2G wrote on 3/16/2021 12:46 PM:
On Tuesday, March 16, 2021 at 5:57:05 AM UTC-7, Eric Greenwell wrote:
2G wrote on 3/15/2021 10:59 PM:
...
Those must be flat-landers that don't have to clear even taller hills, let alone mountains. Your self-retrieve "distance" vanishes the moment you have to climb to clear an obstacle. Also, the electric self-launchers like the GP15 don't specify the retrieve distance when launching at MTOW. Think of it as getting you to a safe out-landing field which is how one pilot did at Ely last summer (and he took tows).
According to figures I have for the GP15, launching to 2600' agl at 8.5lb/ft2 uses about 20% of
the available energy (big battery); launching at 12 lb/ft2 would use about 28%. So, max
retrieve range would decrease comparably from 93 sm to 84 sm. Catch a thermal sooner, stop the
motor at 2000' agl, and it'd use 22%, so wold get 90 sm with the 12 lb/ft2 launch.

How often have you had to motor home more than 90 sm?
--
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

Just a few times, but I wasn't flying a 15M glider, either. In two seasons of flying the 31Mi I have only done one precautionary 5 mile "retrieve" only because I didn't want to do a marginal glide. Again, you ignore having to climb over obstacles. What would happen if you were 70 sm out AND had to climb 3,000 ft? And, then, throw in a 20 kt headwind. I probably wouldn't even consider flying the GP15 at Ely.
The answer to the situation you propose (not enough range to get home) is a simple one: land at
the airport that makes for the shortest retrieve before the battery runs out, wait for the
towplane (or trailer) to come, go home. At Ely, that would be 60+ miles, since airports are so
far apart; at Parowan, or home, as close as 20 miles.

The main difficulty would likely be the wind, not the 3000' climb, as using a climb/glide
flight for the return would already have climbs that exceeded that.

Anyway, relax a bit, don't let your range anxiety cloud your thinking. I have 4000+ hours in a
motorgliders, much of it in places with mountains - as you know. I assure you, I have used all
that experience when considering what glider is suitable for me. After all, I did write the
book on operating motorgliders :^)
--
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

The case I cited the pilot did not come remotely close to making it to an airport: he found a small field that was landable. Retrieve was by 4WD and he got back to Ely at 2am. I considered that fortunate as one of the retrieves I went on the pilot didn't get back until more than a day later. That was the retrieve from hell which included dealing with a thunderstorm.
No, there is no way I would consider flying the GP15 out of Ely and I, too, have in excess of 4,000 hr of cross country glider time.

The Ely type of area is the major reason I chose the 8.4kWh battery for my GP15, instead of the
4.7kWh battery, as it doubles the launch+retrieve distance. The 4.7 kWh battery is more
attractive in areas with more airports, as it allows a lower minimum wing loading, a higher
wing loading with only water ballast, and is $5000 cheaper. But many pilots choose to fly in
Ely conditions with 15M gliders with ZERO self-retrieve distance, and are clever enough to
avoid retrieves from hell. I have good reason to believe I can do the same with "only" 90 miles
of retrieve distance ;^)
--
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

I was stating what I would and would not do - you, of course, have to make your own decisions. Landing out in eastern Nevada is serious business; some may chose to fly non-motorized gliders there (which, in my mind, the GP15 is) and get away with it. I see it done routinely. But I won't be one of them. It also should be noted that they are flying high performance gliders (such as the ASG29) that are heavily ballasted; the GP15 is not in this category. The glider should be able to make a 20 nm glide using no more than 3,000 ft into a headwind. This is what it takes to cross valleys in Nevada and still be above the mountains on the other side with a comfortable margin.

The GP15 has a maximum wing loading of 13.75 lb/ft2, three pounds more than, say, the 10.8
lb/ft2 of an ASH31Mi :^)

More likely, I will be flying it at 11 lb/ft2, which is 2.5 lb/ft2 higher than the ASH26E I
usually fly at Ely. And, since the GP15 L/D is almost identical to my ASH26E, I am sure I will
be even more comfortable than I am now.

--
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