On Thursday, August 13, 2015 at 10:29:55 AM UTC-7, John Carlyle wrote:
This extremely interesting thread started out focusing on using Stealth mode at a US Nationals contest, resulting from a feeling that Flarm was being used as a tactical device during a contest conducted under FAI rules (rules which we know encourage gaggling). During the discussion others stated their belief that non-Stealth Flarm was unsafe because it resulted in too much head down time, and several (tongue-in-cheek?) software specifications were given to improve non-Stealth Flarm leeching. The use of Flarm as a good situational awareness tool (suggested by some) seemed to be discounted because of claims of leeching.

But no solid evidence was presented that leeching really is a problem in US contests. Andy (9B) did an analysis which showed that the use of Flarm in Stealth mode resulted in worse contest finish performance by top pilots than they achieved when using non-Stealth Flarm. However, case for the use of Flarm for being used for leeching was only made anecdotally (at best) by others.

Before changes are made to the US rules regarding Flarm usage, I think it should be determined if leeching is really happening in US contests. This should be possible to determine by (1) defining quantitatively what leeching is, and (2) examining contest log files for instances meeting the definition.

A major hurdle, of course, is the definition of leeching. It's clear you're leeching if you follow someone within a mile of their tail all around the task. But, if KS passes me and I follow him 5 minutes to the next thermal where I lose him, is that leeching? How about if I happen to use 4 out of the 12 thermals he's used in a TAT, but our courses are different? What if all the thermals I use were also used by different top pilots in different classes within a few minutes of me arriving?

If leeching can only be defined by "I'll know it when I see it", then perhaps an adaptation of OLC's MeetingPoints function might help point out places to examine manually to see if leeching is occurring. But one way or another, looking for instances of leeching really should be done to determine if we really have a problem, before we go further on deciding what to do with Flarm in contests.

-John, Q3

I'm working on it.

It is entirely possible to quantify how much leaching is going on by looking at all the flight logs together. Percent of thermals, climb time and altitude gained in your own thermal versus one that was found by someone else. It is also possible to quantify which of the "borrowed" climbs would have been visible under stealth versus no stealth, by looking at the distance to the course line being flown. Lastly, it is possible to measure how much benefit is generated by having a thermal marked for you in terms of comparative climb rates for leeched versus self-sourced thermals. It's more complicated, but it may be possible to document consecutive climbs with the same glider ahead of you. Three climbs in a row is "leechier" that picking up a single marker and then going your own way. Gaggle flying makes this exercise, um, complicated.

I've gotten several PM suggestions on "leech-y" contest days to look at to aid in this effort - thank you to those who made the effort.

9B