My September 2017 visit to GP Gliders

Digging through some old FaceBook postings, looks like Jeta SN 0001 was
issued a CoA from the Slovak Federation of Ultralights on May 30 2018
with a MTOM of 525 KG.

They got that weight by claiming it was 51% homebuilt. Wow.

kinsell wrote on 8/20/2020 6:11 AM:
Digging through some old FaceBook postings, looks like Jeta SN 0001 was issued a
CoA from the Slovak Federation of Ultralights on May 30 2018 with a MTOM of 525 KG.

They got that weight by claiming it was 51% homebuilt.** Wow.

Was the word used really "homebuilt"? Regardless, they built the glider, they
aren't going to sell it, they plan to destroy it for strength testing, and are
expecting the regulations to allow 525 kg in a year or two - I don't see the "wow"
in that claim. And maybe that's SOP for the Slovak authorities; after all, here in
the US we routinely get CoAs in the "Experimental" category for certified gliders.

--
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 8/20/20 12:50 PM, Eric Greenwell wrote:
kinsell wrote on 8/20/2020 6:11 AM:
Digging through some old FaceBook postings, looks like Jeta SN 0001
was issued a CoA from the Slovak Federation of Ultralights on May 30
2018 with a MTOM of 525 KG.

They got that weight by claiming it was 51% homebuilt.Â*Â* Wow.

Was the word used really "homebuilt"? Regardless, they built the glider,
they aren't going to sell it, they plan to destroy it for strength
testing, and are expecting the regulations to allow 525 kg in a year or
two - I don't see the "wow" in that claim. And maybe that's SOP for the
Slovak authorities; after all, here in the US we routinely get CoAs in
the "Experimental" category for certified gliders.


Yes, someone from Belgium asked how they got 525 kg. "Did you apply for
a 51% homebuilt certification?" GP replied "Basically yes".

This is the same glider they put together in a hurry for Sebastian, and
was later used for customer demo flights. I think a legitimate CoA
would have been appropriate. Perhaps that is just how the Slovakian
authorities do business. I think it's clear GP went shopping for a
rather lenient agency to deal with.

On Wednesday, August 19, 2020 at 10:12:43 PM UTC-7, jld wrote:
"My idea of evidence is things like the ultimate breaking strength of a wing taken to destruction (which you must do for EASA certification)"
It is up to GP to negotiate with DULV (Germany), but ultimate load test will have to be performed and DULV will probably ask to go to rupture since it is a brand new design. DULV also has to witness this type tests.
I was skeptical about UL for a long time until I took the time to dig into the different national regulations and realize most countries had very high standards.
if you can read German, here is a link to LTF-UL which defines requirements for approval.
https://www.dulv.de/sites/default/fi...V%201.22_0.pdf
There is an older version in English available from the net: https://drive.google.com/file/d/0BzP...ew?usp=sharing

That is just an organization and training manual.

second link is OK but first link should point to : http://www.dulv.de/sites/default/fil...I_446_19_1.pdf

"regulations to allow 525 kg in a year or two"
Maybe some countries could increase MTOM (up to 600 kg) but don't forget that the glider must still demonstrate a certain Vso at that MTOM.
Given the small surface of the GP15 (7,78 m2), the low relative thickness of the airfoil (required to get to high L/D), it is going to already be excellent if they can meet the 45 Kts Vso limit at 470 Kg (which is 60 kg/m2).
If you register outside EU and the 45 Kts Vso limit does not apply, going to higher WL/Vso means climbing at IAS above 60 kts.

You can always increase WL to improve your task speed but this is not going to help much if you start from a bad polar curve.
If they can get close to their polar and achieve 2 m/s sink rate at 200 km/h with 45 kg/m2 WL, then GP15 will be an excellent cruiser.

One would think that glider structure would be the most important factor when setting the MTOM, but we clearly are not talking about certified glider and it doesn't matter.

krasw wrote on 8/21/2020 4:36 AM:
One would think that glider structure would be the most important factor when setting the MTOM, but we clearly are not talking about certified glider and it doesn't matter.

I think it is the other way around: the designer chooses a MTOM based on many
interacting factors, such as required minimum stall speed, the aspect ratio and
airfoil needed to achieve the desired soaring performance (including the range of
wing loadings). Once a MTOM is selected, the structure is designed to support it;
of course, it is an iterative procedure, as the structure weight may then
require/allow a change in the other factors, or even selecting a different MTOM.

--
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

"One would think that glider structure would be the most important factor when setting the MTOM"
I did not look at CS22 and LTF-UL side by side but for the validation methodology they seem to be very close.
In both regulations structure is designed to be capable of limit/ultimate loads at MTOM.
And in both regulations you need to demonstrate Vso at MTOM.
Therefore if you run out of lift coefficient with flaps setting (which has nothing to do with structure strength), you might have structural margin but be forced to reduce MTOM.
If GP can demonstrate 45Kts Vso at 470kg and demonstrate the structure is capable of 5,3g at 470kg, this will be excellent and no different from what CS22 would require.

On Wednesday, August 19, 2020 at 8:03:49 PM UTC-7, wrote:
I fly NM with water regularly, both in the wings and the tail. I generally fly dry in the early spring when temperatures are still sub freezing at 17,000+ and start filling up during the summer. No problems so far, but if I do decide to use water in the tail tank when it's really cold, I can always add some propylene glycol antifreeze. Several of our more manic pilots do that and it seems to work well.
Not telling you what to do but in the Truckee/Minden area it is routine to fill the tanks and fly all day at sub freezing temps - probably 4 - 5 hours below freezing. We did have one case of the tail tank dump valve on a DuoDiscus leaking, which dribbled water onto the rudder hinge and controls, which froze the rudder in position. Pilot flew carefully home on a 200 mile final glide, descending through warmer temps and it melted enough to break loose.