People often ask about the performance improvements, which they will receive from their new propeller. Aircraft in the general aviation fleet today vary widely in condition, making it difficult to make blanket statements about performance improvements.
STC performance testing is generally done using unmodified aircraft that are in very “clean” condition. Test results must be at least as good as the original propeller to obtain the STC from the FAA. Many STCs are obtained on an “as good or better” performance basis.
This means that while performance benefits are often gained, many times credit is not taken for the improvement to avoid having to prepare a complete set of new performance data for the airplane. In these cases, the AFMS will often state “No Change” under the performance section.