My September 2017 visit to GP Gliders

2G wrote on 8/18/2020 10:10 PM:
On Tuesday, August 18, 2020 at 7:26:51 PM UTC-7, Eric Greenwell wrote:
2G wrote on 8/18/2020 3:07 PM:
On Tuesday, August 18, 2020 at 1:49:35 PM UTC-7, andy l wrote:

GP doesn't just claim "lower weight," but "far lower weight" than other gliders, but w/o any evidence to support this claim. The only real evidence I have seen is that Sebastian Kawa was very unhappy with the glider GP delivered to him and switched gliders at the last minute. Kawa also had a propulsion failure while flying a GP-14 in Italy, yet GP gliders makes this bizarre claim on their website:

"The motor can be deployed and running at full power within five seconds providing confidence in the event of when a ‘low save’ is on the cards."

I guess Sebastian didn't get the memo on how reliable GP propulsion systems are. You are certainly welcome to accept all of GP's claims w/o any evidence, but I won't. And I certainly wouldn't send them six figures in cash for it.
The motor can indeed be deployed and running in 5 seconds, and with considerable
confidence. The original mechanical mast switch, external to the mast, was deemed
too vulnerable to damage after Kawa's accident with the prototype glider. It was
replaced with two redundant, buried solid state switches to prevent a repeat of
the problem. You've had a similar switch failure on your Schleicher glider, but
were lucky that it eventually worked after repeated attempts. Other Schleicher
owners have also experienced mast switch failures, but Schleicher still uses the
external mechanical switches. Maybe they didn't get the memo?
--
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

I DIDN'T have a similar failure - in fact, I had no failure at all. The switch was in perfect working order, the only explanation was flying a little too fast for the mast to deploy fully. In any event, this has NOTHING to do with the outrageous claims being made by GP Gliders. No one should depend upon propulsion to start in an emergency.

My main point was we shouldn't judge a product on a failure in a prototype a
couple years ago, as there have been many changes made since then.

My apologies - I did not realize you'd concluded it was pilot error that caused
your problem; even so, other pilots have had failed switches, including myself.
For the particular failure I had, Schleicher did respond by switching to more
water resistant switches.

This is off topic, but since I fly a Schleicher glider with the same engine
system, how fast were you flying when the problem occurred?

--
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

jld wrote on 8/19/2020 3:01 AM:
Certification requirements have forced manufacturers to significantly increase the weight of their gliders (e.g. cockpit protection). Because more recent airfoils are tolerant to higher WL, this has not been a significant issue, except for the fact MTM goes up and self launchers need more power!
By using experimental in US and UL in EU, GP has more design freedom. For example, not proposing a heavy 16G cockpit but a rescue parachute instead!

Do you know how much the "16G cockpit" adds in weight, compared to the cockpit
requirement of a glider with a rescue parachute? Or asking another way: is a
glider designed to the "16G cockpit" standard heavier than one designed with a
rescue parachute (and including the parachute weight)?

--
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 Wednesday, 19 August 2020 at 11:02:00 UTC+1, jld wrote:
""GP doesn't just claim "lower weight," but "far lower weight" than other gliders, but w/o any evidence to support this claim""
The evidences are in the design and certification choices.

GP15 is about same empty weight as the H301 which was a fiberglass ship, so there is nothing new. Carbon now allows to use lower relative thickness airfoil and higher aspect ratio wings to get to higher performance.

Certification requirements have forced manufacturers to significantly increase the weight of their gliders (e.g. cockpit protection). Because more recent airfoils are tolerant to higher WL, this has not been a significant issue, except for the fact MTM goes up and self launchers need more power!
By using experimental in US and UL in EU, GP has more design freedom. For example, not proposing a heavy 16G cockpit but a rescue parachute instead!

You suggested this company has better materials and design techniques than its rivals. It's somewhat fatuous to then introduce a 55+ year old design into the discussion.

If you were giving us this somewhat patronising explanation in 1980, you might have a point. Schempp-Hirth were able to use knowledge gained from prototype wind turbine blades to build an all carbon wing for the Mini Nimbus. I said to the agent in our country why don't they produce a new design with thinner and higher aspect ratio wings. I'm sure they had the idea themselves without any help from me

Certification standards aren't just random paperwork for the fun of it

You laud the idea of reducing cockpit strength. Oh great. I've seen the floppy cockpit sides on another recent lightweight glider. A friend held both side rails and moved them an inch or two in and out; he might have been able to snap or peel something apart with a bit more effort. Another glider type a few years ago achieved the distinction of being banned from operating at one club, and I can't say I'm surprised, given what a different friend found

Another place to try to save weight is on control surfaces. There's geared extra payback from reducing mass balances. For the rudder this can get extra gearing again for the minimum cockpit weight. Is mass balancing going to be an area where this glider will save weight? How fast will it go?

Another post above mentions wings drooping fore and aft of the spar due to insufficient curing. I hadn't heard that before, but sorry, if true this just sounds amateurish. The rivals post cure in the moulds overnight, carefully controlled and logged temperature and time. Some parts of the process don't have shortcuts.

..

On Wednesday, 19 August 2020 at 16:29:13 UTC+3, Eric Greenwell wrote:
jld wrote on 8/19/2020 3:01 AM:
Do you know how much the "16G cockpit" adds in weight, compared to the cockpit
requirement of a glider with a rescue parachute? Or asking another way: is a
glider designed to the "16G cockpit" standard heavier than one designed with a
rescue parachute (and including the parachute weight)?
--
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

I asked few years ago german glider producer CEO (you quess) about future of std. class. He said that they could design and build better std. class ship than previous generation (they all are from late 90s), but performance gain would be offset by requirement to build stronger fuselage than previous gen. glider that would weigh a lot more.

"No they don't. You have a 470kg glider in UL class that has MTOM of 472,5 kg (if national regs allow). Now EASA says that you can design and build an UL aircraft that has MTOM of 600kg (if national regs allow). The 470 kg GP fits into that weight limit perfectly"

Maybe I was not clear enough and we fail to communicate.
With new EASA limit (i.e. 600kg) the national limitS are being updated.
If you check updated UL national regulations you will discover that there is more than MTOM being updated and influencing your design (Empty weight, minimum Payload, Vso, etc.).
Controlling the empty weight is certainly on the critical path to meet a lot of the requirements.

"is a glider designed to the "16G cockpit" standard heavier than one designed with a rescue parachute (and including the parachute weight)?"

A designer would give you a precise answer but if you consider that you trade your back parachute against a rescue system, the delta is probably no more than 3kg (11kg - 8kg).
This is likely much less than the additional weight required by latest EASA regs on cockpit integrity.
The problem is that if you certify under EASA, you don't have the choice to go one way or the other. Therefore if you want the rescue system, weight goes up.

"You suggested this company has better materials and design techniques than its rivals"
You should rad post more carefully, I don't recall having suggested GP has better materials. My only point was that the weight they are claiming aren't so incredible.

I will not challenge your other statements since you seem be astute in aircraft design, certification and manufacturing.

On Wednesday, 19 August 2020 at 17:47:52 UTC+3, jld wrote:
"No they don't. You have a 470kg glider in UL class that has MTOM of 472,5 kg (if national regs allow). Now EASA says that you can design and build an UL aircraft that has MTOM of 600kg (if national regs allow). The 470 kg GP fits into that weight limit perfectly"
Maybe I was not clear enough and we fail to communicate.
With new EASA limit (i.e. 600kg) the national limitS are being updated.
If you check updated UL national regulations you will discover that there is more than MTOM being updated and influencing your design (Empty weight, minimum Payload, Vso, etc.).

I checked and can confirm that you are wrong. There are no such regulations, other than allowed MTOM being higher (for sailplanes). For airplanes, only new rule is 45 kts stall speed instead of old 35 kts. I suspect your motivation for telling lies post after post is that you are GP dealer?

