ELT

ELT Installation

Why, you might ask, am I installing the boring, un-glamorous ELT as my first piece of avionics? Why is my panel still bare, yet I'm spending money on an ELT? It's because I want to install those things that are going to become inaccessible once the structure is done (or at least harder to access.)

The logic is this: my next big job is to install the canopy. That requires that I order the finish kit, which currently has an 8 week lead time. So before the canopy is installed, I need to rivet on that missing aft top skin. The ELT and the elevator servo will be much harder to install once that's in place. So, I'm spending only the $3K that I need to now, and postponing all the "fun" electronics until they're needed.

For non-aviation readers, an ELT (Emergeny Location Transmitter) is a radio that automatically goes off if the airplane crashes so that the wreckage can be found. The survivors, if any, are presumably nearby. I chose an Artex 406 MHz model. The search-and-rescue satellites are going to stop monitoring 121.5 MHz in February 2009...by which time my airplane might not yet be flying!

For my friends in the science spacecraft community (I spent four wonderful years here), the ELT provides telemetry coverage for critical phases of the mission, such as planetary encounters, soil sample retrieval, and decelaration events.

I chose this spot for the antenna. It has to be far enough aft to clear the canopy when it's slid all the way aft. It also has to be far enough forward to not be obstructed too much by the vertical stabilizer. Amazingly, many builders put the antennas inside the airframe to avoid the unsightly, drag-producing protrusion. That, to this engineer, is a silly box-checking exercise. It makes about as much sense as putting the landing light inside the tailcone and hoping that some light leaks out.	So the first step was to build a doubler to help the skin take the load. I made a trapezoidal double to pick up one of the stringers that stiffens the skin.
Then I ran the coax down this bulkhead, supporting it every few inches with an Adel clamp. Now, it's a bit of a leap of faith that the antenna, the coax, and the ELT will all remain in contact with one another after a crash. I hope to facilitate that by keeping them relatively close together. But then, we are also assuming that the airplane ends up right-side up.	This is the chosen site for the ELT...it's bolted to the longeron that supports the elevator bellcrank. It's a pretty beefy hunk of structure.
As much of a pain as this position was, it's a lot easier than lying in the tailcone, which would've been my only alternative if I'd riveted on that top skin.	The ELT came with a little buzzer that is supposed to help the Civil Air Patrol find a false alarm when parked on a ramp. I guess they walk along a row of parked airplanes and listen for the buzzer.
The buzzer and the little switch on the instrument panel, complete the installation. The switch, and the "I'm beeping" LED are required and have to be somewhere in the cockpit.