Radar reflectors in Sailplanes?
I wrote the following question to the newsgroup "rec.aviation.soaring"
Here is the interesting discussion:
Von: Friedel Weber
Firma: DG Flugzeugbau GmbH
Foren: rec.aviation.soaring
During my recent soaring vacation I had the opportunity to discuss with a former officer of our Air Force. We were considering how to reduce the danger of mid air collisions between gliders and motorized aircraft in general and especially with military aircraft.
He suggested to install a radar reflector into every glider to improve the "visibility" to the board radar of high performance aircraft and to the ground controllers. If this would work it is a very simple and cheap improvement of safety.
I personally was astonished, that during a midfield crossing of an international airport the controllers could "see" me only in a distance of 15 KM (9 miles), although my glider was made of carbon fiber with an engine inside!
The yacht equipment shops are offering such reflectors in a shape like a stick with many little surfaces and such a reflector could be built into the fin of new gliders with relative low extra cost.
My question is:
Can any "expert" give an estimation, if it will work? (radar controller, scientists for physics, other experts) Are there any studies available, were this already was tested?
Who can give an advise?
--
Always happy landings
Friedel Weber
----------------------------
www.dg-flugzeugbau.de
Manufacturer of high-performance Sailplanes
Here are the most interesting answers:
Von: "Marc Ramsey"
My father, who was a designer of air defense and ATC radar systems, did a study on this 25 years ago. I don't remember all of the details, but the conclusion was that it wouldn't work, as the size of an effective corner reflector was too large to fit in the available space in the fuselage of most gliders. In addition, the Doppler radar systems in use at the time were designed to filter out returns from objects below a certain velocity, I believe it was 60 or 65 knots. Boats can use cute little reflectors because marine radar operates in a different frequency range, and they need only be effective at relatively short range.
I've also heard that, at least here in the US, the standard operator procedure with the modern digital radar systems is to simply remove all non-transponder returns from the display. The controllers task is to provide separation between transponder equipped traffic, if you don't have a transponder, you don't exist...
Marc
Von: RHCMLATC
It's been a few years since I studied this stuff in detail, so use this info
at your own risk...
For ATC, there are 2 types of RADAR PSR and SSR. with SSR bring what they rely
on much more commonly.
PSR uses a reflected return, so some type of reflector might work
somewhat... but modern (even as in late-80's) radar data processors tended to
filter out stuff that isn't moving very fast (i.e. it would remove you if
circling in a thermal).
I remember working in a military ATC unit in Germany in about 89 watching
glider appear and disappear about 10 miles away.
Now SSR has some potential for safety improvements. SSR uses a device that
interrogates a transmitter (transponder) that provides a brief data burst back
to the ATC unit. This same transponder is interrogated and transmits to TCAS
(large aircraft collision avoidance systems).
My personal feeling is that with the technology down to a size and power
consumption that transponders are now feasible for gliders that they will be
mandatory soon - probably first in Europe and Canada who watch what happens
there.
I know just for the ability of big aircraft to see me - I will be voluntarily
putting one in my ship when I purchase it within the next year or so.
Von: Don Johnstone
The points made about primary radar (PSR) and secondary surveillance radar (SSR) are absolutely valid. My syndicate partner
is building a new panel for our ASW 17 at the moment and finding space to fit the instruments we need is difficult enough. I
totally agree that the fitting of a SSR transponder would enhance safety considerably but the implications of cost, space
and power may make implementation difficult especially for older gliders. The question also arises of just who is going to
require the fitting of SSR and who will have the duty to ensure a proper fit. An excellent idea but the practical aspects
are not that simple.
Von: Jim Culp
Gentlemen and Gentle Ladies,
This topic is always interesting as it is an appeal to our need for personal and sport self-preservation.
We can liken ourselves to a few 'Gnats In The Airspace System,' or 'Bugs On The Windshield.'
Sooner or later, one will be squished or zapped.
Are we, as glider pilots, prepared for that event?
It can happen.
A glider, struck by an air plane. Yep. Can happen.
'Yep, you got it, like a Dead Skunk in the Middle of the Road. Stinkin to high heaven.' Credit and thanks to the words
of the famous song by Loudon Wainwright.
The cure will not be radar and transponders for gliders. The hue and cry and reaction among us then may be for radar and
transponders.
That will not be a cure. It will be a response.
Question:
Has there ever been an airplane struck by another airplane and they both had transponders and were radar's working on the
ground?
Probably. Of course.
Our problem is that some gliders want to be 'seen' on the radar and to have all others in the IFR ATC tracking system to be
directed out of our way.
Some may want to be micro managed and for the other aircraft to be micro managed for us. Some may want to play big guy in a
glider,,, and all that stuff talking to controllers... etc.
