Anti-collison lighting circuit assistance needed

Discussion in 'The Projects Forum' started by rleffler, Mar 1, 2009.

  1. rleffler

    Thread Starter New Member

    Mar 1, 2009
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    I am looking for assistance in designing a circuit to be used in my homebuilt experimental aircraft.

    Anti-collison lighting requires that the flash be not less than 40 nor be more than 100 times per minute. I would like the circuit to double flash, 40-50 times per minute.

    The output of the circuit needs to be 5v to trigger a LED driver from LEDdynamics. The link will take you to the driver spec sheet.

    I'm not very electronics saavy from a design perspective, but I am good at assembling and following instructions. Any assistance provded is greatly appreciated.

    bob
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What will be the powersupply for the flasher circuit ?
    What type of led-driver do you have (there are 8 described) ?

    Greetings,
    Bertus
     
  3. rleffler

    Thread Starter New Member

    Mar 1, 2009
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    14v dc

    3021-D-E

    They are all basically the same, the differences are in how the mount (leads vs pcb), external control, and internal dimming.
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What should be the ON / OFF ratio ?
    You could use a 555 circuit with a mosfet power stage.

    Greetings,
    Bertus
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Usually, anticollision lights are Xenon strobes (flash tubes). They're extremely bright, and the flashes are visible for a great distance, even in daylight.

    While LED technology has come quite a ways in recent years, I'm not aware of LEDs (even clusters of them) that can approach the intensity of a Xenon strobe.

    I consider anticollision lights to be a very important safety item, particularly when approaching or inside the pattern at an uncontrolled airport. As such, I strongly recommend that you use a tried and true design, rather than trying to "wing it" (sic) with something that might "look good" on paper but not perform well in use.
     
  6. rleffler

    Thread Starter New Member

    Mar 1, 2009
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    Not necessarrily true. I can tell you as a former tower ATC, they aren't really that visible during daylight hours.


    I agree.

    Who said anything about "winging it"? That's an awful broad assumption.

    The FAR on the anticollision lights are:

    Angle above or below the horizontal plane intensity(candles)------------------------------------------------------------0° to 5°........................................ 4005° to 10°....................................... 24010° to 20°...................................... 8020° to 30°...................................... 4030° to 75°...................................... 20There are LEDs that can easily exceed this specification.
     
  7. rleffler

    Thread Starter New Member

    Mar 1, 2009
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    Good question, I don't have an answer at the moment. There is no spec in the FAR.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Gee, I guess you should know. :) I've spent VERY little time in a tower, but a number of years on airbases - although it's been awhile, I remember the military ACL's being mighty visible. BTW, ATC was one of two MOS's I didn't qualify for due to my nearsightedness; the other MOS was a pilot. :(

    Please don't get me wrong; I much prefer to err on the side of caution.
    You would not believe how many electronic neophytes come here, wanting to do something that just isn't realistic, or might try a project like this using some cheap junk LEDs they bought from E-bay that had artificially inflated specifications due to their narrow focus. Not knowing anything about you except that you're building a homebuilt aircraft of some sort (and having seen some quite scary ideas in homebuilts) I'm naturally cautious.

    Just so that you know I'm not a stranger to aircraft, attached is a photo of one of my old birds; we radar systems techs were checking out the aft missile stations on this F-4J Phantom II while the powerplants techs were putting the finishing touches on an engine installation.
     
  9. italo

    New Member

    Nov 20, 2005
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    SARGE he want to be a wannabe. Some people have great ideas but limited experience and some suceed one in a million or more. I totaly agree with you the LEDS spectrum is just not there for daylight viewing.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    italo,
    I didn't even bother to search before I made my initial post. However, after searching:
    http://www.google.com/search?hl=en&q=Anticollision+light+FAR
    I found this Honeywell patent online:
    http://www.freepatentsonline.com/7414546.html
    So, I stand corrected - there ARE LED anticollision light systems available nowadays, even though they're relatively new.

    My concerns are:
    1) Safety.
    2) The abilities of the original poster to understand electronic schematics, ability to create circuit boards, troubleshoot said boards, etc.
    3) Attempting to design such a device remotely without actually building and testing it relates to 1), above.
    4) Actual performance of the final system.
    5) The time involved to design such a system.

    This isn't going to be simple, nor particularly cheap. There should be built-in fault detection/monitoring, along with redundant LEDs. Heat-sinking the LEDs could get complex; they'll be dissipating a significant amount of power as heat, and they will need to be enclosed behind a clear lens/window of some material (Plexiglas, Lexan or the like).

