Wire guided missile question

I recently saw this picture of a wire guided missile in flight: http://i161.photobucket.com/albums/t205/dennismenace56/untw3.jpg

It reels out fine guidance wires while it travels 620 miles per hour to the target.

Looking at cross section drawings, it appears that the wire dispensers are about 1inch in diameter and about 12 or 14 inches long. There is 2.5 miles of wire packed in them.

This seems incredible to me, since I can’t even cast with a rod and reel without the string getting tangling up inside the reel.

Any SD’rs out there who can fight my ignorance of the manufacturing marvels involved in reeling out 2.5 miles of micro thin wire at 620 mph?

Oooops, my link didn’t work. Here’s the picture:


Found this patent for a fiber optic missile guidance. If you go to the PDF linked on the top left of the page, it goes into a bit of detail about the fiber. Looks like the wire doesn’t get spooled like a fishing rod, but is coiled like a helix with the axis in line with the direction it unwinds into. There some more details but figures 3 and 4 from the PDF gives a good view of how it works.

Fishing line doesn’t start out tangled, it’s just hard to get it back on the reel perfectly after casting. If fishing reels were a one-use item like wire-guided missiles, even the cheapies wouldn’t tangle.

The reason you get backlash when you cast is really because at some point, the reel is spinning faster than the line is coming off the reel. If the lure/bait continued to accelerate away from you, or even kept a constant speed, you’d be fine.

Instead, it starts off fast, and slows down, especially as it hits the water, and that’s usually when the reel backlashes- it’s still spinning, and the lure’s hardly moving.

Same thing works for spinning reels, but you have to work at it more. (I think it’s line momentum that pulls off too much line when the lure stops, since the reel’s fixed)

A missile has close to that constant speed/acceleration, right up until it hits, or gets to the end of the line, hence no backlash.

The military has better R&D then the maker of your reel

Thanks everyone for the very interesting and informative replies.

Thanks Enilno for that excellent link.

I suppose the length of the wire is only limited by how thin it can be drawn and still retain the proper amount of tensile strength. A monumental job for the metallurgists, no doubt. And complicated by the fact that it has to be insulated, as well.


Fun Video.

If you ever find one of the spent rockets, DO NOT try to break those incredibly thin wires with your hands.

that being said, wire-guided missiles did fine back in 1973 during the Yom Kippur war, long before the fiber optic cables. If the Russians can mass-produce it and Egyptian [del]peasants[/del] conscripts can use it with great effect, apparently it’s not the hardest sort of rocket science.

Yeah, I was gonna say I bet your reel doesn’t cost $1MM and isn’t single use.

Another vote for it being pulled off the spool end-wise. There is nothing spinning inside the back of the rocket, it is simply pulling coil after coil off the end.

Kind of like pulling straight up on a coiled extension cord laying on the floor.

And as anyone who has done this has discovered, for each coil, the cord gains one twist. By the time you have pulled off ten coils or so, the thing gets pretty kinked up. I imagine that for a fine wire, these twists won’t matter.

Back in my film projection days, as part of the process of removing old trailers from the head of the movie, we would simply break the splice and pull out the whole section of film that was the trailers—about a half inch or so of the center of the platter, better understood with this picture.
Since we would be holding on to a few hundred feet of coiled film, with no reel, we had to lay it on the floor, stretched out, from one end of the projection booth to the other in order to be able to reload it on to the manufacturer’s small plastic cores they sent them on.

I had developed a technique where I would pull off four loops from one side of the big coil and then four loops off of the other side, alternating like this as I walked from one end of the booth to the other. By doing this, the film would not develop any twists over its length and I could reel it up without trouble.
The other guys would always pull the loops off one side of the coil and struggled with terribly twisted film at the rewind bench.

Actually, I DID find one. Many moons ago. Didn’t touch it, much less break any wires. Did take a picture though.


Although they left it out of the film version of The Hunt for Red October, both for simplicity and because of a key scene near the end that would have been confusing (when the US helo drops the clearly wire-free torpedo but it is still remotely detonated by Adm. Greer), modern torpedoes are wire-guided too. They of course also have (rather sophisticated) built-in AI software for free-running as well (wire runs out, breaks, malfunctions etc.)

What about flossing?

The Germans used them in WW-II as air to air missiles (Ruhrstahl X-4). They had attenuating detonators set to the sound of a B-17 motor. The spools are attached to the winglets and are visible in the picture. WIKI

This is just an educated guess, not a firm answer, since I have no real knowledge of such things.

I would bet you that the coil of wire has no actual core or hub at its center. It is probably just a self-supporting coil with a “hole” in the middle. Then the wire unspools from the inside of the coil, not from the outside. You see this design in some paper hand towel dispensers in public restrooms, the ones where you pull the towel from a plastic “teat” under a vertical drum that holds the paper towel roll.

IMO, inside unspooling is far superior to outside unspooling (like your fishing reel) since the wire unspools itself at its own speed, it does not rub against the still-spooled wire, and there are no real moving parts to interfere with the process.

Not to hijack too much, but does anyone know at a very high level how a wire guided system works? Wikipedia is sparse on details.

I’m imagining that the guidance system at the firing location would have to track both the position of the projectile as well as the target and make adjustment in real time. If that’s the case, how does it keep track of these two without GPS or some similarly accurate positioning system? Or is it done completely differently?

Can you please post a picture of the type of dispenser you mean? I think your idea is interesting.

The operator has to keep the sight pointed at the target while the missile flies. The missile has some sort of light or flare in the back of it. The sight detects that, and sends commands to bring that light into the crosshairs. The missile just flies in a straight line wherever the sight is pointing.