Avionic Antenna and Carbon??

Discussion in 'Composites' started by Tantrum1, Jan 27, 2020.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Jan 27, 2020 #1

    Tantrum1

    Tantrum1

    Tantrum1

    Well-Known Member

    Joined:
    Jul 8, 2016
    Messages:
    155
    Likes Received:
    403
    Location:
    Saint John, NB Canada
    Good day all,
    As some of you know I am building an aircraft with a 4130 chassis and a carbon skin fuselage. I'm stating to plan the avionics packages, and i'm wondering about antennas. I'm trying to eliminate anything that will cause any parasitic drag, ie. Antennas. So my question is can a 406 elt antenna, gps antenna for navigation and the antenna for my WAAS signal for ADS-B be mounted "inside" the fuselage shell, mounted to the 4130 Chassis??
    Now I do have the VHF antenna that can be bonded to composites without a ground plane for my VHF, and I've ordered one for the transponder.
    Thanks
    Mark
     
  2. Jan 27, 2020 #2

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,151
    Likes Received:
    3,460
    Location:
    Saline Michigan
    Graphite is conductive, graphite fibers may be viewed as wires, and while they are not fully interconnected like a metal mesh might be, a graphite fiber composite layer will largely block radio transmission.

    All is not lost. Many folks run GPS and ELT antenna from within the canopy. If you were to make your vertical stabilizer and rudder from fiberglass and/or Kevlar, you could bury a COM antenna in the stab. Fiberglass and/or Kevlar wingtips would also work for places to bury antenna.

    Go to Jim Wier website http://www.rstengineering.com/and read up on what he has to say about buried antenna. He has a booklet on the topic.

    Bill Simpson
     
    BoKu and Pops like this.
  3. Jan 27, 2020 #3

    Tantrum1

    Tantrum1

    Tantrum1

    Well-Known Member

    Joined:
    Jul 8, 2016
    Messages:
    155
    Likes Received:
    403
    Location:
    Saint John, NB Canada
    Hey Bill,
    Thanks I will take a look at that for sure! The tail is completely carbon.
     
  4. Jan 27, 2020 #4

    Aerowerx

    Aerowerx

    Aerowerx

    Well-Known Member

    Joined:
    Dec 1, 2011
    Messages:
    5,269
    Likes Received:
    1,471
    Location:
    Marion, Ohio
    I don't know how it would work in carbon composite, but there is a type of antenna called a "Skeleton Slot". Instead of a wire, you cut a slot in a sheet of metal and it will act like a dipole antenna when fed properly.

    It would take quite a bit of engineering and experimenting to get it to work, though, and I have no idea how well it would work.

    I tried to find a website to link to, but can't find any with basic design info.
     
  5. Jan 27, 2020 #5

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,477
    Likes Received:
    6,447
    Location:
    USA.
    Been using Jim Wier's antennas since the early 1980's for COM, VOR, Glideslope, Marker Beacon. Haven't found any high dollar antenna that worked any better.
    How about in a fiberglass wing tip ?
    His articles in Kitplanes is the reason I get Kitplanes. Also like his style of writing.
     
    wsimpso1 likes this.
  6. Jan 27, 2020 #6

    BoKu

    BoKu

    BoKu

    Well-Known Member HBA Supporter

    Joined:
    Aug 16, 2013
    Messages:
    2,472
    Likes Received:
    3,193
    Location:
    Western US
    Antennas inside a carbon Faraday cage won't work. If you can tolerate a 46" rudder span, I'd make it out of kevlar and put a 1/4 wave dipole com antenna there. Make some of the turtledeck out of fiberglass and put the GPS antenna there. For the transponder I'd recommend a thin blade antenna.
     
    Last edited: Jan 27, 2020
    wsimpso1 likes this.
  7. Jan 27, 2020 #7

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    12,040
    Likes Received:
    3,469
    Location:
    Memphis, TN
    I would maybe make two antennas. One for racing built into/ under the leading edge of the wing skin or wing tip because it’s wood. Build another that can screw in and stick up for better reception on the fuselage. Plug one in the radio for racing. Plug the other in and screw antenna in when just flying around.
     
