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"Sliker" wrote in message
... On Sat, 29 Mar 2008 12:17:48 -0400, "Peter Dohm" wrote: Hmm, that makes me wonder. I couldn't figure out why buried antennas in places like the leading edge of vertical fins weren't getting as good reception as an external antennas. Titanium dioxide in white. And white is what the composite kitplane companies want us all to paint our planes. I wonder where I can get some of that radome coating..... :-) I always wondered why radomes looked a little different, or the shade was off the rest of the plane. There must be something to the paint, or they could just paint the radomes with the same paint as the rest of the plane. Metal-flake is mylar?! that's the one thing I was sure was little flakes of aluminum. No wonder it fades out over time so bad. I can't see metal-flake on a plane though, that stuff is for hot rods and dune buggies. If paint affects radomes, I wonder if radar has different needs than just transmitting and recieving VHF radio signals? And radar had changed so much also. Instead of the old 50,000 watt systems, they now do the same thing with 700 watts. I used to fly a jet with the old 50,000 watt system, and the radar rotated all the way around instead of sweeping back and forth. The airline told us a special paint on the forward bulkhead stopped the beam from entering the cockpit. But I used to worry about some flakes of it falling off... Now that was one paint that definitely would stop all microwave energy, and probably any other radio energy. The problem is if I go to the paint store and buy a gallon of Imron Pewter Metalic, the can really doesn't say what makes up the metallic effect of the paint. Possibly Dupont could supply this info. DuPont is an excellent source, and will also be able to point you to a distributor for their aviation products. The only thing that I remember about the radome paint/coating is that it was very slightly conductive--even at the surface. But the bulkhead was another matter, since the metal bulkhead was a pretty good barrier in its own right and I believe that there was a fairly substantial energy absorbing blanket ahead of the bulkhead for those old C-band Sperry radars. Purely as an aside, I have no idea why they continued to only display 90 degrees of arc long after larger and brighter displays could have easily provided a reliable display of more than 200 degrees--since the only limitation would have been blanketing by the engines and wing tips. Peter .. |
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On the older Glasair kits like mine, it's covered with the dark gray
gelcoat that contains 2% carbon black for UV resistance. I wonder if the carbon interferes with radio reception? I've read that cabon fiber structures block signals, but how much carbon it takes to do that I don't know. But for the Glasair folks to say the radios worked so much better when the moved the antennas outside, makes me think some part of the structure was blocking radio signals.. On Sun, 30 Mar 2008 20:29:38 -0400, "Peter Dohm" wrote: DuPont is an excellent source, and will also be able to point you to a distributor for their aviation products. The only thing that I remember about the radome paint/coating is that it was very slightly conductive--even at the surface. But the bulkhead was another matter, since the metal bulkhead was a pretty good barrier in its own right and I believe that there was a fairly substantial energy absorbing blanket ahead of the bulkhead for those old C-band Sperry radars. Purely as an aside, I have no idea why they continued to only display 90 degrees of arc long after larger and brighter displays could have easily provided a reliable display of more than 200 degrees--since the only limitation would have been blanketing by the engines and wing tips. Peter . |
#3
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![]() "Sliker" wrote in message ... On the older Glasair kits like mine, it's covered with the dark gray gelcoat that contains 2% carbon black for UV resistance. I wonder if the carbon interferes with radio reception? I've read that cabon fiber structures block signals, but how much carbon it takes to do that I don't know. But for the Glasair folks to say the radios worked so much better when the moved the antennas outside, makes me think some part of the structure was blocking radio signals.. I could be wrong, but I recall that Jim Weir has done extensive testing on airplanes, and what structures block radio signals, and carbon fiber has been found to not be a problem. I hope I remembered right, and Jim will probably jump in here and clarify the situation. When it comes to antenna mounting and performance, I think we are lucky to have a resource such as Jim to help us get on the right path. He is an expert on the subject, IMHO. -- Jim in NC |
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"Morgans" wrote in message
... "Sliker" wrote in message ... On the older Glasair kits like mine, it's covered with the dark gray gelcoat that contains 2% carbon black for UV resistance. I wonder if the carbon interferes with radio reception? I've read that cabon fiber structures block signals, but how much carbon it takes to do that I don't know. But for the Glasair folks to say the radios worked so much better when the moved the antennas outside, makes me think some part of the structure was blocking radio signals.. I could be wrong, but I recall that Jim Weir has done extensive testing on airplanes, and what structures block radio signals, and carbon fiber has been found to not be a problem. I hope I remembered right, and Jim will probably jump in here and clarify the situation. When it comes to antenna mounting and performance, I think we are lucky to have a resource such as Jim to help us get on the right path. He is an expert on the subject, IMHO. -- Jim in NC That's very true, and the little that I did was 20 years ago. Jim Weir is current. Peter |
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On Tue, 1 Apr 2008 16:34:13 -0400, Morgans wrote:
I could be wrong, but I recall that Jim Weir has done extensive testing on airplanes, and what structures block radio signals, and carbon fiber has been found to not be a problem. I hope I remembered right, and Jim will probably jump in here and clarify the situation. This is concurred in F1 racing now for better than a decade. -- Remove numbers for gmail and for God's sake it ain't "gee" either! I hesitate to add to this discussion because I'm not an instructor, just a rather slow student who's not qualified to give advice that might kill someone. |
