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  #11  
Old September 24th 19, 07:14 PM posted to rec.aviation.soaring
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On Tuesday, September 24, 2019 at 1:35:38 PM UTC-4, wrote:
The guy in the cockpit makes up for the craising on the wings.
A couple of wrong decisions by the guy flying the super true laminar perfect winged machine, and a few right decisions by the bondo wing flying guy and they'l be tied lol.


True- BUT- All the points made by good glider preparation are points that don't have to be given back.
From a guy who had two 999 point days this year. One of those made the difference between silver and bronze in nationals.
UH
  #12  
Old September 24th 19, 07:30 PM posted to rec.aviation.soaring
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Yes, agreed. I just finished working up an article regarding 5 principles necessary to win at low performance racing. The first principle is all about preparation.

But one of the other (and imop) more important factors is making the proper inflight decisions necessary to fly further or faster.

You know that the presence of a single point difference between 1st and 2nd place amounts to about a single false-thermal attempt, or maybe a few degrees of heading difference along an energy line. Its the "Moffat" principle revisited; namely "win by not loosing".
  #13  
Old September 24th 19, 10:48 PM posted to rec.aviation.soaring
Papa3[_2_]
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To expand on Hank's comment, we've looked carefully at a couple of heavily crazed gliders (a Grob left tied out and an LS4 that was not well maintained) under magnification. After removing the failed gelcoat, the crazing lines are still visible in the glass/epoxy. Our resident materials scientist was able to see small voids in the epoxy (a few 10s of microns deep) and few failures of the glass fiber (individual strands) at the surface level.. Think of it as very shallow "pitting" of the epoxy in the outermost glass layer. There is no sign of it penetrating deeper than that. I've heard of some shops "painting" a warm coat of epoxy into particularly bad areas and others either peeling off the outer glass layer and replacing. Never saw the need to do either of these.

p3





On Tuesday, September 24, 2019 at 10:49:24 AM UTC-4, wrote:
On Tuesday, September 24, 2019 at 10:15:43 AM UTC-4, Tango Eight wrote:
On Tuesday, September 24, 2019 at 9:11:31 AM UTC-4, son_of_flubber wrote:
How much does crazing affect Polar?


Not at all (provided that the surface is being maintained).

As far as "gelcoat cracks propagating into the structure", I'm terribly skeptical. It seems far more likely to this materials engineer that the reverse is what happened in cases where cracks in the structure have been associated with cracks in the finish. Polyester gelcoat simply isn't strong enough to provide meaningful stress concentration in the underlying structure.

T8


I have seen plenty of cases of imprinting on the top layer of the structural laminate under finish cracks. None have progressed beyond the top layer of the laminate. Some of those areas appeared to be compromised to a degree.
These areas are also a path to moisture which can degrade the laminate.
In very thin structures, like control surface trailing edges, the gelcoat does add stiffness. Finish cracks, usually just forward of the trailing edge joint are common on some types of ships. Move away from the crack and the surface is notably stiffer. Sand the gelcoat off and there usually is no underlying structural failure.
Crazing is an indication that future cracking is coming. Crazing is mostly cosmetic. Cracking is not in my experience.
FWIW
UH


  #14  
Old September 25th 19, 01:59 AM posted to rec.aviation.soaring
Charles Longley
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Bit of thread drift but it has to do with gel coat. I am currently doing a life extension on a Libelle (OD). It’s original gel coat is in far better shape then any of the ASW 20’s I looked at including the one I bought. It’s one of the earlier Libelle’s so 12 plus years older then a 20. I am not sure of why the difference? Did Glasflugel have better quality control than Schleicher? Or was it a different material?
  #15  
Old September 25th 19, 07:04 AM posted to rec.aviation.soaring
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Glasflügel used Lesonal Schwabbellack instead of Vorgelat Gelcoat. They also did not paint the seams with a quick drying mixture, including too much hardener.
  #16  
Old September 25th 19, 07:36 AM posted to rec.aviation.soaring
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On Monday, September 23, 2019 at 11:50:30 AM UTC-4, BobWa43 wrote:
Is gel coat crazing purely a cosmetic problem or does it pose a threat to the structural integrity of the underlying fiberglass? I realize this is a controversial issue but I would really like to hear the current opinions of members with experience refinishing gel coated gliders.


