Maybe someone should develop a device like the MRX PCAS which detects
transponders and includes azimuth in addition to range and elevation. Most
of the algorithms have already been developed. There are well established
methods for very accurately locating a transponder. Look up ASDE-X, for
example (LAT/LON/ALT derived from transponder replies). Alas, I suspect
development cost would far outweigh expected return on investment.

Steve makes excellent points, especially the environmental issues with using
consumer electronics in an aviation envrionment. Having said that, I must
ask if Flarm and PowerFlarm have FAA certification, as does a certified
transponder. Steve's post implies that it is but, according to the FAC
posted at gliderpilot.org, it is not, and does not require certification.
As to Steve's question of the veracity of the system under discussion in an
environment including 50 gliders in close formation, consider that this
display has only 64 pixels and 3 of them display the own ship! That would
be a pretty busy display...

According to the NTSB accident database, since 1994 in the USA there have
been exactly 6 midair collisions involving a glider as listed below (9 if
you consider two gliders running into each other):

1999 - Gllider hit tug which was towing another glider
2003 - Piper Cub flew into aerobatic box and collided with glider using the
box
2006 - Glider and corporate jet collided at 16,000' MSL near Reno, NV
2008 - 2 gliders collide while thermalling
2012 - 2 gliders collide head on
2012 - 2 gliders collide while thermalling at the Worlds Championships

I'm going to guess that neither Flarm nor PowerFlarm were available in 2008
or earlier and, if that is the case, then this technology might have
prevented exactly two accidents in the US. I'll bet that both gliders in
the World's were so equipped and the technology failed, so I'm still waiting
for difinitive proof that it's worthwhile. In most cases, a good outside
scan would also have prevented an accident. In response to the anticipated
statement that we'll never know how many accidents were actually averted by
Flarm, I can only say that a good traffic scan is usually all that's
required, or rejecting or leaving a crowded thermal (competition excepted).

I used the keywords "midair" and "glider" in my search but there may well be
others which I missed. My point is that, considering the number of glider
flights conducted in the US, the risk of a midair is extremely low and, in
my opinion, does not warrant the expense, complexity, or distraction of a
collision warning device for most of the glider flying done in the US.
Competition flying is different, of course, as it concentrates so many
gliders in the same airspace. Europe is much more congested and has far
more glider flights than we do and I can see more of a benefit for them.

And, finally, for a good many of us glider pilots, we cannot simply lay down
for an ASG-29, full panel, and Cobra trailer. For us, the sport is somewhat
cost driven.

"Steve Koerner" wrote in message
...
This is interesting and clever.

But it does not work with Flarm! Flarm/PowerFlarm is seeing rapid adoption.
A system that competes with Flarm has only the possibility of reducing
safety during the time frame that I expect to remain an active glider pilot.
Though competition is usually good, it is not a good thing to have
competition in this case. What makes it worse is the possibility that any
pilot might consider waiting for this instead of installing Flarm/PowerFlarm
right now.

Just like Flarm, this system requires that both gliders be like equipped.
Having a contingent of Flarm users and a contingent of WiFi users at a
contest means that we cannot get to the significant level of safety
improvement that would be otherwise achievable with fully adopted Flarm or
PowerFlarm.

As I read through the material I couldn't find a single element of technical
superiority over PowerFlarm. It seems to me that for one technical standard
to replace another established standard it needs to be distinctly better
than the first. Being equivalent (if it were) is not near good enough, even
if the cost is lower. Soaring is not so strongly cost driven as consumer
products for example and in general having an avionic component supported by
a manufacturer is a very important benefit.

Starting from where the developers are now, they are very far behind
PowerFlarm. Part of the goodness of PowerFlarm is the years of evolution in
the algorithms for the collision risk analysis. In a fast changing
environment of side by side cruising and close thermalling, PowerFlarm makes
good determinations. Even the most brilliant programmer on earth cannot
just sit down and write that code. It takes years of observation and
feedback to make it work really well in the real world. The electrical
components are not the major part of the problem; the magic is really in the
software.

And for close proximate flight, I'm led to wonder how the designers might
have come to the conclusion that 2-3 second latency would be acceptable for
good warnings? Having flown with PowerFlarm, I have to believe that the
latency is lower than that.

On the hardware side, I think there are things the developers are not
considering well. The use of a high gain (5 dBi) antenna is not advisable.
It's important to use a low gain dipole pattern antenna in order to couple
well with turning gliders. With a low gain antenna at both TX and RX, the
link analysis will be significantly impacted and you will not have the range
that has been speculated. PowerFlarm uses a simple dipole for this reason
and yet has greater range than is contemplated with the high gain antennas
suggested here.

Also related to the coupling matter is the choice of frequency. 2.4 GHz
will be significantly more impacted by the nearby human body and other items
of near wavelength dimension in the environs of the antenna. This can be
overcome to a certain extent with power margin but there isn't power margin.
PowerFlarm provides an auxillary receive channel to partially address this
issue. An auxillary channel is needed in spades at 2.4 GHz.

There is no mention in the article as to the level of degradation that might
be expected in a contest environment with say 50 gliders all within radio
range. What is the duty cycle of the waveform? How much would 50 gliders
be expected to further reduce functional range?

In this self assembly scenario, who does the testing? One of the things
about electronics in general and avionics in particular is the need for
sophisticated testing. Having a manufacturer behind an avionics product
means that the items have been tested. There is the production testing of
each article as it leaves the assembly area. Even more important is that
all of the components that go into the design have been technically
qualified as suitable. That means that they are tested for operation over a
wide temperature range as well as shock and vibration and humidity and
pressure. They are tested for having a suitably small degree of parameter
variance over the environmental range. All of the USB consumer items that
are identify for this project are items that are generally made in China and
are intended only for use at room temperature in benign environments. It
would be almost remarkably if they all happen to also work over aviation
temperature range. I'd be particularly suspicious about the radio module
power output and the radio sensitivity over temperature; especially for a
device that was never actually intended for operation over temperature.

In fairness the original poster, he did not describe the system as intended
to be a replacement for Flarm/PowerFlarm. Yet as described, that would be
the obvious thing that many readers might be considering here. For that
reason it is worthwhile to point up these considerations and limitations.

Even as I hope that it eventually works well for OP's club, I'm also hoping
that no US pilots in particular might be looking at this as a suitable
substitute for PowerFlarm.