On Sunday, May 5, 2019 at 7:19:22 AM UTC-7, wrote:

...I am often amazed by the owners that think they can legally experiment with changes to an experimental glider...

To expand slightly on this:

It depends entirely on what sort of "experimental" we're talking about, and the operating limitations attached to the airworthiness certificate for the specific glider in question.

First off are experimental amateur-built sailplanes such as the ones I promote, make kits for, and train people to fabricate and assemble. For these, experimentation is definitely baked into the boilerplate text of the operating limitations issued by FAA and designated inspectors. Anybody can legally work on them, and major repairs, modifications, and alterations are relatively straightforward.

As for experimental, exhibition and experimental, racing, the operating limitations are much less uniform than for amateur-built, and much more subject to the discretion of the inspector and context of the issuance. And they are definitely negotiable. For some they say that the aircraft must be maintained per the manufacturer's instructions. But for some others this proviso is omitted, or has actually been removed in an amended re-issuance of the operating limitations.

Thanks, Bob K.