    For an aircraft that might rack up tens of thousands of flight-hours, the time and cost for developing such a system would be well worth the trouble.

    However, (to be continued...)
    [eta] (...continuing)
    Xenon flash tubes have been in use for quite a while (longer than I've been around), they're really fairly simple to get flashing, don't have complex cooling requirements, and are plenty reliable for small (and large) aircraft use.
     
    Last edited: Mar 3, 2009
  11. TWRackers

    Active Member

    Dec 29, 2008
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    I'm attempting something similar. I'm building a 10-foot long, 6-inch diameter rocket which I'll be launching (hopefully) at the Red Glare VI launch in Maryland this coming April (http://www.mdrocketry.org/launches/redglare6/). The simulations of the rocket's flight predict a peak altitude of between 7,000 and 10,000 feet, depending on how the rocket's final weight comes out. So I'm outfitting the trailing edge of each of the four fins with a pod containing one of these (http://www.superbrightleds.com/pdfs/XLamp7090XR-E.pdf) 1-watt white LEDs mounted in a 30° focuser. The LEDs can actually be overdriven (when properly heat-sinked) up to 1 AMP (really), which is more like 3 watts. The specs rate this LED at 100 lumens at 1 watt. Conversion between lumens and candela or foot-candles is non-obvious, but I've measured one of these LEDs at 750 mA as putting out 1,300 foot-candles. And daytime sunshine is about 10,000 foot-candles.

    So will these LEDs be visible from a mile or two up? That's what I'm going to try to find out.

    Oh, they'll be strobing at 2 Hz during descent under the drogue chute, so hopefully they'll be visible from the ground. At those altitudes, the rocket itself is going to be too small to be seen. (Just in case, it will have a tracking radio transmitter onboard too.)
     
  12. SgtWookie

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    While your rocket application may at the outset seem similar, it's really quite different. ;)

    ACL's are there to help ensure that pilots don't have midair collisions.

    You're just trying to keep track of where your rocket is for recovery operations.
    If you've followed FAA rules, NOTAMs will be posted to keep aircraft out of your area.
    (off topic) Are you NAR HPR class 3 certified? You're aware of the recent FAA rule changes, right? What size engine will you be using?

    Anyway, since your application might initially seem similar, it's really a very different application. Safety is not nearly as much of an issue, since once the rocket is in stable flight off the ground, humans won't be anywhere near it. Cooling may become an issue due to restrictions in building materials, depending upon the current and duty cycle of the LEDs. You'll need to consult NAR rules/guidelines.

    The LEDs you're considering have a fairly narrow pattern, which would be OK from high altitude. You might consider one per fin, angling them outwards perhaps 5°-15°. You might incorporate an absolute pressure sensor to switch to a different set of LEDs depending upon the altitude of the rocket; at lower altitudes you will need a more horizontal spread of light.

    Since this is really a different subject, it should have it's own topic. Perhaps a Moderator will move it to it's own thread.
     
  13. TWRackers

    Active Member

    Dec 29, 2008
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    You're correct, the motivation for my application is very different, but the need to drive bright LEDs visible from a distance is similar. The launch event will have an FAA waiver and NOTAMs in effect, as do all such organized launches. The flight I was describing is my NAR Level 3 certification flight. The motor is an M.

    There is one LED per fin, all pointed directly aft. The unfocused beam pattern of each LED is 90 or 100 degrees wide, depending on which spec sheet you read. I'm using the optional 30 degree reflector/lens focusers to direct more light downward (assuming the drogue chute does its job of keeping the rocket vertical during descent from apogee).

    I didn't intend to focus (bad pun) on the rocket here, just on the problem of making LED-based strobes that are (hopefully) visible from the air.
     
  14. SgtWookie

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    Jul 17, 2007
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    OK.

    Why not test them horizontally? Is there a stretch of land near you where you could get up to 2 miles away from such a strobe?

    How long will it take for the rocket to return to earth from 10,000 feet after deployment of your recovery system? And are you simply deploying a parachute, or starting off with a streamer for stabilization and later releasing a 'chute? Knowing the estimated flight time will help to nail down your power requirements.

    What do you have in mind for a power source? Batteries don't last long when heavily loaded; the higher the power demand, the more power is dissipated across the internal resistance of the battery. If you want to flash all four LEDs simultaneously, it may work out best to wire them in series. It's possible to use an inductor (in conjunction with battery power) to generate higher voltage than the batteries will output by themselves, but if you're considering running them at near peak current, that's quite a bit of power.
     
