On 1/21/2011 4:49 PM, Jim Logajan wrote:
For most collision avoidance, I don't think one needs information on the
entire sphere around an airplane. If you have coverage of +/- 30 degrees of
your average flight plane, I believe you would be covered for most
reasonable climb and descent angles that you and other aircraft can muster.
I was thinking of a previous poster's distinction between "dependent"
(like Flarm) and "independent" collision avoidance technologies (like
airborne radar). If the radar doesn't have full coverage, then it's in
the "dependent" group. With the coverage you mention, it probably does
cover most of what you need. Now I'm trying to imagine where a dome that
size is placed on a glider. It's 11" by 19", 16 pounds, so an image of
an AWACS plane is forming in my mind.
Not sure I follow - what do you think the accuracy is today and why you
think it isn't sufficient? The Lowrance/Simrad/Northstar unit has a
claimed target resolution of 2 to 3 meter at 10 miles.
I saw that statement under the video on YouTube (first link), but not on
the Lowrance site. The claim I saw there was a 5 degree width beam, and
I have no idea how a beam that wide could "resolve" targets 2 or 3
meters across at 10 miles. I can imagine it would _detect_ targets that
small at 10 miles, but it would not be possible to distinguish between
two targets even 20 or 30 meters apart at 10 miles.
It is interesting to
view their video ads to see what they can and can't do, particularly in
areas with lots of nearby targets:
http://www.youtube.com/watch?v=TEPgcPM6EmY
Two notable examples in the video: when their radar imaged birds on the
water and when it imaged a parasailor (their printed material says they can
image birds out to 500 feet at most, though:
http://www.lowrance.com/Products/Mar...oadband-Radar/ )
The modern units are much better than I found last time I looked, and
$2000 doesn't seem too bad. The power consumption is reasonable if you
scale it for the much smaller range the glider would need. The antenna
looks awfully big for a glider, and you need the width to keep that 5
degree beam size. If you aren't concerned about the elevation to the
target, then the vertical antenna dimension can remain small. Possibly,
a higher frequency could be used in a glider, allowing a smaller antenna.
and you'd also
have know the glider's attitude, altitude, and position to make sense
of the radar return.
I'm not sure why I would need anything other than range and direction to a
possible collision hazard. More than that would be "too much information."
With a moving map of collision hazards, I think I could mentally project
where things are going well enough to avoid them, even with only "raw"
depiction of radar returns.
If all you want is knowing something is out there, it really simplifies
things; still, I wonder what the screen image would look like as the
glider banks and pitches. It seems like it would be useless in a thermal
or near a gaggles, the times you would really like to know where people
are, especially vertically.
It'd be fun to explore the possibilities, but I'm not radar-savvy enough
to do it. All I can imagine is a lot of problems that make me think it
would be better to talk other pilots into getting PowerFlarm and MRX units.
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz