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RNO Air Races Crash

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The Fox news theory from a GA mechanic is disgusting. They even rotated the photo 90 degrees to fit their story. I realize this aircraft was highly modified but a stock Mustang seat, which I would guess is engineered to well in excess of 12 G, only adjusts in the vertical. The rudder pedals are adjustable fore and aft, not the seat. Typical lack of knowledge from a media organization in an attempt to get out in front of everyone else.

What's amazing is the quality and sharp focus of that photo (in a vertical dive). When I first saw it, I was convinced it was photoshopped and they forgot to erase the tailwheel, but apparently, it legit!

I agree. I doubt the seat failed and I doubt this aircraft has the control authority to fail the seat, but I consider it irrevelent anyway because an unexpected pull up in excess of 9 or ten G is enough to incapacitate the pilot. Fighter pilots sustain 9G only because they are ready for it. Even the G-suit doesnt help if you dont do your part first. You cant play catch up with 9 g's if you aren't on top of it first. Unfortunately, the pilot in the case most likely wasn't part of the equation after the initial pull up.
 
I have personally experienced GLOC as a back seater in the F-4 during an airshow in El Toro many years ago. Going thru a divorce and was tired and only had coffee all morning are my excuses. After our part of the show was done the pilot reefed on more than the usuall G's during the overhead break and I didn't "wake up" until wings level on downwind so I'm estimating 4 to 5 seconds in la la land. It kind of looks like from high G pull up to impact it wast much more than that so I think you are right about the pilot not being part of the equation. I've always enjoyed those races and I think they will recover after this trajedy.
 
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Todays WSJ echoed these sentiments. They're estimating a 10g uncontrolled pitch-up after the trim tab failed. That would knock out anyone. I would imagine that the seat would fail somewhere between 8-12g's as that would be more than enough for a pilot without a g suit. Also, strengthening a seat beyond that would add weight that they don't want to deal with.
Can anyone explain how a trim tab failure results in a 10G pull-up? How does the hinge fail before the bolt/bellcrank without taking the rear spar of the horiz stab with it. There's alot more area of the elevator trying to stay in one place than there is of the trim tab trying to move it.
 
My first thoughts too. Why couldn't he overpower the trim tab? Voodoo, an almost identical P51, had the same thing happen in 98 and pulled 10 G's with a much younger pilot and blacked him out too. He kept going up thousands of feet and as the speed fell off recovered.
 
Can anyone explain how a trim tab failure results in a 10G pull-up? How does the hinge fail before the bolt/bellcrank without taking the rear spar of the horiz stab with it. There's alot more area of the elevator trying to stay in one place than there is of the trim tab trying to move it.

I'll take a stab at it.

All conventionally rigged aircraft need more nose down trim the faster they go until you get into mach tuck regions. That's basic static stability, go faster the nose comes up. Remember that every stable aircraft has a basic speed it wants to fly which is determined by the position of the trim. If the trim tab is missing there's still a basic speed it wants to fly which is the same as a neutral trim position. Go faster than that speed it wants to pull up, go slower it wants to dive.

Unlimited warbirds are frequently modified with greater trim tab authority so they can go faster without running out of down trim. When they're going real fast the trim can be full down and applying considerable force to the elevator. Of course they may also play with the elevator incidence, maybe center of gravity to try to limit that, but fundamentally you need to make a compromise between high speed and low speed trim authority and basic stability.

The trim tab is servo tab applying force directly to the elevator not the bellcrank. When you're running at 490mph with the trim full down, the force on the elevator bellcrank is minimal. The force on the trim tab hinge is very large, it is forcing the elevator down and that's the thing opposing the natural tendency of the nose to come up. The elevator is fighting mightily to return to neutral, the trim tab is opposing it.

When that hinge fails due to the load, or the tab flutters and breaks off (which can happen in a fraction of a second), the elevator returns to neutral and suddenly the aircraft is nowhere near it's stable speed. It would require considerable down stick to hold the nose down. Maybe more strength than a man has. If you weren't right on top of it, the resultant pull up will knock you unconscious and the rest is history.
 
The elevator is used to keep the nose up (more forward trim) as speed increases. Correct? While in a turn, more nose-up trim is used to hold the nose up? Correct? The question really is, What is that tab doing to the elevator while it's partially detached? Did it result in a control jam? What was the pilot doing with the trim while in the turn? Was he trimming? Remember, he was in a 70-80º bank, reference the other aircraft in the videos. Was the trim control jammed, and/or suddenly release, resulting in a pitch up. The other tab was still attached. Or, was the elevator jammed and the pilot using the trim, excessively, to try and trim the nose up while in the turn. I doubt we'll know until the investigators find that "magic BB." Lots of aerodynamics going on here that will make you dizzy.

As with most crashes, it isn't any ONE thing.
 
I'll take a stab at it.

All conventionally rigged aircraft need more nose down trim the faster they go until you get into mach tuck regions. That's basic static stability, go faster the nose comes up. Remember that every stable aircraft has a basic speed it wants to fly which is determined by the position of the trim. If the trim tab is missing there's still a basic speed it wants to fly which is the same as a neutral trim position. Go faster than that speed it wants to pull up, go slower it wants to dive.

Unlimited warbirds are frequently modified with greater trim tab authority so they can go faster without running out of down trim. When they're going real fast the trim can be full down and applying considerable force to the elevator. Of course they may also play with the elevator incidence, maybe center of gravity to try to limit that, but fundamentally you need to make a compromise between high speed and low speed trim authority and basic stability.

The trim tab is servo tab applying force directly to the elevator not the bellcrank. When you're running at 490mph with the trim full down, the force on the elevator bellcrank is minimal. The force on the trim tab hinge is very large, it is forcing the elevator down and that's the thing opposing the natural tendency of the nose to come up. The elevator is fighting mightily to return to neutral, the trim tab is opposing it.

When that hinge fails due to the load, or the tab flutters and breaks off (which can happen in a fraction of a second), the elevator returns to neutral and suddenly the aircraft is nowhere near it's stable speed. It would require considerable down stick to hold the nose down. Maybe more strength than a man has. If you weren't right on top of it, the resultant pull up will knock you unconscious and the rest is history.

See, another theory. 5 minutes before mine. Entirely plausible, and probably more correct.
 
So Ack, you're saying that the entire airplane is riding on the bolt that holds the trim pushrod on? When I said bellcrank, I guess what I meant was the trim control horn, technically. Your explanation sounds plausible.
 
I've worked on and inspected my fair share of old airplanes. I'm not sure I'm 100% correct, but it might be time to park some of this WWII stuff? I know a good portion of the airplane has been replaced, but most of the mods are done to make it go faster. Racers might ought to be built from scratch and built just to race. The P51 was engineered to carrry weapons and fight.
 
Ack, very well written explanation of how trim works. I think you hit the nail on the head; when that tab came off the nose came up so fast that he didn't have time to react before the G's took him out.

To HalinTexas, you trim for level flight, not for a turn. You're going way off the grid talking about turning and trimming.
 

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