On Sunday, April 26, 2020 at 12:24:31 PM UTC-7, Dan Daly wrote:
On Sunday, April 26, 2020 at 1:38:33 PM UTC-4, Kenz Dale wrote:
What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.

The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.

And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.

So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.

So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?

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

When reading the manufacturer's sales brochure, remember that the advertised climb will usually be for standard atmosphere at sea level. For gas engines, the climb rate will be significantly less if you plan to fly in the US western states in summer.