A basic chore associated with airplanes is making something flash. Sometimes you want them to flash fast, other times you want it to go slow. What's getting flashed may demand a couple of amps whereas other circuits may need only a fraction of an ampere. This can lead to the use of half a dozen different flashers, resulting in a heavy and complicated circuit.
The circuit shown here is a basic One-Size Fits All.
The basic idea is to use an integrated circuit (ie, the Ne-555 chip) to toggle the circuit at a given rate. The output of the flasher is then fed to a small RELAY capable of handling about an amp. If you need to flash a higher amperage you simply wire the existing relay to one having a higher rating.
This isn't a new circuit. If you dig around you can probably find a circuit-board mask for it in one of the archives. The advantage of this circuit is that it's very inexpensive and may be sized to handle anything from a 1A nav light to a 10A strobe by simply selecting a suitable relay.
NOTE (17 SEPT 2008)
One of the comments suggests replacing the fixed resistors R1 & R2 with variable resistors. In fact, that is what I did when bread-boarding this circuit. Once I'd found a setting that gave the approximate flash rate & duration needed for an automotive turn signal, I lifted one leg of the variable pots and measured their resistance. This was matched to the nearest standard value FIXED resistor. The purpose was to make the module easy to fabricate by guys who weren't born with a soldering iron in their hand. Fabricated from all fixed or sealed components, the finished circuit could then be potted with epoxy or similar sealant, rendering it weather-proof. The relay of course may be mounted almost anywhere. -- rsh