On Sunday, April 26, 2020 at 11:59:57 PM UTC-4, Eric Greenwell wrote:
Kenz Dale wrote on 4/26/2020 10:38 AM:
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?

I don't think you should pay any attention to estimated thrust. What you want to
know is the climb rate, and that is always given by the brochure or handbook, and
most owners know about what their plane really does.

Based on 25 years of flying my ASH26E, I want at least 500 fpm at the weight I
would normally expect to fly. Don't use MTOW, as that gives you a very distorted
picture if you compare a Silent 2 Electro with a GP15, which can fly at a far
higher wing loading than the Electro.

The GP15 is rated at 865 fpm (large battery, 705 lbs takeoff weight, 8.4 lb/ft2).
That's a lot better than an Electro or miniLak, two of the gliders I considered
before deciding to buy the GP15. Compare it to my ASH26E, which is around 600 fpm
at the same wing loading, and drops off at higher density altitudes. So, the GP15
should be significantly better at places like Minden, Ely, and Parowan, as it's
electric propulsion does not lose nearly as much power at those places.

The maximum weight I expect to fly at (1010 lbs) gives a 12 lb/ft2 wing loading,
and I estimate the climb rate would be about 600 fpm.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

At 8.5 lb wing loading an ASW-24E, on engine power of 17KW, gets 300 ft/ minute.
25KW should get it to about 450. These are the numbers I expect with my electric conversion. Color me skeptical that the GP15 is going to get 600. I don't doubt it will be very good, but think projections are optomistic.
FWIW
UH