NTSB Releases some Reports on GG Reno Crash from 2011

[k5083]

Actually the P-51 was known for a relatively high incidence of structural failure under high G combat maneuvering compared with most fighters of the era.

August

[snj-5]

GG had clipped wings (substantially clipped), which, in theory, should make
the airframe withstand more G than a stock P-51 with full-length wings.

Bela P. Havasreti

[mustanglover]

They were trying to go with a Stiletto clone but research about the flight characteristics of Stiletto were obviously not payed attention to.

Skip had reported a significant divergent longitudinal oscillation that could happen which as he described could have a destructive mode with any large upset.

I think we all know now, from reading the NTSB report, that GG was potentially an accident waiting to happen and we all should learn from this accident.

[bdk]

Skip had reported a significant divergent longitudinal oscillation that could happen which as he described could have a destructive mode with any large upset.

Was this flight characteristic ever addressed on Stiletto? I would be surprised if it was not corrected.

I think we all know now, from reading the NTSB report, that GG was potentially an accident waiting to happen and we all should learn from this accident.

I don't know how you could make a blanket statement that it was an accident waiting to happen. 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.

[N3Njeff]

Dont watch the national news tonight. Its going to be a rough ride for the next few days!!

[Fouga23]

http://edition.cnn.com/2012/08/27/us/ne ... ?hpt=us_c2

[51fixer]

They were trying to go with a Stiletto clone but research about the flight characteristics of Stiletto were obviously not payed attention to.

Skip had reported a significant divergent longitudinal oscillation that could happen which as he described could have a destructive mode with any large upset.

I think we all know now, from reading the NTSB report, that GG was potentially an accident waiting to happen and we all should learn from this accident.

The same guy originally built both airframes.
One had the radiators in the wings and the other kept the scoop when the wings were configured.

[mustanglover]

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........

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.

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.

[CoastieJohn]

"mustanglover
If they were not known, they probably could have been discovered with even a minimal flight test program........

Do these racing airframes that are modified go thru some type of wind tunnel testing to look for potential problems? If so, is it a requirement mandated somewhere?

[51fixer]

"mustanglover
If they were not known, they probably could have been discovered with even a minimal flight test program........

Do these racing airframes that are modified go thru some type of wind tunnel testing to look for potential problems? If so, is it a requirement mandated somewhere?

No. Not required for wind tunnel testing. Nasa shut down the one at Langley a couple years back.

[mustanglover]

"mustanglover
If they were not known, they probably could have been discovered with even a minimal flight test program........

Do these racing airframes that are modified go thru some type of wind tunnel testing to look for potential problems? If so, is it a requirement mandated somewhere?

No and no.

[CoastieJohn]

"mustanglover
If they were not known, they probably could have been discovered with even a minimal flight test program........

Do these racing airframes that are modified go thru some type of wind tunnel testing to look for potential problems? If so, is it a requirement mandated somewhere?

No and no.

Thanks.

Is it possible wind tunnel testing could have identified the problems these modified airframes could encounter?

[51fixer]

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........

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.

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?

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.

[bdk]

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.

I agree, that was a big FAIL. Basic maintenance/annual inspection should have caught that and corrected it. So should have the RARA inspectors at Reno, not to mention the pilot or crew on a preflight.

Was the cause of Voodoo's upset ever determined? You would think that would be a Reno watch item after that incident.

[Badman]

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.

I agree, that was a big FAIL. Basic maintenance/annual inspection should have caught that and corrected it. So should have the RARA inspectors at Reno, not to mention the pilot or crew on a preflight.

Was the cause of Voodoo's upset ever determined? You would think that would be a Reno watch item after that incident.

My recollection was Voodoo's elevator trim tab failure was caused by the crew putting speed tap over the gap between the tab and elevator that caused flutter of the tab. The fix was to not install speed tape in this area.