Right, coowulll, just up to the point where they get a Notice of Violation.
But we don't fit within how it is set up for the ATC system for typical transport airplane movement:
I think the ATC system is like a slotted schedule system of movement of identified game pieces across a game board at
certain rates and with assigned or played given changes and movements off the great game board in the sky. A few scattered
unknown game pieces come into play, but are not the major focus of attention for the very few people staffing the ATC
enroute or approach control screens. We don't fit in how the IFR Air Traffic Control system does its job. We are not, and
I don't think we will be, the focus of their attention.
Praise the Lord.
So, until there is a new approach to aircraft separation, something like a continual gps positioning transpondering system
with all ATC received data processed with the highest speed central processors and feedback to your cockpit with nearly
instantaneous control system inputs or audio/video warnings, then we cannot do more than put a transponder in our
glider... and wonder. Wonder... for what did I do that?
You see, we don't really want to be incorporated into the ATC system the way it is set up. We may think we do, but not
really if we get into it and look at how it works.
What we really want is to maintain our freedom of flight, we want to go into the sky and not get squished or splattered or
blamed.
Our concept of operating area is the SKY. Their concept of operating area is the AIRSPACE SYSTEM. Big difference.
What we want is to do what we want to do, to fly as we want to fly, and to have some sort of special marking that says or
shows effectively, that which is in the poem below:
Ode To The Blameless Glider
Hey,
I am a Glider
Up to Fly,
I go round
and round,
and up
and down,
and scoot across the Sky,
I go slow
and I go low,
Then up to the clouds
sometimes,
When waves are at play
I go higher that day,
higher sometimes
than you know.
I am hard to see,
So don't hit Me,
for
I am a Glider
In the Sky.
Hey.
--------------
So, we may have to prepare ourselves psychologically and emotionally and rationally for the event of glider on the
windscreen. It can happen.
Prepare mind in art of Zen, and peace, and Jesus and fly.
Dancing on clouds,
Keep it up!
Jim Culp USA
Von: "Christopher Nicholas"
There was a solution in embryo in the UK some years ago (when I was the BGA
rep on the then newly formed Radar and Radio Working Group). It depended on
the development of a lightweight, low power transponder (still not in
production, but for years has been always "a few months away with field
trials soon".
Assuming one had the transponder, outside controlled airspace (CAS) it
would have been set to be active above some defined height, say 5,000 feet,
would squawk a code indicating "glider at or above 5,000 feet" and with no
input from the glider pilot would then allow TCAS equipped aircraft to avoid
it. No control of glider by Air Traffic Control (ATC), just sensible
separation handled by the others. IIRC, it would also have enabled the
glider pilot to activate it when entering CAS with permission from ATC.
The project has changed - now at least Mode C (height encoding, not just
position) and the regime it would operate in is likely to be different by
the time it comes in - still some years away at the earliest.
No workload, fully automatic, adds safety (at a cost) but was treated with
greatest suspicion by almost everyone in gliding except me. Maybe because I
fly near a major airport and see airliners outside CAS I had a different
perspective. I agree it would not solve every potential conflict problem
(e.g. Rockwell/glider collision which killed the glider pilot in 197X), but
it would remove some.
If available, I think I would get one.
Chris N.
Von: Chris Ashburn
Hello Karl,
Well, while I have to agree with Jim that a reflector will not prevent
an incident 100% for sure, but it's got to be better than nothing.
Please don't take his reply as being representative of the community.
I'm sure the majority would wish to do something proactive rather than
count down the days to the 'inevitable' and do nothing.
If an incident does occur, if all reasonable precautions have been taken
to prevent it, the repercussion will be REDUCED.
These things DO occur, but have not been a huge media event recently.
See www.sims.ndo.co.uk/airspace.htm and search for Manchester
Smaller 2-3 people mid-air collisions occur here in the USA ALL THE
TIME. Usually within the bounds of 'controlled' airspace, and there's
no reaction. That does not indicate what the reaction would be to
a 737 vs. 1-26 incident (or Libelle or ...... so I don't get any flack
;-)
(The Manchester link above mentions a 'hand gun' incident that throws
light on the UK/USA sensitivity issue that's interesting... but another
thread!)
Having a good return from the glider might result in a controller seeing
a target on the screen, maybe not..
(see home.columbus.rr.com/lusch/selrej.html for some background
in software signal processing, probably the reason you're DG800 was
in stealth mode)
Here's a couple of test's that have been undertaken in the gliding
community:
There's a mention of it in an broken link to the Arizona Soaring Assoc
Feb 1997 newsletter.