    BoKu likes this.
  8. Jan 27, 2020 #8

    Victor Bravo

    Victor Bravo

    Victor Bravo

    Well-Known Member

    Joined:
    Jul 30, 2014
    Messages:
    6,574
    Likes Received:
    5,349
    Location:
    KWHP, Los Angeles CA, USA
    I just can't wait to hear about why you need those avionics in a Snoshoo...

    VHF Com, GPS, ADS-B, ELT - that sounds like at least five or six pounds with wiring and antennas, even with modern radios.

    Jon Sharp used to take the altimeter and airspeed out of the airplane before the race, leaving oil temperature as the only instrument. The reason? "So I can make use of the lightening holes in the panel".
     
    mcrae0104 and BJC like this.
  9. Jan 27, 2020 #9

    Tantrum1

    Tantrum1

    Tantrum1

    Well-Known Member

    Joined:
    Jul 8, 2016
    Messages:
    155
    Likes Received:
    403
    Location:
    Saint John, NB Canada
    Victor Bravo,
    I get it! BUT my wife would have my head on a pike if I had spent all this money and time to build an airplane that would only fly once a week. hahahaha..
    I do plan on doing some sport flying. So need to lay out the equipment within the build, however lots of it will be removed for racing.
     
  10. Jan 27, 2020 #10

    Mcmark

    Mcmark

    Mcmark

    Well-Known Member

    Joined:
    Sep 24, 2013
    Messages:
    291
    Likes Received:
    148
    Location:
    Owings, MD
    A friend put his in the leading edge of his wing. Acrosport IIS with ply leading edges. Hasn't had any problems, been flying a little over a year. It's the yellow and black one that was in Sport Aviation last year.
     
  11. Jan 27, 2020 #11

    Victor Bravo

    Victor Bravo

    Victor Bravo

    Well-Known Member

    Joined:
    Jul 30, 2014
    Messages:
    6,574
    Likes Received:
    5,349
    Location:
    KWHP, Los Angeles CA, USA
    Excellent idea McMark, before Tantrum closes the wing skins perhaps lay an antenna into the wing skins. If you are going to fiberglass the wing with light cloth, then you need to check whether glass will also act like a Faraday Cage.

    I would also consider making a one-piece avionics "tray" that removes form the aircraft with 4 screws and one multi-pin connector. All the avionics and battery and everything else should be on that tray, and it comes out before the race.

    All the wiring and large diameter power cable form the engine driven alternator, and the alternator, is going to have to come out too.
     
  12. Jan 27, 2020 #12

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,477
    Likes Received:
    6,447
    Location:
    USA.
    Wood and or fiberglass is OK over the antenna elements. All the antennas on my Falconar F-12 were in the rear of the fuselage. Same for the SSSC and now same for the JMR. Neighbor installed the RST copper foil com antenna in the rear fuselage of his Champ and couldn't tell any difference than an antenna on the outside. Just keep the elements as far away from any metal as possible. Cut the coaxial cable a fundamental length of the wavelength of the center of the freq band for the lowest SWR.
     
    BoKu likes this.
  13. Jan 27, 2020 #13

    Aerowerx

    Aerowerx

    Aerowerx

    Well-Known Member

    Joined:
    Dec 1, 2011
    Messages:
    5,269
    Likes Received:
    1,471
    Location:
    Marion, Ohio
    Just off the top of my head I would say no. BUT, it might affect the length of the antenna, which would have to be longer or shorter to work on frequency (most likely shorter).

    Just keep in mind that free advise is worth what you pay for it!;)
     
    BoKu likes this.
  14. Jan 27, 2020 #14

    BJC

    BJC

    BJC

    Well-Known Member HBA Supporter

    Joined:
    Oct 7, 2013
    Messages:
    10,202
    Likes Received:
    6,933
    Location:
    97FL, Florida, USA
    I agree with several comments already made, but FWIW, here is what I would do.

    I would not install an ELT, unless it is required in Canada. If required, I would put it in the fuselage, antenna too, and have it easily removable.