  15. TWRackers

    Active Member

    Dec 29, 2008
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    One mile, yes. Two miles, no.

    Four-foot cross-shaped chute as drogue, twelve-foot round chute as main (deployed around 1,000 feet AGL).

    Descent time on the order of 3 minutes from apogee to ground.

    800 mA-hour LiPo 2S1P battery for strobe power source; all other electronics run on separate 9v batteries (two altimeters plus one BASIC Stamp board). Each LED is driven by an IRLZ14 MOSFET.

    From launch to main deploy, strobes flash at 10% on-time, probably at about 90% full power on each flash. From main deploy to power-down on the ground, strobes run at about 75% full power using PWM, so they'll appear to be on continuously (more like landing lights).

    The main motivator for this strobe project is to attempt to track the rocket visually at high altitude, which I don't believe has been attempted before. There will also be a tracking radio transmitter on board.

    I think you're right, that if this discussion continues, it should be on a separate thread rather than hijacking the original poster's thread.
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I can't help myself due to the thread title, and Sgt's + OP's background * ...

    On the serious topic...

    A common frquency is 2 signals per second, as it is easy to generate accurately and falls at the high middle of FAA Acceptable variance from 70 to 140 per minute. 10 degree projection from horizontal, or +/- 5 degrees. 100 to 400 candela brightness per signal flash. Using "Napkin Calc"®, around 30-50mS ON, 470mS OFF to be recognizeable as a xenon tube, unless I couldn't read my own writing, which is common.

    I agree that LEDs would work, and could be worthy of testing. They are now used as Vehicle Headlights in some new Infiniti (or Audi?) models. I'd add this though: WITH backup strobes. Possibly use LED's with a photodetector in each housing to activate hot standby xenon strobes and stop the LED driver in the event of a failed LED strobe, so the problem could be debugged without a "ticket", or worse.

    The wide ambient temperature swing in a short time of the operating device is a large concern for anything on an aircraft, especially in a warmer climate.

    I'd suggest contacting Luxeon directly to work with them on the system. If they are already in the game, check another large Plant. They might be kind on your wallet in exchange for test flights, or at least more helpful with design considerations.

    For the rocket project - Maybe repurpose some "manual" mid-power 80's era Vivitar flashes from a pawn shop or photo store? With mount/adjustments removed, they can be even more compact, weight of battery is a concern, but would be more visible than LED at 10k+ feet.
    _______
    * They've probably heard that a million times though....
     
    Last edited: Mar 3, 2009
  17. SgtWookie

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    Jul 17, 2007
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    OK, so if you have a 1-mile ground "straight shot", you could try running your strobe at 1/4 power to check visibility at a simulated 2-mile range.

    Light diminishes as the square of the distance. If you're standing 1 foot from a light source, then 2 feet away, the light is 1/4 of the intensity that it was at 1 foot.

    If your LEDs have a 30° focusing lens, they'll probably appear to be mighty dim (if even visible) at such a range. Burnt fuel (smoke/haze) will further obscure your beacon.

    There's also a question of the possibility of the reflectors being fouled by exhaust at takeoff; on a related note the issue of drag created by having reflectors at the trailing edges of the fins. Looking at the specs for the reflector, the OD is 23.6mm; having four such non-aerodynamic reflectors hanging out in the breeze represents a good bit of drag at the speeds your rocket will want to travel.

    You're still going to need to provide a heatsink for each LED. One of the best materials (that isn't outrageously expensive) for heat dissipation is copper, but it's quite heavy, and there is the issue of the use of metal near the motor. Aluminum is much lighter, but only half as effective at conducting away heat, you can't solder to it, and there's still the issue of metal near the motor. Besides, any added weight at the tail will need counterbalancing to keep the CG far enough forwards...

    You might be better off using fiber optics, or perhaps a Lucite/Plexiglas/acrylic rod to transmit light down the side of the rocket body from inside the telemetry section. This might simplify a few things (wiring, avoiding metal near the motors, excess weight/drag on the fins, etc.) and perhaps even result in a lighter rocket. You might use a thin copper sheet wrapped around the outside for heat dissipation. The complicated part would be getting the light into the rod at the telemetry section.
     
