From time to time at the flying field I’m frustrated by my heli not arming, even after waiting long enough for a good satellite fix. I know I ccould set LOG_DISARMED to 1 or 2 to create logs prior to arming, the penalty being a much bigger log file. Is there any chance there could be an extra configuration that would record pre-arming data, but then delete it immediately arming is achieved and continue logging the flight as normal?
What problem are we trying to solve?
It seems like your complaint is a lack of real-time information in the field regarding pre-arm status, but your proposed fix is one that would optionally allow post-event forensics after a failure to arm (which is incongruous).
What are you using in the field to monitor pre-arm status? Do you use any GCS or RC handset with telemetry available?
You’re right; it’s the lack of pre-arm information. But I disagree about the incongruity, for knowing what’s going on might allow me to make some adjustments after the event – i.e. back in my workshop. The scenario is that sometimes I power up and the copter doesn’t arm even though the GPS LED tells me it’s got a fix (but, admittedly, maybe not good enough fix for Arducopter) and several minutes have elapsed. So I disconnect the battery, sit down and have a cup of tea and a natter, then power up again and the copter arms within about a minute, as expected, and flies in stabilised, alt-hold, pos-hold, and RTL modes without any glitch.
I use FrSky Taranis Tx and FrSky receivers. Some time back I was told about some telemetry that can link Arducopter to my Tx, but I can’t remember what it was and I couldn’t figure out how to install/configure it. Also I feel more comfortable making adjustments in the workshop, rather than in the field.
I think the fixes are these:
Most easily:
Enable LOG_DISARMED for a few sessions out in the field. When you have one of those prearm issues, download the most recent log and share it. I suspect you simply need to relax the HDOP requirement, and all will be well forever.
Slightly more complex but arguably most correct:
Bring a laptop to the field and monitor the prearm checks over radio telemetry to see which one is failing most frequently.
Most complex (to configure), but most easily employed on a routine basis:
Use the Yaapu telemetry script, which sounds like it is very likely compatible with your RC hardware.
I’m not sure we want to enable a feature where we auto-delete logs of any sort.
Thanks for your reply Yuri_Rage. I’ll follow your ‘Most easily’ suggestion and see where it takes me 
I’m not keen on taking a laptop to the field because it’s another thing to carry and we have to park over 100yds away from the pits.
Yaapu was what people had suggested to me a while back (can’t remember why), and is compatible with my Taranis, but I couldn’t get my head around how to set it up.
It would be worth working thru Allan. Rare that I need a Ground Station on-site and it gives’s you most of what you need.
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