I find it quite amazing that GP has been selling (though obviously not producing) GP15s for years and now they state that they "freeze the design" by Q1 2021. I mean what the actual f*ck? They are still designing it!? I saw prototype flying in 2018. Well good luck for those who have paid in advance.

Remember your high school chemistry (or was it physics?).Â* Water gives
up 1 calorie per gram per degree C while cooling.Â* To transition from
water at zero deg C to ice at zero deg C requires the loss of 80
calories per gram per degree C.Â* That's a lot of heat to be lost!Â* Sure,
you have a large surface area, but you have a very large volume as
well.Â* It would take quite some time to freeze a ballast tank.

Bottom line is I never worried about icing the ballast tanks (when I had
them) at sub-freezing temperatures.Â* Now freezing the dump valves is a
different issue, but not really if you fly your glider all the way to a
stop.Â* I once landed my LAK-17a with nearly 50 gallons on board and
didn't notice until after getting out of the glider.Â* Another time, one
dump valve stuck closed and, again, I landed with 25 gallons in one wing
and empty in the other.Â* I didn't notice until coming to a stop and the
full wing dropped heavily.

On 8/18/2020 8:06 PM, Eric Greenwell wrote:
wrote on 8/18/2020 3:54 PM:
On Tuesday, August 18, 2020 at 10:39:00 AM UTC-7, Eric Greenwell wrote:
jld wrote on 8/18/2020 9:57 AM:
Â*Â* "Glider pilots on the Allegheny Ridges (ridge soaring), in
Western US high deserts (thermal soaring), and in the Sierra wave
sometimes use higher wing loading"

Then the GP15 might be able to satisfy these US pilots as long as
they use antifreeze in the ballast :-).
Also you might not be able to get all the benefits of high WL if
you are limited by Vne due to high altitude.

I have been lucky to fly in Minden before.
Unless you compete in the WGC or are trying to beat a world record,
60 kg/m2 would already be A lot.

Bottom line, lets look for news from GP or the dealers to get
confirmation of configuration and delivery dates...

No antifreeze needed in the summer, as the temperatures at 18,000'
are not cold
enough to freeze the water in the wings. Winter wave flying is much
colder, of
course, and wave runners that get permission to fly above 18,000'
have to consider
the temperature at any time of the year.

According to the recent provisional manual, the GP15 VNE is 162 kts
IAS up to 3000
meters; 143 kts IAS at 6000 meters. That's about 195 kts TAS from
3000 meter on
up, so a pretty high limit, especially compared to my ASH26E, with
it's 143 kt
VNE. I don't know what modern gliders have for VNE, or wing loading,
for that matter.



Eric, what air temp do you regard as cold enough to freeze water in
the wings?

The situation I mentioned - summer in high desert areas - means ground
elevations of 5000' or more, and with ground temperatures of 90+, it
will be 25 deg F at 18,000. With the ups and downs of thermal flying,
the average temperature will be around freezing, so the water ballast
won't be cold enough long enough to freeze.

For other situations, I really don't know. In thermal conditions, I
wouldn't worry unless the minimum temperature went below 20 deg F.
Perhaps a temperature meter with a remote probe in the wing tank is
the safest thing. The glider handbook may have guidance, too. A
wireless sensor might be easiest to use for the wing



--
Dan, 5J

On Wednesday, 19 August 2020 at 16:27:43 UTC+1, jld wrote:
"You suggested this company has better materials and design techniques than its rivals"
You should rad post more carefully, I don't recall having suggested GP has better materials. My only point was that the weight they are claiming aren't so incredible.

I will not challenge your other statements since you seem be astute in aircraft design, certification and manufacturing.

No need for the sarcasm.

I'm not any better informed than average, and I'm not pretending to be

You however have been smearing companies who have been making thousands of gliders for decades, airworthiness authorities in several countries, and more besides, and your expertise, whatever it is, propounds the low weight benefits of weaker cockpits (a claim not made by the manufacturer) and the cleverness or convenience of bypassing other standards

Yes, certification does cost money, so finding another category with less of it can be an advantage, but you may cause concern if it sounds like you suggest glossing over design work too.