CC makes a good point regarding the unlikelihood of wake turbulence being a potential factor in the left wing drop just prior to the pullup. With the wind blowing, there is plenty of ground features in that area of the course which could produce turbulence. In fact it's not unusual to see race planes bobble a bit while rounding the pylons whether from wake or other reasons.

I'm not sure about the trim tab failure being the cause of the rolling moment because the turn did not appear to tighten. Instead, the airplane appears to roll towards a wings level attitude before the increase in gee loading becomes apparent. I've thought from the start that the pitch up was due to the trim tab failure, but have no idea how much forward stick force would have been required to overcome the trim change resulting from the loss of the tab force. I suspect it's quite allot.

I've never flown a Mustang or any such high performance piston single and the highest IAS I've ever flown at is 360 KIAS, Vmo for a Westwind I. (nearly full nose down trim) Trying to imagine the trim suddenly going to neutral or less at that speed doesn't paint a pretty picture. Even the simulated trim runaway can be a handful at high speed if you don't push the trim disconnect pretty fast. Such a sudden change of required control force at near 500 mph in a Mustang must be much worse. I tend to doubt that Jimmy or anyone else would have had much chance of stopping the pitchup. Perhaps the final report will contain an analysis of the stick force change resulting from the trim tab failure. It's my feeling that any substantial instantaneous force change would likely be unrecoverable until the speed fell way off. Hannah was luckier in that his airplane climbed long enough for him to wake up.

As for all the talk about control surface stalls and high speed stalls, I just don't think that's a player here. The way I see it with the info we have right now, the tab broke, the airplane pitched up and put Jimmy to sleep with his head forward and down. With the Gee loaded on, the airplane slows down in the climb and P-factor or lack of corrective control input (pilot unconscious) rolls the plane into what amounts to a half barrel roll ending at the VIP boxes. It never looks stalled and the flightpath could easily be explained by the scenario above. As time goes on, newly revealed facts could certainly justify altering the theory to align with the new facts.

Like everyone else, I'll be interested to see a detailed accounting of all the factual data available to the NTSB team when they release it. As much as I respect their analysis of accidents, I like to do my own as well rather than just waiting to read the probable cause finding. As of today, no public docket info is yet available.

@Clipped Cub

Instead of pointing out what's wrong with my statements, you suggest google and then ask if I am a pilot.

Are you one? Really?

What is Leeward doing about his trim entering turns? Is he working it less Nose Down? Needing Pitch Up in the turn, he doesn't want trim Down, does he?

If he's leaving the tab up through the turn, using leverage at the stick to overcome it, for lack of time to neutral the Tab, his Nose up will greatly increase the Tab's exposure and angle to the slipstream. This greatly exaggerates the stress on the Tab. If it is at this point the Tab breaks, The Pitch Up will be disastrous, as per VooDoo.

Since the snap left was the first noticeable part of the Upset, It is reasonable to assume that this is where the Tab released its mounting.

I'm a humble Commercial Pilot, retired, without your degrees, but I venture to say I have a bit more courtesy than you.

What are your thoughts re: trim? Need a picture?

westhawk. The turn did tighten, and that may have been what caused the unwanted roll. In a steep turn, a Pitch up increases Roll into the turn. Left, in this case.

Found this in another forum (and this was also not the origin):

Interesting what Jackson has to say. I would ask whether this aft CG induced pitch instability was noted during practice and qualifying. If so, wouldn't it have been addressed? I would tend to think so, but I wasn't there and am not privy to what went on inside Jimmy's team. Maybe Matt is...

I'd also be interested in knowing more about the sound of the trim tab breakage on tape. Which tape? Was the microphone in the airplane or somewhere on the ground? I ask only because I want to confirm that the sound noted is time synced with the visual and telemetry data.

As for the rumors about NTSB recommendations and insurance company willingness to issue policies for future races, that's reassuring even if only a rumor. I hope it's true and that the FAA won't come up with ridiculous rules. I also hope the race haters in Lemon Valley don't gain any extra traction because of the crash.

Couple of thoughts wrt trim specifically.

I doubt there would be a working of the trim in the turns. In my humble aero experience, we generally trim for a fairly high speed, and accept the pull elsewhere. Main reason for this is that the human arm works pretty well at holding and measuring a pull, much less accurately a push. I would imagine this holds for the racers too.