  18. SgtWookie

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    Actually, that's a very interesting possibility ... even salvaging the Zenon flash tube "guts" out of a disposable camera would likely do the job for a few minutes. The electrolytic caps in those disposable camera flash circuits usually have too low of a voltage rating for long-term use, but a suitable replacement wouldn't be outrageously expensive.

    Of course, if an original high-quality flash unit could be found, so much the better.
     
  19. TWRackers

    Active Member

    Dec 29, 2008
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    True for a point source. Approximately true for a focused source, more so in the far field.

    I don't follow, it sounds like you're implying the focusers would reduce the intensity.

    See attached photo. The LEDs in their focusers are in pods on the fins, about two inches ahead of the nozzle. The pods have clear domes protecting the lamps. Admittedly a teardrop shape on the domes would be more aerodynamic than hemispheres, but they'd be less effective optically and would be prone to breakage upon landing. And "fouling" on the aft ends of these rockets is negligible; the blast deflectors on the pads direct the exhaust more or less parallel to the ground a foot or two below the rocket.

    For a sense of scale, the rocket's airframe is 6 inches in diameter. The rocket's total length is 10 feet.

    The LEDs already have heatsinks, but I'm adding copper sheet to the back of each heatsink and running up the inside wall of each pod, to add some thermal mass. For a 30-ish pound rocket, the added weight of the heatsinks is not going to move the CG more than a fraction of an inch. Metal near the motor isn't really an issue, since the motor casing is machined aluminum anyway. As is the motor retainer ring.

    I doubt acrylic rod would save me any weight over running wires from the avionics bay at the rocket's midsection down through aluminum tubing to the LED pods.

    Trust me, I've considered a lot of options over the past twelve months that I've been working on this. The launch is scheduled for just over six weeks from now, so the design is pretty much frozen. Must allow enough time for testing the avionics and the recovery system, and getting a test flight in on a K or L motor.
     
  20. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Regarding the 30 degree spread making the lights harder to see.

    Your eye is only going to capture a fraction of that 30 degrees, the rest is focused elsewhere, so it will appear more dim than if it were a narrower beam.

    I understand that for locating you need a larger source, but at the altitude you are reaching for, you are going to need a LOT of light. 10% of daylight spread into an approximately 1 mile "spot" on the ground at apogee is NOT going to be very visible in daylight, unless you know exactly where to look already with high power optics, at which point you might see the rocket itself first.

    The Acyclic rods + Tweaked high power flash that the Seargent mentioned would give MANY points of intense light with narrow spread. It would be a pulsed application (1 per second at most without extra cooling and one unit), but if general area is known, several discrete beams could be provided 360 degrees on the radial, with varied elevations on the axial, all from a single high powered strobe light source. Also, if canopy is reflective, irregularities could be added, prisms the size of sand grains, which would Definitely allow for identification once chute was open, provided everything else proceeds correctly.

    For the flash, I'm referring to mid to high mid range flash units, available for under $50, they are semi compact, yet pack enough punch to properly expose an image of a house 20 feet away in the dark. It would need similar or more cooling than LEDs, The lighting wouldn't be continuous, but once identified and optically tracked, the pulses of light would be visible, which is why your application came up in an ACL thread. :D

    As for the power of LEDs vs. Xenon Strobe tubes, Have you ever heard of an LED Strobed laser? Some of these units put out enough power to literally burn your hand with one full power flash if it happens to be a few inches in front of it. Using two units, weight would be close to what is being hauled for the LED arrays/controllers, maybe a bit more due to the large caps. Strobe output is measured in Watt-Seconds. Small ones are tens of watts, and all of that is unleashed in a very short time, "pumping" the effective instantaneous watt output into 6+ digits.

    I am really NOT trying to tell you not to use LEDs, Just as I am telling the OP, but for different reasons. I'd like him to live, and you to have a very successful certification flight!

    Do you have a pilot friend? Try stopping by your local business aviation or flight learning school and explain your ambitions on the project "For Safety". Bonus if you are attending some educational facility and can work your results into a something to make the prof smile.

    Test "in reverse" so people don't think there is a distress call. Set up a friend with the LED Arrray, AND A 1Hz Strobe on the ground away from things. Fly over at 5k AGL, roll 80 degrees, and take a look to see which is more visible. Repeat at 10k AGL.

    Seriously, this could be groundbreaking territory. As you stated, it hasn't been tried before. If your payload permits, do one LED and strobes (depending on literal-preflight results, above), then write a peer review paper on the merits of each and send it to a rocketry magazine and get a free subscription (or at least a copy of the edition.....).
     
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