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They are calculated, and also a bit out of date, as better batteries are now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