Gliders and Transponders......again.

There are a number of other issues associated with Mode S Transponders. BTW
they would have to be Mode S in the UK, not Mode A/C. They would also have
to be professionally fitted and tested by a licenced radio engineer, which
is unlikely to be cheap!

1) Would they still work if a glider is in a tightly banked thermal turn,
with the ground plane at a considerable angle, and the glider just moving
with the wind? Don't they (ATC) filter out slow moving objects anyway so
they don't see clouds, flocks of birds, etc.

2) Would a glider climbing rapidly in a thermal or wave towards the base
of an airway or controlled upper airspace (with no intention of entering
it), or flying just below it, generate spurious TCAS alarms that might
unnecessary frighten the jet jockeys into making violent avoidance
manoeuvres and upsetting their passengers?

3) What effect would a whole gaggle of competition gliders have on ground
radar services or TCAS? Indeed the CAA has suggested turning them off in
such circumstances, but then what's the point of having them fitted in
the first place? I understand that Air Traffic Control can selectively
filter out some returns, but again what would happen if they selected the
one that was an actual threat?

Basically I object to having to pay out the best part of £2k to fit
unproven (for gliders) technology to my £8k glider, that will probably be
out of date anyway in a few years time.

I am also unconvinced that an unshielded 120 Watt RF output is not a
health hazard, when even 4 watt microwaves are considered dangerous.

I understand that some of the UAVs will be operated in the Poodle 51st
State (i.e. the UK) by the good ol' USAF, which is another reason to hate
the Yanks, if Iraq and Afghanistan aren't already bad enough!

Derek C

At 16:25 19 January 2009, Darryl Ramm wrote:
On Jan 19, 12:00=A0am, Derek Copeland wrote:
As a UK glider pilot, I would be happy to fit a Mode S transponder to
my
glider if only they where cheap, ran all day on a small battery, gave
ME
some form of collision warning (TCAS?) from other gliders and light
aircraft, and didn't fry my n*ts off with 120 Watt Radio Freqency
being
emitted from an antenna 6 inches behind my unshielded backside.

There is a GPS based collision avoidance system called Flarm which
meets
most of my requirements and could be cheaply fitted to all aircraft
including airliners. Our CAA won't even countenance this, as it is
not
compatable with their existing WW2 technology Radar Systems. The push
to
fly UAVs all over our isle may also come into this.

I should add that in the UK commercial aircraft generally fly in
segregated Class A, B, and D airspace, and gliders in the rest, so
conflicts are exceedingly rare.

Derek Copeland

I really don't want to get into a debate about UK and USA transponder
issues. I think some of the issues facing the UK are different,
including issues with attempts to grab airspace and UK specfic UAVs
issues (we may have some of our own here) etc. However yet again in
this transponder debate people keep raising red herrings or offering
misinformation. I hope the BGA and others in the UK are not using all
these sorts of arguments in their debate, because some of them are
embarrassingly silly and would take away from other valid points.

So lets waste more space on this..

There is no reason to believe that you would get excessive RF exposure
form a properly installed transponder antenna. Most antennas are 1/4
wave stubs or blades that require a ground plane and when mounted
where glider manufactures recommend (on the underbody of the fuselage
near the undercarriage) just won't expose the pilot to significant RF
radiation. If your glider is metal or carbon fibre you have even more
isolation. Also be careful when comparing to other RF sources -- the
power specifications of transponders are the peak pulse power. The
duty cycle is quite low even in an environments with lots of active
TCAS interrogations. I've seen transponder antennas installed between
pilots legs, nearly in contact with he pilot. Darwin has something to
say about that.

As for power requirements there are several choices of transponder
that along with an encoder draw ~0.5 A. This is the sort of power
consumption that if your glider's batteries are absolutely already at
the maximum could usually be met by the addition of a small 7Ah
battery VRLA batttery. Say derating the battery 7Ah spec by 50% (for
operating temps below 20C and the load being above 0.05C) would gives
7 hours of run time. Mode-S transponders like the Becker will work
fine down to 10V (which at a 0.5 A load is lower then the discharge
point voltage used to calculate VRLA battery specs). How long are
typical flying days in the UK? The worse case is going to be long cold
wave flights and they may well need a larger battery or use a more
advanced technology battery. But these devices are already in the "use
small battery" category in my book. And I know installing that
battery (or even better a 12Ah battery if you have space) may be a
pain in the neck and cost some money but it is a tough argument to try
to push onto the traveling public, airline and jet owners etc. If I
was the CAA and having to put up with these arguments. I'd be making
the point by showing actual 7Ah battery sizes to highlight the (small)
problem glider pilots and owners are facing.

