As I recall from the NTSB report video, it was noted that the nuts in questioned had to be tightened in the days leading up to the incident. That tells me that these were "inspected", found to be loose and subsequently tightened. I am sure there is someone out there wishing they had replaced those loose nuts instead of simply tightening them.

+1
yes, it was Broke. Gee Wally why is the screw loose?

Sad the accident was preventable if one person would had spoken up or used his/her brain,, But no, 11 people are dead and dozens injured, a sport in turmoil

Originally Posted by qmulus

As I recall from the NTSB report video, it was noted that the nuts in questioned had to be tightened in the days leading up to the incident. That tells me that these were "inspected", found to be loose and subsequently tightened. I am sure there is someone out there wishing they had replaced those loose nuts instead of simply tightening them.

Yes, but I'm fairly certain from reading the report that the locknuts weren't the ONLY thing that caused the accident. The primary cause I think was the filler added to the trim tabs (some places up to 1/8" thick), to smooth them out and fair them into the stab. This added material moved the CG of the surface aft, and made it much more susceptible to flutter, which is ultimate what caused the trim tab failure, which then caused the 17g pitchup, and that was all she wrote.

Originally Posted by Shaker

The asymmetric trim tab setup is designed to reduce drag as only one tab is deflected into the airflow, but you're absolutely right that it caused torsional loading on the fuselage, which had already been weakened by the removal of the belly scoop.

Thanks, Doug, for the explanation. I'm an electrical engineer, not an aeronautical engineer, but I do know physics. Not to belabor the point, but it seems it wouldn't make any more drag having two symmetrical trim tabs than having one asymmetrical trim tab. If you double the tab area, you should be able to lessen the angle that it is deflected into the airstream to get the desired vector forces. And the two tabs would be equally loading the horizontal stab.

Maybe I'm missing something.

(actually, now that I read more of the thread, I see Bob Black Sheep asked the same question)

Originally Posted by nordqk

Thanks, Doug, for the explanation. I'm an electrical engineer, not an aeronautical engineer, but I do know physics. Not to belabor the point, but it seems it wouldn't make any more drag having two symmetrical trim tabs than having one asymmetrical trim tab. If you double the tab area, you should be able to lessen the angle that it is deflected into the airstream to get the desired vector forces. And the two tabs would be equally loading the horizontal stab.

Maybe I'm missing something.

(actually, now that I read more of the thread, I see Bob Black Sheep asked the same question)

Yes, you are missing something....one elevator has a workable trim tab,,,the other is locked in....the problem with only one being used and the other locked is....DRAG... you have one that needs to deflect more to get the desired trim causing drag on one side of the stabilizer....example,
put your hand out you car window at 60mph...when it is level no drag....you turn your palm slightly up or down and feel the drag.....now imagine a 2 foot trim tab at 400+ knots, the drag on one side of the stabilizer and none on the other has got to be tremendous

Originally Posted by flyin4fun

Yes, you are missing something....one elevator has a workable trim tab,,,the other is locked in....the problem with only one being used and the other locked is....DRAG... you have one that needs to deflect more to get the desired trim causing drag on one side of the stabilizer....example,
put your hand out you car window at 60mph...when it is level no drag....you turn your palm slightly up or down and feel the drag.....now imagine a 2 foot trim tab at 400+ knots, the drag on one side of the stabilizer and none on the other has got to be tremendous

Yeah, that explains it.

Originally Posted by flyin4fun

Yes, you are missing something....one elevator has a workable trim tab,,,the other is locked in....the problem with only one being used and the other locked is....DRAG... you have one that needs to deflect more to get the desired trim causing drag on one side of the stabilizer....example,
put your hand out you car window at 60mph...when it is level no drag....you turn your palm slightly up or down and feel the drag.....now imagine a 2 foot trim tab at 400+ knots, the drag on one side of the stabilizer and none on the other has got to be tremendous

That's what I was saying! Operating 2 at less deflection should creat less drag AND no twisting force through the aft fuse area. I thought aviation was all about balance and symetry, in this case balanced trim tabs...............
Shaker is right too with the CG being moved aft contributing to the flutter but I'm sure loose hinge screws would not have helped either!

Deleted

Originally Posted by Black Sheep

That's what I was saying! Operating 2 at less deflection should creat less drag AND no twisting force through the aft fuse area. I thought aviation was all about balance and symetry, in this case balanced trim tabs...............
Shaker is right too with the CG being moved aft contributing to the flutter but I'm sure loose hinge screws would not have helped either!

In normal flight this would be true......but you need to realize that these aircraft were built for speed an to race making only left hand turns......think about how a NASCAR race car is setup.

