Locating Transponder Antenna on top of the fuselage instead of under it. [Archive]

Darryl Ramm

December 27th 19, 10:22 PM

On Friday, December 27, 2019 at 11:34:32 AM UTC-8, wrote:
> Hi all,
> Planning to install a Transponder Antenna on my Ventus CM.
> Schempp Hirth indicates the possibilty of installing on top of the fuselage , behind the engine compartment doors.
> Regarding being seen by ATC and Airlines, would that location perform better/worse/same as the standard location on side of fuselage - above gear doors ?
> Dan

The preferred location should be below. That is more visible to ATC SSR, and indirectly providing ADS-R/TIS-B services to other aircraft. Close by aircraft with TCAS (or ADS-B In if you have ADS-B Out) that are a collision threat to you usually have no problem seeing your glider transponder. And arguably below is more a blind spot for gliders so maybe putting more signal there even if everything else did not matter makes sense (and it should also provide good coverage behind).

"on the side above the gear doors??? I've never seen a transponder antenna installed "on the side". Many are behind the gear doors and offset slightly from the centerline. The antenna needs to be mostly vertical since transponders, SSR, and TCAS use vertical polarization. Yes aircraft bank, but you need to start with the antenna somewhat vertical, slightly off centerline is fine.

Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important.

---

Interesting things may happen in Canada and other countries with Aerion satellite based 1090ES reception is being used. The satellites (much further away than threat aircraft) need good top antennas. That *might* lead to aircraft (including gliders?) using diversity (top and bottom) transponder antennas at some future time... not supported by the transponders we use today (GA works so well with just a bottom antenna it's not been needed until...)..

[email protected]

December 28th 19, 01:22 AM

I put mine on a turtle deck on my ASW 27 and it works fine no issues with anyone seeing me or even worrying about it I really like the fact that it's there and was really easy to install compared to down by the gear

George Haeh

December 28th 19, 02:05 AM

I had a standard length PowerFLARM and ADS-B antenna through a hole in the glareshield of my ASW-27. After upgrading to dual long PF antennas that I placed on opposite sides of the canopy with Velcro, I placed an internal L2 transponder antenna in the glareshield hole reaching to just below the canopy favoring visibility to TCAS above and satellites. Being a long way from any big airports, I haven't verified with ATC, but suspect I'm visible to ground installations unless close in above or pointed directly away when my body and carbon fiber will be in the way.

Darryl Ramm

December 28th 19, 04:28 AM

On Friday, December 27, 2019 at 6:05:20 PM UTC-8, George Haeh wrote:
> I had a standard length PowerFLARM and ADS-B antenna through a hole in the glareshield of my ASW-27. After upgrading to dual long PF antennas that I placed on opposite sides of the canopy with Velcro, I placed an internal L2 transponder antenna in the glareshield hole reaching to just below the canopy favoring visibility to TCAS above and satellites. Being a long way from any big airports, I haven't verified with ATC, but suspect I'm visible to ground installations unless close in above or pointed directly away when my body and carbon fiber will be in the way.

Uh this seems pretty bad advice. And there are great reasons why glider manufacturers do not have anything like this as a recommended installation.

You are bathing all the other avionics with high-energy RF pulses from the transponder. An external quarter wave antenna with a ground plane helps get that energy away from the other avionics and pilot. A L2 type wave antenna for mounted inside a non-conductive fuselage should normally be mounted back in the fuselage away from the pilot and avionics. And things like PowerFLARM 1090ES In are designed to work by seeing somewhat reduced power leakage of your transponder signal, not being blasted by the direct high-energy signal.

You may be operating the FLARM antennas closer to a transponder antenna than a good idea (~30cm minimum recommended by FLARM... but that's when both externally mounted, this may be worse mounted inside). I'm not even sure something as close as 30cm is a good idea externally. Does ownship PowerFLARM transponder identification work OK? Or do you have to disable PCAS etc.? FLARM range checks all look good? How do you know if the Transponder is working OK until you check/ask?. You also might be flying in a remote enough area that you get few transponder interrogations, so things seem to work OK. A close encounter with a TCAS equipped aircraft might result in a chirp of ~1kHz transponder interrogations. Even if things are are working OK now who knows what that will do to your electronics, PowerFLARM, traffic display, etc. when you might need to most rely on it.

You likely have lots of conductive objects within the antenna RF near field near field (including the Schleicher panel support brass rod, all the usual wiring and conductive instrument cases). That can significantly affect the radiation pattern in ways unlikely to be obvious.

And you are possibly exposing yourself to excessive RF radiation.

In the USA I would expoect that an A&P doing a transponder RF check would not sign off on such an install.

Tango Whisky

December 28th 19, 08:26 AM

My transponder hs 250 W output, no way I would want that any place near my head or my balls.

Darryl Ramm

December 28th 19, 09:02 AM

On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
> My transponder hs 250 W output, no way I would want that any place near my head or my balls.

I don't want your balls near my transponder either. :-)

To be fair it's a low average duty factor (<1%) so you don't see all that power. But it's enough for some folks to worry about that folks do pay attention. RF exposure to low-power TABS and ADS-B systems for example designed to be close to wetware are a part of regulatory discussions.

Dan Marotta

December 28th 19, 04:14 PM

And yet, how many folks spend a major part of their lives with a radio
transmitter (cell phone) strapped to the side of their head or in their
pocket?

On 12/28/2019 2:02 AM, Darryl Ramm wrote:
> On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
>> My transponder hs 250 W output, no way I would want that any place near my head or my balls.
> I don't want your balls near my transponder either. :-)
>
> To be fair it's a low average duty factor (<1%) so you don't see all that power. But it's enough for some folks to worry about that folks do pay attention. RF exposure to low-power TABS and ADS-B systems for example designed to be close to wetware are a part of regulatory discussions.

--
Dan, 5J

jfitch

December 28th 19, 04:55 PM

On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
> My transponder hs 250 W output, no way I would want that any place near my head or my balls.

The normal location (recommended by many manufacturers) just ahead of the gear doors is much closer to your balls than an L2 in the nosecone (or the instrument pod), if that worries you. Probably less than 2' away. I always wear tin foil underwear to match my tin foil hat. But my transponder antenna is in the nosecone and works perfectly as tested by external radiated power and FCC ADS-B out reports.