WRT the tab's AOA, it's angle to the free airstream may be increased, but I would question whether it would see much real AOA change - it is hung on the back of a big plate (elevator), which is conditioning a very large part of it's airflow. Further, at those sort of speeds, I doubt there's very much angular movement of the elevator (if you see what I mean). I'm also rather unsure about an increase in 'pull' increasing the roll. You need to increase the roll to maintain level flight/avoid a climb yes, but I don't believe it is causitive. There may be some aerodynamic effect that causes this in theory, however in my experience if I'm hanging out at big bank angles and whale on the stick, it doesn't effect roll one bit.

WRT a trim failure - I suspect the issue is less the overall stick force required for level flight, but the transient. Imagine you're flying along with a slight pull on the stick, and suddenly the trim force is removed. The stick smacks back at you; even assuming perfect conditions, it will take you some time to react and recover equilibrium. This presumably is behind the (much) earlier reported comments from someone saying that they told the race pilots not to use trim. Now assume you've been pulling 4g for a few seconds, and the event suddenly smacks you into the 10+G regime.. Not hard to imagine the world going black before you get it sorted.

I follow that. As seen, Leeward was pulling substantial g in the turn; acclimated to that, and pulling against trim to begin with, if it let go (the tab) the a/c would Pitch Up immediately, we saw VooDoo do that.

If the cg was too far aft, the a/c has a second instant problem, augmented climb. Additional Pitch UP. Since the a/c was wings vertical, the drop of the tail would cause wicked Yaw left. One g would express itself 'laterally' instead of 'vertically', relative to the airframe.

Turbulence? Causative? Hmmm. It may have been additive, but I doubt it was responsible. I'll go with it, if it helps politically. I think scrutiny of the Class will happen anyway, and we'll see 'improvements' in structures and policies? Regs?

Jackson himself let's the cat out anyway, describing the Ghost as 'unstable'. An entire lap of instability can't be down to wind. Is he some kind of "Spokesperson"? I'm just guessin' and readin'; sharper minds than mine will out.

If you look closely, you can see a sudden nose-up pitch while in the turn. But I've still not sure about the trim tab failure sequence causing the the rolling moment either, just leaning. The aircraft quit rolling at wings level, so the stick didn't stay over-to-the-right after the correction.

If I had to guess, Leeward felt the sudden pitch in the turn, knew what was coming from prior airplane tab scenarios, and went to wings level to give himself a chance. He was already clinced to counter the turn g, so when the g shot up, his current body configuration probably bought him another fraction of a second to react.

They set the cg to what they are confortable with. Matt's reference to an overly aft cg is conjecture.

They trim and go. Rarebear's the worse for stick force changes around the course. The Mustangs sticks are relatively light.

The answers to some of the statements are intuitive, generally basic and can be looked up. Didn't come here to school, since like most here, am still putting the pieces together. I haven't written you off, you have some good to contribute - like realizing that the seat bottom is under load and not the seat back.

PPL. Still have the Cub I learned in at 16. Flew loops, rolls, ... in a stock Mustang as a treat. Ailerons and rudder gets stiff at speed. Soloed a T-6G. Currently own Yak-52, Chipmunk, Cubs, trainer types.

That's probably true. I try to write factually.

Trim's untouched during the race. Pilot workload's enough, and it changes the airplane when you don't want it to change.

Somewhere in here, Penny talked about Rarebear trim. Ignore the stagnation point/ versus shock strength portion. That part's wrong.

"Trim is untouched during the race."

That too is conjecture.

In the slomo run, I pay close attention to AoA as the roll left stops. From the constant perspective of the camera, we start to see more and more of the belly, out of sync with turn rate. This indicates a Nose UP trend, at least to me. There is a flash of up left aileron in the right reversal, suggesting the pilot was not in control, but that the ailerons were driven by airstream, not stick. I don't conclude that the pilot had time enough to recover from the left roll, nor that he had time to Rudder. If there is this flash of Nose UP, I think the pilot was out instantly. This Pitch caught him and his upper body left of the stick, and he was forcibly slumped into the left space, inputting an inadvertent right roll.

Some maths genius should calculate the g in the video supplied by the 'wrench'. He got 500 feet in less than ? seconds. I doubt 21g, but math is not me.

Thanks greatly for the RareBear vid. Takes stones to call Penny "wrong".

You are a hardass..... :ok:

It isn't only up to skull oxygenation, as you know. G can be a full on haymaker from a very big fist. Acceleration of the skull can lights out the brain in milliseconds. Plenty of O2.

That from the person without experience pulling g.:rolleyes:
We are not discussing direct impact to the skull. The Martin Baker back breaker used to give people an 18 g launch until the back injury statistics got out of line. Then they reduced the charge and added rocket motors to spread the impulse. But that 18 g kick did not put your lights out.

