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External antennas on composite plane (was Alternator article

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gmcjetpilot

Joined: 04 Nov 2006
Posts: 170

Posted: Wed Feb 13, 2008 7:15 am Post subject: External antennas on composite plane (was Alternator article

Walter three or four things:

   

  External antennas are better performing in general, even 

  on a fiberglass plane.

   

  Cost to bond in antennas is more than off the shelf 

  antennas that bolt on (externally). All they have to do is 

  put a metal ground plane (the size of a large round or 

  square serving plate) under the antenna. Done.

   

  Last, some one told me (I don't know this for sure) the 

  Columbia has some kind of lighting protection in the 

  layup, to route a lightning strike through and out the 

  plane. I have not confirmed this, but this would make 

  internal antennas as impractical as they are in metal 

  planes. 

   

  In the area of pure gussing, it might also be a certification 

  issue, meaning its easier and  cheaper to use exisiting 

  products. It is a fact that the DRAG from an antenna or 

  two is small. Why bother? George

   

   

   

  >On an unrelated matter, I notice that most of the type 

  >certified composite aircraft (columbia, cirrus and diamond) 

  >have external antennas. Do you know if this is a requirement 

  >for certification? Is there any reason that blind antennas 

  >cannot be just as effective as external antennas?

 	  Quote: 	
		  Best Regards

Walter Fellows


	


   [quote][b]

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Bruce(at)glasair.org
Guest

Posted: Wed Feb 13, 2008 7:58 am Post subject: External antennas on composite plane (was Alternator article

Antennas reside quite well internally in composite, fiberglass airplanes, as long as the structure is fiberglass. As soon as you move to carbon based cloth, external antennas are needed. Some carbon cloth kits (Lancair) have specific areas of fiberglass cloth instead of carbon to allow internal antennas.  

   

Lightning protection is another issue. The accepted way of protecting a fiberglass (Glasair) or carbon (Lancair) or certified composite (Columbia, Cirus) airframe is to place a layer of copper mesh in the last few (outer) laminates of the structure. This means that all antenna have to be external.  

     

Bruce  

www.Glasair.org  

  

   

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longg(at)pjm.com
Guest

Posted: Wed Feb 13, 2008 8:12 am Post subject: External antennas on composite plane (was Alternator article

Internal antennas are for esthetics and the micro speed conscious. I  have love washing my airplane and not having to go around everything in the  process. One clean sweep on the belly. They do not necessarily work better  or worse. I have noticed little difference having everything inside. If you  crash your ELT antenna will be outside after you land, so problem solved. Yes,  Columbia (Cessna) and Lancair have a lightning kit which routes energy out the  tail. It requires a new paint job when added as it must be bonded to the skin.  It is basically uses thin copper material bonded to the skin with whips on  the tail or elevator.

  

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