Nearly Mid-Air Collision at Estrella

Gary Evans skrev den 2 Feb 2004
15:32:41 GMT:

Do military aircraft utilize transponder signal based
collision avoidance systems?

Yes, and this does not amuse controllers as they have a fast jet blasting
upwards at umpteen thousand fpm, setting off all the TCAS bells in the
traffic above the sector.

Cheers,
Fred

Fredrik Thörnell wrote in message ...
Gary Evans skrev den 2 Feb 2004
15:32:41 GMT:

Do military aircraft utilize transponder signal based
collision avoidance systems?

Yes, and this does not amuse controllers as they have a fast jet blasting
upwards at umpteen thousand fpm, setting off all the TCAS bells in the
traffic above the sector.

Cheers,
Fred

It depends. The newer, large transport (and tanker?) military
aircraft probably have TCAS, since they are usually equipped to
airliner standards. But they also will almost always be on an IFR
flight plan.

Fighters are a whole different bag of fish: Most have air-to-air
radar that may or may not see a glider (I have seen F-16 radar detect
and lock on to a glider). Some Harriers have a radar, but not all.
Some fighters also have the capability to interrogate a transponder,
much like ATC does; this includes F-15s and some F-16s, not sure about
the radar equipped Harrier 2. In this case, a transponder in the
glider will help a lot. As far as I know, no fighter-type aircraft
have TCAS or similar.

All military aircraft have transponders and are squawking mode 3 and
mode C - but if there are two fighters in formation usually only the
flight lead will be squawking - the wingman will be in STBY as long as
he is part of the formation. So a TCAD or similar device in a glider
may not detect all the threats.

Kirk

Kirk Stant skrev den 2 Feb 2004 11:15:10 -0800:

All military aircraft have transponders and are squawking mode 3 and
mode C - but if there are two fighters in formation usually only the
flight lead will be squawking - the wingman will be in STBY as long as
he is part of the formation. So a TCAD or similar device in a glider
may not detect all the threats.

My mistake. I was reading 'transponder equipped'. And I agree, I have yet
to see TCAS in fighters. No space, no way of effectively fitting it into
the already complicated peacetime cognitive system without reducing the
wartime capability of same.

Thanks for correcting me!

Cheers,
Fred

If radar getting you is a problem, for boats they make fairly
compact aluminum "radar reflectors" that are pretty lightweight.
Dunno if they'd fit in a tail section though, kinda
"ship-in-a-bottle" maybe?

(Mark James Boyd) wrote in message news:401ec338$1@darkstar...
If radar getting you is a problem, for boats they make fairly
compact aluminum "radar reflectors" that are pretty lightweight.
Dunno if they'd fit in a tail section though, kinda
"ship-in-a-bottle" maybe?

I am planning to fit a marine aluminium corner cube into the fuselage
of the Pirat. It's about 12" on each side, very light, and can be
assembled in situ. There more compact reflectors for marine use which
are claimed to have larger radar cross sections, but the emphasis has
to be on "claimed" there.

Active reflectors are also coming in for marine use. They are
not-quite-transponders: when they hear a pulse they send one, or in
some cases several, back. I don't know how compatible they'd be with
airborne radar systems, though.

Ian

On 3 Feb 2004 04:55:56 -0800, (Ian Johnston)
wrote:

(Mark James Boyd) wrote in message news:401ec338$1@darkstar...
If radar getting you is a problem, for boats they make fairly
compact aluminum "radar reflectors" that are pretty lightweight.
Dunno if they'd fit in a tail section though, kinda
"ship-in-a-bottle" maybe?

I am planning to fit a marine aluminium corner cube into the fuselage
of the Pirat. It's about 12" on each side, very light, and can be
assembled in situ. There more compact reflectors for marine use which
are claimed to have larger radar cross sections, but the emphasis has
to be on "claimed" there.

Sounds interesting. Can you supply more detail yet, like cost, weight,
sources?



