Life glider hours with winch

On Friday, March 22, 2019 at 9:15:42 AM UTC-4, José Ignacio Otero wrote:
Hi Bob.

Thanks for the reply, it was what I looking for !!

I think that the pilots how said that, were thinking that because the 3.52 g that the glider "suffer" during the wich start.

Have a nice day, José


El jueves, 21 de marzo de 2019, 23:02:51 (UTC-3), Bob Kuykendall escribió:
What I've read is that the bending forces applied to the wings and tail during a typical winch launch are roughly equivalent to 3.5g flight. That is comfortably below the load limit of every common glider. However, it is high enough that repeated launches will eventually shorten the service life of an aluminum glider. The Blanik designers understood this very well, and the original service documentation was quite explicit about logging operations carefully so the service life could be tracked. Unfortunately, most operators did not do so.

Normal winching operations probably has no appreciable effect on the composite parts of a composite glider. However, I believe it was BGA analysis of repeated winch launch stresses that initiated the service bulletin on the steel end-pins ("spigots") on Grob 102, 103 and 109 series sailplanes.

As for wood sailplanes, my concern would mostly be around the age and condition of the structure, since many wood gliders are now half a century old. Since you don't feel the added stresses of winch launching the way you feel the g of vertical acceleration, it would be easy to get into the gray area between what the structure was originally built to sustain, and what it can actually sustain after fifty years of operation, repairs, and deterioration.

--Bob K.

Guys - let's stop making the winch launch sound like it is a glider shredding method! The force introduced into the glider's structure is limited by a weak-link. The max. breaking strength of these weak-links together with the Vw are determined by the designer and documented in the POH.
I am just referencing two popular two-seat trainers he
ASK-21 - MTOW of 600kg, black weak-link of 1,000kg, ratio 1:1.66
G103 Twin-II - MTOW 580kg, red weak-link of 750kg, ratio 1:1.29
(may the gods of physics forgive me for mixing mass and force units here!)
There is a load added during the launch when the glider transitions from the initial shallow climb into the full climb (akin to performing a small segment of a looping) but all this will not get you near the mentioned 3.5g!
However, all this is predicated on the use of proper weak-links. If you ignore these safety devices, then all bets are off. To the best of my knowledge, there hasn't been a properly maintained glider launched with the correct weak-links, that got pulled apart during the launch!

Uli
'AS'

Hi Uli,

I like the idea to use winch luch but I do not know about it, talking with some instructor and pilot of my country (winch is not popular here) I listen many times about this "structure fatigue" but I do not found any about that, and that is the reason of my question.
Your argument is clear and reasonable. Do you have any winch launch procedure file or something similar to know more about it?

Thanks for your time, José.


El viernes, 22 de marzo de 2019, 12:17:47 (UTC-3), AS escribió:
On Friday, March 22, 2019 at 9:15:42 AM UTC-4, José Ignacio Otero wrote:
Hi Bob.

Thanks for the reply, it was what I looking for !!

I think that the pilots how said that, were thinking that because the 3..52 g that the glider "suffer" during the wich start.

Have a nice day, José


El jueves, 21 de marzo de 2019, 23:02:51 (UTC-3), Bob Kuykendall escribió:
What I've read is that the bending forces applied to the wings and tail during a typical winch launch are roughly equivalent to 3.5g flight. That is comfortably below the load limit of every common glider. However, it is high enough that repeated launches will eventually shorten the service life of an aluminum glider. The Blanik designers understood this very well, and the original service documentation was quite explicit about logging operations carefully so the service life could be tracked. Unfortunately, most operators did not do so.

Normal winching operations probably has no appreciable effect on the composite parts of a composite glider. However, I believe it was BGA analysis of repeated winch launch stresses that initiated the service bulletin on the steel end-pins ("spigots") on Grob 102, 103 and 109 series sailplanes.

As for wood sailplanes, my concern would mostly be around the age and condition of the structure, since many wood gliders are now half a century old. Since you don't feel the added stresses of winch launching the way you feel the g of vertical acceleration, it would be easy to get into the gray area between what the structure was originally built to sustain, and what it can actually sustain after fifty years of operation, repairs, and deterioration.

--Bob K.

