I'm not sure I entirely agree with you John, although I've not seen much theoretical work to justify my point, a few practical experiences suggest to me that there are variations.
Example #1 was a 2-seat turbo-prop training aeroplane. For reasons that were never satisfactorily explained, about 1 aircraft in 20 would roll inverted if you stalled it with full flaps. We were just starting to get into a deep and meaningful investigation into this when some bright squadron SEngo decided to start swapping rear fuselages around. Within a few weeks, he'd eliminated the problem across the fleet without any significant "highbrow" effort at-all, so we at BDN gave up and got on with something else.
Example #2 is a 2 seat piston-prop trainer / private light aircraft. It has neutral spiral stability, except in the post-build air tests about 1 in 10 has postive spiral stability.
Example #3 is a flexwing microlight, about 1 in 3 on initial post-build air test has a marked tendency to turn which requires adjustment to "trim out".
Example #4 was a high wing 2-seat light aircraft, cleared for deliberate spinning which decided after a service to take 4-6 turns each time to recover from a spin that should have taken ½-1 turn. This was eventually tracked down to tolerances in wing rigging.
Example #5 was a derivative of #2 which turned out to drop a wing about 70° at the stall. This turned out to be down to freeplay (and to an extent manufacturing tolerances) in the linkages between two sides of elevator. Eventually eliminated the problem by introducing a mandatory mod incorporating two penny washers to bring the worst case freeplay down to tolerable limits.
Examples #6, #7 were two different aeroplanes I had to look into that owners complained "floated" forever on landing causing them to use far too much runway. Both, as it turned out, had - for reasons never fully established but somewhere in the construction of the pitot-static systems, moderately (10-15kn) underreading ASIs. So, pilots were approaching and landing 10-15kn too fast, and using too much runway.
Having said that, I think the issue is primarily one of consistency, #1 is the only such case I've seen that was genuinely dangerous. So, the issue is more (in my opinion) of whether every aeroplane in a fleet is the same, and whether the published handling and performance material (POH, AFM, etc.) truly reflect the individual aeroplane. That, I suspect, is not looked into enough - how many manufacturers or authorities really insist on post build test on investigating the differences from "standard" and documenting them for that aircraft?
G
Last edited by Genghis the Engineer; 23rd October 2002 at 19:24.