Can they see us on radar?

[Old Koreelah]

Controllers rely on transponders these days, but in case I wander into the wrong territory, can their radar see every type of small aircraft? Wood and composite presumably return less radar. I lined the inside of my plywood fuselage with alfoil in the hope I'd be seen by a low-flying jet jockey- and then realised that it would interfere with my internal dipole antenna, so ripped it out again.

 

Perhaps the ATC people on the forum can advise.

 

 

[rhysmcc]

It all depends on the location and type of radar being used. Generally if your anywhere near a class C control zone the primary radar will pickup light aircraft without a transponder, what those aircraft are made of I wouldn't be able to tell you. I have seen hang gliders and parachutes picked up on the primary radar, but it doesn't always.

 

 

[Guest Andys@coffs]

Going back a bit in time to when I was an RAAF Radtech, generally primary radars have an ability to set a movement threshold. if between one paint and the next the object isn't moving faster than the set threshold speed then the return is inhibited from display. That is used to remove any ground clutter returns etc that don't move.....that said that was status quo 30 years ago so things may well have changed..... Back then it wasn't done with Doppler shift because that only works for movement with some component of towards or away from the radar...fly a constant distance from the head and there is no Doppler shift and therefore no speed component can be calculated...

 

Most aircraft have one hell of a big lump of metal in the engine which is enough for reasonable returns......

 

But Radar then, and presumably now, was never foolproof which is why I can see the drive for ADSB.... a much simpler solution not at all subject to the same vagaries and providing much more detailed advice than the current system which only provides a 2D primary return (actually it does provide some alt info but it was pretty course and variable with distance from the transmitter head) relying on Mode 3C transponder returns for the usable 3rd dimension.

 

Back then I would have thought the speed of a hangglider was generally slow enough to be supressed, and parachutes are likely to move only at wind speed also supressed.....ground speed suppression was generally set so that a ground return from a car or truck wouldn't trigger a return on the display.... so >60kms/hr etc

 

Andy

 

 

[rhysmcc]

The issue with ADSB, much like Transponders, relies on the aircraft having the equipment turned on, it doesn't really aid in "protecting" airspace from those who aren't doing the right thing. That's why we still have primary radar at Class C aerodromes even though secondary (transponders) gives us more information. Further away from the airports, secondary radar is generally only used, close in we have both.

 

 

[frank marriott]

The advantages of having a transponder are worth the extra expense (if you are doing realistic Xcountry flights - otherwise might not be worth it)

 

Apart from the CTA aspects, which if you are accessing you will already know, there is real seperation assistance

 

e.g. 1. If you are using an airport with the larger RPT aircraft, TCAS + radio makes seperation easy (and less stressful - many operators don't want to get close to an RAA call sign - unless I know them nor do I for that matter)

 

2. Even flying OCTA enroute, although not mandated for VFR, you will be given as unidentified 1200 traffic to conflicting IFR traffic - which you will hear, provided of course you are monitoring the appropriate freq. In the north at least, where traffic density is low, CEN will advise the VFR traffic directly also of conflicting IRF traffic normally.

 

If flying your bug smasher above 5000' especially, a transponder although not mandatory is certainly advisable.

 

 

[Russ]

So me Putin along at 100kts, at around 6.. 7....8 thou...( under 10k ) transponder on....the bigger boys are alerted if a possible conflict is probable. .??

 

( bigger boys, ie...basic GA, and bigger )

 

 

[Guest Howard Hughes]

So me Putin along at 100kts, at around 6.. 7....8 thou...( under 10k ) transponder on....the bigger boys are alerted if a possible conflict is probable. .??( bigger boys, ie...basic GA, and bigger )

Most larger aircraft (above 5700kg) will have TCAS fitted and will be able to see you directly, if ATC are picking up your transponder they will provide advisories to IFR and VFR following aircraft in your vicinity.

 

 

[Yenn]

One of my planes doesn't have a transponder. I feel OK flying below where I expect the RPT traffic to be. Away from airports most RPT is well above 5000'. in the other plane the transponder is on and I feel OK going up to 9500' I hear ATC telling RPTs that there is unidentified VFR traffic at wherever I am, and I can speak up. It all commits to more safety. I have never heard ATC mentioning my plane that doesn't have the transponder, so I assume I am probably invisible to them. All the more reason to monitor the radio on the proper channel.

 

 

[Old Koreelah]

... I have never heard ATC mentioning my plane that doesn't have the transponder, so I assume I am probably invisible to them...

I guess that means your plywood Corby hasn't been noticed.

 

 

[SDQDI]

I often wonder what they make of me, I came back over the coolah tops at 9500ft but my groundspeed was only around 60 knots (was getting no help or hindrance from the wind) but anyway I have a transponder and I just always wonder if they are there laughing at how slow I'm going:happy:

 

 

[Downunder]

Is TCAS 360 degrees around an aircraft or more directional (to the front)?

 

 

[Guest Andys@coffs]

TCAS uses the same technology as the transponder, simply tx's a very low power interrogation request the same as the ground station (except its high power) , the normal transponders in other aircraft hearing the close (due to low power) request respond and the TCAS simply calculates distance as a function of time from Tx to Rx of the response. the closer you are the faster the response comes back. There are also passive TCAS systems that don't tx an interrogate signal relying on ground stations to do that...which is good if you are in coverage of one, or an active tcas that can also get other aircraft transponders talking......but not so good for a lot of Australia...except that most aircraft with TCAS wont be down, generally, in G class or E class airspace where we are.

