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Since one cannot see the propeller, once you are in the seat, I worry about people walking into it. When in motion, it is unlikely since a person would have to walk behind the wing and in front of the horizontal stabilizer. And most adults would not do this with the engine running while the FireFly is motionless. But, it does not take too many air shows or fly-ins to figure out that small children are unpredictable. With the installation of the fuselage fairing, it was possible to install some bright flashing LED's, and to hopefully will draw attention to the propeller when the engine is running.
Six ultra bright LED's were mounted the positions shown to the left or above. They were placed in the next to top level fairing foam piece. LED positions were chosen so that individual beams would spread and overlap at about two feet from the fairing. This ensures that very short individuals will be able to see the flashing lights too. |
A small pencil soldering iron was used to make the holes in the fairing fabric and foam. The LED's were glued into position, and then they were wired in series. Although only six can be seen out side the fairing, a seventh LED was wired in to keep the individual LED voltage drop with in limits (13.8 volts).
Timer and switching circuit design information was found by using Google.com. A 555 timer chip and some resistors and a capacitor were purchased from the local Radio Shack, and the circuit was "spider" assembled. After testing, the "spider" circuit was flattened, and the whole works glued into place below the top fairing foam piece. All wire leads were glued to foam to prevent vibration from breaking the wires.
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A hole was burnt in the fuselage fabric to pass the power leads. The leads were attached to the regulator power output terminals. When ever the engine is running the LED's are flashing. The LED's are on about one-half the time, and when they are the current draw is about 0.03 ampere. Weight added to the FireFly was less than one ounce. Component cost was less than ten dollars.
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