[email protected]

December 28th 19, 06:36 PM

Regarding performance only, is there any study indicating that top of the fuselage location is worth than the normal under fuselage location?
Dan

George Haeh

December 28th 19, 06:44 PM

"You are bathing all the other avionics with high-energy RF pulses from the transponder... A L2 type wave antenna for mounted inside a non-conductive fuselage should normally be mounted back in the fuselage away from the pilot and avionics. And things like PowerFLARM 1090ES In are designed to work by seeing somewhat reduced power leakage of your transponder signal, not being blasted by the direct high-energy signal."

The avionics, except for the Oudie, are all in metal enclosures.

"You may be operating the FLARM antennas closer to a transponder antenna than a good idea (~30cm minimum recommended by FLARM... but that's when both externally mounted, this may be worse mounted inside). I'm not even sure something as close as 30cm is a good idea externally.
Does ownship PowerFLARM transponder identification work OK? Or do you have to disable PCAS etc.? FLARM range checks all look good?"

The PF Flarm and ADS-B antennas are mounted on the sides of the canopy quite some distance from the xpdr antenna which itself is about a foot forward of the instrument panel. The PF range is better than the four other gliders I've checked. No PF problem with own glider xpdr.

"How do you know if the Transponder is working OK until you check/ask?. You also might be flying in a remote enough area that you get few transponder interrogations, so things seem to work OK. A close encounter with a TCAS equipped aircraft might result in a chirp of ~1kHz transponder interrogations.. Even if things are are working OK now who knows what that will do to your electronics, PowerFLARM, traffic display, etc. when you might need to most rely on it."

Will be doing another transponder check in the spring.

"You likely have lots of conductive objects within the antenna RF near field near field (including the Schleicher panel support brass rod, all the usual wiring and conductive instrument cases). That can significantly affect the radiation pattern in ways unlikely to be obvious."

Most of the unshielded wiring is in the bottom of the instrument enclosure directly below the L2 antenna where the radiated energy may be lower. But so far, everything seems to be working.

"And you are possibly exposing yourself to excessive RF radiation."

My lower legs are about a foot away while the rest of me is 2 to 4 feet away. I found a research paper that showed the radiation hazard was low.

Darryl Ramm

December 28th 19, 08:10 PM

On Saturday, December 28, 2019 at 10:44:46 AM UTC-8, George Haeh wrote:
> "You are bathing all the other avionics with high-energy RF pulses from the transponder... A L2 type wave antenna for mounted inside a non-conductive fuselage should normally be mounted back in the fuselage away from the pilot and avionics. And things like PowerFLARM 1090ES In are designed to work by seeing somewhat reduced power leakage of your transponder signal, not being blasted by the direct high-energy signal."
>
> The avionics, except for the Oudie, are all in metal enclosures.
>
> "You may be operating the FLARM antennas closer to a transponder antenna than a good idea (~30cm minimum recommended by FLARM... but that's when both externally mounted, this may be worse mounted inside). I'm not even sure something as close as 30cm is a good idea externally.
> Does ownship PowerFLARM transponder identification work OK? Or do you have to disable PCAS etc.? FLARM range checks all look good?"
>
> The PF Flarm and ADS-B antennas are mounted on the sides of the canopy quite some distance from the xpdr antenna which itself is about a foot forward of the instrument panel. The PF range is better than the four other gliders I've checked. No PF problem with own glider xpdr.
>
>
> "How do you know if the Transponder is working OK until you check/ask?. You also might be flying in a remote enough area that you get few transponder interrogations, so things seem to work OK. A close encounter with a TCAS equipped aircraft might result in a chirp of ~1kHz transponder interrogations. Even if things are are working OK now who knows what that will do to your electronics, PowerFLARM, traffic display, etc. when you might need to most rely on it."
>
> Will be doing another transponder check in the spring.
>
> "You likely have lots of conductive objects within the antenna RF near field near field (including the Schleicher panel support brass rod, all the usual wiring and conductive instrument cases). That can significantly affect the radiation pattern in ways unlikely to be obvious."
>
> Most of the unshielded wiring is in the bottom of the instrument enclosure directly below the L2 antenna where the radiated energy may be lower. But so far, everything seems to be working.

Yes with wires running into them, and power cables, and metal construction is not perfectly RF tight, all of which will leak some RF power into the enclosures. And none of which are designed to be close to high power transponder signals.

That you can't find any problem so far does not make this a good idea for others.

December 28th 19, 11:14 PM

On Saturday, December 28, 2019 at 12:10:29 PM UTC-8, Darryl Ramm wrote:
> On Saturday, December 28, 2019 at 10:44:46 AM UTC-8, George Haeh wrote:
> > "You are bathing all the other avionics with high-energy RF pulses from the transponder... A L2 type wave antenna for mounted inside a non-conductive fuselage should normally be mounted back in the fuselage away from the pilot and avionics. And things like PowerFLARM 1090ES In are designed to work by seeing somewhat reduced power leakage of your transponder signal, not being blasted by the direct high-energy signal."
> >
> > The avionics, except for the Oudie, are all in metal enclosures.
> >
> > "You may be operating the FLARM antennas closer to a transponder antenna than a good idea (~30cm minimum recommended by FLARM... but that's when both externally mounted, this may be worse mounted inside). I'm not even sure something as close as 30cm is a good idea externally.
> > Does ownship PowerFLARM transponder identification work OK? Or do you have to disable PCAS etc.? FLARM range checks all look good?"
> >
> > The PF Flarm and ADS-B antennas are mounted on the sides of the canopy quite some distance from the xpdr antenna which itself is about a foot forward of the instrument panel. The PF range is better than the four other gliders I've checked. No PF problem with own glider xpdr.
> >
> >
> > "How do you know if the Transponder is working OK until you check/ask?. You also might be flying in a remote enough area that you get few transponder interrogations, so things seem to work OK. A close encounter with a TCAS equipped aircraft might result in a chirp of ~1kHz transponder interrogations. Even if things are are working OK now who knows what that will do to your electronics, PowerFLARM, traffic display, etc. when you might need to most rely on it."
> >
> > Will be doing another transponder check in the spring.
> >
> > "You likely have lots of conductive objects within the antenna RF near field near field (including the Schleicher panel support brass rod, all the usual wiring and conductive instrument cases). That can significantly affect the radiation pattern in ways unlikely to be obvious."
> >
> > Most of the unshielded wiring is in the bottom of the instrument enclosure directly below the L2 antenna where the radiated energy may be lower. But so far, everything seems to be working.
>
> Yes with wires running into them, and power cables, and metal construction is not perfectly RF tight, all of which will leak some RF power into the enclosures. And none of which are designed to be close to high power transponder signals.

