2G wrote on 3/15/2021 3:31 PM:
On Saturday, March 13, 2021 at 7:59:59 PM UTC-8, Eric Greenwell wrote:
2G wrote on 3/13/2021 11:55 AM:
On Friday, March 12, 2021 at 7:27:24 PM UTC-8, Eric Greenwell wrote:
Dan Marotta wrote on 3/12/2021 10:30 AM:
Hows a self launch starting at 6,200' MSL up to 18,000' MSL followed by a distance of 350
nautical miles? That's what I'll be doing in June to relocate the Stemme from Moriarty, NM to
Rifle, CO. And it might use half a tank of gas.

Of course, I'll only do it that way if soaring conditions don't support gliding the whole way.

Dan
5J

On 3/11/21 6:18 PM, Eric Greenwell wrote:


How long a self-retrieve distance is the minimum acceptable to you?

Ok, you are not a current candidate for an electric motorglider (I knew that already :^) )

But, I'm still interested in Waremark's far smaller requirements. So far, the majority of the
pilots I've talked to that are considering moving to an electric self-launcher think 100 sm is
enough retrieve distance, and some think 50 miles is plenty. These are the people that are
willing to drive from where they live to where they want to fly. I'm one of those people,
because my wife and I like to travel in a motorhome with her sewing projects and sewing machine
in it.

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