It is likely unrealistic to expect airliners and fast jets to use
flarm. Most of these aircraft have sophisticate TCAS systems. I hope
glider pilots are not presuming somebody just installs a flarm into
the airliner cockpit. Any flarm type input would need to be integrated
into the TCAS so it can provide s single traffic display and issue a
single RA. This is unlikely to be a low cost modification and why
should those owners do something to accommodate gliders which could
just "get with the system" and install transponders? Then there may be
technical issues with flarm like effective range (can flarm be
modified to respond to airliner interrogations at tens of km? TCAS can
work over distances like that, giving pilots a head's up of traffic
before a RA is required). While flarm seems a fantastic technology
where it is used (not in the USA) I suspect it is a read herring when
talking about providing airliners and fast jets tools to avoid
collisions with gliders.

As for wanting a Mode-S transponder with "TCAS" display. You can get
this today. In the USA PCAS units like the Zaon MRX are popular and
use very low power and relatively low cost (~$500). They provide an
alert but no RA or direction information. But they are impresssively
effective at highlighting traffic (I've flow with one for three
years). They work fine with Mode-S transponders. Yes I know this may
seem a waste of money if you already have a flarm unit. But back to
where I think the Examiner opinion article was trying to focus and
where I'd argue the higher risk to our aport is -- avoiding a
collison with a airliner or passenger carrying jet -- then the glider
does *not* need PCAS or TCAS type capablities. Letting ATC, and if
that fails, TCAS-II in the jet, deal with the conflict is going to be
highly effective.

Darryl

To get away from the hot air and spoil the argument with some hard facts.

Transponders and Flarm are similar ideas, but for completely different
scenarios.

So the anal response is - Why not have a Mode-S transponder for those
fast heavy things, and Flarm for the light slow targets.

Best of both worlds and the top of the line for each of those represents
2.06% of the total purchase price of a new two seater. Real numbers for
a January 2009 delivery aircraft. That is adding the Flarm option to an
LX8000, and fitting a TRT800 transponder and encoder. Both with remote
displays for the RSO...

OK - that is not counting the extra battery and the solar panel for
ensuring one never runs out of electrons. Add an antenna and all the
labour and it is still 3%.

Now compared to the total worth of my 38 year old Std Cirrus the cost is
quite substantial and I can see it might push people out of the sport,
but there really is no justification for not fitting these in a new
airframe.

Percentage wise the fancy urethane paint is a bigger investment than the
safety / compliance stuff. Lets not get emotional about this. Rationally
there is no question.

Bruce

Darryl Ramm wrote:
On Jan 19, 12:00 am, Derek Copeland wrote:
As a UK glider pilot, I would be happy to fit a Mode S transponder to my
glider if only they where cheap, ran all day on a small battery, gave ME
some form of collision warning (TCAS?) from other gliders and light
aircraft, and didn't fry my n*ts off with 120 Watt Radio Freqency being
emitted from an antenna 6 inches behind my unshielded backside.

There is a GPS based collision avoidance system called Flarm which meets
most of my requirements and could be cheaply fitted to all aircraft
including airliners. Our CAA won't even countenance this, as it is not
compatable with their existing WW2 technology Radar Systems. The push to
fly UAVs all over our isle may also come into this.

I should add that in the UK commercial aircraft generally fly in
segregated Class A, B, and D airspace, and gliders in the rest, so
conflicts are exceedingly rare.

Derek Copeland

I really don't want to get into a debate about UK and USA transponder
issues. I think some of the issues facing the UK are different,
including issues with attempts to grab airspace and UK specfic UAVs
issues (we may have some of our own here) etc. However yet again in
this transponder debate people keep raising red herrings or offering
misinformation. I hope the BGA and others in the UK are not using all
these sorts of arguments in their debate, because some of them are
embarrassingly silly and would take away from other valid points.

So lets waste more space on this..

