On Monday, September 14, 2020 at 9:06:08 PM UTC-7, wrote:
Hi Eric,

I agree with you in principle, that for higher output powers, things must get bigger/heavier. However, I don't think this is the case here. The 2x batteries they use (datasheet below) are spec'd for ~40 kW discharge rate. The more realistic limiting factor might be how quickly they can dissipate heat from the batteries' internal resistance out of the battery compartment, but according to Matthew, this hasn't been a problem.
http://www.front-electric-sustainer....% 20v1.25.pdf

They would have to have a bigger inverter to handle the 40% higher input current when the batteries discharge from 4.2v-3.0v, but these ~20 kW class inverters weigh nothing (1-2 kg) compared to the batteries.
https://www.mgm-compro.com/brushless...e-controllers/

I'd be interested to hear FES's reasoning, or other owners' experiences on why the power dropoff is so significant.

Patrick Grady

I am amazed that this is even being speculated upon. How hard is it to do FES climb performance runs? You simply take off and climb until the battery (or controller) shuts down. Then, you repeat this test 5-10 times. Then you repeat that test for a different glider. Why isn't this data readily available? I can only guess that this test has been done and it is not favorable to FES.

There are many FES installations out there - if you have one, do this test and report the results.

Tom