Best option for electric self starting glider

wrote on 4/10/2020 9:01 AM:
On Friday, April 10, 2020 at 4:46:52 PM UTC+1, Magnus wrote:
On Wednesday, April 8, 2020 at 5:14:54 PM UTC+2, wrote:
Hello Magnus,

I can't respond to flight characteristics of the two self-launchers you mentioned (LAK-17C and GP-Gliders JETA). But, I can say that I sat in a JETA and also have JETA serial number 5 on order.

The JETA MTOG, per the provisional flight manual, is 525KG (1157 lbs). Below are the advertised self-launch numbers with the larger battery:

a) 5 x takeoff and climb to 800 m (2,600 feet) altitude, or
b) 1 x takeoff and climb to 800 m altitude + 150 km (80 nm) autonomy, or
c) 1 x takeoff and total climb to 4 500 m (14,700 feet)
d) my number: aero tow and 185 km (100nm) autonomy based on 20 nm/launch.

Climb rate: 3,7 m/s (728 fpm or 7.2 knots)

takeoff distance: 180 m (590 feet)

I visited the GP-Glider factory near Krosno, Poland (jokingly to make sure that they weren't operating out of a tent). I was happy that they were doing things correctly. A visit to the LAK factory would have given me a balanced experience, but I was not able to do that.

Raul Boerner
LS-6BWL

Hi Raul,
When is your delivery of the Jeta? I am really interested in your experiences. Where are you flying?
According to the max wing loading of 60/37 kg/m2 the MTOM is below 475/285kg UL with a wing area of 7.77m2 - this also is indicated on the website. I suppose the take-off distance is without ballast but it is still good. How/where do you register it as UL?

Absent from those endurance/climb figures is the weight at which these are achieved, which is going to have a huge impact on the figures. Does anyone know the weight?
And are they are calculated or experimentally tested?

The quoted numbers are likely based on..

220kg empty weight + 21kg for large battery + pilot (75 kg? no mention) = 316 kg

The weight affects the climb proportionately, but I think the reduction in range
is not as much; mainly, the battery charge is not quite as much after the climb to
800 m. Note: the Vne is 300 kph, not the 275 I saw mentioned elsewhere.

The specifications are on this page:

https://www.gpgliders.com/offer/gp-15-e-se-jeta

They are calculated, and also a bit out of date, as better batteries are now
supplied, and also some changes in the controller, and aerodynamic refinements.


--
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

kinsell wrote on 4/9/2020 1:38 PM:
On 4/9/20 12:20 PM, Eric Greenwell wrote:
Magnus wrote on 4/8/2020 7:11 AM:

Where do you find the information about the LAK 17C? I can not find any, not
even on the LAK site.

My dream is for a smaller, lighter, simpler self-launcher, but with the same
performance as my ASH26E. I considered the miniLak, AS34, and the GP15. The
miniLak did not have enough wing loading, L/D, and powered range for the
Nevada/Utah area I often fly in, and the AS34 was just as big and heavy as the
ASH26E. So, I have ordered a GP15 for delivery next year, as it promises the
best compromise. It will be a few months, maybe longer, before we know if it
begins to fulfill it's promise.


Typing "lak 17c" into Google brings up multiple results, including an Oct 2018
test flight in FB.* Also been discussed on R.A.S.

I did that, and didn't find very much information. If it's not on the factory
site, it does not seem like a good choice to consider by a pilot that wants a
glider for next year's season. But, given it's an 18 m glider, it is unlikely to
meet my "smaller, lighter, easier) criteria.
--
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 4/10/20 11:55 AM, Eric Greenwell wrote:
kinsell wrote on 4/9/2020 1:38 PM:
On 4/9/20 12:20 PM, Eric Greenwell wrote:
Magnus wrote on 4/8/2020 7:11 AM:

Where do you find the information about the LAK 17C? I can not find
any, not even on the LAK site.

My dream is for a smaller, lighter, simpler self-launcher, but with
the same performance as my ASH26E. I considered the miniLak, AS34,
and the GP15. The miniLak did not have enough wing loading, L/D, and
powered range for the Nevada/Utah area I often fly in, and the AS34
was just as big and heavy as the ASH26E. So, I have ordered a GP15
for delivery next year, as it promises the best compromise. It will
be a few months, maybe longer, before we know if it begins to fulfill
it's promise.


Typing "lak 17c" into Google brings up multiple results, including an
Oct 2018 test flight in FB.Â* Also been discussed on R.A.S.

I did that, and didn't find very much information. If it's not on the
factory site, it does not seem like a good choice to consider by a pilot
that wants a glider for next year's season. But, given it's an 18 m
glider, it is unlikely to meet my "smaller, lighter, easier) criteria.