Originally Posted by flyin4fun

In normal flight this would be true......but you need to realize that these aircraft were built for speed an to race making only left hand turns......think about how a NASCAR race car is setup.

Oh OK, so that set up was to suit the circuit? If so, that makes sense Still someone should have realized the twisting forces that were going to be encounted with that set up.

Originally Posted by Black Sheep

Oh OK, so that set up was to suit the circuit? If so, that makes sense Still someone should have realized the twisting forces that were going to be encounted with that set up.

The trim tab in the left side elevator was (because of the high speed left turn oval circuit) was also subject to more disturbed air than the "locked in" trim tab on the right side elevator,causing more flutter and magnifying the twisting, not to mention the alterations to the aircraft, being the removal of the scoop and the lowering of the turtledeck, changing the structural integrity

It seems it is very difficult to know the precise order of events related to the trim tab. The tab leaving the airplane caused the pitch up and crash..OK. But in what order did the other things occur? Bent then broken trim tab link rod (think of the links used for servos to the horn) from load allowing tab to flutter, fail and depart and the super high frequency vibration loosening the screws. Or was it flutter that failed the rod and then the rest? The report states an order they think it happened but it would be hard to know for sure. The report states the rod in the fixed righthand tab was bent too.

Balance is a major issue with aircraft control surfaces. Some are very critical while others are not. I am not familiar with the elevator and trim tab balancing on the mustang but I am familiar with the rudder balancing having covered about 6 P51 rudders where an extra coat of paint is a big deal.

As for the yellow paint on the parts, research this airplane and find out it has had many names over the years. It was yellow for a long time up until being renamed back to the first race name, Galloping Ghost just a few years ago.

As for 2 tabs shallow being less drag than one steep, I would have to see your 400+knot P51 test data to believe it to be true. One needs to understand the concept of elevator trim systems and trim drag to know for sure. The tab is there to create enough force in one direction to cause the elevator to move from neutral to a new down angle. The elevators are many times larger than the trim tabs. At a given speed, the elevators must be deflected to a given angle for that speed to have proper stick force and pitch setting desired by the pilot. The deflected elevator will be a much larger drag producer than the 2 tabs. One tab at a greater angle may indeed still give the required elevator deflection and produce less overall drag. What is questionable is the linkage which was no longer stock P51. This linkage was not strong enough to take the flight loads on the tab.

Those who can't understand why lock nuts would not have been changed need to look at photo 14 (I think that is the correct #) in the report pdf. You can see the old nut in the hinge block and what appears to be a similar example in New Old Stock condition. Note these are Fiber Lock nut INSERTS not nylon lock nuts most of you are familiar with. These are not just some common nut available from any aircraft bolt supply house. These are the old fiber style as were all the nuts of this type and on nut plates in WWII. When new, they don't hold as good as today's nylon insert nuts. Look at the hinge unit with the nut in it. The thing is somehow crimped into the aluminum block as if the aluminum is pressed to fold over the nut and hold it into the cutout. I would think changing that nut insert would be difficult thing to do IF you wanted to save the hinge. Maybe 26 years ago the hinges were replaced with new old stock parts instead of the nuts being changed as most are thinking. Maybe there are no new hinges with nuts in them or maybe they cost some crazy amount of money. Maybe the screws in these have never been problematic in mustangs until now. I don't know. I just look at the part and how the nut insert is mounted in it and can't see a way I could change it and not ruin the hinge block.

Tragedy always seems to bring awareness and from that, we get change. We know cigarettes are bad for us now but years ago, it was a pro health product. We know asbestos and sunlight are bad too. We know seat belts save lives and that it is good to have a spotter with you when flying RC models. Why? Because bad things happened and we as a race, did not see the future until it is the past. Same here. Air Racing and warbird maintenance have learned some hard lessons. The air racing world will be better from this just as the lessons learned in other examples. The people who were injured or died didn't know it would happen in that moment. Nor did Jimmy or his crew. If any of them did know, they would not have participated. The edge of life is sharp and narrow for those playing on it or standing next to it watching.

As usual, good description

Good explanation/analysis, Mr. Kimball! Thank you....

Originally Posted by kjkimball

As for 2 tabs shallow being less drag than one steep, I would have to see your 400+knot P51 test data to believe it to be true.

I'm sure there's no test data either way. Much of this stuff is tweak and fly and see if it works. I doubt the Galloping Ghost crew were using finite element modeling to test the structural stress loads with any of these modifications. Heck, they didn't even seek approval from the FAA for the changes they made. I guess they figured it worked for Stilletto so it should work for them.

BYW, use of a single left trim tab was cited by the NTSB report as one of the factors that contributed to the tab failure by placing excessive stress on the one tab (vs. spreading the load across two) along with the flutter induced by the tab cg change and the worn nylok.