 

ADSB does away with all that timedelay and bearing maths and simply looks at your GPS Data as presented to your ADSB and the GPS data in other ATSB responses. It has accuracy of GPS (x2) where as mode 3C transponder is nowhere near as accurate, but fit for purpose..... Ultimately the usefulness of traditional TCAS comes down to the accuracy of everyones Altitude encoder and transponder. If its out of calibration then the TCAS in the RPT might call for an incorrect avoidance resolution......

 

So...all around the aircraft in terms of technology....but TCAS knows in an aircraft that the greatest risk comes from the front so its zones of response in terms of Traffic advisor (lowest level of alert) and Resolution advisory (start puckering now!!!) is greatly weighted to the locations in front of the aircraft.

 

 

[nathan_c]

Simple answer is if I was controlling a sector close to the cities or anywhere a primary radar is installed (i.e anywhere that has an approach sector like Brisbane, Sydney, Melbourne etc), yes I would be able to see you as a return on my screen. However the primary radars have limited range, and they give me zero information about you except for your location. I cant see your speed, altitude, whether you are VFR, IFR, Military, nothing. All I see is a small cross.

 

Anywhere else, like my sector where I dont get primary radar coverage, you are invisible to me. If you dont have a transponder, or do not have it turned on, I get absolutely no indication that you are there at all, because secondary surveillance radar can not pick you up without it. If you do have a transponder than even squawking 1200 I can get your position, height, and an indication of your speed and can give a proper traffic statement on you. This is all obviously only valid in the J curve (basically east coast), anywhere else regardless of whether you have a transponder or not I wont see you without ADSB.

 

 

[Ultralights]

A savannah is easily seen on primary radar, being a slab sided metal aircraft, its a given, but i have first hand knowledge that the spped threshold for primary radar is 40Kts. approaching Bankstown one day into a strong sea breeze, our speed dropped below 40kts on approach, Bankstown tower asked us to confirm Ops normal as we dropped of primary radar at Sydney. they were a bit concerned and told us if we go below 40kts the radar dismisses the echo as ground clutter.

 

 

[kaz3g]

I often wonder what they make of me, I came back over the coolah tops at 9500ft but my groundspeed was only around 60 knots (was getting no help or hindrance from the wind) but anyway I have a transponder and I just always wonder if they are there laughing at how slow I'm going:happy:

I was asked why I had stopped on base at Albury one day. I was still doing more than 40 KN!

 

kaz

 

 

[Old Koreelah]

Kaz we might need a thread just for slow people. Hornets, Austers...

 

I believe the POH of the An-2 cautions against flying slower than 24kt.

 

 

[jeffd]

Kaz we might need a thread just for slow people. Hornets, Austers...I believe the POH of the An-2 cautions against flying slower than 24kt.

hey old koreelah this is away from the topic and not knowing how to send a message here yet ,im sure i will find out if i look harder, i had to tell u that there is a jodel d9 on the recreational aviation site for 8000 ,?build date 64 i think it was

 

 

[Exadios]

Controllers rely on transponders these days, but in case I wander into the wrong territory, can their radar see every type of small aircraft? Wood and composite presumably return less radar. I lined the inside of my plywood fuselage with alfoil in the hope I'd be seen by a low-flying jet jockey- and then realised that it would interfere with my internal dipole antenna, so ripped it out again.Perhaps the ATC people on the forum can advise.

If you actually want to be seen by the primary you need to put a corner reflector radar target inside your aircraft. They are quite small and will return a lot stronger signal than, for instance, an aluminum aircraft skin. They are also very easy to construct.

 

 

 

[Birdseye]

If you actually want to be seen by the primary you need to put a corner reflector radar target inside your aircraft. They are quite small and will return a lot stronger signal than, for instance, an aluminum aircraft skin. They are also very easy to construct.

I haven't seen many in the West, but similar reflectors were commonly put at the mast head of sailing boats in Europe.

 

 

[jetjr]

And heres how

 

~ 30cm diameter

 

Could you rig it up in the empty tail section somehow?

 

http://productimageserver.com/literature/ownersManual/45959OM.pdf

 

 

[Birdseye]

You could always install a chaff dispenser. Set it to fire off every minute or so and they would be sure to see you :-)

 

 

[Guest Andys@coffs]

Actually the purpose of chaff is to fool a radar into seeing many returns with a hope that the real return gets lost in the clutter.......These days pretty easy to get around with quality signal processing at the receiver...chaff generally decelerates from fighter speed to spinning leaf speed...something that a real fighter finds a real challenge to achieve........

 

Back in WW2 times radar frequencies were fixed per site so chaff was cut to length to suit the specific frequency....we aren't so constrained these days.....

 

Andy

 

 

[Birdseye]

Not in the ADR world, no.

 

 

[Guest Andys@coffs]

http://www.globalsecurity.org/military/systems/aircraft/systems/chaff.htm

 

small Extract:-

 

Chaff is intended to act as decoy for radar and/or increase ground clutter at the same time. However, modern pulse-doppler radar can recognize such decoys, especially in the lookdown/shootdown mode. This is particularly true because simple decoys, in contrast to true targets, do not exhibit a corresponding doppler shift in the radar band.

 

I

 

 

[jeffd]

well if u flew around the raaf bases and dropped chaff im sure u would get some1s attention b 4 to long