$1 billion BMS Ooops...

India November wrote on 3/18/2021 8:50 AM:
On Wednesday, March 17, 2021 at 9:00:04 AM UTC-4, Eric Greenwell wrote:
2G wrote on 3/16/2021 10:17 PM:
On Tuesday, March 16, 2021 at 3:48:54 PM UTC-7, Eric Greenwell wrote:
2G wrote on 3/16/2021 12:46 PM:
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 forgot to respond to the "non-motorized" portion of your remarks. Perhaps you will be
surprised (or at least interested) to learn the GP15 climb rate from the runway on a typical
flying day at Ely will be nearly double the climb rate of my ASH26E. A major reason is the
electric motor still has the same power at 9000' DA, while the carbureted Wankel has lost about
18%. The better climb on takeoff in high density altitudes was an important factor in my
choice. It's not important at Ely, but it is at Parowan, and a few other places I've flown (or
wanted to fly but decided it was marginal).

Now, I realize you think 90 miles of self-retrieve is the same as zero miles, but that view is
not shared by every "pure" glider pilot out there!
--
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

Where do you get 90 miles? GP's website doesn't list it. Their numbers are dry - if you can trust them (nobody's verified them and they may be estimated for all you know). The self-retrieve distance they list for the B battery is 100km (63 miles) with a 800m launch with no ballast. Now add ballast, add an 3,000 ft obstacle and a 20kt headwind (all realistic conditions at Ely) and refigure what the hypothetical retrieve distance is, if any.

Take a look at this page: https://www.gpgliders.com/offer/gp-15-e-se-jeta Here's the pertinent
portion:

Usable battery capacity: 9,23 kWh
Operational battery capacity: 8,36 kWh (10% buffer to preserve battery life)
Weight: 52 kg (115 lb)

Motor glider’s self-launch and climb performance on a single charge, equipped with “B” battery
pack (TOW: 320 kg [705 lb]):

5 x take-off and climb to 800 m (2 625 ft) altitude
or 1 x take-off and climb to 800 m (2 625 ft) altitude + 150 km (93 mi) range
or 1 x take-off and total climb to 4 000 m (13 120 ft)
Max. climb rate: 4,4 m/s (8,55 kts)
Ground-roll take-off distance: 180 m (197 yards)

Because the wing area is 84 ft2, the 705lb TOW = 8.4 lb/ft2, about the same wing loading I have
in the ASH26E, unballasted.

Eric, I'm curious about the wing loadings quoted for the Jeta from 7,58-13,72 lb/ft^2. For the conditions I fly in Ontario where thermals average 2 to 4 kts, I see these heavy wing loadings as a disadvantage even in a flapped ship. I fly my D2 mostly dry at less than 6 lb/ft^2. What am I missing?
Ian IN

Are you really sure of that wing loading? The numbers on the Schmepp site suggest a wing
loading for a pilot 165lb pilot with a 15 lb parachute is over 6.5 lb/ft2. But even it's 7
lb/ft2, it is definitely a lighter wing loading than the newer flapped 15m gliders; eg, the new
AS33-15M has a minimum wing loading of 8.5 lb/ft2, and that is without a motor.

As Dave mentions, span loading (weight/span^2) is a better indicator of thermalling ability,
and since the Discus 2A and the Jeta have the same span and about the same minimum weight
(using the weight from the Schmepp site), I'd expect them to thermal the same. It may seem
strange a lighter wing loading doesn't help more, but aspect ratio matters: the Discus has a 22
ratio, while the Jeta has 29.

And, the Jeta has a motor, so even if it did not thermal quite as well as your Discus, you'd
still have fewer landouts in it than the Discus 2. Plus, you'd love the extra speed the higher
wing loading allows during the cruise, at least 15% faster (and with a higher glide ratio, due
in part to the higher aspect ratio).