Well, they BETTER be! Any aircraft can be expected to have a transponder with an antenna at a unknown location, so it must be assumed that the antenna is close to the particular avionics. The transponder response is only 25 microsec long, so you are being exposed to an RF pulse that averages 1 to 2 mW, depending upon the code and altitude being transmitted (1202 has only 3 ONEs out of a possible 12, and each ONE bit has power on for one third of the bit time). By way of comparison, a cell phone transmits at 600 mW, and as much as 3 W - and you are holding that thing right next to your head and think nothing of it.

Tom

Darryl Ramm

December 28th 19, 11:34 PM

Any aircraft can be expected to have the transponder antenna stuck amongst equipment in the instrument panel? What RF shielding requirements/standards do you think typical glider cockpit avionics, including all the non-regulated, non-certified devices are built against.

In typical ras fashion somebody asking a reasonable question
has degenerated to nonsense. There are perfectly good documents from glider manufacturers that recommend where/how to install transponder antennas. None describe stuffing it in the instrument panel.

[email protected]

December 29th 19, 12:10 AM

"Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
Dan

Richard Pfiffner[_2_]

December 29th 19, 12:28 AM

Dan Marotta

December 29th 19, 12:39 AM

The ground plane in my glider is mounted to the inside of the carbon
skin and I'm told my transponder is quite visible.Â* My installation also
passed the ADS-B test with flying colors.

On 12/28/2019 5:10 PM, wrote:
> "Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
> Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
> Dan

--
Dan, 5J

December 29th 19, 02:02 AM

On Saturday, December 28, 2019 at 3:34:09 PM UTC-8, Darryl Ramm wrote:
> Any aircraft can be expected to have the transponder antenna stuck amongst equipment in the instrument panel? What RF shielding requirements/standards do you think typical glider cockpit avionics, including all the non-regulated, non-certified devices are built against.
>
> In typical ras fashion somebody asking a reasonable question
> has degenerated to nonsense. There are perfectly good documents from glider manufacturers that recommend where/how to install transponder antennas. None describe stuffing it in the instrument panel.

I didn't say IN the panel, but near it. I once had a transponder antenna in a DG-400 that was mounted just below my right knee. Everything in the panel worked fine. There is, at times, good reasons for putting the antenna in the nose. You can always do a compatibility test on your own with a temporary antenna mount, or just hand-hold the antenna and move it around near the panel.

Tom

Darryl Ramm

December 29th 19, 02:43 AM

On Saturday, December 28, 2019 at 4:10:30 PM UTC-8, wrote:
> "Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
> Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
> Dan

The ground plane you install would normally be inside the CF fuselage. And the antenna manufacture or glider manufacturer should provide instructions on how to do this properly. A part of the point of that aluminium plate or foil tape ground plane is to help with a good connection to the coax cable ground. In some cases you might scuff the inside of the fueslage to help make additional electrical connection to the carbon fibre weave. *Follow the directions your glider manufacturer provides.* A plate especially can also help provide a good solid surface for antenna lock washers to engage with. Clearly here the CF will act in part as a ground plane (even without a good direct electrical connection, but by backing it with a better conductor with good connection to the coax you are helping things along).

[email protected]

December 29th 19, 05:23 AM

Well here is a link to a picture of a Ventus with the transponder antenna located as per Schempp Hirth.
Seems to work well only is straight flight. In any banking flight, the antenna is shadowed by the fuselage and/or wings.
Maybe a location on the turtledeck is better ?

https://www.airliners.net/photo/-/Schempp-Hirth-Ventus-2c/5730753/L?qsp=eJwtjEsKAkEMBe%2BStRsRXMxOL6ALLxCShw6O000SP8 0wdzc27ooqqIWkzIFPXFoFDeRgkxttqLLxw2lY6I72LqbJ9MIc T8/qxeLY0igHDiKoAf37kynsl%2BDSR9ccbxNg586026fX0evE/YHgcaJ1/QJ2lC9A

Dan

Darryl Ramm

December 29th 19, 06:27 AM

On Saturday, December 28, 2019 at 9:23:02 PM UTC-8, wrote:
> Well here is a link to a picture of a Ventus with the transponder antenna located as per Schempp Hirth.
> Seems to work well only is straight flight. In any banking flight, the antenna is shadowed by the fuselage and/or wings.
> Maybe a location on the turtledeck is better ?
>
> https://www.airliners.net/photo/-/Schempp-Hirth-Ventus-2c/5730753/L?qsp=eJwtjEsKAkEMBe%2BStRsRXMxOL6ALLxCShw6O000SP8 0wdzc27ooqqIWkzIFPXFoFDeRgkxttqLLxw2lY6I72LqbJ9MIc T8/qxeLY0igHDiKoAf37kynsl%2BDSR9ccbxNg586026fX0evE/YHgcaJ1/QJ2lC9A
>
> Dan

Thanks for the photo, ouch yep that looks like a dopey position, if above is the only other practical option I'd do that.

Dan Marotta

December 29th 19, 04:02 PM

I think while Darryl's suggestion will work quite well, it is more
effort than is required.Â* The BNC connector and the nut and washer of a
rod antenna will provide the necessary electrical connection to the
ground plane.Â* With a blade antenna, the mounting studs will make a good
mechanical connection.

In my former LAK-17a, I used an aluminum square cut to the dimensions
specified in the antenna installation sheet and rolled it over an oxygen
tank to match the internal curvature of the fuselage aft of the landing
gear.Â* I glued it in place with contact cement knowing that the studs
and BNC would make a good mechanical and electrical connection.Â* It
worked great!Â* I mounted the antenna offset to one side for two
reasons;Â* first, the joint line of the fuselage halves was thicker than
the length of the studs and BNC, and second, it insured that the blade
antenna would not catch on the ramp when loading and unloading the
fuselage in the trailer.

