Re: Armor

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi David,

At 11:00 AM 2/4/2003 -0600, you wrote:
>Hi All,
>
>With all the talk about Kevlar and protective panels for the prop gap, as 
>a former wearer of body armor, I know a little about their construction.
>
>For soft armor, such as flak jackets, they use either polyethelene, 
>Kevlar, or nylon.  The military flak jacket is constructed of multiple 
>layers of ballistic nylon.  The layers of nylon are about 1/2" thick when 
>sewn together. Polyethelene panels about 1/16" thick are tack sewn to the 
>fabric to help prevent bunching of the fabric.  Bunched fabric loses it's 
>protective properties.  My tests on a flak jacket stopped a .22LR, but 
>failed to stop a 9mm 115gr FMJ at point blank ranges.  Kevlar and Spectrum 
>(polyethelene) are used in higher threat vests.  In SWAT team vests 48 
>layers are used along with titanium or ceramic plates.

Interesting!  Apparently the air bags in cars are ballistic nylon.  I have 
seen sharp objects fired at UHMW PE and I was not real impressed.  I think 
the PE (PolyEthylene) also needs the ballistic fiber stuff in there 
too.  It is sort of a "total system" thing.

>
>In the military, I had to wear the kevlar/ceramic vests that could stop 
>7.62mm.  In the OH-58 helicopter, we had problems with the torque meter 
>gear exploding in the accessory gearbox on the engine. This gear was 
>spinning at about 32-36,000 RPM, and when it went, it blew scrapnel thru 
>the back seat area of the aircraft.  We had to keep the ceramic armor 
>panels on the front seats at all times.  If we had passengers, they rode 
>in the front seat, while I as crew chief, had to put on the armor vest and 
>helmet to ride in the back.  It's fun when your aircraft is built by the 
>deepest pocket/lowest bidder.

"My" first thought would be to put the bullet vests around the "gear 
box"...  Much as we are thinking here with the rotary gaps.  Better to 
armor the source rather than the people...  Of course, who am I to argue ;-))

>
>For something like the prop gap, I think 1/4" HDPE cutting board would do 
>fine in catching the electrode chunks.

Probably, but don't use any thinner.  A high speed tungsten rod that 
impacts on the tip could have a lot of penetrating power.  I don't think 
carpet would stop that.

>For a large ASRG, I would consider anything that could stop a 30-06 or better.

Lets see, a chunk flying off a 12 inch diameter rotor at 10,000 RPM travels 
at say 520 feet per second (350MPH).  Well below bullet velocities, but 
those chunks can be very heavy and very sharp.  Kevlar "may" stop that 
while being light and flexible (might need many layers which would be a 
problem).  6-4 titanium is another material that would work great if you 
can find big enough chunks of the cheap scrap stuff (preferably, already 
the right size so you don't have to try and cut the stuff).  I worry about 
wood, carpet, simple plastics since odd things happen at ballistic 
speeds.  Seemingly hard materials can shatter like glass at high speeds.

Of course, 90% of gaps probably don't need "real armor".  But I have seen 
some big high speed gaps (one has 1/4 pound electrodes!) that definitely 
look like they are in the land mine catagory shrapnel wise.

Cheers,

         Terry


>
>David E Weiss