# Mirror flashing at aircraft **URL:** \ **Category:** Factual Questions\ **Created:** [June 5, 2020, 5:58am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089 "2020-06-05T05:58:17Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [June 5, 2020, 7:15pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/21 "2020-06-05T19:15:15Z")
As some neighbor kids of mine found out a few years ago, hard drive disks make excellent mirrors plus they already have a hole in the middle. I live about 6 miles from an international airport, they thought it would be fun to shine the light from the disks at airplanes as they flew overhead. It didn’t take long and a number of different law enforcement agencies were in the neighborhood. Fortunately, they didn’t tell the police that I gave them the disks. ---
**Author:** ![Spiderman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spiderman/32/230_2.png) [@Spiderman](https://boards.straightdope.com/u/Spiderman)\ **Post date:** [June 5, 2020, 11:17pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/22 "2020-06-05T23:17:59Z")
**Banksiaman** , you better hope it was owned by a little old lady who kept it in the garage & only drove it on sunny Sundays in the summer. How much degradation is there is a 50-60 yo mirror that’s been out in the elements all those years? > [@Dr.Strangelove](#): > > The OP could use a rock to gently abrade a small hole in the reflective coating. That might make aiming slightly easier. or it could break the mirror; I wouldn’t chance it since there’s no parts store on your deserted island. > [@Dr.Strangelove](#): > > 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. Unless you can be sure to mount it perfectly in synch with your stick I’d recommend against that. A ¼° or a ½° deviation at arms length isn’t much but it’s enough to miss an airplane at least 10 miles away (35,000’ up + whatever horizontal separation) by a wide margin. > [@Darren\_Garrison](#): > > 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. :dubious: It’s a good thing there’s [fish](https://www.youtube.com/watch?v=T8XeDvKqI4E&t=14s) around that island. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [June 5, 2020, 11:24pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/23 "2020-06-05T23:24:49Z")
> [@Spiderman](#): > > Unless you can be sure to mount it perfectly in synch with your stick I’d recommend against that. A ¼° or a ½° deviation at arms length isn’t much but it’s enough to miss an airplane at least 10 miles away (35,000’ up + whatever horizontal separation) by a wide margin. The sun itself has an angular diameter of ½°, so you aren’t doing better than that anyway. I’m not sure about the flatness of a VW mirror, but any deviation from pure flatness will make things worse yet. This isn’t a laser. Still, the fact that a hand-held mirror has been used to signal an airplane at 35k feet without any extra equipment probably recommends against doing anything tricky. ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [June 6, 2020, 1:57am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/24 "2020-06-06T01:57:55Z")
> [@Darren\_Garrison](#): > > 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. 😕 :dubious: :D:D:D Bravo! ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [June 6, 2020, 2:34am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/25 "2020-06-06T02:34:13Z")
The mirror doesn’t need to have a hole in it, but it should be held right next to the eye that you are using to sight with. The outstretched arm with spread fingers is good to aim with, but extending that even a foot with a bit of forked stick would improve the accuracy. ---
**Author:** ![Banksiaman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/banksiaman/32/3334_2.png) [@Banksiaman](https://boards.straightdope.com/u/Banksiaman)\ **Post date:** [June 6, 2020, 10:40pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/26 "2020-06-06T22:40:48Z")
Thanks for useful information from everyone, especially the wise Namaisknab who lives inside the mirror. The good news is that the mirror flash should carry the distance, and its always very sunny, and that the flights are regular. The bad news is that I did not realise i would have to pretty much hit the plane with the flash. I kind of assumed a flash would be generally noticed like on a camera at a party. Not so. With an Airbus A380 240 feet long side-on at 30,000 feet I have a moving target of less than half a degree across, which is a bit wider than a darts bullseye but 29,990 feet further away [I’m a metric guy but I only have real human feet to work with]. My solution is to build a heliograph. There are lots of palm fronds to work with. I can strip and lash sturdier stem sections together to make a fairly robust length that will support its own weight, say 15 feet long. I can lash the mirror at one end, and make a sight about half an inch across at the other. If I tether the whole thing to the palm tree I can swivel it so the flash is centred through the target sight and it should be steady enough to track the plane and the flash beam precise enough to light the plane. All good so far. The problem now becomes one of sighting it. The mirror is in its housing and I don’t have tools to free the mirror. How do i sight my McGuyver-Gilliganesque bastard heliograph so I can hit this tiny moving target five miles away? I can’t get true line of sight through the mirror, and any tiny error will be see it miss the plane. I have palm fronds, sand, urine and the bleaching bones of the other three. And Namaisknab is getting impatient. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [June 6, 2020, 11:56pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/27 "2020-06-06T23:56:55Z")