On 12/28/2019 7:43 PM, Darryl Ramm wrote:
> On Saturday, December 28, 2019 at 4:10:30 PM UTC-8, wrote:
>> "Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
>> Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
>> Dan
> The ground plane you install would normally be inside the CF fuselage. And the antenna manufacture or glider manufacturer should provide instructions on how to do this properly. A part of the point of that aluminium plate or foil tape ground plane is to help with a good connection to the coax cable ground. In some cases you might scuff the inside of the fueslage to help make additional electrical connection to the carbon fibre weave. *Follow the directions your glider manufacturer provides.* A plate especially can also help provide a good solid surface for antenna lock washers to engage with. Clearly here the CF will act in part as a ground plane (even without a good direct electrical connection, but by backing it with a better conductor with good connection to the coax you are helping things along).
>

--
Dan, 5J

Jonathan St. Cloud

December 29th 19, 05:15 PM

On Saturday, December 28, 2019 at 8:55:37 AM UTC-8, jfitch wrote:
> On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
> > My transponder hs 250 W output, no way I would want that any place near my head or my balls.
>
> The normal location (recommended by many manufacturers) just ahead of the gear doors is much closer to your balls than an L2 in the nosecone (or the instrument pod), if that worries you. Probably less than 2' away. I always wear tin foil underwear to match my tin foil hat. But my transponder antenna is in the nosecone and works perfectly as tested by external radiated power and FCC ADS-B out reports.

But you don't wear tin-foil socks, do your toenails grow faster during soaring season? Would like to get a bit more information on the tin-foil hat, I think I need one. I have my transponder antenna in the fin works great, no need for time foil panties.

jfitch

December 29th 19, 05:53 PM

On Sunday, December 29, 2019 at 9:15:03 AM UTC-8, Jonathan St. Cloud wrote:
> On Saturday, December 28, 2019 at 8:55:37 AM UTC-8, jfitch wrote:
> > On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
> > > My transponder hs 250 W output, no way I would want that any place near my head or my balls.
> >
> > The normal location (recommended by many manufacturers) just ahead of the gear doors is much closer to your balls than an L2 in the nosecone (or the instrument pod), if that worries you. Probably less than 2' away. I always wear tin foil underwear to match my tin foil hat. But my transponder antenna is in the nosecone and works perfectly as tested by external radiated power and FCC ADS-B out reports.
>
> But you don't wear tin-foil socks, do your toenails grow faster during soaring season? Would like to get a bit more information on the tin-foil hat, I think I need one. I have my transponder antenna in the fin works great, no need for time foil panties.

There's not much point in the tin foil hat, when 5G is deployed we will be dying and/or mutating by the 10s of thousands. I read that on the internet, so I'm certain it's true.

In the Ventus picture, you can see that the antenna is about half the distance to the pilots privates than it would be up in the nose cone.

Eric Greenwell[_4_]

December 29th 19, 06:07 PM

jfitch wrote on 12/29/2019 9:53 AM:
> On Sunday, December 29, 2019 at 9:15:03 AM UTC-8, Jonathan St. Cloud wrote:
>> On Saturday, December 28, 2019 at 8:55:37 AM UTC-8, jfitch wrote:
>>> On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
>>>> My transponder hs 250 W output, no way I would want that any place near my head or my balls.
>>>
>>> The normal location (recommended by many manufacturers) just ahead of the gear doors is much closer to your balls than an L2 in the nosecone (or the instrument pod), if that worries you. Probably less than 2' away. I always wear tin foil underwear to match my tin foil hat. But my transponder antenna is in the nosecone and works perfectly as tested by external radiated power and FCC ADS-B out reports.
>>
>> But you don't wear tin-foil socks, do your toenails grow faster during soaring season? Would like to get a bit more information on the tin-foil hat, I think I need one. I have my transponder antenna in the fin works great, no need for time foil panties.
>
> There's not much point in the tin foil hat, when 5G is deployed we will be dying and/or mutating by the 10s of thousands. I read that on the internet, so I'm certain it's true.
>
> In the Ventus picture, you can see that the antenna is about half the distance to the pilots privates than it would be up in the nose cone.

Since it's quarter wave antenna, I'm guessing the radiation pattern means a lot
less power is radiated to the pilot than a dipole in the nose cone.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

December 29th 19, 06:11 PM

On Friday, December 27, 2019 at 5:22:04 PM UTC-8, wrote:
> I put mine on a turtle deck on my ASW 27 and it works fine no issues with anyone seeing me or even worrying about it I really like the fact that it's there and was really easy to install compared to down by the gear

Long ago someone (I believe from Arizona) posted here about doing some research by talking to folks very familiar with FAA radar design about putting the transponder antenna on top of the fuselage. The conclusion was that if very near and above the radar site, the signal *might* be blocked. Other than that, it should be fine. Since we do a lot of turning, the antennal will be blocked for times anyway.

One reason for a transponder is to be seen by large aircraft TCAS, it's more likely they will be descending on a collision course, so having the antenna on top is a better idea....

5Z

Darryl Ramm

December 29th 19, 08:23 PM

On Sunday, December 29, 2019 at 9:53:24 AM UTC-8, jfitch wrote:
> On Sunday, December 29, 2019 at 9:15:03 AM UTC-8, Jonathan St. Cloud wrote:
> > On Saturday, December 28, 2019 at 8:55:37 AM UTC-8, jfitch wrote:
> > > On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
> > > > My transponder hs 250 W output, no way I would want that any place near my head or my balls.
> > >
> > > The normal location (recommended by many manufacturers) just ahead of the gear doors is much closer to your balls than an L2 in the nosecone (or the instrument pod), if that worries you. Probably less than 2' away. I always wear tin foil underwear to match my tin foil hat. But my transponder antenna is in the nosecone and works perfectly as tested by external radiated power and FCC ADS-B out reports.
> >
> > But you don't wear tin-foil socks, do your toenails grow faster during soaring season? Would like to get a bit more information on the tin-foil hat, I think I need one. I have my transponder antenna in the fin works great, no need for time foil panties.
>
> There's not much point in the tin foil hat, when 5G is deployed we will be dying and/or mutating by the 10s of thousands. I read that on the internet, so I'm certain it's true.
>
> In the Ventus picture, you can see that the antenna is about half the distance to the pilots privates than it would be up in the nose cone.

And uh.... not relevant... the pilot is inside his carbon fiber partial faraday cage cockpit, and (agreeing with Eric) the pattern from the 1/4 wave antenna with groundplane shields the pilot from the antenna.

Over a beer some time: details of teaching assistants punking male students in their undergrad physics lab classes into wearing aluminium foil "mini skirts" during a _very_ low power microwave experiment. Oh so well done.

[email protected]

December 29th 19, 08:26 PM

The Jonker website says that they are putting both the transponder antenna and the Flarm antenna in the vertical tail. Any reports on how that is working out?