It's on the Blanik America website with base price of 99.500 euros.
Nice list of accessories. I saw a claim it was just a 17B-FES with a
new wing profile, if that's true then you would have the weight info.

http://home.nwi.net/~blanikam/ba/lak_prices.htm

Given GP's record in delivering gliders, I would take their promised
delivery dates with a huge grain of salt.

-Dave

GP are getting their act together and increasing their manufacturing footprint.
We should finally see GP's coming out of the factory door.

Even if there is a little bit more complexity with a pylon mounted motor, there are clear advantages over the FES solution.
- more powerful motor
- better cooling
- better prop efficiency
- no prop strike risk
Another advantage of GP with large batteries is that, beside the larger energy capacity, the cells are discharged at lower amps rating and therefore run cooler.

The climb performance seems to be in line with flight test results.
As discussed before the published climb perf are without WB. Therefore TOM 320-330 kg. Even when flying empty, the typical WL will be ~42 kg/m2 which is already nice.
GP has made some good choices:
- light weight to allow very good electric climb performance (climb rate and altitude gain)
- high aspect ratio/low wing surface to achieve high L/D and higher WL. Maybe Max L/D will be a little bit less than 18m like ASH26 or DG800, but the L/D above 150 km/h should be better.

BTW, you need to add fixed ballast to get to 525 kg MTOM.

Regards,
JL

I looked at your email address website (sculptressfashions.com) and
didn't see anything aircraft related.Â* Did I miss something?

Regarding starting your motor or engine at 200' agl dismisses the
possibility that it can start, let you pitch up, and then fail, possibly
catastrophically.Â* I like your dream of flying deep into tiger country,
but I've had a couple of engine failures (6 to be exact) and so I don't
trust any engine to prevent a land out.Â* If I'm over an airport, I'll
descend to 1,000' before starting the engine.Â* The further out I am, the
higher I will start.

On 4/9/2020 8:32 PM, wrote:
On Thursday, April 9, 2020 at 4:46:57 PM UTC-7, wrote:
but this would be very easy to do with electric.

I love it when armchair aircraft designers tell us something is "very easy."
"armchair aircraft designers"... lol. I'll have to show you some of my more challenging, and very much finished, aerospace projects someday

I'm currently installing a Rotax on my ship. Electric is interesting, and I can certainly understand why it appeals to many. I personally favor the increased range of gasoline over the cleanliness and convenience of electric. Others will have different preferences. Either option can eliminate tows and retrieves, which is all well and good. However, a motor glider that "will start" can do a lot of things that a motor glider that "will probably start" cannot.

It would be a game changer if I could "safely" fly deep into unlandable terrain, or ridge soar the lip of the grand canyon. I'd love to plan some epic soaring safaris to rugged areas of Alaska, or make first flights in magnificent places. It would also be a whole new ballgame if I could reduce my restart altitude to something like 200ft. That sounds crazy until you figure out that's about 90 seconds at typical sink rates. If it takes only 10 seconds to transition to a powered climb, then 90 seconds provides plenty of margin.

The first electric motor gliders borrowed the retractable mast from their gasoline counterparts. Later, folks figured out that the smaller electric motor could fit in the nose. I think it's only a matter of time before people discover that we can use more than one motor, as is the trend for VTOL. Perhaps I'll get around to this at some point but I currently have a couple of more pressing crazy projects on my plate.



--
Dan, 5J

On Friday, April 10, 2020 at 6:30:28 PM UTC-7, Dan Marotta wrote:
I looked at your email address website (sculptressfashions.com) and
didn't see anything aircraft related.Â* Did I miss something?

Regarding starting your motor or engine at 200' agl dismisses the
possibility that it can start, let you pitch up, and then fail, possibly
catastrophically.Â*

Dan, I looked up your email address at earthlink.net and didn't see anything about aviation either Feel free to check out motorcyclepilot.com for some of my cooler aviation products. My company primarily mods special mission aircraft and I've also produced tooling for a number of consumer products, such as the shapewear you found. Lately, I've been working mostly with airplanes, motorcycles, and boobs. It's a fun job, but somebody has to do it!

Yes, I'm proposing that it is possible to dismiss off field landings. Don't forget that airlines safely fly 4 billion passengers each year over unlandable terrain and oceans. There are multi-engine airplanes, helicopters and ultralights... it's not science fiction to put a second sustainer on a motor glider. Besides, we don't need to match the reliability of an airliner; we only need to achieve a level of risk that's appropriate for the sport of cross-country soaring.

Let's assume that a modern FES system has a 1 in 200 chance of failure. I would expect pilots to encounter a failure every few years and it sounds like this has been your experience. Now, if you can install a second sustainer with the same reliability (1 failure in 200), then the chance of a double failure works out to 1 in 40,000. If the failure rate of each sustainer happens to be more like 1 in 400, then the chance of a double failure rate would be only 1 in 160,000!

