February 19, 20179 yr Why are the strobes on the PMDG 747 synced? Or do they start synced and then go out of phase to variables in the power supplies and/or bulbs? See video for example. Start viewing at 31 seconds in the video. Ric Elmore
February 19, 20179 yr I don't know what's going on in that video. The strobes are supposed to flash at approximately 48 flashes per minute. The video aircraft seems to miss a flash now and then. There are timing circuits, and, because they use the same 400Hz power supply, in theory, they should all be in sync... but the flash rate is quoted at 48~60 flashes/minute. Quartz watches they are not Cheers John H Watson John H Watson (retired 744/767 Avionics engineer)
February 19, 20179 yr Hi Ric, I don't think that this has anything to do with the 747 strobes as such. In my opinion, this is more related to the video itself. Since strobe flashes are so short, they might not be captured by the camera. Imagine a camera taking 25 frames per second and the flash happening right in between those frames. I have seen many videos with the same effect, hence my conclusion. Cheers, Mark Mark van Wissen
February 20, 20179 yr Author Hi Ric, I don't think that this has anything to do with the 747 strobes as such. In my opinion, this is more related to the video itself. Since strobe flashes are so short, they might not be captured by the camera. Imagine a camera taking 25 frames per second and the flash happening right in between those frames. I have seen many videos with the same effect, hence my conclusion. Cheers, Mark With that theory then you would not see a flash on one wing tip and not on the other, correct? Ric Elmore
February 20, 20179 yr With that theory then you would not see a flash on one wing tip and not on the other, correct? Possibly. Look at how irregular the tail strobe is in the video. If it was that unreliable in real life, it would need to be changed. Something must be causing the flash not to be seen and, I agree with Mark, it has to be the video recorder. Also, in real life, depending on ambient light conditions and observer position, it may be difficult to see the flash on both wings at the same time. During daylight (especially), after changing a strobe light or power supply, I sometimes tried viewing the wingtip from various points inside the aircraft, but most times, I would have to walk downstairs and out to the wing to see the strobe. When checking the logo lights in daylight, we sometimes had to run the stab trim full nose up and open the upper deck doors and look out to see if they were working. Speaking of visibility.... A bit of trivia.... The Upper Red Beacon/Strobe is located 5 inches to the right of the aircraft centreline. Even though it is only 5 inches, it was much easier to check the light from the right side of the aircraft (from the ground). We would have to walk much further from the aircraft to see it on the left side. I'm not sure if this is modelled in PMDG Cheers John H Watson John H Watson (retired 744/767 Avionics engineer)
February 21, 20179 yr Author Ok, I found a video that clearly shows the 747 strobes on the wing tips and tail flash in unison. The upper and lower beacons flash in unison usually shortly after the white strobes or shortly before, I believe this has to do when they are turned on in relationship to each other. Ric Elmore
February 21, 20179 yr I'm pretty sure that the "missing flashes" are a camera effect. A modern digital video camera may be set to shoot at 30 or 24 frames per second, but the exposure time of each individual frame can be extremely short - well under 1/1000 of a second. The duration of each strobe light flash event is also extremely short. It is not unusual for the camera to miss individual flashes for that reason. I've seen this happen when shooting videos of aircraft taking off at night even with my iPhone's video camera. I can see every individual flash of the white or red beacons with my eyes, but the flashes often "go missing" on the phone's screen at the same time. The extremely short exposure times of digital video cameras produce another effect commonly seen in YouTube videos of propeller-driven aircraft, in which each individual blade can be clearly seen - (as if the prop was turning very very slowly). This happens when the prop RPM is close to being a multiple of the camera's frame rate... i.e. 2400 RPM with a camera shooting 24 FPS. Jim BarrettLicensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.
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