Lyman is well known from the AF447 threads, and his strengths appear to be in the legal direction rather than the aerodynamic ones, however he is not hesitant in trying to tell you his version of events, sometimes with fanciful additions.:hmm: I wouldn't absolutely discount his ideas, but instead examine them with a great deal of caution.

Skilled pilots do not use trim to fly the aircraft.

The elevator trim is set for a specific pitch attitude and left like that until another specific pitch attitude is required.

It's one of the first lessons of flying.

I have been all over the net regarding this iincident, and have seen a bunch of locked threads please don't let this happen here. This thread is amazing, thanks for all the insight. That said, Lyman any new thoughts on the aileron swap? Clipped, r u leaning towards the tt failing in the turn? Thanks again you guys.

It was Matt Jackson who accused Leeward of flying with trim, not an opinion of mine.

At 74 yoa, this pilot had just had `~50 square feet of wing chopped off, along with half his ailerons. As far as we know, he had maybe an hour on the airframe.

In this heat, he was cooking, he's passed RareBear, and his trim tab was costing him maybe 2-3 knots. He won't fly trim?

He needs a note from his Mom?

Machinbird. With a selected ejection, you have your spine, erm, organized.

In a hot little P-51, drooling for the gold heat, Mr. Leeward's noggin was ready for 10 g's? It didn't bounce off the plex like the nine ball on a break?

You assume too much, and you question too little.

Btw, listening to Penny, you pilots are the last gladiators....auto racing is childs play.....I feel so unworthy....lol

There's another reason not to touch the trim. The pilot can monitor aircraft status during the race. If the airplane exhibits any pitch changes, or stick force changes, that would be an indication to the pilot that the airplane configuration has changed.

Thanks for the heads up.
Lyman, you're requiring an emotional response and your posts, to me anyway, appear random, scattered with a lack of restraint, reduced self filtering, and now a lack of respect. Requires too much energy to find any worthy thought, and I don't have time to read your posts anymore so I'll be skipping over them. That also means I won't be responding to them. Nothing personal, there's room for all kinds of people in the world, I just choose who I communicate with whenever I can.

"pilots are the last gladiators"

Oh please. Yuck.

-drl

Not sure I'm entirely in agreement with this analysis. As I stated earlier, I think I'm seeing some differential movement of the elevators in one of the left bank event initiation videos. If correct, this implies a similar failure to the Voodoo Chile pitch up.
http://warbird.com/voodoo3.jpg
Looking at the Voodoo Chile picture of the tail after the event, the elevators are clearly pointing in different directions.

If you look at the elevator actuating bellcrank and a sample elevator, the most logical point of failure on Voodoo would be something like the 3 hole bracket on the end of the torque tube where it is riveted to the torque tube with what appears to be AN470 rivets
If the torque tube sheared outboard of that location, you would likely lose the entire elevator. since the center and outboard pivot points should fail sequentially if the inboard attachment is lost. The bracket collar would act to restrain the inboard end of the elevator torque tube if the rivets sheared.
http://i2.photobucket.com/albums/y17...pboard02-1.jpg
http://home.comcast.net/%7Eshademake...lBellcrank.JPG

Does anyone here actually know where the elevators separated/sheared on Voodoo? :confused: Could shearing of torque tube rivets be an initiating event for what we saw happening on GG?

Given all the obvious talent commentating on here, I am somewhat shocked that this little gem alledgely attributable to the NTSB has not drawn comment...

From my dictionary

Accident...

An unfortunate incident that happens unexpectedly and unintentionally

Fluke...

Unlikely chance occurrence

Not just semantics...I've never known an accident board to be the business of quantifying the part that lady luck has played in each and every accident (aviation or otherwise) since the dawn of time. I thought accident boards existed for the purpose of human enlightenment and such applications as the management of risk?

That statement could easily be construed as " sh1t happens...move on". Nothing wrong with that as a (somewhat unsophisticated) philosophy..but I hope the guy making that statement is not drawing a very large salary.

From what I understand, the torque tube sheared the retaining fasteners, whether at the pictured housing or internal to the elevator. They assumed the tab actuator rod failed from fatigue.

Could be a likely event considering the single tab configuration, though the opposite elevator attachment would have been the side that failed. In the Voodoo case, after departure of the tab, the elevator would become more overbalanced.

Found some g vs aging data, turns out we're pretty wimpy when we're young.