There is no reason to believe that you would get excessive RF exposure
form a properly installed transponder antenna. Most antennas are 1/4
wave stubs or blades that require a ground plane and when mounted
where glider manufactures recommend (on the underbody of the fuselage
near the undercarriage) just won't expose the pilot to significant RF
radiation. If your glider is metal or carbon fibre you have even more
isolation. Also be careful when comparing to other RF sources -- the
power specifications of transponders are the peak pulse power. The
duty cycle is quite low even in an environments with lots of active
TCAS interrogations. I've seen transponder antennas installed between
pilots legs, nearly in contact with he pilot. Darwin has something to
say about that.

As for power requirements there are several choices of transponder
that along with an encoder draw ~0.5 A. This is the sort of power
consumption that if your glider's batteries are absolutely already at
the maximum could usually be met by the addition of a small 7Ah
battery VRLA batttery. Say derating the battery 7Ah spec by 50% (for
operating temps below 20C and the load being above 0.05C) would gives
7 hours of run time. Mode-S transponders like the Becker will work
fine down to 10V (which at a 0.5 A load is lower then the discharge
point voltage used to calculate VRLA battery specs). How long are
typical flying days in the UK? The worse case is going to be long cold
wave flights and they may well need a larger battery or use a more
advanced technology battery. But these devices are already in the "use
small battery" category in my book. And I know installing that
battery (or even better a 12Ah battery if you have space) may be a
pain in the neck and cost some money but it is a tough argument to try
to push onto the traveling public, airline and jet owners etc. If I
was the CAA and having to put up with these arguments. I'd be making
the point by showing actual 7Ah battery sizes to highlight the (small)
problem glider pilots and owners are facing.

It is likely unrealistic to expect airliners and fast jets to use
flarm. Most of these aircraft have sophisticate TCAS systems. I hope
glider pilots are not presuming somebody just installs a flarm into
the airliner cockpit. Any flarm type input would need to be integrated
into the TCAS so it can provide s single traffic display and issue a
single RA. This is unlikely to be a low cost modification and why
should those owners do something to accommodate gliders which could
just "get with the system" and install transponders? Then there may be
technical issues with flarm like effective range (can flarm be
modified to respond to airliner interrogations at tens of km? TCAS can
work over distances like that, giving pilots a head's up of traffic
before a RA is required). While flarm seems a fantastic technology
where it is used (not in the USA) I suspect it is a read herring when
talking about providing airliners and fast jets tools to avoid
collisions with gliders.

As for wanting a Mode-S transponder with "TCAS" display. You can get
this today. In the USA PCAS units like the Zaon MRX are popular and
use very low power and relatively low cost (~$500). They provide an
alert but no RA or direction information. But they are impresssively
effective at highlighting traffic (I've flow with one for three
years). They work fine with Mode-S transponders. Yes I know this may
seem a waste of money if you already have a flarm unit. But back to
where I think the Examiner opinion article was trying to focus and
where I'd argue the higher risk to our aport is -- avoiding a
collison with a airliner or passenger carrying jet -- then the glider
does *not* need PCAS or TCAS type capablities. Letting ATC, and if
that fails, TCAS-II in the jet, deal with the conflict is going to be
highly effective.

Darryl

At 20:28 19 January 2009, Bruce wrote:
To get away from the hot air and spoil the argument with some hard
facts.

Transponders and Flarm are similar ideas, but for completely different
scenarios.

So the anal response is - Why not have a Mode-S transponder for those
fast heavy things, and Flarm for the light slow targets.

Best of both worlds and the top of the line for each of those represents

2.06% of the total purchase price of a new two seater. Real numbers for
a January 2009 delivery aircraft. That is adding the Flarm option to an
LX8000, and fitting a TRT800 transponder and encoder. Both with remote
displays for the RSO...

OK - that is not counting the extra battery and the solar panel for
ensuring one never runs out of electrons. Add an antenna and all the
labour and it is still On Jan 19, 12:00 am, Derek Copeland wrote:
As a UK glider pilot, I would be happy to fit a Mode S transponder to
my
glider if only they where cheap, ran all day on a small battery, gave
ME
some form of collision warning (TCAS?) from other gliders and light
aircraft, and didn't fry my n*ts off with 120 Watt Radio Freqency
being
emitted from an antenna 6 inches behind my unshielded backside.

There is a GPS based collision avoidance system called Flarm which
meets
most of my requirements and could be cheaply fitted to all aircraft
including airliners. Our CAA won't even countenance this, as it is
not
compatable with their existing WW2 technology Radar Systems. The push
to
fly UAVs all over our isle may also come into this.

