| I saw a Hobico "Air Alert" or "Plane Alert" that beeps when the Tx is | turned off, but it was not loud enough for me to hear at a reasonable | distance.
You'd be surprised. As long as you mount it outside the plane, or cut a hole in the fuse so that the speaker sticks out of the plane, you can hear it at a few hundred yards if things are relatively quiet.
As long as you have a general idea of where the plane went, it'll turn what could be many hours of searching into 5 minutes of searching.
Most of my planes have Air Alerts in them, especially the slope soaring planes. Even when the wind is howling around me, I've never had a case where the Air Alert didn't quickly bring me to my plane. (Now reaching it in the tree 30 feet up, that's another matter ...)
The only time it came close is where I accidently found myself `flying' somebody else's plane (i.e. I thought their plane was my plane) and by the time I realized that `my' plane wasn't doing what I told it to, I had no idea where my plane had gone and neither did anybody else. But even then, 60 seconds of walking around and carefully listening for my plane found the Air Alert and I found my plane shortly afterwards.
And foliage doesn't really muffle the Air Alert sounds much at all ... the big problem would be noise (like a nearby road, or lots of wind) and even that's not very big.
| I found a piezo speaker at Radio Shack that gave a 90 db intermitten | very loud sound (really loud) when connected to a 12 V source. Problem | is it is on all the time. It would be great if it could be turned off | durning flight and turned on when needed. The current draw is only 15 | mah.
That would be relatively easy to make. Any of the circuits out there for turning on a digital camera electronically (rather than using a servo to push the button) would work. (Assuming you want to put it on a channel, of course.)
You'll have 5 volts, not 12 volts, but a DC-DC convertor could fix that, as could simply picking another buzzer that uses 5 volts.
| Another idea would be a light weight system that releases a tall plume | of none fire hazard smoke, visible above the foliage. I believe this | woud be preferred over sound because smoke could be seen when sound may | be muffled by the wind through foliage.
1) it would be much larger and heavier than the Air Alert.
2) make sure it never goes off on accident in your car :)
3) foliage will `muffle' small amounts of smoke too.
I think it would be a bad idea, but if you do decide to make it, if anybody sells smoke systems for electrics that would probably be what you needed.
| Could an elctronic expert or chemist make either one of the above | possible?
I doubt you'd need experts or chemists. What you need for the first is easily found online, and then you just need to do some soldering. The second sounds similar, but I've not tried it.