Guys - let's stop making the winch launch sound like it is a glider shredding method! The force introduced into the glider's structure is limited by a weak-link. The max. breaking strength of these weak-links together with the Vw are determined by the designer and documented in the POH.
I am just referencing two popular two-seat trainers he
ASK-21 - MTOW of 600kg, black weak-link of 1,000kg, ratio 1:1.66
G103 Twin-II - MTOW 580kg, red weak-link of 750kg, ratio 1:1.29
(may the gods of physics forgive me for mixing mass and force units here!)
There is a load added during the launch when the glider transitions from the initial shallow climb into the full climb (akin to performing a small segment of a looping) but all this will not get you near the mentioned 3.5g!
However, all this is predicated on the use of proper weak-links. If you ignore these safety devices, then all bets are off. To the best of my knowledge, there hasn't been a properly maintained glider launched with the correct weak-links, that got pulled apart during the launch!

Uli
'AS'

On Friday, March 22, 2019 at 11:55:34 AM UTC-4, José Ignacio Otero wrote:
Hi Uli,

I like the idea to use winch luch but I do not know about it, talking with some instructor and pilot of my country (winch is not popular here) I listen many times about this "structure fatigue" but I do not found any about that, and that is the reason of my question.
Your argument is clear and reasonable. Do you have any winch launch procedure file or something similar to know more about it?

Thanks for your time, José.


El viernes, 22 de marzo de 2019, 12:17:47 (UTC-3), AS escribió:
On Friday, March 22, 2019 at 9:15:42 AM UTC-4, José Ignacio Otero wrote:
Hi Bob.

Thanks for the reply, it was what I looking for !!

I think that the pilots how said that, were thinking that because the 3.52 g that the glider "suffer" during the wich start.

Have a nice day, José


El jueves, 21 de marzo de 2019, 23:02:51 (UTC-3), Bob Kuykendall escribió:
What I've read is that the bending forces applied to the wings and tail during a typical winch launch are roughly equivalent to 3.5g flight. That is comfortably below the load limit of every common glider. However, it is high enough that repeated launches will eventually shorten the service life of an aluminum glider. The Blanik designers understood this very well, and the original service documentation was quite explicit about logging operations carefully so the service life could be tracked. Unfortunately, most operators did not do so.

Normal winching operations probably has no appreciable effect on the composite parts of a composite glider. However, I believe it was BGA analysis of repeated winch launch stresses that initiated the service bulletin on the steel end-pins ("spigots") on Grob 102, 103 and 109 series sailplanes.

As for wood sailplanes, my concern would mostly be around the age and condition of the structure, since many wood gliders are now half a century old. Since you don't feel the added stresses of winch launching the way you feel the g of vertical acceleration, it would be easy to get into the gray area between what the structure was originally built to sustain, and what it can actually sustain after fifty years of operation, repairs, and deterioration.

--Bob K.

Guys - let's stop making the winch launch sound like it is a glider shredding method! The force introduced into the glider's structure is limited by a weak-link. The max. breaking strength of these weak-links together with the Vw are determined by the designer and documented in the POH.
I am just referencing two popular two-seat trainers he
ASK-21 - MTOW of 600kg, black weak-link of 1,000kg, ratio 1:1.66
G103 Twin-II - MTOW 580kg, red weak-link of 750kg, ratio 1:1.29
(may the gods of physics forgive me for mixing mass and force units here!)
There is a load added during the launch when the glider transitions from the initial shallow climb into the full climb (akin to performing a small segment of a looping) but all this will not get you near the mentioned 3.5g!
However, all this is predicated on the use of proper weak-links. If you ignore these safety devices, then all bets are off. To the best of my knowledge, there hasn't been a properly maintained glider launched with the correct weak-links, that got pulled apart during the launch!

Uli
'AS'


Hello José,

Try this manual for starters, which was put together by Bill Daniels here in the US using data and procedures from various sources:
http://www.pas.rochester.edu/~cline/...20Rev%2012.pdf
I don't know of any similar documents in Spanish but I am sure they exist.
Good luck,


Uli
'AS'

Many thanks Uli, it look very complete.

Have a nice weekend, José.



El viernes, 22 de marzo de 2019, 13:36:51 (UTC-3), AS escribió:
On Friday, March 22, 2019 at 11:55:34 AM UTC-4, José Ignacio Otero wrote:
Hi Uli,

I like the idea to use winch luch but I do not know about it, talking with some instructor and pilot of my country (winch is not popular here) I listen many times about this "structure fatigue" but I do not found any about that, and that is the reason of my question.
Your argument is clear and reasonable. Do you have any winch launch procedure file or something similar to know more about it?

Thanks for your time, José.


El viernes, 22 de marzo de 2019, 12:17:47 (UTC-3), AS escribió:
On Friday, March 22, 2019 at 9:15:42 AM UTC-4, José Ignacio Otero wrote:
Hi Bob.

Thanks for the reply, it was what I looking for !!