G-induced loss of consciousness: case-control study of 78 G-Locs in the F-15, F-16, and A-10.
[My paper] Nereyda L Sevilla, John W Gardner

If the elevators had lost continuity along their hinge line, that should leave one operating, and one in trail. Since the assembly (gross) seems to have survived a potential fracture, there could have simply been a misalignment between the two, as shown in your pic of VooDoo. Had there been an actual separation at the bell crank center, the elevators would have shown some level of partition in the video, I think.

The design of this system shows an obvious plan for symmetrical Stress.

From a design standpoint, had there been a desire to allow differential forces on each elevator, the Torque Tube would have been one piece, not halves. The bell horn would have been halved, and surrounded the tube, in clam shell, or other, perhaps splines, allowing for erm, Torque.

Defeating this design (disabling trim on one side) appears to have some drawbacks in operation.

Machinbird's catch on VooDoo shows a greater up load on the left elevator, consistent with carrying chronic ND trim with only one elevator.

Nitpick. The picture of the elevator with tab on the bench is of the Ghost, not VooDoo. The image signature is "Scott Germain" proprietary to GG. So, we do not know the method of attachment of the tube to the retainer/cup on VooDoo. Likewise, the "Rivets" might be bolts; The join carries such stress, aluminum fasteners seem wrong.

Old Fat One. Absolutely, that word was not NTSB-ish. It was probably Jackson's. In American, "Fluke" means "Next to impossible" and "unrelated to responsibility". The only way to convey more innocence would be to call it an "Act of God".

I've heard about something called 'stick free neutral point'. If the CofG was aft and fuel was being used from the wings, could the rearward moment arm have contributed to this condition?

SGC

Sir George.

The engine is cooled with 'evaporative cooling'; as the coolant evaporates, it is vented out, and lost. So there would be a loss of mass associated with cg also? I believe the evaporative cooler is behind the cockpit, so would this serve to improve the aft cg? Assuming there is always liquid to cool the engine, the mass of the coolant (Water/Methanol) would diminish from behind cg?

The racers have played around with ballast, they know their cg vs consumables loading chart, and they set the cg to what they can handle throughout the race. Leeward had GG flying for a few years so wouldn't think he'd be pushing that on a Friday, though anything's possible. He did demonstrate he could handle the airplane for 3 laps, so he felt comfortable enough to continue.

The problem though is that he required a lot of trim to get the stick force managable. The one trim tab did double duty and is a significant departure from the original design. They would have tested this configuration to Vdive at altitude, but the dynamic pressure is a lot lower up high as opposed to the 5,100 ft race altitude, and the test would have been done at 1 g.

In terms of stick-free stability, I've included a simple pdf explanation without the eye glossing equations.

http://www.flightlab.net/Flightlab.....c%232BA158.pdf

Intend to go back to the video to visualize a new failure sequence with the starboard elevator shearing and going stick free on that side. This would assume turbulence causing the left roll disturbance and top rudder and stick forward and to the right as recovery inputs. They're briefed, as if Leeward wouldn't already know, to fly those inputs when they find themselves even slightly inverted.

In the turn, the shock wave on the wing moves the N.P. aft and increases stability. That shock induced increase in stability goes away under 1 g.

With the Pitch Up at wings vertical after the snap left, I'd assume the elevators did not shear, for if one did, Pitch authority would diminish, and the Pitch Up would stop. Then again, having one elevator inop at the start of the right reversal, would explain the wicked Torsion visible in the tail (video).

From ClippedCub
Speeds such as VD are specified as Equivalent AirSpeeds in the standards - hence altitude should not be an issue. The exception is when mach number is a limit - MD rather than VD.

Was this aircraft actually tested to a declared VD?

As a matter of interest, does anyone know to what extent these aircraft are tested against standards? As an experimental aircraft they are obviously not expected to meet all standards (eg FAR23), but is there a set of minimums that are applied?

That is a terrific question.

If there are Standards, there have to be predecessors, How does Burt Rutan make a living? Some one has to be first?

Experimental?

Who would allow asymmetrical Tab stress? Who will disallow it? Frankly, how much power does RAR have?

Trying to keep it simple. MD is 0.80. VD is 505 IAS at race altitude and up to a certain altitude that I forget.

The teams have competent structural engineers from industry and the owners listen to them. If they required a test, they would have gotten it. They would have corrected to VEAS where they could, but doubt they would have done it at 3-5 g's. There's a perception that the airplanes are being pushed beyond the original design limits, but the Mustang guys honor the 505 IAS limit, and frankly they're having a hard time getting there. Though there might be some truth in that since the 505 IAS limit wasn't established at 3-5 g to begin with.

