 100 kg.
>
>By the way, fuel cells require cryogenic (e.g. below -150 deg. C) liquid
>storage. How would this look to IR sensors?
Fuel/air fuel cells that operate off methanol and ordinary air have been demonstrated. These require a catalyst operating at 400 degrees C to work. That is not too bad if the ceramic reaction chamber is covered in good insulation. Room temperature catalysts are being actively sought. Unlike IC engines which are basically air pumps, this fuel cell has almost no exhaust until high demand is placed on it. It's IR signature is low except at full output when the motion of the suit would be visible anyway. Even then it's exhaust is orders of magnitude less than an IC air pump. If suitable room temperature catalysts are found, it will have almost no heat signature at all.
On the battery front, slurry primary cells are becoming available that can be refilled with the reactant slurry quickly. These have better power/weight ratios than any rechargeable cell though still not as good as the fuel/air cells. They have the advantage of working at room temperature today.

A turbine would be the power source of last resort. It's best run at constant speed for good efficiency. It accelerates to speed relatively slowly. It has a hot exhaust. And it emits a loud whine. While it's light, it's fuel requirements are not. Since the suit must be powered at some level at all times, even when stationary, the turbine is a bad choice for supplying power over the wide range required. Consider also the problem of trying to hear enemy movements while an 8 hp IC engine or a turbine is running on your back. If that's all that's available, then we might as well scrap the idea of powered suits right now.

Somebody mentioned logistics for PA. I would guess that platoon level support vehicles would be required to carry fuel, spare parts, and an armorer. There would be a need for depot level maintenance as well. This is not as bad as what is required for real armored vehicles, but we do need to think in similar ways about logistic support.
Depending on the mobility of the particular battlefield, it would be relatively easy to outrun your supply train. However, supply needs for PA could be handled by helos or air drops, something not feasible for heavy armor.

Gary


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