The glider discharge currents are nowhere near 50-80 times capacity, but more in the 4C range,
so the number of cycles should be much higher; also, you would rarely go to full discharge
(more like 20%-40%) during each flight, which also increases cycle life substantially.

Yes... and no. If you're only going for a single launch, then ideally your pack would be at 20% SoC at the end of the launch. After all, the reserve capacity isn't valuable if you never use it. Assuming 600fpm, and a 2k launch, that yields about 15C as the target discharge rate.

The reason why we have big battery packs in eGliders right now is because 15C is too much discharge for Li-ion technologies. So the pack manufacturers have to make them 3x bigger to get the current to a 4-5C discharge rate. The manufacturers now have a big, heavy, and expensive pack in the plane, but with a lot of reserve capacity. All is not lost, though-- that reserve capacity can be used for sustainer or saves.

Currently, batteries are improving extremely rapidly in ways which are highly relevant to eGliders. The energy density might not be going up very quickly, but we simply don't need it. At 200-250kWhr/kg, we need about 1kg of battery to launch 30kg of glider, so doubling the energy density is only going to shave a few kg off the overall weight. We're already in the realm of diminishing returns at that point.

What we need is power density in a (fire) safe package:

* Li-ions are quite safe, and LiPos are reasonably safe. LiPos are getting safer by the day.
* LiPos far exceed the required power density, and Li-ions are getting there.

As it's not a moonshot to ask for a mild convergence of two sibling technologies, I feel we'll continue to see tangible improvement in the next couple years.We might not see that in the mainstream manufacturers, as they've already locked in their packs and will not be able to change for the foreseeable future, but small projects such as in the aforementioned eGlider group are iterating rapidly.

On Saturday, March 6, 2021 at 10:13:38 AM UTC-5, Herbert Kilian wrote:
Still, you are lucky to get 50-100 cycles out of the now listed 50-80C LiPo batteries we fly in RC. Nothing on the horizon that even promises a doubling of capacity. Give me a self-launcher that replaces the tow plane (2k-3k launch) and lets me replace the low cost but fire-safe batteries easily. I'd be interested.

This is one of the open questions. Do we really want to have an hour cruise left over, or is the biggest value just getting in the air at all?

I predict that people just want to launch. If we can use 8-10kg of 20C LiPos to get to 1k', with 5 minutes of cruise left over, and a freshly charged pack waiting on the ground, then it's basically a winch launch. And as those of us who have flown in the EU know, winch launches are great ways to get flying.