To put this into perspective, the Soaring Safety Foundation estimates that soaring pilots have accidents every few thousand hours. Amatuer Built airplanes, such as the ones that I fly, have a fatality every 18,000 hours. I would personally feel very comfortable making occassional low saves and trusting a twin propulsion system with a failure rate of 1 in 160,000. Instead of worrying about a double motor failure, I'd be far more concerned about stall/spin while soaring at low altitude.

Also consider that off field landings are risky business. Preparing for off field landings is great, but avoiding them is all the better. If you could eliminate 99.75% of off-field landings via reliability, then I think you'd see an overall safety gain, even if some of saves happened at low altitude..
Indeed with increasing reliability, a threshold exists at which it would be safer to attempt a LOW save in an EXTREMELY realiable motor glider, than it is to attempt a 1,000ft save in a traditiol motor glider. I've done some preliminary spreadsheet models and I believe this objective is feasible for a a sailplane with two sustainer systems.

I'm interested in this concept for adventure soaring. However, there are also obvious competitive advantages with being able to stray far from landing fields, or safely restart from 200ft.

On Saturday, April 11, 2020 at 7:46:26 AM UTC+1, wrote:
On Friday, April 10, 2020 at 6:30:28 PM UTC-7, Dan Marotta wrote:
I looked at your email address website (sculptressfashions.com) and
didn't see anything aircraft related.Â* Did I miss something?

Regarding starting your motor or engine at 200' agl dismisses the
possibility that it can start, let you pitch up, and then fail, possibly
catastrophically.Â*

Dan, I looked up your email address at earthlink.net and didn't see anything about aviation either Feel free to check out motorcyclepilot.com for some of my cooler aviation products. My company primarily mods special mission aircraft and I've also produced tooling for a number of consumer products, such as the shapewear you found. Lately, I've been working mostly with airplanes, motorcycles, and boobs. It's a fun job, but somebody has to do it!

Yes, I'm proposing that it is possible to dismiss off field landings. Don't forget that airlines safely fly 4 billion passengers each year over unlandable terrain and oceans. There are multi-engine airplanes, helicopters and ultralights... it's not science fiction to put a second sustainer on a motor glider. Besides, we don't need to match the reliability of an airliner; we only need to achieve a level of risk that's appropriate for the sport of cross-country soaring.

Let's assume that a modern FES system has a 1 in 200 chance of failure. I would expect pilots to encounter a failure every few years and it sounds like this has been your experience. Now, if you can install a second sustainer with the same reliability (1 failure in 200), then the chance of a double failure works out to 1 in 40,000. If the failure rate of each sustainer happens to be more like 1 in 400, then the chance of a double failure rate would be only 1 in 160,000!

To put this into perspective, the Soaring Safety Foundation estimates that soaring pilots have accidents every few thousand hours. Amatuer Built airplanes, such as the ones that I fly, have a fatality every 18,000 hours. I would personally feel very comfortable making occassional low saves and trusting a twin propulsion system with a failure rate of 1 in 160,000. Instead of worrying about a double motor failure, I'd be far more concerned about stall/spin while soaring at low altitude.

Also consider that off field landings are risky business. Preparing for off field landings is great, but avoiding them is all the better. If you could eliminate 99.75% of off-field landings via reliability, then I think you'd see an overall safety gain, even if some of saves happened at low altitude.
Indeed with increasing reliability, a threshold exists at which it would be safer to attempt a LOW save in an EXTREMELY realiable motor glider, than it is to attempt a 1,000ft save in a traditiol motor glider. I've done some preliminary spreadsheet models and I believe this objective is feasible for a a sailplane with two sustainer systems.

I'm interested in this concept for adventure soaring. However, there are also obvious competitive advantages with being able to stray far from landing fields, or safely restart from 200ft.

Cargo pods, handbags and ugg boots, that's an eclectic mix - I think that website has been hacked? See http://motorcyclepilot.com/contact.php (caution advised)

Note that at LAK17C max power is 30kW. With such power climb performance are very good as there is no pylon drag.

The propulsion efficiency has much more direct effect than pylon drag.
In fact, for Takeoff and climb performance, the overall glider drag has secondary effect compared to aircraft weight and available thrust.
Without fuselage interference and opportunities for larger props, the pylon mounted motor provides a significant efficiency advantage. This has a direct effect on climb performance in terms of climb rate and altitude gain.
Running large battery packs, beside running cooler, also provides better energy efficiency and installing large batteries in the wing reduces overall structure weight and provides better flying handling characteristics due to CG.

FES is a nice solution, especially for retrofit of existing gliders.
For a brand new design, there are opportunities for better optimizations.
Is GP at the optimum, probably not (yet:-), but they have certainly made good design decisions for both teh glider and the propulsion.

This thread gets better and better!

"obvious competitive advantages with being able to stray far
from landing fields, or safely restart from 200ft"

Not sure about a "competitive advantage" but you must be in
the running for a Darwin Award. Obviously Covid-19 holds no
fears for you.