On 10/28/2010 10:38 PM, Eric Greenwell wrote:
On 10/28/2010 4:03 PM, Mike Schumann wrote:
On 10/28/2010 3:36 PM, Eric Greenwell wrote:
I can think of three situations where the time involved can be reduced:

1) two gliders approaching head on. At 100 knots each - a 200 knot
closing speed - that's only 18 seconds or so to collision. How many
seconds of warning do you lose while collecting enough points to make a
good estimate of the projected paths - 5 seconds, 10 seconds? I don't
know, but I'd prefer to know sooner than later.

2) Ridge or mountain flying, where the transmissions are blocked by the
terrain. Once they round the corner of the ridge, there may not be
enough time to calculate a projected path.

3) shortened range due to signal blockage by the wings or fuselage.
The proper logic on unexpectedly seeing a new target close by without
have a chance to compute trajectory is to use a worse case scenario.
Granted, having the trajectory as part of the transmission would be
helpful in this instance.
And which way do you turn, when you don't know where the threat is going?


It appears that ADS-B does transmit the location as well as the
instantaneous velocity vector each second, so if you have a graphical
display, you will be able to see the orientation and physical location
of the aircraft immediately. It doesn't currently transmit any turn
rate info. I don't know if it gives you any data on rate of climb /
descent.

A basic FLARM unit, without a graphical display, won't give you any
hints of which direction the target is moving in. It will only give you
a rough idea of where the threat target is, so you have to use your eyes
and judgment to take evasive action.

I suspect that a graphical display is primarily useful to identify the
location and course info for aircraft in your area before you get into
an alarm condition. Once the alarm goes off, you should probably be
looking outside. (Not having flown with these types of units, others
probably have better insights into this).

--
Mike Schumann