Aerodynamics isn't the issue - gelcoat failure can progress until it's a structural issue.

There are many early Cirrus & Libelle (amongst others) from the early / mid 70s that still flying with original gelcoat without any signs of failure.

Nick.

On Wednesday, August 31, 2016 at 5:23:44 AM UTC+9:30, Bruce Hoult wrote:
On Tuesday, August 30, 2016 at 11:53:20 PM UTC+12, Dan Daly wrote:
The site says something like approved life of 3000 hours with extensions so maybe that's the one that's now been upgraded to 12,000 hours. (will check) That's one reason I was looking for a more recent model in case GRP gliders do have problems in later life. Just about anything will outlast me but I'm thinking resale value.

http://szd.com.pl/downloads/4fdeffe8...l-10039816.pdf is the document which extends the life of all SZD-55 to 12k. The associated Flight Manual must be amended with the 2012 changes, which is noted at the end of the EASA document. Mainly they talk about what inspections have to be done periodically, and change the bits of the manual that talk about the authorized lifespan of the glider.

Most gliders get an initial 3,000 hr approval, then as they approach that, they are assessed by the factory to see if they have problems. If not, additional 3,000 hrs. As they approach 6,000, same, etc., until design life is reached. I don't know what the design life of Schempp-Hirth, Schleicher, etc are (I know ASK-21's are at 18,000 hrs). I think of most GRP gliders as having infinite lives, though gelcoat must be refinished periodically.

OK .. *why* must gelcoat be refinished periodically?

I suppose eventually it might start letting moisture through into the structure, but I suspect most people are refinishing it at less than 50% (maybe much less) of its potential protective lifetime for purely aesthetic reasons.

Does cracked gelcoat have much of an effect on aerodynamics? One that someone other than a top competition pilot would notice?