ELT antenna

[wirejock]

Now there's an idea!

Originally Posted by 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.

See below. Already planned

Originally Posted by wirejock

<snip>
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.

<snip>

[dmattmul]

Originally Posted by Carl Froehlich

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

Carl

Yes, plans call for penetration through 2 bulkheads complete with snap bushings for the 14. I think a "crash loop" would help but that I'm pretty sure was not in the plans.

[Mel]

Originally Posted by 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.

Absolutely not! A certain amount of "crush" is designed into many tail cones to relieve pressure on the shoulder harness and avoid back injuries.

[Mikeyb]

Attached is the seminal report on ELT crash performance. Earlier studies showed as many as 15 percent of ELT failures in survivable crashes were due to antenna/cable issues. However during full scale crash tests roughly half resulted in damage to antenna connectors themselves. None were from cable shearing. It also found that many of the cable connectors provided by ELT vendors were not fabricated to MIL-DTL-17 and failed with 1/5th of the mechanical load. The report concluded that the problem could indeed be solved by adding a 10 inch length of cable at both ends using MIL-DTL-17 cable.

https://ntrs.nasa.gov/api/citations/...0170002586.pdf

Mike

[bjdecker]

From the Installation Manual for the ACK ELT-04, page 4:

"...and should avoid crossing aircraft production breaks (i.e. riveted fuselage sections)..."

I don't see how drilling a hole in the webbing of a bulkhead, insulating it with a plastic snap bushing, violates the letter or spirit of the installation guidance.

However, for argument's sake, refer to RV-7 DWGs 21 and 26. Drilling a routing hole in the area where the bulkhead halves overlap and are riveted together, wouldn't be recommended (e.g. Detail B, DWG 21).

[claycookiemonster]

So, it seems that all the official manufacturer's advice for mounting antennas assumes they will be mounted externally. Nobody here seems to want to do that, which I understand.
So, either the antenna goes aft and under the empenage fairing where it will be horizontal (wrong according to the manufacturer) but very survivable and no bulkhead's need be penetrated, or it can go vertically mid-cockpit (correct, according to the manufacturer) but must past through several bulkheads to a less survivable location. Also, there is ZERO advice on exactly how much of this antenna must be exposed above the canopy rail, since Artex assumes the entire antenna is external.

It feels like everyone is lawyering up around this, sticking to their official and impractical decrees, and no one is speaking realistically or practically. Frustrating.

[rapid_ascent]

Larry,

Here are a couple of pics that show what I'm doing. It is a work in progress but I think you can get the ideal. I'll loop the coax under the bulkhead and continue forward with this method as soon as I make a few more of these little brackets. Once I get the entire route figured out I'll distribute any left over cable into loops as available.

I'm sure others may have comments on my approach, but its the way I'm doing it so...

[fl-mike]

I would ditch the Adels.
This is one area where you want WEAK cable support, like small zip-ties, that will break if stressed due to structure deformation.

You do not want to rip the cable out of the antenna or any other connector.

https://ntrs.nasa.gov/citations/20160009372