--
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

On Thursday, March 18, 2021 at 5:42:22 PM UTC-4, Eric Greenwell wrote:
India November wrote on 3/18/2021 8:50 AM:
On Wednesday, March 17, 2021 at 9:00:04 AM UTC-4, Eric Greenwell wrote:
2G wrote on 3/16/2021 10:17 PM:
On Tuesday, March 16, 2021 at 3:48:54 PM UTC-7, Eric Greenwell wrote:
2G wrote on 3/16/2021 12:46 PM:
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 forgot to respond to the "non-motorized" portion of your remarks. Perhaps you will be
surprised (or at least interested) to learn the GP15 climb rate from the runway on a typical
flying day at Ely will be nearly double the climb rate of my ASH26E. A major reason is the
electric motor still has the same power at 9000' DA, while the carbureted Wankel has lost about
18%. The better climb on takeoff in high density altitudes was an important factor in my
choice. It's not important at Ely, but it is at Parowan, and a few other places I've flown (or
wanted to fly but decided it was marginal).

Now, I realize you think 90 miles of self-retrieve is the same as zero miles, but that view is
not shared by every "pure" glider pilot out there!
--
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

Where do you get 90 miles? GP's website doesn't list it. Their numbers are dry - if you can trust them (nobody's verified them and they may be estimated for all you know). The self-retrieve distance they list for the B battery is 100km (63 miles) with a 800m launch with no ballast. Now add ballast, add an 3,000 ft obstacle and a 20kt headwind (all realistic conditions at Ely) and refigure what the hypothetical retrieve distance is, if any.

Take a look at this page: https://www.gpgliders.com/offer/gp-15-e-se-jeta Here's the pertinent
portion:

Usable battery capacity: 9,23 kWh
Operational battery capacity: 8,36 kWh (10% buffer to preserve battery life)
Weight: 52 kg (115 lb)

Motor glider’s self-launch and climb performance on a single charge, equipped with “B� battery
pack (TOW: 320 kg [705 lb]):

5 x take-off and climb to 800 m (2 625 ft) altitude
or 1 x take-off and climb to 800 m (2 625 ft) altitude + 150 km (93 mi) range
or 1 x take-off and total climb to 4 000 m (13 120 ft)
Max. climb rate: 4,4 m/s (8,55 kts)
Ground-roll take-off distance: 180 m (197 yards)

Because the wing area is 84 ft2, the 705lb TOW = 8.4 lb/ft2, about the same wing loading I have
in the ASH26E, unballasted.
Eric, I'm curious about the wing loadings quoted for the Jeta from 7,58-13,72 lb/ft^2. For the conditions I fly in Ontario where thermals average 2 to 4 kts, I see these heavy wing loadings as a disadvantage even in a flapped ship. I fly my D2 mostly dry at less than 6 lb/ft^2. What am I missing?
Ian IN

Are you really sure of that wing loading? The numbers on the Schmepp site suggest a wing
loading for a pilot 165lb pilot with a 15 lb parachute is over 6.5 lb/ft2.. But even it's 7
lb/ft2, it is definitely a lighter wing loading than the newer flapped 15m gliders; eg, the new
AS33-15M has a minimum wing loading of 8.5 lb/ft2, and that is without a motor.

As Dave mentions, span loading (weight/span^2) is a better indicator of thermalling ability,
and since the Discus 2A and the Jeta have the same span and about the same minimum weight
(using the weight from the Schmepp site), I'd expect them to thermal the same. It may seem
strange a lighter wing loading doesn't help more, but aspect ratio matters: the Discus has a 22
ratio, while the Jeta has 29.

And, the Jeta has a motor, so even if it did not thermal quite as well as your Discus, you'd
still have fewer landouts in it than the Discus 2. Plus, you'd love the extra speed the higher
wing loading allows during the cruise, at least 15% faster (and with a higher glide ratio, due
in part to the higher aspect ratio).
--
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

Interesting, thanks Eric. And yes, I meant 6.8ppsf min loading in my D2. What was I thinking!
Ian IN