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#51
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
On Monday, December 30, 2019 at 6:44:50 AM UTC-8, Dan Marotta wrote:
In the absence of antenna diversity, I'm pretty sure all general aviation factory built aircraft have the transponder antenna on the bottom of the aircraft.Â* I would think the manufacturers must know something. When transponders first came out, the only receiver/interrogator was ground based. So anything certificated prior to TCAS, would definitely have the antenna on the bottom. Then TCAS came along, and now ADS-B. These will interrogate/receive from any direction. So to be visible from any direction, one should probably have an antenna on top as well as bottom... And satellite based ADS-B likely demands it. I'm sure Darryl has all the gory technical details :-) But my guess is that unless told otherwise, and considering cost of certification, etc., putting the antenna "where it's always been" is why it's on the bottom. :-) 5Z |
#52
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
On Monday, December 30, 2019 at 10:34:25 AM UTC-5, wrote:
UH, as I said in my earlier post it was way easier to install on the turtle deck than down by the gear. In my 27, it took less than 4 hours from start to finish including the transponder and power routing. The longest portion was the routing of the antenna cable up through the tunnel to the panel, not alot of room in there I didnt crimp on the bnc to that end until after I fished it up to the panel. I mounted the blade as far back as I could possibly reach in the fuselage which is close to the junction of the flap and wing. CH I was thinking about the first message. Ventus CM would be an easy bottom install in the front of the engine bay. Re '27. I did one behind the gear before the Schleicher tech note came out. Behind the gear was painful. The Schleicher TN installs through the oxygen cylinder area which is easy peasy. I like to put ugly stuff where it shows less. FWIW UH |
#53
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
Thanks all for the great response and information !
I will contact Schenpp Hirth and get information/drawing about the fuselage top location option. Don't want to drill holes in the fuselage before that.... Dan |
#54
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
Although the faired blade antenna has a theoretical drage coefficient less than a rod, in practice you have to align the blade with the local flow in the area of the attachment point. If the blade is not parallel with the streamlines, I suspect it potentially could add more drag than a plain ole' rod.
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#55
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
Please let us know what you learn. I am thinking of an xponder install on my D2b.
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#56
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
I believe drag is related to the square of the speed.Â* How often do you
fly your glider at 250 kts? On 12/30/2019 3:52 PM, wrote: O And since you asked about different style 1/4 wave dipoles. The rods, blades etc. should all behave the same from a RF viewpoint. They are effectively the same internally. Rods/single attach point style antennas may be easier to attach/mount on curved surfaces, but have higher drag than a blade if that small drag worries you. I've also seen A&Ps recommend the rod style so that if you do manage to crunch it will bend and hopefully do less damage to the fuselage/finish. Transponder rod antennas spec drag at .41 lbs at 250 MPH and blade antennas at .09 lbs at 250 MPH. That seems to be a big difference but anyone have a comment to what this measures in the gliding world? -- Dan, 5J |
#57
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
I will let you know what I found and what decided.
Dan |
#58
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
I am thinking of the theoretical advantage in drag coefficient of a blade vs rod antenna which holds for any speed.
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#59
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
On Wednesday, January 1, 2020 at 8:32:48 AM UTC-6, India November wrote:
I am thinking of the theoretical advantage in drag coefficient of a blade vs rod antenna which holds for any speed. Assuming, as previously stated, that the blade antenna is aligned with the airflow around the fuselage at that point. I would think that the drag of a misaligned blade antenna could be significantly higher than the perfect alignment drag. For that reason, I'm personally going with a rod and ball antenna. The manufacturer's recommendation for mounting a transponder antenna is in an area where I have no idea how the air really flows. Does anyone know if the difference between a perfectly aligned blade antenna and a rod and ball antenna is at all significant at, say, 100 kts airspeed? Lou |
#60
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Locating Transponder Antenna on top of the fuselage instead ofunder it.
Just anecdotal evidence here, but my Stemme came with a rod and ball
transponder antenna under the nose bowl.Â* I mounted a blade type antenna about 6 inches aft of that for the Flarm B.Â* I haven't noticed any difference in flying qualities, drag, etc.Â* Maybe it's measurable but who cares?Â* I'm not in contention for a world record or title. On 1/1/2020 1:36 PM, MNLou wrote: On Wednesday, January 1, 2020 at 8:32:48 AM UTC-6, India November wrote: I am thinking of the theoretical advantage in drag coefficient of a blade vs rod antenna which holds for any speed. Assuming, as previously stated, that the blade antenna is aligned with the airflow around the fuselage at that point. I would think that the drag of a misaligned blade antenna could be significantly higher than the perfect alignment drag. For that reason, I'm personally going with a rod and ball antenna. The manufacturer's recommendation for mounting a transponder antenna is in an area where I have no idea how the air really flows. Does anyone know if the difference between a perfectly aligned blade antenna and a rod and ball antenna is at all significant at, say, 100 kts airspeed? Lou -- Dan, 5J |
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