VHF Antenna woes

[Electricsnail]

Hi all hope you can help me. I purchased a kit that was already covered. The previous owner had planned for the IFR panel, but did not buy it from cub crafters and did not install the two grounding planes in the false spar. In an effort, not to have to uncover the wings, I’m trying to look for workarounds. I know I can put the dual GPS VHF antenna in the center on the top. For the second VHF antenna I am considering putting this VHF-5 in the aft of the fuselage. I am thinking I can suspend it off the stringers. I am hoping that somebody has some input. Theoretically it sounds good however I have not been able to communicate with the manufacturer for any pitfalls… Thanks for the input

[Andy]

I don't have an answer for you but I am interested in the problem.

I have an FX-3 that was built as G3X VFR but has since been converted to IFR capable by adding a G5, GPS 175, and pitot heat. I plan to add a GTR 20 as second COM to supplement the existing GTR 200. I shall need a new antenna for the GTR 20 in addition to the turtle deck mounted combined COM/GPS antenna that is factory standard.

Can you share a drawing of the ground plane plate(s) that is (are) missing from your wings? I'm wondering if these were included in my FX-3 wings as I feel structure in that area.

My planned use for the second COM is 90% receive only and I was considering adding a "rubber duck" type antenna to the belly panel. I do not plan to fit a remote audio panel and transmit on COM 2 would require a MIC select switch.

[Electricsnail]

Hey Andy, it’s pretty unlikely that your fx has the grounding planes. Here’s a few pics. I’m also considering a lower antenna, tho the vhf-5 is cheap enough to give a shot!

20220413_085159.jpg20211209_114004.jpg20220413_085159.jpg

[Andy]

Thanks for the pics! The structure I feel in the wing root area is far narrower than these ground planes so they were not standard fit on the FX-3 when mine was built.

[Pete D]

An alternate location you might consider is a bent COM antenna on the triangular belly antenna. This was the original location on the early Carbon Cubs. You would have to relocate the transponder antenna, maybe to the boot cowl on one side of the tunnel like what is done for a belly pod. This may be easier than retrofitting ground planes in other areas.

The false spar just behind the fuel tank has been recently revised to incorporate the ground plane so going forward new aircraft and new kits will be prepped for dual com regardless if spec'd for it or not as it is proving to be a popular option.

[Andy]

Thanks Pete.

Did/does the mod center ever retrofit the false spar ground planes? I don't think I'd want to do it but it does appear that the fabric could be cut, lifted, and replaced. Wouldn't the double thickness tapes at the ribs be the only thing showing it had been done?

[Pete D]

Thanks Pete.

Did/does the mod center ever retrofit the false spar ground planes? I don't think I'd want to do it but it does appear that the fabric could be cut, lifted, and replaced. Wouldn't the double thickness tapes at the ribs be the only thing showing it had been done?

It is probably technically possible, though not something we have done here. In order to glue fabric to fabric all of the paint needs to be removed down to bare fabric for it to adhere properly which takes quite a bit of careful hand work and MEK and you still end up with a patched wing. The polyurethane paint typically can't be feathered/blended into the existing paint so you would have a paint line that will show even if you "hide" it along a tape edge.