Look around–can you form some sort of rudimentary lathe? ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [June 7, 2020, 5:14am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/28 "2020-06-07T05:14:25Z")
> [@Darren\_Garrison](#): > > Look around–can you form some sort of rudimentary lathe? **This**! This is why many away team members never made it back.:eek:😃 ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [June 7, 2020, 8:34am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/29 "2020-06-07T08:34:27Z")
> [@Banksiaman](#): > > Thanks for useful information from everyone, especially the wise Namaisknab who lives inside the mirror. > > The good news is that the mirror flash should carry the distance, and its always very sunny, and that the flights are regular. The bad news is that I did not realise i would have to pretty much hit the plane with the flash. I kind of assumed a flash would be generally noticed like on a camera at a party. Not so. With an Airbus A380 240 feet long side-on at 30,000 feet I have a moving target of less than half a degree across, which is a bit wider than a darts bullseye but 29,990 feet further away [I’m a metric guy but I only have real human feet to work with]. It’s worse than that, you have to hit the pilot’s eyeball with it! > [@](#): > > My solution is to build a heliograph. There are lots of palm fronds to work with. I can strip and lash sturdier stem sections together to make a fairly robust length that will support its own weight, say 15 feet long. I can lash the mirror at one end, and make a sight about half an inch across at the other. If I tether the whole thing to the palm tree I can swivel it so the flash is centred through the target sight and it should be steady enough to track the plane and the flash beam precise enough to light the plane. All good so far. > > The problem now becomes one of sighting it. The mirror is in its housing and I don’t have tools to free the mirror. How do i sight my McGuyver-Gilliganesque bastard heliograph so I can hit this tiny moving target five miles away? I can’t get true line of sight through the mirror, and any tiny error will be see it miss the plane. I have palm fronds, sand, urine and the bleaching bones of the other three. > > And Namaisknab is getting impatient. You don’t try to be precise. If you point it steadily in the wrong direction, the pilots will never see it, but if you move it around back and forward, up and down, you are bound to flash them a few times. The other thing working in your favour is that it is not a laser, the light is spreading out from the mirror and so, although you have a small target to hit, your “projectile” is huge. This kind of question comes up around flashing airliners with lasers. Surely it’s too difficult to get a laser beam to go through a cockpit window and hit the pilot’s eyes from miles away? Well no, the laser beam spreads a little bit and if it’s moving around a lot but aimed in the right general direction it will inevitably wander across the cockpit area. It happens a lot. ---
**Author:** ![Banksiaman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/banksiaman/32/3334_2.png) [@Banksiaman](https://boards.straightdope.com/u/Banksiaman)\ **Post date:** [June 7, 2020, 9:43am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/30 "2020-06-07T09:43:26Z")
> [@Darren\_Garrison](#): > > Look around–can you form some sort of rudimentary lathe? If my shipmates had been more like Dr Lazarus than that redshirt Guy coming up with dumb ideas, they’d likely not have been killed and eaten one by one by somebody. I think the backwards and forward motion is going to happen naturally as I try to shift and re-aim the palm frond heliotrope to keep up with the plane. But trying to catch the plane as it flies towards rather than away will increase the odds of alerting and blinding the pilot. Maybe they’ll crash and given me company! ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [June 7, 2020, 11:28am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/31 "2020-06-07T11:28:54Z")
> [@CalMeacham](#): > > 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. There’s something special going on with those aiming holes, right? You would know better than I. But I got one of those mirrors as a gift, and there seems to be something special embedded in the aiming hole. It looked to me like screen or scrim that had shiny hairs or bristles clinging to the fibers, like crystals grown on the screen. I figured there was something special happening with their chatoyancy. What was I seeing in there and how does it work? ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [June 7, 2020, 11:32am UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/32 "2020-06-07T11:32:23Z")