Eric Greenwell[_4_]

December 29th 19, 11:27 PM

5Z wrote on 12/29/2019 10:11 AM:
> On Friday, December 27, 2019 at 5:22:04 PM UTC-8, wrote:
>> I put mine on a turtle deck on my ASW 27 and it works fine no issues with anyone seeing me or even worrying about it I really like the fact that it's there and was really easy to install compared to down by the gear
>
> Long ago someone (I believe from Arizona) posted here about doing some research by talking to folks very familiar with FAA radar design about putting the transponder antenna on top of the fuselage. The conclusion was that if very near and above the radar site, the signal *might* be blocked. Other than that, it should be fine. Since we do a lot of turning, the antennal will be blocked for times anyway.
>
> One reason for a transponder is to be seen by large aircraft TCAS, it's more likely they will be descending on a collision course, so having the antenna on top is a better idea....

Near airports, airliners are descending and ascending; in between they are above
18K. In our area, the C-17s cruise high and low; the low ones (<2000' agl) are
never a problem, but the other ones do cross our normal altitudes at least twice
each flight. I'm skeptical that they are mostly descending, but I think their TCAS
can easily detect us when they get within a few miles, regardless of the
top/bottom location.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

December 30th 19, 02:48 AM

On Saturday, December 28, 2019 at 6:43:02 PM UTC-8, Darryl Ramm wrote:
> On Saturday, December 28, 2019 at 4:10:30 PM UTC-8, wrote:
> > "Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
> > Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
> > Dan
>
> The ground plane you install would normally be inside the CF fuselage. And the antenna manufacture or glider manufacturer should provide instructions on how to do this properly. A part of the point of that aluminium plate or foil tape ground plane is to help with a good connection to the coax cable ground. In some cases you might scuff the inside of the fueslage to help make additional electrical connection to the carbon fibre weave. *Follow the directions your glider manufacturer provides.* A plate especially can also help provide a good solid surface for antenna lock washers to engage with.. Clearly here the CF will act in part as a ground plane (even without a good direct electrical connection, but by backing it with a better conductor with good connection to the coax you are helping things along).

Not all transponder antennas need a ground plane:

https://wingsandwheels.com/avionics-instruments/antennas/l2-aae.html

Darryl Ramm

December 30th 19, 02:58 AM

On Sunday, December 29, 2019 at 6:48:52 PM UTC-8, 2G wrote:
> On Saturday, December 28, 2019 at 6:43:02 PM UTC-8, Darryl Ramm wrote:
> > On Saturday, December 28, 2019 at 4:10:30 PM UTC-8, wrote:
> > > "Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
> > > Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
> > > Dan
> >
> > The ground plane you install would normally be inside the CF fuselage. And the antenna manufacture or glider manufacturer should provide instructions on how to do this properly. A part of the point of that aluminium plate or foil tape ground plane is to help with a good connection to the coax cable ground. In some cases you might scuff the inside of the fueslage to help make additional electrical connection to the carbon fibre weave. *Follow the directions your glider manufacturer provides.* A plate especially can also help provide a good solid surface for antenna lock washers to engage with. Clearly here the CF will act in part as a ground plane (even without a good direct electrical connection, but by backing it with a better conductor with good connection to the coax you are helping things along).
>
> Not all transponder antennas need a ground plane:
>
> https://wingsandwheels.com/avionics-instruments/antennas/l2-aae.html

You are replying to a thread that clearly stated "with any of the standard external transponder 1/4 wave antenna." Are you adding value here?

December 30th 19, 03:32 AM

On Sunday, December 29, 2019 at 6:58:38 PM UTC-8, Darryl Ramm wrote:
> On Sunday, December 29, 2019 at 6:48:52 PM UTC-8, 2G wrote:
> > On Saturday, December 28, 2019 at 6:43:02 PM UTC-8, Darryl Ramm wrote:
> > > On Saturday, December 28, 2019 at 4:10:30 PM UTC-8, wrote:
> > > > "Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
> > > > Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
> > > > Dan
> > >
> > > The ground plane you install would normally be inside the CF fuselage.. And the antenna manufacture or glider manufacturer should provide instructions on how to do this properly. A part of the point of that aluminium plate or foil tape ground plane is to help with a good connection to the coax cable ground. In some cases you might scuff the inside of the fueslage to help make additional electrical connection to the carbon fibre weave. *Follow the directions your glider manufacturer provides.* A plate especially can also help provide a good solid surface for antenna lock washers to engage with. Clearly here the CF will act in part as a ground plane (even without a good direct electrical connection, but by backing it with a better conductor with good connection to the coax you are helping things along).
> >
> > Not all transponder antennas need a ground plane:
> >
> > https://wingsandwheels.com/avionics-instruments/antennas/l2-aae.html
>
> You are replying to a thread that clearly stated "with any of the standard external transponder 1/4 wave antenna." Are you adding value here?

Yes.

Jonathan St. Cloud

December 30th 19, 05:22 AM

On Sunday, December 29, 2019 at 12:26:19 PM UTC-8, wrote:
> The Jonker website says that they are putting both the transponder antenna and the Flarm antenna in the vertical tail. Any reports on how that is working out?

See above, I mentioned how that is working out.

GliderCZ

December 30th 19, 05:36 AM

On Saturday, December 28, 2019 at 10:27:43 PM UTC-8, Darryl Ramm wrote:
> On Saturday, December 28, 2019 at 9:23:02 PM UTC-8, wrote:
> > Well here is a link to a picture of a Ventus with the transponder antenna located as per Schempp Hirth.
> > Seems to work well only is straight flight. In any banking flight, the antenna is shadowed by the fuselage and/or wings.
> > Maybe a location on the turtledeck is better ?
> >
> > https://www.airliners.net/photo/-/Schempp-Hirth-Ventus-2c/5730753/L?qsp=eJwtjEsKAkEMBe%2BStRsRXMxOL6ALLxCShw6O000SP8 0wdzc27ooqqIWkzIFPXFoFDeRgkxttqLLxw2lY6I72LqbJ9MIc T8/qxeLY0igHDiKoAf37kynsl%2BDSR9ccbxNg586026fX0evE/YHgcaJ1/QJ2lC9A
> >
> > Dan
>
> Thanks for the photo, ouch yep that looks like a dopey position, if above is the only other practical option I'd do that.

I've got a Ventus 2c with a flexible antenna positioned exactly like that, per SH recommendations, and have passed a dozen ADS-B checks in the last year, with lots of low altitude yanking and banking.

