Transponder Antenna Placement Fuselage Bottom - Minimize Damage? Exact Location

WaltWX

unread,

Jan 17, 2015, 7:50:16 PM1/17/15

to

Planning on install of a Trig T22 on my Discus 2A. I see that SH recommends installation on bottom of fuselage near gear door canted off at an angle:

http://www.schempp-hirth.com/fileadmin/tmdocs/360-4-D-2070.pdf

Any recommendations from experience on exactly where to place a stub antenna in such a way to minimize damage while moving into and out of trailer? Also, comments on pluses minuses of adding a ground plane?

Walter Rogers - WX

Cookie

unread,

Jan 17, 2015, 8:03:13 PM1/17/15

to

http://www.advancedaircraft.com/

The L2....

If your glider has fiberglass tail boon (no carbon fiber) this is a great solution....

We installed about 10 or 12 of these in gliders with no problems at all...

Cookie

clewi...@gmail.com

unread,

Jan 17, 2015, 8:55:45 PM1/17/15

to

I installed a flexible transponder antenna in the exact location specified by Schemmp-Hirth in a Discus B. If you were to hit it during loading, unloading or outlanding it just bends out the way. XPDR performance has been great to date though I'm yet to test it at maximum range. Though in gliding, maximum range is really not necessary. I did have to trim the mesh ground plane to fit due to control rods and fibreglass brackets in the area but again, no degradation of performance evident.

http://www.lxavionics.co.uk/transflex-mesh-antenna.htm

Case

Dave Nadler

unread,

Jan 17, 2015, 10:04:20 PM1/17/15

to

On Saturday, January 17, 2015 at 8:03:13 PM UTC-5, Cookie wrote:
> http://www.advancedaircraft.com/
>
> The L2....
>
> If your glider has fiberglass tail boon (no carbon fiber) this
> is a great solution....
>
> We installed about 10 or 12 of these in gliders with no problems at all...
>
> Cookie

If you install an L2, MAKE SURE IT IS INSTALLED VERTICALLY !
"Works Great!" said the mechanic who glassed in some of these
horizontally. Don't do that!

Eric Munk

unread,

Jan 18, 2015, 4:00:10 AM1/18/15

to

If externally fitted, go for flexible. Fixed ones break and bend very
easily during operations. We did on our Discus b.

Bob Pasker

unread,

Jan 18, 2015, 9:40:48 AM1/18/15

to

I'm sure everyone knows this already, but its worthwhile saying again: transponder antennas need to go on the bottom of the aircraft so they can have line-of-sight to the radar facility, without being in the shadow of the fuselage or the wings.

Dan Marotta

unread,

Jan 18, 2015, 12:42:26 PM1/18/15

to

I mounted a blade antenna for my TT22 on the bottom of my LAK-17a as follows:

Sufficiently aft of the gear door to allow a good margin (a couple of inches) between the aft edge of the gear well and the forward mounting screw of the antenna.

Sufficiently off center (right side in my case) because the fuselage bonding joint is too thick for the length of the mounting screws.

Ground plane as described in the Trig installation manual. Transponder check at the local avionics shop showed somewhere around 275 watts peak power radiated by the antenna (IIRC).

As to damaging the antenna during trailering, I don't have a problem with my LAK glider and trailer. The fuselage cradle holds the glider high enough to prevent banging the antenna on the ramp. On landout I suppose it's possible to come close enough to an obstruction to miss the gear but hit the antenna, but I think the likelihood is pretty slim.

Here's a picture of my antenna as installed: https://www.dropbox.com/s/bl0263bjmlfcxxp/view%20antenna.jpg?dl=0

And here's the installation drawing for that antenna: https://www.dropbox.com/s/msfnn6x10hzc9lj/transpondereinbau%20lak17a.jpg?dl=0

Good luck!

Dan

--
Dan Marotta

Cookie

unread,

Jan 18, 2015, 1:25:16 PM1/18/15

to

Well, yes on a METAL aircraft...and maybe carbon fiber...but fiberglass...no...the L2 antenna usually goes on the inside wall of the tail boom....radio waves go through fiberglass...

Cookie

Peter Purdie

unread,

Jan 18, 2015, 2:15:22 PM1/18/15

to

But most 'modern' composite gliders have carbon in the fuselage, so act
like metal for RF purposes.

As far as sailplane antennas go, the AV-22 'lollipop stick' is far too
fragile; blade antenna looks prettier but the flex is probably optimal; I
back up the conductive fuselage with a mesh screen inside the skin as 'belt
and braces'.

Mike the Strike

unread,

Jan 19, 2015, 6:00:18 PM1/19/15

to

I installed a blade antenna with groundplane (yes, you need one!) in the lower fuselage (where the factory said) on my Discus 2b and it has worked well for ten years and never been knocked off by ground handling.

If you decide to put it in the tail, make sure you have low-loss coaxial cable.

Mike