I should add that in the UK commercial aircraft generally fly in
segregated Class A, B, and D airspace, and gliders in the rest, so
conflicts are exceedingly rare.

Derek Copeland

I really don't want to get into a debate about UK and USA transponder
issues. I think some of the issues facing the UK are different,
including issues with attempts to grab airspace and UK specfic UAVs
issues (we may have some of our own here) etc. However yet again in
this transponder debate people keep raising red herrings or offering
misinformation. I hope the BGA and others in the UK are not using all
these sorts of arguments in their debate, because some of them are
embarrassingly silly and would take away from other valid points.

So lets waste more space on this..

There is no reason to believe that you would get excessive RF exposure
form a properly installed transponder antenna. Most antennas are 1/4
wave stubs or blades that require a ground plane and when mounted
where glider manufactures recommend (on the underbody of the fuselage
near the undercarriage) just won't expose the pilot to significant RF
radiation. If your glider is metal or carbon fibre you have even more
isolation. Also be careful when comparing to other RF sources -- the
power specifications of transponders are the peak pulse power. The
duty cycle is quite low even in an environments with lots of active
TCAS interrogations. I've seen transponder antennas installed between
pilots legs, nearly in contact with he pilot. Darwin has something to
say about that.

As for power requirements there are several choices of transponder
that along with an encoder draw ~0.5 A. This is the sort of power
consumption that if your glider's batteries are absolutely already at
the maximum could usually be met by the addition of a small 7Ah
battery VRLA batttery. Say derating the battery 7Ah spec by 50% (for
operating temps below 20C and the load being above 0.05C) would gives
7 hours of run time. Mode-S transponders like the Becker will work
fine down to 10V (which at a 0.5 A load is lower then the discharge
point voltage used to calculate VRLA battery specs). How long are
typical flying days in the UK? The worse case is going to be long cold
wave flights and they may well need a larger battery or use a more
advanced technology battery. But these devices are already in the
"use
small battery" category in my book. And I know installing that
battery (or even better a 12Ah battery if you have space) may be a
pain in the neck and cost some money but it is a tough argument to try
to push onto the traveling public, airline and jet owners etc. If I
was the CAA and having to put up with these arguments. I'd be making
the point by showing actual 7Ah battery sizes to highlight the (small)
problem glider pilots and owners are facing.

It is likely unrealistic to expect airliners and fast jets to use
flarm. Most of these aircraft have sophisticate TCAS systems. I hope
glider pilots are not presuming somebody just installs a flarm into
the airliner cockpit. Any flarm type input would need to be integrated
into the TCAS so it can provide s single traffic display and issue a
single RA. This is unlikely to be a low cost modification and why
should those owners do something to accommodate gliders which could
just "get with the system" and install transponders? Then there may
be
technical issues with flarm like effective range (can flarm be
modified to respond to airliner interrogations at tens of km? TCAS can
work over distances like that, giving pilots a head's up of traffic
before a RA is required). While flarm seems a fantastic technology
where it is used (not in the USA) I suspect it is a read herring when
talking about providing airliners and fast jets tools to avoid
collisions with gliders.

As for wanting a Mode-S transponder with "TCAS" display. You can get
this today. In the USA PCAS units like the Zaon MRX are popular and
use very low power and relatively low cost (~$500). They provide an
alert but no RA or direction information. But they are impresssively
effective at highlighting traffic (I've flow with one for three
years). They work fine with Mode-S transponders. Yes I know this may
seem a waste of money if you already have a flarm unit. But back to
where I think the Examiner opinion article was trying to focus and
where I'd argue the higher risk to our aport is -- avoiding a
collison with a airliner or passenger carrying jet -- then the glider
does *not* need PCAS or TCAS type capablities. Letting ATC, and if
that fails, TCAS-II in the jet, deal with the conflict is going to be
highly effective.

Darryl

So now I have to buy two bits of kit, instead of one! Not everyone (even
syndicates) can afford a new, top of the range, two seater sailplane. One
of the gliders I fly on a regular basis, and enjoy doing so, is probably
worth less than a transponder!

Derek C


At 20:28 19 January 2009, Bruce wrote:
To get away from the hot air and spoil the argument with some hard
facts.

Transponders and Flarm are similar ideas, but for completely different
scenarios.

So the anal response is - Why not have a Mode-S transponder for those
fast heavy things, and Flarm for the light slow targets.

