On Thursday, March 5, 2020 at 1:22:48 AM UTC-5, son_of_flubber wrote:
I'd rather take my chances on something that would accelerate the glider 0-50 knots in 50 meters with the FES running from the very start of the roll. This would increase available runway ahead for launch failure and conserve a bit of battery power. Fully automated with pilot pushing the go button.


This is really the idea right here. As we increasingly embrace self-launch eGliders, I think we'll see more and more gliders operating out of small airports without the benefit of a club. Thus, what's missing in the conversation is a consideration of the CONOPS (CONcept of OPerationS) for single-person launching.

Gliders have a major limitation in requiring a team to get a single pilot airborne. Having a catapult, which terminates before the runway begins, would get the plane airborne without requiring outside help. It could be semi-permanently installed and not require setup or teardown. The energy needed to accelerate a 300kg plane to 25m/s fits in a battery the size of a tangerine.

When the planes are reported as typically using only 20% of their packs to go fly, I feel this tells us that the major risk isn't climb out, it's takeoff.

Ignoring the risk imparted by the catapult, there are several consequent risk reductions:

1) At a 10% climb grade, a catapult on a 3000' runway would allow a plane to reach 100' with 2000' of runway to spare. An engine failure suddenly becomes a very easy straight-ahead recovery. Contrast this to a more leisurely ground roll on grass which eats up 1000' and where an engine failure at 100' is a real cause for sphincter puckering.
2) For FES-style systems, the prop can be started once off the ground, eliminating the possibility of a ground strike
3) No chance of ripping the wings off the plane due to an over-exuberant winch operation
4) Reduced chance of ground-looping on roll-out, esp. in cross-wind scenarios.
5) Everything that goes wrong goes wrong at low altitude at low speeds
6) Does not impact the runway or leave anything on or near the runway

Relatedly, any kind of automated winch or autotow system requires serious thought about what to do with the launch system once the pilot flies away. A catapult doesn't have this problem since it is installed before the threshold.

I'm not saying getting the catapult right would be easy, but it definitely has a different operational spec than a winch or autotow.