[email protected]

December 30th 19, 05:47 AM

Do you have the Blade type antenna or the cylinder/ball one ?
Thanks, Dan

GliderCZ

December 30th 19, 06:06 AM

On Sunday, December 29, 2019 at 9:47:45 PM UTC-8, wrote:
> Do you have the Blade type antenna or the cylinder/ball one ?
> Thanks, Dan

Flexible, similar to the one linked (not HpH branded, as far as I know).
https://wingsandwheels.com/hph-transflex04-flexible-transponder-antenna.html

Darryl Ramm

December 30th 19, 06:08 AM

On Sunday, December 29, 2019 at 10:11:09 AM UTC-8, 5Z wrote:
> On Friday, December 27, 2019 at 5:22:04 PM UTC-8, wrote:
> > I put mine on a turtle deck on my ASW 27 and it works fine no issues with anyone seeing me or even worrying about it I really like the fact that it's there and was really easy to install compared to down by the gear
>
> Long ago someone (I believe from Arizona) posted here about doing some research by talking to folks very familiar with FAA radar design about putting the transponder antenna on top of the fuselage. The conclusion was that if very near and above the radar site, the signal *might* be blocked. Other than that, it should be fine. Since we do a lot of turning, the antennal will be blocked for times anyway.

Unfortunately "it's more complex" applies to lots of stuff with aircraft surveillance.Â*And I would hope any research folks did thought about some of the things I'll describe here.

My concern with upper surface antennas is more blanketing from the wing, and that includes to distant SSR sites. The fuselage directly blocking the antenna like when near/overhead an SSR is not the main concern I have because already the SSR likely can't see you.Â*(OK sure if the long length of the fuselage points directly at the antenna you might have an issue).

If you are very near, i.e. ~overhead a radar site you may well be in the "cone of silence" of both the primary radar and SSR and likely not seen regardless of transponder antenna location or orientation. SSR and primary radar have a fairly wide cone of silence/shallow viewing angle above the horizon.. Think things like an SSR sees things only below ~30 degrees above the horizontal around the antenna.

Transponder antennas also have a cone of silence pointing out the end of their antenna. Hopefully a bit narrower than the SSR cone.

An antenna mounted on an upper fuselage area on a glider might be helped by diffraction around the glider fuselage, and that weak diffracted part of the signal may be OK when closer to a SSR (or ADS-B ground site) but still within that say 30 degree angle above the horizon. As the transponder antenna looks out more towards a distant SSR antenna the angle shallows and hopefully seeing a bit better signal due to decreased angle, but you can have significant range loss, especially say if relying on a distant (up to ~200NM!) en-route SSR to fill in details). But it's complex and would need modeling to see what happens.

Ah the irony is that very local overhead performance to an SSR antenna may depends on other (possibly quite distant) SSR sites.... SSR cones of silence get somewhat addressed by integrating together data from overlapping radar systems.Â*That is what the FAA Fusion system does, and it also folds in ADS-B data. (And ADS-B ground stations themselves have similar cone of silence issues, and a similar solution of adjacent ground towers partially covering each other).Â*

Any analysis you would want to look at upper and lower antenna performance to local SSR interrogators at around that 30 degree angle, and at more distant SSR sites that are filling in the data for the cone of silence at shallower angle. And my concerns again are more things like wings obscuring line of site, and wanting to make sure that any ground plane and antenna installation is as good as posible to maximize signal quality to/from more distant SSR sites regardless of wether the antenna is top or bottom mounted.

And I sure appreciate Dan posting a followup link to that picture of the antenna stuck out the side of a fuselage. I had never seen that before, much worse than I had imagined, and I sure did not want to seem to be recommending it.. blanketed directly above by the wing, blanketed to the side by the fuselage and side/below by the gear when extended, and ~90 degree crossed signal polarization when the glider is banking left.Â*

> One reason for a transponder is to be seen by large aircraft TCAS, it's more likely they will be descending on a collision course, so having the antenna on top is a better idea....
>
> 5Z

Like Eric I don't understand why TCAS threats are assumed to come from above. I would suspect an equal distribution, and threats are going to be approaching near the same altitude with a relatively shallow climb or descent angle. In a bad case TCAS IIÂ* is going to command an RA which could put you relatively close laterally but above or below the threat aircraft... and I would assume those RA directions are equally distributed as well. And you've already executed the RA command before the angle above/below the threat gets very steep. I think there are studies/modeling of aircraft showing TCAS performance with single antennas if I can find them I'll point them out (but the system exists as it does with all light aircraft largely having single lower antennas).

With it being hard to guess/know how well things are really working one thing I have thought would be neat is a transponder antenna performance test tool similar to FLARM range tool or OGN/KTrax used ground and/or airborne 1090 MHz/ADS-B receivers. (Mark Hawkins are you looking for a project? :-))

jfitch

December 30th 19, 06:16 AM

On Sunday, December 29, 2019 at 12:23:28 PM UTC-8, Darryl Ramm wrote:
> On Sunday, December 29, 2019 at 9:53:24 AM UTC-8, jfitch wrote:
> > On Sunday, December 29, 2019 at 9:15:03 AM UTC-8, Jonathan St. Cloud wrote:
> > > On Saturday, December 28, 2019 at 8:55:37 AM UTC-8, jfitch wrote:
> > > > On Saturday, December 28, 2019 at 12:26:15 AM UTC-8, Tango Whisky wrote:
> > > > > My transponder hs 250 W output, no way I would want that any place near my head or my balls.
> > > >
> > > > The normal location (recommended by many manufacturers) just ahead of the gear doors is much closer to your balls than an L2 in the nosecone (or the instrument pod), if that worries you. Probably less than 2' away. I always wear tin foil underwear to match my tin foil hat. But my transponder antenna is in the nosecone and works perfectly as tested by external radiated power and FCC ADS-B out reports.
> > >
> > > But you don't wear tin-foil socks, do your toenails grow faster during soaring season? Would like to get a bit more information on the tin-foil hat, I think I need one. I have my transponder antenna in the fin works great, no need for time foil panties.
> >
> > There's not much point in the tin foil hat, when 5G is deployed we will be dying and/or mutating by the 10s of thousands. I read that on the internet, so I'm certain it's true.
> >
> > In the Ventus picture, you can see that the antenna is about half the distance to the pilots privates than it would be up in the nose cone.
>
> And uh.... not relevant... the pilot is inside his carbon fiber partial faraday cage cockpit, and (agreeing with Eric) the pattern from the 1/4 wave antenna with groundplane shields the pilot from the antenna.
>
> Over a beer some time: details of teaching assistants punking male students in their undergrad physics lab classes into wearing aluminium foil "mini skirts" during a _very_ low power microwave experiment. Oh so well done.