Best of both worlds and the top of the line for each of those represents

2.06% of the total purchase price of a new two seater. Real numbers for
a January 2009 delivery aircraft. That is adding the Flarm option to an
LX8000, and fitting a TRT800 transponder and encoder. Both with remote
displays for the RSO...

OK - that is not counting the extra battery and the solar panel for
ensuring one never runs out of electrons. Add an antenna and all the
labour and it is still

On Mon, 19 Jan 2009 10:06:40 -0800, Darryl Ramm wrote:

I know nothing about UK airspace (besides being stuck in it for far too
much time as a passenger holding over Heathrow), but it sounds like the
existing separation of airliner and jets in UK airspace is a key point
you folks should be arguing.

Yes, agreed. The public will be with us on noise grounds if the commuter
airlines get their way and start flying direct routes through class G
airspace - this is something they can't do at present, but the CAA's
transponder consultation seems designed to let them do it.

And again only one of the transponder aircraft needs to be talking to
ATC/radar facilities or have PCAS or higher. I don't know PCAS (and
higher-end systems) adoption in low-end GA aircraft in the UK, but in
the USA it seems pretty high (purely an anecdotal impression). I've
asked before but could not get adoption numbers for the USA.

I've not seen figures either, but the GA density is probably lower here.
There are flying schools on either side of our club field and there's no
doubt that our weekend movements vastly outnumber both of theirs.

In the Libelle you might be able to make up a mount for a Zaon MRX under
the opaque areas of the front of the canopy.

There's less space there than you might imagine. The panel is inset no
more than 65mm (2.5"), so an end-on cigarette pack would not fit under in
font of the panel while anything thicker would start to hide the top row
instruments.

It might be canted over parallel to the surface,

It would have to be. If it was in the center it would interfere with the
canopy lock. On the other hand, the antenna is probably not an issue - a
remote one could be mounted above the instrument tray that forms the
front of the panel. My GPS antenna is mounted there and gets an excellent
view of the sky.

I wouldn't want anything much bigger than a MH flowmeter on the cockpit
wall in front of me: lets just say the cockpit is 'snug'.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Jan 19, 11:45 am, Derek Copeland wrote:
[snip[
1) Would they still work if a glider is in a tightly banked thermal turn,
with the ground plane at a considerable angle, and the glider just moving
with the wind? Don't they (ATC) filter out slow moving objects anyway so
they don't see clouds, flocks of birds, etc.

With a transponder you should be seen. Velocity filtering is exactly
one of the reasons you want a transponder. Having a transponder
ensures that velocity filtering of primary targets does not filter
your glider. Cars on highways is one issue, another significant
problem one in some location is power generating windmill farms. Non-
transponder equipped aircraft are effectively invisible in some pretty
busy airspace due to this (e.g. to Travis Approach, over the
Sacramento Delta in California, this transponder caution finally made
it onto sectional charts.

I would encourage pilots to try to go visit a radar facility (I have
no idea how hard this is nowadays), and see how the rest of the world
operates. It may be eye opening how outside the system you are without
a transponder.

2) Would a glider climbing rapidly in a thermal or wave towards the base
of an airway or controlled upper airspace (with no intention of entering
it), or flying just below it, generate spurious TCAS alarms that might
unnecessary frighten the jet jockeys into making violent avoidance
manoeuvres and upsetting their passengers?

Still fishing for more of those red herrings? :-) I suspect in reality
TCAS works pretty well, but I'm sure some pilots feel they may already
get too many false alerts. TCAS-II would give an TA (traffic advisory)
or RA (resolution alert) based on predicted time to impact or being
within a certain altitude band. The fixed band and predicted miss
altitudes are pretty small (e.g. I believe 600' for RA and 850' for TA
at 10,000'). The predictive part is essential time to closest approach
based (e.g. 30 seconds at 10,000'?) and I suspect this is what would
actually alert in the scenario described. For more info on the
predictive alerts look at the closure speed and rate of climb charts
in the FAA document "Introduction to TCAS-II" (e.g. at
http://www.sisadminov.net/tcas/docs/TCAS_II_V7.pdf).

And if even if a glider was climbing rapidly just below the base of
airspace in the vicinity of an airliner or similar and this did
trigger a TA or RA? Is this really going to happen that often? I am
guessing that if this is an issue at all it will already be more so
with jets descending (at potentially several thousand fpm) near the
bottom of their airspace and GA aircraft flying level under that
airspace. And if the pilot's can't see the gliders even after a TA and
the system ends up issuing an RA then that may be all good, they after
all don't want to need to know or guess what your intentions may or
may not be.