They're licensed in the eperimental catagory, maybe experimental/exhibition. Don't think they're restricted. Basically means you can do what you want as long as the hardware is airworthy and is signed off by the mechanics. The teams I contacted about mods were very concerned about safety, and we convinced ourselves we had the same level of concern when it came to modifying the airplane, i.e., I was originally concerned they might slap something on and go fly at Reno, and they assured me they wouldn't. In this sense, think the FAA is/was comfortable with owner's getting with the profesionals for any mod program.

Lyman, fair question, I'll attempt to answer.
There are many examples of light aircraft with asymmetrical trim tabs. The concept in itself is not the problem. The application of the concept to an experimental aircraft such as GG would be an issue if complete engineering and testing was not done before adopting that design.
My understanding of the regulations affecting experimental aircraft is as follows:
(Feel free to shoot me down if I'm wrong." )

As a US based experimental aircraft, construction merely needs to be performed in a workmanlike manner and to survive a certain amount of flight time before being permitted to be flown out of the designated test area. The regulations recognize that experimental aircraft may experience unexpected events and kill the 'test' pilot. The idea is to minimize the potential for for injury to others if the worst happens.

The problem with experimental aircraft is that the test program may not evaluate the full potential aircraft envelope. In the case of air racing, it is entirely possible to be exploring new ground during a race.

Thanks Machinbird. It makes sense to me. I saw Red Baron with Steve Hinton and its six blades chopping up the air I think it was '80.

I did not see LearFang, but saw Rare Bear with Lyle Shelton in it when it was wide winged and all Navy Blue. I think Strega was all Red at one time, and forget the name of the lime colored P-51.

Hinton's Engine seized, and the props stopped just as he was about to land after a Mayday. He impacted over the hill on (near) 08 and the plume of black smoke was visible for five minutes before the announcer said he'd died. There was absolute quiet, it was near the end of the day, and everyone walked to their cars in disbelief.

He survived. These guys are a breed apart, and they take monster risks.
I've been to the show at Reno dozens of times. It doesn't get old.

There is something about a half dozen unlimiteds with 18000 horsepower that touches ones soul. Charging down the start, everything vibrates.

I fon't know who said it first, but it's rumored to be Lyle Shelton.
"What do you do at Reno, Sir?"

"We turn money into noise".

ClippedCub, is the VD / MD limit specified by the contest rules?

Extract of LurkerBelow post
Thus far people have been concentrating on the trim tab as the initiator of events, where as perhaps its failure was a consequence of events, as with the extension of the tail wheel and the loss of its gear doors.

It's understandable why a racer would want the CofG as far aft as possible - less drag and hence more speed. How far aft is aft enough though?

As airspeed varies from a trimmed condition, the column force required to maintain a new speed (without re-trimming) is a measure of static longitudinal stability. For any conventional airplane, the location of the CG has the strongest influence on static longitudinal stability. For a statically stable airplane the required column force, as speed varies from the trimmed condition, is less at an aft CG than it is at a forward CG. As the CG moves aft, it reaches a point where the stick force per knot drops to zero, then reverses. This location is called the neutral point. The difference between the actual CG location and the neutral point is called the static margin. With a CG forward of the neutral point, an airplane has a positive static margin and positive static longitudinal stability. At a CG aft of the neutral point, an airplane has a negative static margin, is statically unstable, and may require some form of augmentation (computers) to be flown with an acceptable workload eg relaxed stability fighters F-16.

The result of moderate instability might be a flyable aircraft, but the workload goes up. If you pulled back on the stick the aircraft will pitch up and slow. But if you let go of the stick the nose will continue to pitch up, since a positive pitching moment will remain. It will require a push force to maintain a climb angle, not the mandated pull. If you pitched down and let go, the nose will tend to tuck under. You’d have to apply a pull force to hold your dive angle, not the mandated push. That’s how the Spirit of St. Louis behaved.

Manoeuvring stability, like static stability, is influenced by CofG location. However, when the CofG is aft and near the neutral point, then altitude also has a significant effect. Since air density has a notable impact on the damping moment of the horizontal tail, higher pitch rates will result for the same elevator deflections as altitude increases. From the pilots perspective, as altitude increases, a pull force will result in a larger change in pitch angle, which translates into an increasing angle of attack and g. While a well-designed flight control system, either mechanical or electronic, will reduce the variation of stick force with CofG and altitude, it is very difficult to completely eliminate the variation due to design limitations.

