bdk wrote:
Were all those things in the NTSB report knowable before the upset? The report even concludes that there is no way to know what effect wake tubulence or a gust might have contributed to the excitation. The upset was not recoverable once it started, Stiletto's was, and was therefore less severe. Stiletto suffered from instability, not a catastrophic flutter event.
If they were not known, they probably could have been discovered with even a minimal flight test program........
Quote:
The accident airplane had undergone many structural and flight control modifications that were undocumented and for which no flight testing or analysis had been performed to assess their effects on the airplane's structural strength, performance, or flight characteristics. The investigation determined that some of these modifications had undesirable effects. For example, the use of a single, controllable elevator trim tab (installed on the left elevator) increased the aerodynamic load on the left trim tab (compared to a stock airplane, which has a controllable tab on each elevator). Also, filler material on the elevator trim tabs (both the controllable left tab and the fixed right tab) increased the potential for flutter because it increased the weight of the tabs and moved their center of gravity aft, and modifications to the elevator counterweights and inertia weight made the airplane more sensitive in pitch control. It is likely that, had engineering evaluations and diligent flight testing for the modifications been performed, many of the airplane's undesirable structural and control characteristics could have been identified and corrected.
mustanglover wrote:
And BDK, you and I both know that even the smallest problem with "looseness" of a flight control surface, especially something like a elevator trim tab, can have catastrophic consequences if not corrected.
Loose screws, did they cause the flutter or did the flutter episode cause the loose screws?
mustanglover wrote:
Also, filler material on the elevator trim tabs (both the controllable left tab and the fixed right tab) increased the potential for flutter because it increased the weight of the tabs and moved their center of gravity aft, and modifications to the elevator counterweights and inertia weight made the airplane more sensitive in pitch control.
Have you ever balanced Control Surfaces? The counterweights for the elevators were modified and had weight added in order to balance the Elevators to neutral. The added filler material and alum trim tabs with filler along with paint was already dealt with by increasing the weight of the balance weights. If they were balanced that could not be an instability issue by itself or every P-51 with elevators balanced to neutral would be having pitch stability issues. This is well defined in manuals particularly the structural repair manual where the weight of a repair (extra material added that wasn't there originally) is compensated with the balance weight. The inertia weight was designed as a stability aid. I believe it was a benefit in rough air for keeping guns on a target. I know of P-51s that fly fine without them. I believe the inertia weight wasn't found in the wreckage IIRC and it may not have been installed.
There are some obvious issues involved here that we have to look at as a horrible event that we now have to use to learn a lesson in operating these racers. Everyone involved surely wishes this had a different outcome.
That said the NTSB produces factual reports based on what they look at. I don't know if they hit every nail on the head. I see a couple of potential misses. Maybe they didn't think some things were worth looking at.
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