Swiss Army Knife

[Fred Brackin]

Originally Posted by Flyndaran

I did not know it had been rebooted.

I was really confused by your first sentence about cell phones.

Yes; it's actually broadcast on CBS rather than streamed or something like that. It is adequately cute for its' role as light entertainment and you've missed the entire first season.

[jason taylor]

One trick Mac tried was to make a heliograph by extending all the blades and shine them in the sun. It wouldn't work(and come to think of it didn't even work on tv).

I have another one(not a Swiss) which has a mirror in it. Someone or other said it could be a heilograph which of course it can't{I'm sure a mirror needs a lot more juice for that). It would be good for shaving though.

[malloyd]

Originally Posted by jason taylor

I have another one(not a Swiss) which has a mirror in it. Someone or other said it could be a heilograph which of course it can't{I'm sure a mirror needs a lot more juice for that).

Actually no. The sun is so much brighter than the typical surroundings that you don't really need a very big mirror for a functional heliograph. The portable military ones, which were perfectly adequate for signaling a few tens of miles - i.e. far as the horizon was ever likely to be - mostly used 2 to 3 inch diameter mirrors. Your knife blade will probably fail because it isn't either flat or shiny enough to make a decent signal mirror, but it's not hopelessly small. Signaling passing airplanes with the mirror in your compact is entirely doable if they are looking for you and you have the right geometry.

[Anthony]

Originally Posted by malloyd

Actually no. The sun is so much brighter than the typical surroundings that you don't really need a very big mirror for a functional heliograph.

The sun is about 400,000 times as bright as the full moon, which means its reflection is similarly bright per unit area as compared to typical backgrounds; you'd get a noticeably bright pixel if a mirror covered 1/400,000 of it, which at human peak visual resolution is a 1" mirror at 35 miles. There's enough other visual noise that you'd want a larger reflector than that, of course, but your main problem will be aiming, the spot created by the reflected light is invisible beyond very short range, making it extremely difficult to figure out if you've actually aimed your mirror at your chosen viewer.

[Bruno]

Originally Posted by Anthony

...your main problem will be aiming, the spot created by the reflected light is invisible beyond very short range, making it extremely difficult to figure out if you've actually aimed your mirror at your chosen viewer.

The typical way to do that with a "real" heliograph is to have a hole in your mirror and sight your target through it (ideally with a short tube so you have to line up both ends). The various geegaws on a multiknife don't have the sighting tube, but you can arrange some of them to at least have a small hole to sight through.

I suppose you could drill the decorative outer casing over the hinge-pin at one end and replace the pin with a hollow one, thereby providing your sighting tube. That's custom work, and you'd want to be sure it's made from a suitably hardy material that using the knife in a normal fashion won't break it.

[Anthony]

Originally Posted by Bruno

The typical way to do that with a "real" heliograph is to have a hole in your mirror and sight your target through it (ideally with a short tube so you have to line up both ends).

That's going to require multiple mirrors or some fairly elaborate mechanisms, as with a single mirror the angle is not constant.

[Bruno]

Originally Posted by Anthony

That's going to require multiple mirrors or some fairly elaborate mechanisms, as with a single mirror the angle is not constant.

That's what the tube is for. It acts like iron sights on a rifle barrel, or lining up a telescope - if you can't see your target through the tube, you're not pointed at the target. The narrower the tube, the shorter it can be (but of course the worse the pinhole problem gets).

[Anthony]

Originally Posted by Bruno

That's what the tube is for. It acts like iron sights on a rifle barrel, or lining up a telescope - if you can't see your target through the tube, you're not pointed at the target. The narrower the tube, the shorter it can be (but of course the worse the pinhole problem gets).

Missing the issue. The problem is that the angle at which a mirror reflects light is equal to the angle of the incoming light, which means your simple tube setup doesn't actually show you what direction light will be reflected. You can solve it with some slightly more complicated mechanisms, but they're still tough to build out of improvised tools. Two methods spring to mind:

Method 1: you have a movable mirror mounted on the end of your tube; you aim the tube at the target, and then you move the mirror until the reflected light is passing down the center of the tube. Measuring the direction of reflected light is a bit tricky, but something like a ring in the middle of the tube, and you're on target if the entire ring is sunlit, would probably work.

Method 2: you have two tubes; you point one at the sun, and the other one at your target. They are connected by gears that also move a mirror so it is angled properly to reflect light coming through one tube down the other tube.

There are almost certainly multiple mirror geometries as well, but they'll be more complex than either of the above -- and I wouldn't want to try the above without a tripod or other mounting bracket.

[jason taylor]

Isn't one of the key problems simply that they won't know I'm there? If Medevac was doing a flyover after a battle they would probably expect to find it(even there one might be suspicious; several planes flew over the Samar island castaways and they knew they were there and roughly where and didn't spot them.

In most cases the plane won't be expecting emergency signals because they would not know someone is in distress.

[Imbicatus]

If I were going to use a Swiss Army knife as a weapon, I wouldn't use the blade. I'd use the awl punch and use it as a makeshift punch dagger / yawara. There is no way I'd ever attempt to use the main blade as a weapon. It's far to likely to injure your hand.