#6
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There are hundreds of variations of carbon fiber "mixes". Some have
absolutely no effect on internal antennas, and some that are absolutely wonderful Faraday shields (blocks) of radiation performance. My work with Rutan on Voyager pretty much proved that. HOWEVER, having said that, we proved in the Bellanca experiments that regular old silver UV dope on fiber has absolutely no effect on internal antennas. Even the FAA accepted our experiments on that. On the other hand, mixing carbon black, which is not a conductor, nor an insulator, but a lossy medium is in fact an antenna attenuator. For some manufacturer of kits to come out and say, "hey, we started putting in carbon black to our mix and now we've got internal antenna problems" isn't a great surprise. I work real cheap. I'm not a thousand dollar an hour consultant. You'da thought that all you who are spending tens of thousands of dollars a kit would have had professional antenna consulting from these yahoos who are all of a sudden discovering that moving this or changing that is having an effect on their antenna performance would come to the source for advice. Not a one of them, other than Bellanca and Beech. Cheap *******s. To the person that asked whether carbon black has an influence with internal antennas, I pose the following question: We proved at Bellanca that reflection from aluminum particle to aluminum particle to the outside world didn't affect transmission through "silver dope" UV protectant to any measurable degree. However, carbon black is not a reflector, but an absorber. Signals don't get reflected in carbon; they get converted to heat and absorbed. That ain't rocket science; that's what I teach to my freshman engineering students. Is that understood? You folks that are paying tens of thousands of dollars for your kits need to have your vendors take my freshman engineering class. Jim -- "If you think you can, or think you can't, you're right." --Henry Ford "Morgans" wrote in message ... "Sliker" wrote in message ... On the older Glasair kits like mine, it's covered with the dark gray gelcoat that contains 2% carbon black for UV resistance. I wonder if the carbon interferes with radio reception? I've read that cabon fiber structures block signals, but how much carbon it takes to do that I don't know. But for the Glasair folks to say the radios worked so much better when the moved the antennas outside, makes me think some part of the structure was blocking radio signals.. I could be wrong, but I recall that Jim Weir has done extensive testing on airplanes, and what structures block radio signals, and carbon fiber has been found to not be a problem. I hope I remembered right, and Jim will probably jump in here and clarify the situation. When it comes to antenna mounting and performance, I think we are lucky to have a resource such as Jim to help us get on the right path. He is an expert on the subject, IMHO. -- Jim in NC |
#7
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Sounds like the carbon black mixed into the gelcoat could have been
the culprit. But I know how to fix that! the 'ole power sander in the areas where the antenna's are. That carbon black will sand off, and is not structural at all. And a good layer of primer and paint will provide enough UV resistance, especially for a plane stored in hangar. I've noticed that the tech support folks at the old Stoddard-Hamilton would advise to sand off the gray primer at the drop of a hat for just about any issue. Such as possible fuel leaks over the spar, they would just say to sand off the gray primer to make the structure underneath transparent, and the leak easier to find. Or if any laminates needed to be applied in areas of the primer, off it comes again. The carbon black was probably a bad idea in hindsight, and no doubt why they quietly stopped using it. Thanks for the great insight! The main negative to sanding off the gray gelcoat is it opens up the pinholes. And I'm just getting into dealing with those. I hear so many different ways to cover them up. Some say mix some dynalight bondo with acetone and use a razor blade to sqeege it inside the holes. I just wish that carbon black was never used in the first place. More work for us builders. Rich On Tue, 1 Apr 2008 23:47:30 -0700, "RST Engineering" wrote: There are hundreds of variations of carbon fiber "mixes". Some have absolutely no effect on internal antennas, and some that are absolutely wonderful Faraday shields (blocks) of radiation performance. My work with Rutan on Voyager pretty much proved that. HOWEVER, having said that, we proved in the Bellanca experiments that regular old silver UV dope on fiber has absolutely no effect on internal antennas. Even the FAA accepted our experiments on that. On the other hand, mixing carbon black, which is not a conductor, nor an insulator, but a lossy medium is in fact an antenna attenuator. For some manufacturer of kits to come out and say, "hey, we started putting in carbon black to our mix and now we've got internal antenna problems" isn't a great surprise. I work real cheap. I'm not a thousand dollar an hour consultant. You'da thought that all you who are spending tens of thousands of dollars a kit would have had professional antenna consulting from these yahoos who are all of a sudden discovering that moving this or changing that is having an effect on their antenna performance would come to the source for advice. Not a one of them, other than Bellanca and Beech. Cheap *******s. To the person that asked whether carbon black has an influence with internal antennas, I pose the following question: We proved at Bellanca that reflection from aluminum particle to aluminum particle to the outside world didn't affect transmission through "silver dope" UV protectant to any measurable degree. However, carbon black is not a reflector, but an absorber. Signals don't get reflected in carbon; they get converted to heat and absorbed. That ain't rocket science; that's what I teach to my freshman engineering students. Is that understood? You folks that are paying tens of thousands of dollars for your kits need to have your vendors take my freshman engineering class. Jim |
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