Maybe some of the airline or corporate jet pilots might want to
comment on these possible excessive TCAS alerts (paging Captain
Jim...).

3) What effect would a whole gaggle of competition gliders have on ground
radar services or TCAS? Indeed the CAA has suggested turning them off in
such circumstances, but then what's the point of having them fitted in
the first place? I understand that Air Traffic Control can selectively
filter out some returns, but again what would happen if they selected the
one that was an actual threat?

I am guessing the issue here is more likely to be TCAS limits (systems
are required to process up to 30 targets at a time I believe) than SSR
systems, but maybe they also have local problems, but can clearly
handle larger numbers of targets. How rare are large gaggles outside
of a few large competitions? Has anybody talked to the TCAS
manufacturers about how their systems would actually handle this? I
agree the CAA response seems a little Monty Python-esque.

Basically I object to having to pay out the best part of £2k to fit
unproven (for gliders) technology to my £8k glider, that will probably be
out of date anyway in a few years time.

Unproven? The ability of a transponder to help avoid collision with
fast jets and airliners is very well proven technology...
transponders, SSR radar equipped ATC and TCAS have been well
demonstrated to avoid all sorts of collisions between all sorts of
aircraft... The development of TCAS was motivated by collisions of
passenger jets and relatively slow flying GA aircraft. Whether that is
the real motivation for the CAA requiring mode-S in the UK or not is
something I cannot judge, but I have some level of skepticism about.
Many of us who do fly gliders with transponders and operate around
busy airspace and/or communicate with ATC prove all the time that
transponders work well. Traffic advisories, hearing and seeing heavy
iron vectored around you happens enough to convince you quickly that
the system works. At the other end of the spectrum, away from busy
airspace, we are often reminded of other gliders or GA traffic by our
PCAS systems.

I do sympathize with the cost issue, and even more so with bureaucracy
around the installation process. It sound like you have to do much
more work than say compared to a 337 form in the USA. But I suspect
the traveling public won't care what your glider costs. And I'm not
sure this is an argument I'd be making publicly.

I am also unconvinced that an unshielded 120 Watt RF output is not a
health hazard, when even 4 watt microwaves are considered dangerous.

Unshielded? The point is there is an RF ground plane between you and
the antenna. The 120W (or 250 or whatever) pulse power and the
(presumably continuous wave) 4W microwave power you are talking about
is like comparing apples and snow globes and we are *not* talking
about exposures or a pilot with properly installed antenna that
normally should be within orders of magnitude of direct exposure to
the transponder antenna RF radiated field. If this really worries you
in a fiberglass (not carbon) or wood glider have the installer add
some extra adhesive ground plane material (more than the normal ground
plane) around the antenna or under your seat. There may be lots of
complex technical debate around safe RF exposure levels, population
vs. occupational exposure, etc. in the microwave frequencies but you
get a lot of exposure in other places as well (door openers, cell
phones, your handheld VHF radio, nearby VHF/UHF radio transmitters,
etc.). The ground plane is the key thing here. There is significantly
more credibility in raising issues in not mounting the antenna in
plain sight of the pilot, and in applications like hang gliders or
paragliders where there may be no way to install a ground plane and
orient this away from the pilot but with a ground plane and 1/4 wave
antenna shielded from the pilot I think this is stretching credibility
a long way.

Darryl

I happen to know that tests on a lightweight, low powered transponder for
hang gliders and paragliders proved unsuccessful, because most of the RF
output was being absorbed by their pilots' bodies! Ground radar and TCAS
where unable to detect these aircraft at any significant distance at all.

Derek C


At 22:08 19 January 2009, Darryl Ramm wrote:
I am also unconvinced that an unshielded 120 Watt RF output is not a
health hazard, when even 4 watt microwaves are considered dangerous.