You'd need to show me the data on that. A minimally conductive carbon fuselage with some huge holes in it, a very imperfect 1/4 wave vs. twice the distance. We're talking r^3 here. I'm not actually sure what measurements might show, and I wouldn't bet my glider on one answer over the other.

[email protected]

December 30th 19, 06:43 AM

Well, Here is a picture of Schlicher's recommended location for the Antenna-same as Schempp Hirth-Above landing gear doors.
Interesting.

https://www.alexander-schleicher.de/wp-content/uploads/2015/06/AW017_Transpondereinbau-27.pdf
Dan

Darryl Ramm

December 30th 19, 07:13 AM

On Sunday, December 29, 2019 at 10:43:44 PM UTC-8, wrote:
> Well, Here is a picture of Schlicher's recommended location for the Antenna-same as Schempp Hirth-Above landing gear doors.
> Interesting.
>
> https://www.alexander-schleicher.de/wp-content/uploads/2015/06/AW017_Transpondereinbau-27.pdf
> Dan

Dang. Well I don't like that either :-)

My ASH-26E has a more central transponder antenna location behind the gear (and offset to avoid the fuselage join seam and a fuel pump on one side) as can an ASH25 and some others, so I guess I've mostly noticed those. And ASH-30/31 etc. owners all seem to be ordering the tail mounted antenna (which is what I'd do on a new glider).

Again, if I was looking at your glider, based on gut feel (and some background in microwave engineering), I personally would install the upper antenna, I wonder if SH came out with that to improve on the lower location, or to make the install easier or both....

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.

Tango Whisky

December 30th 19, 08:34 AM

Yep, but there is a carbon shell between antenna andthe pilot's privates.

[email protected]

December 30th 19, 01:47 PM

On Friday, December 27, 2019 at 2:34:32 PM UTC-5, wrote:
> Hi all,
> Planning to install a Transponder Antenna on my Ventus CM.
> Schempp Hirth indicates the possibilty of installing on top of the fuselage , behind the engine compartment doors.
> Regarding being seen by ATC and Airlines, would that location perform better/worse/same as the standard location on side of fuselage - above gear doors ?
> Dan

After reading lots of comments I am still wondering why not just mount on the bottom of the fuselage in the conventional manner?
UH

Dan Marotta

December 30th 19, 02:44 PM

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.

On 12/30/2019 12:13 AM, Darryl Ramm wrote:
> On Sunday, December 29, 2019 at 10:43:44 PM UTC-8, wrote:
>> Well, Here is a picture of Schlicher's recommended location for the Antenna-same as Schempp Hirth-Above landing gear doors.
>> Interesting.
>>
>> https://www.alexander-schleicher.de/wp-content/uploads/2015/06/AW017_Transpondereinbau-27.pdf
>> Dan
> Dang. Well I don't like that either :-)
>
> My ASH-26E has a more central transponder antenna location behind the gear (and offset to avoid the fuselage join seam and a fuel pump on one side) as can an ASH25 and some others, so I guess I've mostly noticed those. And ASH-30/31 etc. owners all seem to be ordering the tail mounted antenna (which is what I'd do on a new glider).
>
> Again, if I was looking at your glider, based on gut feel (and some background in microwave engineering), I personally would install the upper antenna, I wonder if SH came out with that to improve on the lower location, or to make the install easier or both....
>
> 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.
>
>
>
>

--
Dan, 5J

[email protected]

December 30th 19, 03:34 PM

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

Eric Greenwell[_4_]

December 30th 19, 03:53 PM

jfitch wrote on 12/29/2019 10:16 PM:
>> And uh.... not relevant... the pilot is inside his carbon fiber partial faraday cage cockpit, and (agreeing with Eric) the pattern from the 1/4 wave antenna with groundplane shields the pilot from the antenna.
>>
>> Over a beer some time: details of teaching assistants punking male students in their undergrad physics lab classes into wearing aluminium foil "mini skirts" during a_very_ low power microwave experiment. Oh so well done.
> You'd need to show me the data on that. A minimally conductive carbon fuselage with some huge holes in it, a very imperfect 1/4 wave vs. twice the distance. We're talking r^3 here. I'm not actually sure what measurements might show, and I wouldn't bet my glider on one answer over the other.

Not r^3, but only r^2 for antenna field strength reduction. It's an area thing,
not a volume thing.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Darryl Ramm

December 30th 19, 10:00 PM

On Monday, December 30, 2019 at 5:47:51 AM UTC-8, wrote:
> On Friday, December 27, 2019 at 2:34:32 PM UTC-5, wrote:
> > Hi all,
> > Planning to install a Transponder Antenna on my Ventus CM.
> > Schempp Hirth indicates the possibilty of installing on top of the fuselage , behind the engine compartment doors.
> > Regarding being seen by ATC and Airlines, would that location perform better/worse/same as the standard location on side of fuselage - above gear doors ?
> > Dan
>
> After reading lots of comments I am still wondering why not just mount on the bottom of the fuselage in the conventional manner?
> UH

I was assuming with a CM there may be issues, never looked inside one but is there space given the engine bay and other junk?

Anyhow clearly the right thing to do is buy a new glider with transponder antenna in the tail. "It's for collision avoidance safety honey. You want me to be safe? Right?" :-)

MNLou

December 30th 19, 10:21 PM

I tried that argument earlier today Darryl.

Got shot down quickly:(

Lou

[email protected][_2_]

December 30th 19, 10:52 PM

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?

Darryl Ramm

December 30th 19, 11:23 PM

On Monday, December 30, 2019 at 2:52:49 PM UTC-8, 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?

The simplest answer: parasitic drag ~ V^2. So at (100mph/250mph)^2 * 0.4 = ~0.07 lb. = ~1 oz.

I suspect this has been flogged to death on r.a.s. before.

"Honey I need a new glider with a tail mounted transponder antenna because it's lower drag. And I'll win more contests. Honey?" :-)

December 31st 19, 12:10 AM

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

[email protected]

December 31st 19, 12:19 AM

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

[email protected]

December 31st 19, 01:19 AM

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

India November[_2_]

December 31st 19, 12:17 PM

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.

India November[_2_]

December 31st 19, 12:19 PM

Please let us know what you learn. I am thinking of an xponder install on my D2b.

