Antenna mounted inside fiberglass belly panel

[David Lloyd]

I have a one piece fiberglass belly panel installed.  The Stormscope antenna has be mounted behind this panel since installed.  Stormscope works, at least it lights when the gear moves up and down.  I don't think I have seen it detect lightning...well, maybe once.  Does anyone else have a Stormscope antenna mounted behind a fiberglass panel like this?  Does it work?  The install manual says it should be mounted with a 12" radius ground plane and the antenna never painted.  It'll be a pain to move but I will if a couple people say what I have won't work.

[ArtVandelay]

Well if can’t be painted I doubt it will work behind some fiberglass.
My marker beacon antenna is behind the panel but my stormscope wasn’t.

[milotron]

On my K, it had a one piece belly added many moons ago and the beacon antenna relocated underneath. The lightning detector and ADF antenna were not relocated underneath, presumably because they wouldn't work as well. They look like they would be less drag  than the beacon antenna remaining exposed.

 

iain

[larryb]

The problem is knowing how well it does or doesn’t work. There could be attenuation that affects the range calculation. There could be reflections causing error in the direction calculation. If the unit was not installed in accordance with the install instructions you just don’t know how well it is working.

 

That said, I have my ADSB antenna for the GDL52R mounted behind the belly pan and it works great. I even receive ground stations while on the ground at my home airport. In the air the signal is always reported as excellent. But I would not put my storm scope antenna there.

[carusoam]

Find out where newer planes have their strike finders mounted...

White paint and TiO₂ go together... which is something that you don’t want to paint an antenna with....

I don’t recall where mine is... 

Best regards,

-a-

[M20F]

I have a WX-900 and it works great. I fly in/around a lot of terrible weather.  It doesn’t paint much because for the most part we don’t fly in weather as bad as we think we do (minus a select few). 
 
You also need to use a skin mapper to determine where to mount it so electrical activity on the plane doesn’t interfere with it.  Check with a real deal avionics shop. 

[kortopates]

Not a fan of antenna farms on my plane, I am one that went to great lengths to bury as many of the antennas as possible - at least for the non-low profile antenna's. I have my two Nav antenna's with one in each wingtip - which I've done twice since I had to go to a new antenna design when I did the Encore conversion because of the larger aileron control weights. My marker antenna is in the belly above the one piece fiberglass belly pan - I might eventually pull it since very few markers still exist. That leaves 2 Com antenna's, 2 GPS antenna's, 1 Transponder and my Storm Scope antenna. The WX-500 STC install manual had very specific guidance for installation including the requirement to test the suitability of the candidate location before installing. This was a long time ago, but I remember needing to pull some shielded cable wiring for the now removed strobe power supply in the tail to bring down noise. I don't have the RF engineering knowledge myself to fully appreciate the details but recognizing the importance of a proper install for a sensitive spherics device I put my trust an avionics shop with the prerequisite test equipment to do so. Therefore I wouldn't consider moving it without enlisting somebody with the equipment and knowledge to test and verify before doing so.I just wish I had some of the EE & RF knowledge some of folks here like @larryb and some others here that help us all out. @M20F just used the proper term for the equipment so vital to a storm scope install above - Skin mapper - a requirement if you really expect its going to work when you need it.

Edited July 19, 2020 by kortopates

[David Lloyd]

Thanks guys.  Don't see this thing working properly under the fiberglass panel.  It is a shame someone wasted money years ago mounting the antenna in such a location and never receiving any benefit from owning a Stormscope.  Will get with a shop that knows what they are doing and get it moved.

[RLCarter]

Not an avionics guy, antennas need ground planes. Have a shop mount a ground plane to the fiberglass belly under the antenna.
Kinda curious what moving the gear up & down has to do with it

4 hours ago, David Lloyd said:

Stormscope works, at least it lights when the gear moves up and down.

 

[David Lloyd]

Stormscope picks up the gear motor starting or stopping, or maybe switches making or breaking contact.  Same thing with a Bonanza I had and the Stormscope worked great in that.

[carusoam]

Anything on the plane that generates a spark... will appear as if it is lightning...   

To a lightning detector...

Motors have a tendency to generate tiny sparks while they are running...