I think that the pilots how said that, were thinking that because the 3.52 g that the glider "suffer" during the wich start.

Have a nice day, José


El jueves, 21 de marzo de 2019, 23:02:51 (UTC-3), Bob Kuykendall escribió:
What I've read is that the bending forces applied to the wings and tail during a typical winch launch are roughly equivalent to 3.5g flight. That is comfortably below the load limit of every common glider. However, it is high enough that repeated launches will eventually shorten the service life of an aluminum glider. The Blanik designers understood this very well, and the original service documentation was quite explicit about logging operations carefully so the service life could be tracked. Unfortunately, most operators did not do so.

Normal winching operations probably has no appreciable effect on the composite parts of a composite glider. However, I believe it was BGA analysis of repeated winch launch stresses that initiated the service bulletin on the steel end-pins ("spigots") on Grob 102, 103 and 109 series sailplanes.

As for wood sailplanes, my concern would mostly be around the age and condition of the structure, since many wood gliders are now half a century old. Since you don't feel the added stresses of winch launching the way you feel the g of vertical acceleration, it would be easy to get into the gray area between what the structure was originally built to sustain, and what it can actually sustain after fifty years of operation, repairs, and deterioration.

--Bob K.

Guys - let's stop making the winch launch sound like it is a glider shredding method! The force introduced into the glider's structure is limited by a weak-link. The max. breaking strength of these weak-links together with the Vw are determined by the designer and documented in the POH.
I am just referencing two popular two-seat trainers he
ASK-21 - MTOW of 600kg, black weak-link of 1,000kg, ratio 1:1.66
G103 Twin-II - MTOW 580kg, red weak-link of 750kg, ratio 1:1.29
(may the gods of physics forgive me for mixing mass and force units here!)
There is a load added during the launch when the glider transitions from the initial shallow climb into the full climb (akin to performing a small segment of a looping) but all this will not get you near the mentioned 3..5g!
However, all this is predicated on the use of proper weak-links. If you ignore these safety devices, then all bets are off. To the best of my knowledge, there hasn't been a properly maintained glider launched with the correct weak-links, that got pulled apart during the launch!

Uli
'AS'


Hello José,

Try this manual for starters, which was put together by Bill Daniels here in the US using data and procedures from various sources:
http://www.pas.rochester.edu/~cline/...20Rev%2012.pdf
I don't know of any similar documents in Spanish but I am sure they exist..
Good luck,


Uli
'AS'

On Friday, March 22, 2019 at 8:17:47 AM UTC-7, AS wrote:

Guys - let's stop making the winch launch sound like it is a glider shredding method!...

ASK-21 - MTOW of 600kg, black weak-link of 1,000kg, ratio 1:1.66...

Let's remember that the critical factor here is wing root bending moment, which relates much more closely to the non-lifting mass than it does to the total mass.

Taking the ASK21 maximum non-lifting mass of 410 kg as our metric, the ratio in question is 1000/410 = 2.43.

True, not the 3.5 I cited, but still a substantial value.

--Bob K.

On Friday, March 22, 2019 at 1:22:07 PM UTC-4, Bob Kuykendall wrote:
On Friday, March 22, 2019 at 8:17:47 AM UTC-7, AS wrote:

Guys - let's stop making the winch launch sound like it is a glider shredding method!...

ASK-21 - MTOW of 600kg, black weak-link of 1,000kg, ratio 1:1.66...

Let's remember that the critical factor here is wing root bending moment, which relates much more closely to the non-lifting mass than it does to the total mass.

Taking the ASK21 maximum non-lifting mass of 410 kg as our metric, the ratio in question is 1000/410 = 2.43.

True, not the 3.5 I cited, but still a substantial value.

--Bob K.

No doubt, Bob - thanks for that additional clarification! And that's why I am a stickler for the correct weak-link and adherence to Vw during the full climb phase of the launch. :-)

Uli
'AS'

On Friday, March 22, 2019 at 10:22:07 AM UTC-7, I wrote:

Taking the ASK21 maximum non-lifting mass of 410 kg as our metric, the ratio in question is 1000/410 = 2.43.

I think I miscalculated.

If we're considering the root bending moment caused by a launch that applies 1000 kg downward to an ASK21, we also have to consider the load applied by the non-lifting mass of the glider itself. The load being reacted by the wings is actually:

1000 kg delivered by winch cable
410 kg delivered by non-lifting mass of glider
------
1410 kg

The ratio 1410/410 = 3.44 is the equivalent g load of the bending moment reacted by the wings. Which puts us back in the neighborhood of the 3.5g I originally cited.

--Bob K.