    I would install the GPS antenna in the wing root, assuming that the plywood wing will be covered with polyester fabric.

    I would mount the transponder / ADS-B antenna to a metal ground plane / inspection port cover out in the wing.

    I would mount an external VHF antenna to an inspection plate on the bottom of the fuselage near where you will need to get to the brake cylinders, rudder pedals and springs.

    All inspection plates would be temporarily replaced with smooth plates for racing.

    I would follow VB’s advice about having everything removable.


    BJC
     
    mcrae0104 and wsimpso1 like this.
  15. Jan 27, 2020 #15

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    7,327
    Likes Received:
    2,107
    Location:
    North Carolina
    A slot antenna was my first thought too. Since carbon is conductive, but not very conductive, I'd make a slot antenna as follows:

    1. Laminate some metal foil to the outside of the carbon with suitable connecting wires.
    2. Cut the slot.
    3. Make it structurally sound again with glass or kevlar.

    This will be pretty light and zero drag if done while making a skin on a mould.

    It may take a few goes to get the slot right. Build a test panel(s) before trying this on the actual plane. Buy a friendly ham some beer or a geek toy (tool) and work through design and test with him.
     
  16. Jan 27, 2020 #16

    BoKu

    BoKu

    BoKu

    Well-Known Member HBA Supporter

    Joined:
    Aug 16, 2013
    Messages:
    2,472
    Likes Received:
    3,193
    Location:
    Western US
    Horizontally oriented antennas are kind of sucky for vertically polarized signals like aircraft com. It'd work fine at each end of the course, but not so much down the straightaways.
     
  17. Jan 27, 2020 #17

    Aerowerx

    Aerowerx

    Aerowerx

    Well-Known Member

    Joined:
    Dec 1, 2011
    Messages:
    5,269
    Likes Received:
    1,471
    Location:
    Marion, Ohio
    IIRC, the polarization of a slot antenna is opposite to that of the slot orientation. That is, for vertical polarization you want to make the slot horizontal. But then you would have a lousy radiation pattern---not omnidirectional like you want.
     
  18. Jan 28, 2020 #18

    mcrae0104

    mcrae0104

    mcrae0104

    Armchair Mafia Conspirator HBA Supporter

    Joined:
    Oct 27, 2009
    Messages:
    3,098
    Likes Received:
    2,135
    Location:
    BDU, BJC
    This idea of making lots of things removable is interesting but it makes me wonder, does RARA have an MEL? And even in a race, wouldn't 91.205 still apply (tomato flames)?
     
  19. Jan 28, 2020 #19

    Victor Bravo

    Victor Bravo

    Victor Bravo

    Well-Known Member

    Joined:
    Jul 30, 2014
    Messages:
    6,574
    Likes Received:
    5,349
    Location:
    KWHP, Los Angeles CA, USA
    I have no idea what the current RARA rules are, but in my prehistoric day they did not require any radio equipment for the F-1 class, because we did not do an air start.

    I recommend strongly against traditional polyester fabric covering on the wing. I recommend 1 ounce fiberglass for the covering, since it can be sanded and filled smooth and painted with hard sandable paint. The epoxy for the glass cloth strengthens and plasticizes the plywood, and the fiberglass becomes structural.
     
  20. Jan 28, 2020 #20

    Tantrum1

    Tantrum1

    Tantrum1

    Well-Known Member

    Joined:
    Jul 8, 2016
    Messages:
    155
    Likes Received:
    403
    Location:
    Saint John, NB Canada
    A lot of what you all have mentioned has already been taken into consideration as well as some of it is even in the works. Almost all avionics are going to be installed on one "rack" and will be removed for racing applications. As for the leading edge install of the antenna that won't work for the antenna I had planned, but I do like that idea and might explore that one further. As for Canada, yes we require an ELT on any flight that is 25NM away from airport base of operations.(I do need to confirm that exact verbiage in the Reg, but that's the short answer) for racing RARA requires us to have one VHF installed and it has to be working and audible at all times. Thanks for the input guys!!
     

Share This Page

Group Builder
arrow_white