Set the way back machine to 1965.... remember watching model trains and slot cars... when you turn the lights out...

Sparks flying everywhere...

I’m sure our Servo motors are better at this... but our lightening detectors are very sensitive...

Best regards,

-a-

[JETmachine]

The STC calls for the Strikefinder to be placed here (arrow). This antenna was installed 20 yrs ago and shows lightning in the Sierras when flying around San Francisco.  Last winter when working in the hangar during a storm, the Strikefinder lit up during lightning strikes. The VOR antennas are in the wing tips. The ELT is in the glass dorsal fin and checks Okay with ground control. That said, the Strikefinder is sensative to about 200 miles in this position. jt

[ArtVandelay]

Anything on the plane that generates a spark... will appear as if it is lightning...   
To a lightning detector...
Motors have a tendency to generate tiny sparks while they are running...
Set the way back machine to 1965.... remember watching model trains and slot cars... when you turn the lights out...
Sparks flying everywhere...
I’m sure our Servo motors are better at this... but our lightening detectors are very sensitive...
Best regards,
-a-

Don’t forget the alternator.

I assume basic algorithm is to measure EMP and base distance on strength of pulse. I wonder if they have improved it to be able to eliminate onboard sparks? Does Strikefinder do any better or worst?

[carusoam]

20 hours ago, ArtVandelay said:

Don’t forget the alternator.

I assume basic algorithm is to measure EMP and base distance on strength of pulse. I wonder if they have improved it to be able to eliminate onboard sparks? Does Strikefinder do any better or worst?

I’m not familiar. With the deep technicals for the strike finder... but, it doesn’t show anything sparking in my immediate neighborhood...
 

So, it may have a filter to ignore  anything within the confines of the plane..?

Best regards,

-a-

[EricJ]

14 hours ago, carusoam said:

I’m not familiar. With the deep technicals for the strike finder... but, it doesn’t show anything sparking in my immediate neighborhood...
 

So, it may have a filter to ignore  anything within the confines of the plane..?

Best regards,

-a-

The range estimation is very primitive, and therefore the range estimations are not very accurate.   My understanding is that for the most part they use signal strength and frequency components to estimate range, but neither provide a reliable estimate since the behavior of lightning is not consistent (intensity can very, even the number of strokes can vary, etc., etc).   For this particular application neither range or direction have to be highly accurate, so it still provides a very useful display.

If an emission from inside the airplane looks a bit like any of the common forms of lightning, it may have difficulty excluding it.

Also, an installation that yielded more signal attenuation than expected would likely just result in the display showing the strikes further away than it would otherwise.

Edited July 27, 2020 by EricJ

[David Lloyd]

The electric gear or flaps causing enough activity for the Stormscope to display is not a big deal.  What, 5 seconds for each, presumably with the runway right in front of the plane?  If the alternator was loosing enough electrons to display on the scope, it would probably be causing other problems.  A properly installed Stormscope or Strikefinder will not display anything in the airplane normally.  

I bought a WX-8 in 1984 and the range estimation was primitive.  Large, active storms appeared closer. A very strong lightning discharge would light a number of segments at the same time, often in a row toward the airplane.  Seeing that happen a number of times, you would learn what was happening.  The clear button was your friend for helping understand how far away and how strong the storm activity was.  Just like radar interpretation, it takes some learning and experience.  Way back when, the Stormscope directions explained this pretty well.  The basic instruction of don't fly into the dots or lighted segments worked pretty good back then. And today.

[G Miller]

Fiberglass is used for the nose radomes for commercial aircraft. They offer very low loss to microwave signals. The Stormscope is sensing much lower frequencies so the belly panel should not interfere with the operation of the antenna at all. There is a lot of metal underneath the belly panel and that should provide an adequate ground plane for the antenna. I suspect the antenna or the RF cable is bad. Ideally the antenna should be mounted to metallic structure and the RF cable should be routed underneath the ground plane and then connected to the antenna.

Retired Boeing Electromagnetics Engineer

[carusoam]

1 hour ago, G Miller said:

 

Retired Boeing Electromagnetics Engineer

This would make a great detail for your signature line... 

Best regards,

-a-