Dan Marotta

December 31st 19, 03:41 PM

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

[email protected]

December 31st 19, 05:04 PM

I will let you know what I found and what decided.
Dan

India November[_2_]

January 1st 20, 02:32 PM

I am thinking of the theoretical advantage in drag coefficient of a blade vs rod antenna which holds for any speed.

MNLou

January 1st 20, 08:36 PM

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 Marotta

January 1st 20, 08:43 PM

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

[email protected]

January 1st 20, 09:08 PM

From the Aircraft Spruce website, the drag spec on a rod and ball transponder antenna is listed as 0.41 lbs. at 250 kts. The blade type lists as 0.09 lbs. at 250 knots. Drag increases by the square of the speed, so at half the speed (125 knots), the drag is around 1/4 the numbers listed. If you are concerned about the .0225 lbs. in extra drag vs. the .01025 lbs., buy the blade type and keep the yaw string straight. You will probably increase your final glide numbers by at least a couple of yards.

Martin Gregorie[_6_]

January 1st 20, 09:56 PM

On Wed, 01 Jan 2020 06:32:46 -0800, India November wrote:

> I am thinking of the theoretical advantage in drag coefficient of a
> blade vs rod antenna which holds for any speed.

I found this: https://www.grc.nasa.gov/www/k-12/airplane/shaped.html
which may help sort things out for you, though these numbers are for 3D
shapes while what you really want is drag comparisons for 2D shapes with
the shape extending right across the wind tunnel or (better) with one end
attached to a side wall that's in the airstream.

Other, less well written web pages, suggest that a teardrop shape with a
blunt LE and max thickness at around 30% chord and slightly convex
surfaces behind max thickness that terminate at a sharp TE should have
about half the drag of a cylinder with the same frontal area.

As others have said, drag will rise sharply if the AOA of the streamlined
shape isn't zero and this will get worse as the max thickness moves back
toward 50% and/or the LE becomes sharper.

If you're really worried, find a University with an aerodynamics dept and
try to persuade a student to write a term paper based on wind tunnel
tests on a rod antenna and the best shaped blade antenna you can find.

Now, you can calculate your glider's drag at, say, best glide and max
cruise (easy to do from its flying weight and glide polar) and then
calculate how much each adding each antenna would affect the glide angle
at those speeds.

We'll all be interested to see just how much effect the antenna has.

--
Martin | martin at
Gregorie | gregorie dot org

Eric Greenwell[_4_]

January 1st 20, 10:33 PM

Martin Gregorie wrote on 1/1/2020 1:56 PM:
> On Wed, 01 Jan 2020 06:32:46 -0800, India November wrote:
>
>> I am thinking of the theoretical advantage in drag coefficient of a
>> blade vs rod antenna which holds for any speed.
>
> I found this: https://www.grc.nasa.gov/www/k-12/airplane/shaped.html
> which may help sort things out for you, though these numbers are for 3D
> shapes while what you really want is drag comparisons for 2D shapes with
> the shape extending right across the wind tunnel or (better) with one end
> attached to a side wall that's in the airstream.
>
> Other, less well written web pages, suggest that a teardrop shape with a
> blunt LE and max thickness at around 30% chord and slightly convex
> surfaces behind max thickness that terminate at a sharp TE should have
> about half the drag of a cylinder with the same frontal area.
>
> As others have said, drag will rise sharply if the AOA of the streamlined
> shape isn't zero and this will get worse as the max thickness moves back
> toward 50% and/or the LE becomes sharper.
>
> If you're really worried, find a University with an aerodynamics dept and
> try to persuade a student to write a term paper based on wind tunnel
> tests on a rod antenna and the best shaped blade antenna you can find.
>
> Now, you can calculate your glider's drag at, say, best glide and max
> cruise (easy to do from its flying weight and glide polar) and then
> calculate how much each adding each antenna would affect the glide angle
> at those speeds.
>
> We'll all be interested to see just how much effect the antenna has.

A 50:1 900 lb glider at best L/D has 18 lb of drag; the rod antenna at 62 knots
has a drag of 0.41lb/16 = 0.025, or 0.14%. That's about 0.07 L/D loss.

The rod drag quadruples at 125 knots, but the drag of the glider would increase
substantially, also, so maybe the percentage doubles, which is still only 0.3% of
total drag.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Martin Gregorie[_6_]

January 1st 20, 11:06 PM

On Wed, 01 Jan 2020 14:33:36 -0800, Eric Greenwell wrote:

> Martin Gregorie wrote on 1/1/2020 1:56 PM:
>> On Wed, 01 Jan 2020 06:32:46 -0800, India November wrote:
>>
>>> I am thinking of the theoretical advantage in drag coefficient of a
>>> blade vs rod antenna which holds for any speed.
>>
>> I found this: https://www.grc.nasa.gov/www/k-12/airplane/shaped.html
>> which may help sort things out for you, though these numbers are for 3D
>> shapes while what you really want is drag comparisons for 2D shapes
>> with the shape extending right across the wind tunnel or (better) with
>> one end attached to a side wall that's in the airstream.
>>
>> Other, less well written web pages, suggest that a teardrop shape with
>> a blunt LE and max thickness at around 30% chord and slightly convex
>> surfaces behind max thickness that terminate at a sharp TE should have
>> about half the drag of a cylinder with the same frontal area.
>>
>> As others have said, drag will rise sharply if the AOA of the
>> streamlined shape isn't zero and this will get worse as the max
>> thickness moves back toward 50% and/or the LE becomes sharper.
>>
>> If you're really worried, find a University with an aerodynamics dept
>> and try to persuade a student to write a term paper based on wind
>> tunnel tests on a rod antenna and the best shaped blade antenna you can
>> find.
>>
>> Now, you can calculate your glider's drag at, say, best glide and max
>> cruise (easy to do from its flying weight and glide polar) and then
>> calculate how much each adding each antenna would affect the glide
>> angle at those speeds.
>>
>> We'll all be interested to see just how much effect the antenna has.
>
> A 50:1 900 lb glider at best L/D has 18 lb of drag; the rod antenna at
> 62 knots has a drag of 0.41lb/16 = 0.025, or 0.14%. That's about 0.07
> L/D loss.
>
> The rod drag quadruples at 125 knots, but the drag of the glider would
> increase substantially, also, so maybe the percentage doubles, which is
> still only 0.3% of total drag.

I thought it was likely to be a pretty small effect. Thanks for
confirming.

--
Martin | martin at
Gregorie | gregorie dot org