--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

we have no problems with local ATC radar picking up our Grob 103, LS-4,
Libelle, and of course.. the Schweitzer Iron, 2-33 and 1-26

but they have to be looking at Primary Radar.. and not just the transponders
BT

"Martin Gregorie" wrote in message
...
On 3 Feb 2004 04:55:56 -0800, (Ian Johnston)
wrote:

(Mark James Boyd) wrote in message
news:401ec338$1@darkstar...
If radar getting you is a problem, for boats they make fairly
compact aluminum "radar reflectors" that are pretty lightweight.
Dunno if they'd fit in a tail section though, kinda
"ship-in-a-bottle" maybe?

I am planning to fit a marine aluminium corner cube into the fuselage
of the Pirat. It's about 12" on each side, very light, and can be
assembled in situ. There more compact reflectors for marine use which
are claimed to have larger radar cross sections, but the emphasis has
to be on "claimed" there.

Sounds interesting. Can you supply more detail yet, like cost, weight,
sources?



--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

On Tue, 3 Feb 2004 16:36:06 UTC, Martin Gregorie
wrote:

: On 3 Feb 2004 04:55:56 -0800, (Ian Johnston)
: wrote:

: I am planning to fit a marine aluminium corner cube into the fuselage
: of the Pirat. It's about 12" on each side, very light, and can be
: assembled in situ. There more compact reflectors for marine use which
: are claimed to have larger radar cross sections, but the emphasis has
: to be on "claimed" there.
:
: Sounds interesting. Can you supply more detail yet, like cost, weight,
: sources?

Any chandler will sell them. I'm not sure who does mail order these
days, as a coupleof big names went bust. Gaelforce in Inverness,
maybe, or Jimmy Green in Devon?

I think they are about thirty quid and the one I have on the boat
weighs less than a pound.

Ian

Ian Johnston skrev den 3 Feb 2004 04:55:56 -0800:

I am planning to fit a marine aluminium corner cube into the fuselage
of the Pirat. It's about 12" on each side, very light, and can be
assembled in situ. There more compact reflectors for marine use which
are claimed to have larger radar cross sections, but the emphasis has
to be on "claimed" there.

It'd be interesting to find out what the speed threshold for the doppler
radars typically is. Unfortunately, that is not a piece of information
they go out of their way to make available. The question is, above or
below the speed of a glider in a thermal?

Cheers,
Fred

Fredrik Thörnell wrote:
Ian Johnston skrev den 3 Feb 2004 04:55:56 -0800:

I am planning to fit a marine aluminium corner cube into the fuselage
of the Pirat. It's about 12" on each side, very light, and can be
assembled in situ. There more compact reflectors for marine use which
are claimed to have larger radar cross sections, but the emphasis has
to be on "claimed" there.


It'd be interesting to find out what the speed threshold for the doppler
radars typically is. Unfortunately, that is not a piece of information
they go out of their way to make available. The question is, above
or below the speed of a glider in a thermal?

Cheers,
Fred

In an air surveillance radar the doppler information (instantaneous
radial velocity) is used primarily to reject stationary targets that
creep in via the sidelobes (as opposed to a weather radar which is
really interested in all the IRV data it can gather). In my experience
the doppler clutter threshold was set very low - say 1 or 2 knots. My
experience is military, where the cutoff was set as low as possible to
counter the postulated "spiral in at low radial velocity" attack, but I
believe ATC radar would also have compelling reasons to keep the doppler
cutoff very low (don't want tangential targets disappearing on you).

Where gliders are likely to disappear is in the processing of multiple
radar returns into tracks. A variety of clutter rejection algorithms
can be used, and we never used anything quite as simple as "under X
knots, throw it out". We did, however, try very hard to eliminate bird
tracks, and glider flight patterns obviously have much in common with
certain birds. The distinction is between "visible to ATC" and "tracked
by ATC" - and we'd really like to be tracked.

In short, I don't think there is any simple answer to at what speed a
glider will be tracked by ATC. And while I think using a corner
reflector to provide a great big RCS is a great idea, I can still
imagine the ATC software thinking, "Hmmm, that must be a GREAT BIG hawk
out there...".

IMHO,
Dave