I also recall an investigation done in the UK that
might have been written up in S+G, I'll check my issues.
I think there's an issue with the wavelength of radar in use between
marine and aviation, but it may not matter with a particular design
of reflector.
Karl, hope you get a response from someone who have actually tried to
improve the situation rather than those who wish to lament the
consequences of ignoring it.
Chris
Von: "Armand A. Medeiros"
I have done some thinking on this. Unfortunately, I also suffer from some
lack of IFR and airspace experience.
However, as Jim Culp points out, the transponder idea is fraught with
problems and will probably not satisfy what we really want.
I find my views changing... I now want the airliners to stay the hell away
from me and the areas I fly. To that end, I think it would be much more
beneficial if we all learn how to avoid these beasts before the flight and
not give them cause to deviate out of their planned and prepared routes.
Maybe we could "channelise" the victor airways for heavies tightly enough
that anywhere along their routes, their altitude and headings would be
known. Make THEM stay out of the way... not us!
"See and avoid" takes on more and more meaning... do we really want an
airliner to vector OUT of a Victor airway to avoid a single transponder
equipped glider and end up running over a gaggle some distance away? Can we
predict where the airliners are most likely to be and avoid those areas?
All this good for the heavy metal, but we still have the light GA gnats to
deal with too... and ourselves.
Amongst ourselves, we are the hardest to see and most likely to congregate
in the same area.
Armand
Von: "Bill Daniels"
This discussion is essentially backwards looking, focusing on a very old
WWII technology (Radar) and attempting to "fix" it with band aids like
reflectors and transponders. There is a 50 year history of trying these
solutions with mixed results.
While I appreciate the value of a Mode C transponder, I will not buy one
since I expect them to become obsolete within the next few years.
Reflectors will not work since ATC controllers routinely ignore primary
"skin paint" targets if their workload is high.
The real solution is now emerging from the labs and is known as ADS-B
(Automatic Dependent Surveillance - Broadcast) It requires every aircraft
to determine its 3D position to high precision and then to broadcast it,
along with identification data, to everyone in the area. The airborne
equipment will potentially be smaller, lighter, less power hungry and less
expensive than transponders while offering far more utility and protection.
Unlike a transponder, ADS-B equipment will not require any involvement by
the crew.
Bill Daniels
Von: Ruud J. Holswilder
In the Netherlands we had a collision between a F-16 and a PA-28 on
December 22 1999.
(the PA-28 is a Piper Warrior single engine all metal aircraft)
The F-16 was flying at a speed between 450 and 480 Kts at 1000 ft MSL.
I guess that a all metal PA-28 should show up on the on-board radar of
the F-16.
Apparently this speed is to high for a fighter pilot to notice the
conflicting traffic and take evasive action.
I have always said that high speed military traffic and low speed
civil traffic don't mix. Let the fighter pilots play at places where
they can't do much harm, like the most northern part of Canada or
Siberia. Only a few mosquito's will be complaining.
See also the thread "Fight for your air space!!" in this newsgroup.
Von: "Sula"
I once asked a man who did ATC and stared at radar screens all day what a
fiberglass glider looked like. He said "You look like an airplane." He
felt that the metal in the control rods & cables gave enough return, and saw
no reason to try to increase the radar signature. This was just one guy,
but he was experienced and used to seeing powered aircraft and gliders of
all types.
He also said that its common to switch off "primary" returns & concentrate
on transponders, but he frequently switched back, and felt this was
important when giving traffic advisories. Again, one guy, several year ago.
Von: ChrisAtUpw
Please DO get the ADSB publication and read the damn thing. Because of putting
a whole load of other info on the signal, the absolute max no of aircraft is
2000. Now there can be 1,500 gliders in the air in the UK on a good weekend -
not just for short hops, but for hours. This leaves just 500 slots for private
aircraft and none for airliners. So sad! And damn incompetent of the ADSB
designers. You would think that in the age of personal phones the manufacturers
could find someone who knew how to calculate message times and response rates.
And don't rely on Transponders either. At our local airport, they CAN'T SEE
ANYTHING below 3,500 ft because this is below the radar. Ask to have a look at
SSR coverage / height maps! Oh and these poor overloaded air traffic
controllers just SWITCH OFF ALL SSR CODES that are NOT commercial! If they
could put all the gliders on a screen of the UK, you would see nothing else -
not even the hang gliders! If you must persue lunatic policies or trying to
control everything, nothing will work. If you control air lane traffic only,
you have a fair chance of success. Then it is up to all other traffic to avoid
the air lanes, which with GPS, we should have a fair chance of doing.
Chris Chapman
Conclusion:
Obviously the radar reflector will not work. Very pity!
Please also read: Transponder