Help! I’m marooned on a deserted island, the kind that is really small and has a palm tree in the middle.
For reasons I will not go into right now, my only possession is a small rectangular Volkswagen Beetle side mirror. There are planes flying over at 30,000 feet. If I flash them with the mirror at that distance can they see it, or should I just keep combing my long straggly beard with a fish spine?
According to this, a proper survival kit mirror, specifically designed for survival signalling, can be seen by aircraft at 35,000 feet, or by people 100 miles away.
A Beetle mirror might not have quite the same range, but I’d expect it to be useable.
Thanks Peter
Good article - it sent me to look up military heliographs. According to Wikipedia these could manage 10 miles per inch diameter, so 30,000 feet could be in the comfort zone of the VW mirror [for you youngsters its about the size of a mobile phone].
If all you have is a VW mirror (or any little ordinary dime-store hand-held mirror), good luck aiming the reflection to even hit the airplane, let alone the cockpit where the pilot might see it.
Those survival-kit mirrors are special. They have a little window in the middle that you can see through, that you use like the sight on a gun to aim it. The ones I’ve seen also have elaborate instructions printed on the back side that I could never make head or tail of, so I still don’t know how to use one.
You have to aim it just right between the sun and the airplane so the sunlight will reflect at just the right angle to hit the airplane. I couldn’t figure out how to do that.
The site linked by Peter Morris, above, purports to explain how it works. But as soon as I opened that page, it crashed my browser so I’m not going to go there again for another look.
The OP seems to have a lot of time on his hands. If so, he can simply wait until a plane passes close to the sun in the sky. Then aim the mirror at the halfway point between the sun and plane (that’s what you would do anyway, it’s just super difficult for large angles).
The OP could use a rock to gently abrade a small hole in the reflective coating. That might make aiming slightly easier. It could also be mounted to the end of a long stick, so that it could be aimed like a rifle–possibly a tad more accurate.
If you’ve hit the airplane, then you’ve hit the cockpit. The beam will be spread out enough at that distance to more than cover the whole plane.
The way to “aim” the mirror is to hold your left arm out at full length with your thumb extended so that the aircraft is in the V between your thumb and index finger, then holding the mirror in front of your face looking through the aiming hole if it is a proper signalling mirror, or looking along side the mirror aim the flashes so you can see the edges of the flash on both your index finger and thumb
I’ve never tried signalling an aircraft but when I was a boy scout this is how we signaled each other and it works well enough
Yep, this. If you have your thumb or some other rudimentary aiming device over the plane and you are reflecting the light onto your thumb then it is also being reflected at the plane. Twirl it around a bit as well, you only need to flash a few times for it to be picked up.
Have there been any cases of people actually getting rescued after a plane (or boat) has seen flashes from a mirror? Not a pilot, but how is a pilot going to realise that such a flash is a signal rather than random reflection off a wave?
Why wouldn’t people on the plane think it’s just a random reflection off a stretch of water? To make a distinguishable message, wouldn’t you have to get a series of SOS signals in Morse at just the right angle for long enough for people to understand.
Might be more useful to use the mirror to start a signal fire, as in all the best desert island stories.
Apparently so, according to the account linked in the second post in this thread.
I think someone familiar with optics should post. The side mirror on cars is a convex mirror - it takes a wide picture and shrinks it to a small surface. While reflecting sunlight, my guess is that it will spread the light out, so that it will not be visible at 30,000 feet.(?) Can someone good with optics confirm ?
The Heliograph mirrors mentioned in replies above are plane mirrors.
Hopefully he got the left mirror. On North American VWs that’s a flat front-surface mirror, so it ought to be perfect for the job.
Another vote for the “V” technique. No need for fancy mirrors with little aiming holes and such. Indeed, a military training video from WWII that I recently watched explained exactly how to use the little aiming thing, but then went on to describe the “V” technique and said to use whatever you have.
As to who would notice, certainly passengers wouldn’t care about a funny blinking light on a tiny island, but the flight crew should notice and make a report of it. Especially if it’s blinking like mad (no Morse code, just flitting back and forth as our survivor keeps flipping the mirror up and down to ensure some flashes get to the aircraft).
Actually, the “aiming hole” method works extremely well. It was described in an article in the Journal of the Optical Society of America after World War II (it was supposed to appear while the war was actually on, so it could benefit downed airmen. But better late than never, I guess.) Hal Clement later described the method in his novel Cycle of Fire (used by a downed spaceman). It doesn’t require you to hold up your other arm, so it’s arguably less fatiguing, but it does require a mirror with a hole or a lack of mirror material somewhere near the center. I’ve used it to send a beam of sunlight to a piece of retroreflector, and it works beautifully.
Surely it works well, otherwise they wouldn’t make them that way and the military training wouldn’t start with that method and then drop back to the fallback method.
But that assumes you have a proper signal mirror to begin with.
Which is precisely what I just said in my post:
Of course, the dark-adjusted human eye can pick out much smler amounts of light (and therefore a mirror at a longer distance, or smaller mirror) so the ideal situation is to reflect sunlight on the airplane at night.
Were those cool signal mirrors not in use in WWII? If I understand what you are saying correctly.
Now I have to go back and see what year that training video I watched was from.
I also seem to recall seeing a video of a fellow opening a South Pacific flyer’s emergency kit and one of those mirrors was included.
Thank you - I was scared off clicking by the poster who said it crashed their browser, as I had a lot of tabs open at the time. I know, I could have copied and pasted into a different browser - lazy of me.
Mostly when somebody is lost there are people out looking for them. Those people aren’t going to ignore flashes of light even if they are irregular.
I found the video I was thinking of, but it seems to be describing yet another kind of mirror:
The Signaling Mirror: WWII US Government Training Film
I guess the one in the video, with the little cross and a bit of mirroring on the back side, is *not *the one being described here.
Is the kind of mirror mentioned in the quote (“Later testing proved retroreflective…signal mirror aimers were more accurate”) the one that people are talking about with the little hole?