I found some instructions that say: The “BRIGHT SPOT LIGHT” “AIM INDICATOR” produced by the retroreflective mesh in a signal mirror aimer. The spot is a virtual image of the sun in the direction of the reflected column of light from the mirror - not the sun itself ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [June 7, 2020, 6:05pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/33 "2020-06-07T18:05:16Z")
> [@PatrickLondon](#): > > 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. A mirror is not a magnifying glass. When you are aiming at a moving object you will have to follow it. Without even trying you will be giving flashes that will be recognized as directed purposely. I train youth in Hunter Education and teach in evenings so in classroom we use a flashlight that is held simulating the sun and use mirrors with and without the sighting hole and watches, pop can bottoms and other shiny objects. When Hunting in the Olympic Mountains in Washington my brother and i would communicate with portable CB radios (with the LONG telescoping antennas, W/10 nicad battery’s) then pinpoint our positions with signal mirrors. It must have been a mile or more between the summits we were on and it became very easy for one to sweep the summit and the other to respond. I still have the old radio’s but the little fm radio’s are much more practical. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [June 8, 2020, 3:06pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/34 "2020-06-08T15:06:42Z")
I have messed about with two different types of emergency signal mirrors. The first was the official boy scout version. It was metal, polished and chromed on both sides, with about a 1/8" hole in the middle (~3mm). The key is that both sides are mirrors, and that they are exactly parallel. To aim it: 1. With one hand, hold it away from your face, toward the target, sighting the target through the hole. 2. hold your other hand so that it catches the mirror’s shadow. 3. View the shadow on your hand by looking at the back of the mirror. Tilt the mirror so that the shadow of the hole overlays the hole in the actual mirror. It is a little fiddly to do these three things at once, but it only takes a few minutes practice. The main problem with this mirror is that it is easily bent. A CD would probably work as a substitute. The other type is the military style survival mirror. It is a lamination of two sheets of glass. The front (sun facing) glass is a second surface mirror. There is a sizeable hole (3/8" 10mm maybe?) in the mirror coating at the center. Between the two sheets is a mesh material with a retro-reflective coating, and a smallish (5mm?) hole in the middle. This type is held very near your eye, allowing you to brace your hand against your cheek or brow, and can also be held with both hands if you like. When you look through the central hole, the retro-reflective mesh, and the plain (unsilvered) front surface of the front glass cause you to see a dimmed (but still obvious) image of the sun in exactly the direction the rest of mirror is beaming a flash to. Or, said another way, when you look through the hole toward the target, you see an obvious bright spot where the flash will go. The second type is far easier to use, as the mirror is not obscuring any part of the target, and you only have one thing instead of three to align. But being made of glass, they can be broken if stored or handled carelessly. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [June 8, 2020, 3:18pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/35 "2020-06-08T15:18:53Z")
> [@minor7flat5](#): > > …They are also the type sold for decades as the official US Boy Scout signal mirror… I had one of those, back in my Scouting days, but was never stranded on a desert island, disappointingly enough, and never had the chance to use it that way. > [@Darren\_Garrison](#): > > Look around–can you form some sort of rudimentary lathe? I see you managed to get your shirt off. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [June 8, 2020, 3:18pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/36 "2020-06-08T15:18:53Z")
I forgot to mention in my earlier post: If you want to practice your survival signaling, you can use retro-reflectors as a target. Common examples are road signs (e.g. a stop sign) , automotive tail-lights, bicycle reflectors, and safety vests or running shoes with the scotch-bright strips. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 8, 2020, 10:50pm UTC](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089/37 "2020-06-08T22:50:18Z")
> [@am77494](#): > > The side mirror on cars is a convex mirror - it takes a wide picture and shrinks it to a small surface. The OP specifies a WV Beetle mirror and describes it as ‘rectangular’, which I think means it’s from a vintage beetle, not a modern one. I think that will actually be a flat mirror [Previous page](https://boards.straightdope.com/t/mirror-flashing-at-aircraft/855089.md?page=1)