Many thanks to all of you who commented. It was a most enlightening discussion.
  #17  
Old September 25th 19, 11:54 PM posted to rec.aviation.soaring
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True- BUT- All the points made by good glider preparation are points that don't have to be given back.
From a guy who had two 999 point days this year. One of those made the difference between silver and bronze in nationals.
UH


Ironically, UH oversaw/assisted/provided the skilled work (vs. the grunt sanding work) on the glider that was the 1 point beneficiary of a complete refinish job.

No good deed goes unpunished.

JB
  #18  
Old September 26th 19, 01:59 PM posted to rec.aviation.soaring
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On Wednesday, September 25, 2019 at 6:54:50 PM UTC-4, wrote:
True- BUT- All the points made by good glider preparation are points that don't have to be given back.
From a guy who had two 999 point days this year. One of those made the difference between silver and bronze in nationals.
UH


Ironically, UH oversaw/assisted/provided the skilled work (vs. the grunt sanding work) on the glider that was the 1 point beneficiary of a complete refinish job.

No good deed goes unpunished.

JB


The reward was seeing one of my best friends in soaring get his best ever nationals finish.
UH
  #19  
Old September 26th 19, 03:24 PM posted to rec.aviation.soaring
Tango Whisky
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Le mardi 24 septembre 2019 23:48:48 UTC+2, Papa3 a écritÂ*:
To expand on Hank's comment, we've looked carefully at a couple of heavily crazed gliders (a Grob left tied out and an LS4 that was not well maintained) under magnification. After removing the failed gelcoat, the crazing lines are still visible in the glass/epoxy. Our resident materials scientist was able to see small voids in the epoxy (a few 10s of microns deep) and few failures of the glass fiber (individual strands) at the surface level. Think of it as very shallow "pitting" of the epoxy in the outermost glass layer. There is no sign of it penetrating deeper than that. I've heard of some shops "painting" a warm coat of epoxy into particularly bad areas and others either peeling off the outer glass layer and replacing. Never saw the need to do either of these.

p3


These small voids on the outmost epoxy layer are absolutely normal and due to the manufacturing method. The outmost glass fiber layer is laminated into the mould which has been spray-coated with the gelcoat. This process will always trap air between this glass layer and the gelcoat (although curing under vacuum does get rid of most of it).

These small voids are main reason that the first step on a sanded-down wing is to laminate a very thin layer of glass fibers. This layer does not help the structure - it efficiently fills up those small voids. Otherwise, any sprayed-on filler or gelcoat won't be able to fill up the voids due to the relatively high surface tension, creating thousands of nasty litte craters on the filler/gelcoat surface.

Bert
Ventus cM "TW"
  #20  
Old September 26th 19, 04:10 PM posted to rec.aviation.soaring
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On Thursday, September 26, 2019 at 8:59:23 AM UTC-4, wrote:
On Wednesday, September 25, 2019 at 6:54:50 PM UTC-4, wrote:
True- BUT- All the points made by good glider preparation are points that don't have to be given back.
From a guy who had two 999 point days this year. One of those made the difference between silver and bronze in nationals.
UH


Ironically, UH oversaw/assisted/provided the skilled work (vs. the grunt sanding work) on the glider that was the 1 point beneficiary of a complete refinish job.

No good deed goes unpunished.

JB


The reward was seeing one of my best friends in soaring get his best ever nationals finish.
UH


Thanks, Hank! It was one of the high points of my 50+ years in soaring. Just to reinforce your message, on the last day I made a 20 mile desperation final glide thru mostly sinking air and took a small penalty because I was slightly below the floor of the finish cylinder. IIRC, if I had been 3 feet lower, I would have lost that one point. Sure, there were all kinds of things I could have done earlier in the flight to more than make up for that. But I didn't. At the end of the flight, it came down to one tenth of one percent on that glide. That was my reward for all those hours spent with you pulling templates off my ASW 24 wing, removing the old gel coat carefully, and then building the profile back up the right way. Thanks, again, for your care and attention (and patience!) in that effort.

The above situation is rare. More typically, having that small extra percentage makes it possible to stay with the fleet moving down a fast leg on a blue day vs. slowly being dropped. It's probably not worth worrying about it unless you're flying competitively but it is for me. We're all different. Fortunately, soaring accommodates all of us.

Chip Bearden
JB
 




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