But I also pan to my destination as well.
This is why these discussions are so useful! It isn't a given that a ring like this on the map is available when panning. So knowing that is a use case is very helpful.
The math on the distances we are dealing with is useful to frame the discussion about when the ring will be shown though. If you are in a 150 knot airplane, a 30 minute fuel reserve is 75 NM. This will just show up on a 80NM zoom screen. By default, we turn off all the airports at 120NM, so just one more click and you don't have airports shown except the ones in your flight plan, yet you are almost out of fuel.
If you're in an RV at 170 knots ground speed, burning 9 GPH, and have 20 gallons on board, that ring is 378 NM in radius. So you need to zoom to 500NM to find it. Then, if you pan to your destination that is 300 NM away, you will hardly be able to see the fuel ring on the 80NM range, and it will be missing at the 50 and lower zooms. If your fuel flow rate changes by even 0.1 GPH, the ring moves 5 miles. If the wind changes by 1 knot it moves 3NM. When you're zoomed out to 80NM, an airport icon is about 5NM wide on the map.
Thus, the challenge for using it to plan long distance flights is that to actually see your ring you need to zoom way out, find it, then zoom in to an edge of it near where you are going and find the local airports that are inside it.
The glide ring doesn't really have this issue. Most piston powered aircraft have glide ratios of less than 15:1. Thus, at 12,000' AGL, they can glide less than 30 NM. This means a glide ring is visible at most commonly used zoom ranges. By the time your fuel ring shows up on this screen in the same airplane, you're deep into your VFR reserves (12 mins left at 150 knots). When your fuel ring gets inside your glide ring, you should probably start practicing the use of the glide ring....
So that's why we see the trade-off here. Glide rings are great for close-in use, and they show the offset of wind which can make a huge difference to where you can land in the next 6 minutes. For fuel though, if you're planning for your current winds for the next 3 hours and 500NM, and trying to decide on airports 50NM apart, you're fooling yourself.
Don't take any of this as push-back on doing it. Just trying to find out how we can make it most useful! Is there a more useful implementation like highlighting airports that are within your fuel range so that you can tell this even when zoomed in to an airport that is 300NM away while your fuel state is 500NM? What about showing fuel for all your points in the flight plan page? What about an option to shade the map or airports in areas that are outside your fuel range so it's clear your're looking outside your range?
