Minimum acceptable self-launch climb rate

Thanks, Dan, you knocked it out of the park with this answer.

CS 22 - Certification Specifications for Sailplanes and Powered Sailplanes - has standards.

"CS 22.51 Take-off
(a) For a powered sailplane the take-off distance at maximum weight and in zero wind, from rest to attaining a height of 15 m must be determined and must not exceed 500 m when taking off from a dry, level, hard surface. In demonstration of the take-off distance, the powered sailplane must be allowed to reach the selected speed promptly after lifting off and this speed must be maintained throughout the climb.
(b) The selected speed must not be less than;
(1) 1·3 VS1, or
(2) any lesser speed, not less than 1·15 VS1, that is shown to be safe under all reasonably expected operating conditions, including turbulence and complete engine failure.
CS 22.65 Climb
(a) For a powered sailplane the time for climb from leaving the ground up to 360 m above the field must not exceed four minutes with:
(1) not more than take-off power;
(2) landing gear retracted;
(3) wing-flaps in take-off position;
(4) cowl flaps (if any) in the position used in the cooling tests.
(b) For self-sustaining powered sailplanes, the maximum altitude that can be sustained must be determined."
https://www.easa.europa.eu/sites/def...S-22_Amendment 1 revised.pdf