More about perf
Those that know me would also question my grip of the subject, but the main reason for my question is this.
Aircraft has new "thing" bolted to same place as last "thing", empty weight is, surprisingly, only 20 lb greater. Aircraft has to be test flown to ensure new "thing" doesn't affect handling and performance.
The "things" are very similar in size and shape.
Why then does the new thing cause a significant reduction in declared single engine climb performance, when there ain't much to spare.
The reason I cling to my anonymity is that the quote "it must be because we did the testing when it was cold and high pressure so the air must have been descending," comes from very clever people who I respect, yet sounds odd to me.