ELT antenna

[wirejock]

I mounted the "Yak" (ACK) ELT on a Vans mount per plans just behind the F706 baggage bulkhead. That was enough for the day. Dufficult job. Next up is the antenna. The manual says not to pass through any bulkheads.

Does that mean not to actually route the coax through a snap bushing or don't cross a bulkhead at all?

My 7A is a slider. The only place I can mount the antenna to comply with the DAR and Yak manual is centered top aft skin right in front of F708 bulkhead. That means passing F707. The F707 bulkhead is wide open. The coax can pass F707 without touching anything. Is that ok?

Should the coax be secured or just left hanging? If I tie it off, it could get severed in an accident.

I installed nutplates in all the locations on the mount for future use. So many builders have problems with the Yak, I will probably replace it. That mount is not coming out so hopefully the holes match other ELTs.

[terrye]

My understanding is if the coax is routed through a bulkhead (whether a snap bushing or rubber grommet) it could get severed if the bulkhead deforms during a crash. So routing it around a bulkhead, and secured sufficiently, is preferrable.

[Mel]

Originally Posted by terrye

My understanding is if the coax is routed through a bulkhead (whether a snap bushing or rubber grommet) it could get severed if the bulkhead deforms during a crash. So routing it around a bulkhead, and secured sufficiently, is preferrable.

What Terrye said.

[Carl Froehlich]

If memory serves, this means that all RV-14s built per plans will not pass a DAR.

Carl

[wirejock]

Originally Posted by Mel

What Terrye said.

Thanks Mel and Terry
Exactly what I needed.

[Webb]

What would be the preferred method of securing the coax when routing around a bulkhead?

[Scott Hersha]

Getting around a bulkhead that is covered by a baggage bin cover panel that will also need some sort of hole drilled with a snap bushing or something similar, doesn’t seem like it would alleviate the potential shearing of the antenna cable in a crash. To take the bulkhead question out of the equation, you would need to mount the antenna through the skin of the compartment the ELT is in - like through the top/side/bottom of the turtle area skin? What happens when you flip over or that tail cone skin is sacrificed? It doesn’t seem like some non-standard installation would be worth the effort. Is there some data/information that the per plans installation hasn’t worked?

[wirejock]

Originally Posted by Webb

What would be the preferred method of securing the coax when routing around a bulkhead?

I can't speak as an expert, but I hate zip ties with a passion. Not a single one on my airplane.
They hold great till they get brittle. New ones wouldn't release in an crash. Brittle ones just fall apart.
My plan is to leave service loops, aka crash loops secured with self fusing silicone tape. One near the antenna. One at the F707 bulkhead. One at the ELT. It holds very well and tears under pressure. Normally, I would put a tie of waxed lashing string, but that stuff will cut wire. Not a good idea.

If someone has another product, I'm listening.

[wirejock]

Originally Posted by Scott Hersha

Getting around a bulkhead that is covered by a baggage bin cover panel that will also need some sort of hole drilled with a snap bushing or something similar, doesn’t seem like it would alleviate the potential shearing of the antenna cable in a crash. To take the bulkhead question out of the equation, you would need to mount the antenna through the skin of the compartment the ELT is in - like through the top/side/bottom of the turtle area skin? What happens when you flip over or that tail cone skin is sacrificed? It doesn’t seem like some non-standard installation would be worth the effort. Is there some data/information that the per plans installation hasn’t worked?

I'm not passing coax through any bulkhead with a hole. The ELT is AFT of the baggage bulkhead per Vans on a Vans designed ELT mount. The only bulkhead the coax will pass is a huge open area. ELT and antenna are both aft of the fuse/tail cone seam. Antenna is recommended on top. Nothing I can do it if it goes wrong side up. Same problem if not worse to place it on the bottom or a side skin. Plans warn against placing it in wingtips or under fairings. It has to be a certain orientation from vertical.
Per Mel, DAR, it has to be installed per manual or be in violation.
Maybe I'm missing the point.

[Webb]

Maybe I’m being cynical but if a crash is sufficient to deform a rear bulkhead and severe a coax cable, then the forward compartment probably could be used for an aluminum coffin.

But to keep in the spirit of things, perhaps a loop in the coax between the bulkheads to provide the “slack” needed to prevent stretching and potential severing of the coax in the event of a crash.