The other day I saw an Extra 500, covered in cracks.
Is that normal?
I don’t know whether underneath is fibreglass or carbon composite, but if the gelcoat is cracked then surely something is going on?
If it was a boat, cracked gelcoat means too high forces has been applied. Such cracks are usually very localized. It could also be that it has not been taken care of, or perhaps being washed with something it didn’t agree with. Very odd though. I have never seen cracked gelcoat in any plane, or any glider for that matter.
Most composite structures are painted so the first thing to do is establish if the cracks are in the paint finish rather than the structure. Poor painting is far more likely to be the culprit than structural damage but it might require the removal of the paint to establish the situation.
Gelcoat on gliders does crack.
It is due to a combination of straining, thermal effects UV and water damage.
Gliders typically use a polyester gelcoat on top of an glass or carbon/epoxy structures.
Gliders from the 70s used Schwabbellack (unsure if it’s a type or brand) gelcoat which aged very well. My glider is 50 yeqrs old and almost the parts which are still with the original gelcoat are perfect. Exception are aileron and rudder were the structure is very thin and so more deflection and strain.
Then production of Schwabbellack stopped and gliders had to be painted in T35. It is far less flexible and UV resistant. So gliders need to be refinished (old gelcoat sanded, new gelcoat applied and long hours of fine sanding) after ~ 15 years.
New gliders and newly refinished gliders are now T35 gelcoat + PU paint. Gelcoat to allow fine sanding for perfect aerodynamic shape and PU paint for UV resistance + flexibility. Little cracks in the T35 won’t show under the PU paint.
That’s for the long term, wear and tear and environemental cracks.
Then there is the cracks due to shock or over stressing. Conveniently gelcoat is more fragile than the underlying structure so it is a safe indicator. Tap test, ultrasound or grinding the gelcoat away is the next step to investigate.
Crack in the gelcoat will eventually propagate to the structure. So there is a limit on how much cracking in the gelcoat can be accepted from an airworthiness point of view.