Unshielded? The point is there is an RF ground plane between you and
the antenna. The 120W (or 250 or whatever) pulse power and the
(presumably continuous wave) 4W microwave power you are talking about
is like comparing apples and snow globes and we are *not* talking
about exposures or a pilot with properly installed antenna that
normally should be within orders of magnitude of direct exposure to
the transponder antenna RF radiated field. If this really worries you
in a fiberglass (not carbon) or wood glider have the installer add
some extra adhesive ground plane material (more than the normal ground
plane) around the antenna or under your seat. There may be lots of
complex technical debate around safe RF exposure levels, population
vs. occupational exposure, etc. in the microwave frequencies but you
get a lot of exposure in other places as well (door openers, cell
phones, your handheld VHF radio, nearby VHF/UHF radio transmitters,
etc.). The ground plane is the key thing here. There is significantly
more credibility in raising issues in not mounting the antenna in
plain sight of the pilot, and in applications like hang gliders or
paragliders where there may be no way to install a ground plane and
orient this away from the pilot but with a ground plane and 1/4 wave
antenna shielded from the pilot I think this is stretching credibility
a long way.

Darryl

On Jan 19, 10:18*am, Chris Reed wrote:



Second, installation can only be done, as I understand it, if either
(a)
the manufacture has issued an approved scheme for installation
(Ibelieve none have,

--------------------------------------------------------------------

DG has a TN for the installation, probably others do as well, but you
have to dig a bit for it.

I agree that the power issue might not be that important. Selecting a
lower current encoder (ACK?) can help. For my installation I installed
wiring for a second battery but am waiting to see if it's really
needed. It might only be required for unusually long flights, and in
those cases might be avoided by using a 'load shedding' check list- by
using the back-up battery in the vario, shifting the PDA to it's
internal battery, and avoiding idle chatter on the radio you get some
extra hours.

Schempp-Hirth has TNs for transponders as well - permitting three different
antenna types - blade, rod or bendy.

The new Trig Avionics TT21 transponder, with built-in altitude encoder is
estimated by the makers to consume 320 mA from a 12 V battery when busy.
Assuming the 7Ah battery is only delivering 50% of nominal capacity this
equates to 10 hours continuous use.

The controller that needs to be accessed by the pilot is 6.4 x 4.5 x 4.5
cm, the transponder itself can be installed anywhere convenient in the
glider so will fit most gliders. (And I don't have an interest in it.)

At 22:47 19 January 2009, brianDG303 wrote:
On Jan 19, 10:18=A0am, Chris Reed wrote:



Second, installation can only be done, as I understand it, if either
(a)
the manufacture has issued an approved scheme for installation
(Ibelieve none have,

--------------------------------------------------------------------

DG has a TN for the installation, probably others do as well, but you
have to dig a bit for it.

I agree that the power issue might not be that important. Selecting a
lower current encoder (ACK?) can help. For my installation I installed
wiring for a second battery but am waiting to see if it's really
needed. It might only be required for unusually long flights, and in
those cases might be avoided by using a 'load shedding' check list- by
using the back-up battery in the vario, shifting the PDA to it's
internal battery, and avoiding idle chatter on the radio you get some
extra hours.

So do the many wooden and vintage gliders still flying have TNs from their
manufacturers for fitting Mode S transponders then? Somehow I rather doubt
it!

Derek C

At 00:15 20 January 2009, Big Wings wrote:
Schempp-Hirth has TNs for transponders as well - permitting three
different
antenna types - blade, rod or bendy.

The new Trig Avionics TT21 transponder, with built-in altitude encoder
is
estimated by the makers to consume 320 mA from a 12 V battery when busy.

Assuming the 7Ah battery is only delivering 50% of nominal capacity this
equates to 10 hours continuous use.

The controller that needs to be accessed by the pilot is 6.4 x 4.5 x 4.5
cm, the transponder itself can be installed anywhere convenient in the
glider so will fit most gliders. (And I don't have an interest in it.)


At 22:47 19 January 2009, brianDG303 wrote:
On Jan 19, 10:18=A0am, Chris Reed wrote:



Second, installation can only be done, as I understand it, if either
(a)
the manufacture has issued an approved scheme for installation
(Ibelieve none have,

--------------------------------------------------------------------

DG has a TN for the installation, probably others do as well, but you
have to dig a bit for it.

I agree that the power issue might not be that important. Selecting a
lower current encoder (ACK?) can help. For my installation I installed
wiring for a second battery but am waiting to see if it's really
needed. It might only be required for unusually long flights, and in
those cases might be avoided by using a 'load shedding' check list-
by
using the back-up battery in the vario, shifting the PDA to it's
internal battery, and avoiding idle chatter on the radio you get some
extra hours.