For example, for the same control surface movement at constant airspeed, an aircraft at 5,000 ft experiences a higher pitch rate than an aircraft at sea level because there is less aerodynamic damping. The pitch rate is higher, but the resulting change in flight path is not. Therefore, the change in angle of attack is greater, creating more lift and more g. If the control system is designed to provide a fixed ratio of control column force to elevator deflection, it will take less column force to generate the same g as altitude increases. What was the DA at Reno at the time?

Note the increased work load. Matt is quoted as observing Leeward having difficulty flying the course. High work load due aft CofG? Perhaps the workload just got too much and the aircraft caught him out. Time will tell.

Even the experts can get the CofG wrong. An SR-71 was lost on a test flight when the aircraft pitched up uncontrollably and disintegrated. The initiating event was an unstart, but the loss of control was the result of having the CofG too far aft.

Doubt it. Never looked at the rules. What I was trying to do was increase drag divergence Mach number, specify the flight testing required to make me feel comfortable, which would have included VD, and left it up to the teams to determine conformity if any rules were pressed.

Lyman. Goofed and read your post by accident. Didn't realize you were one of us. We've been having some trouble with kids-in-mom's-basement on a financial board I frequent and I was sensitive to elaboration. I'll write you back in if that's ok.:ok:

There's always room for error, but if Leeward felt uncomfortable, he would have aborted. His stability would have increased in the turn after he poured on the coals to make the pass. It would have been more pitch sensitive when he was unloaded.

Corrected link from before on stability.

http://flightlab.net/Flightlab.net/D...c%232BA158.pdf

ClippedCub, any idea if they are forming shocks on the tail at this speed?

And what balance limits do they use of the elevator? Original P51 figures?

Was going to keep this to myself so as not to clutter up the discussion, but the elevator has been reshaped for high speed effectiveness. It's more bulbous. This is to get it out of the boundary layer of the horizontal stabilizer and would have been selected by his aero guys. There is a basis for this from the old NACA reports that I was going to dig through again, but if a shock did form, it will form on the deflected elevator itself and not on the hinge line or ahead.

The tail is at a much lower thickness-to-chord than the wing, so the tail wouldn't have a shock. But shock waves are sensitive to curvature too, and the bulbous elevator will cause a re-accleration of the flow. Doubt there was a shock here, but in the interest of thoroughness, it's on my list to check, if for nothing else, to determine the margin.

Don't know anything about the balance specs, but it's not unusual for the guys do flutter flight tests when needed.

Very interesting, thanks for that. Any idea why they felt the change necessary? Were they running into a (stick force) stability issue?

You're writing me 'back in'? Was I out? :ok:

cheers

There was a lot dive testing going on around the war and they played with shapes to affect the hinge moments and effectiveness. The technology development ended when the Brits figured out the flying tail. GG looks more bulbous, but it could be an illusion from the squared tip, or a later model elevator. I'll be around a stock D model next month and I'll look then.

Wasn't going to bring it up. Think we can figure out the failure sequence collectively without referencing that detail. If we couldn't, was going to spend time looking into the elevator shape, and maybe shock bursting on the wing if the speed and g warranted.

CC, in #251 here there is a link to `hangartalk`,air racing; if on that link you go back to page9 #88 there are 3 photos which show the `oil-canning and the tab deflection from the rear quarter.(if you haven`t seen them already).
The Mustang 4 was limited to 505 MPH or .75 M,but had probably been flown faster in testing.Also the aircraft in those times had fabric covered elevators and wooden or plastic trim tabs and one on each elevator would reduce the loading,fabric covered surfaces tend to distort aerofoil shapes at high speed; later they were made all metal,except the rudder.Since GG is a `racer` the rudder tab is also faired in.
It would be interesting to know if the stbd.tab on GG was `locked` to the elevator,or to the tailplane as a balance tab,to reduce stick forces.
With regard to the `over-bank` at pylon 8, I would consider that to be gust induced,either by the preceding two aircraft and/or natural wind,which may have caused and been sensed by JL as a possible change to his `line` around 8,and preventing a possible `cut`,requiring a quick push,and a bit of roll-out.
It is difficult to see the pylon and aircraft to draw a reference as to how close he was now running,after having passed the `Bear`,and flying a wider pattern to do so.It is a lot harder to run closer to the pylons,with a lot more activity on the controls to get a tighter line.
With regard to the roll, I think that was induced by precession from the prop on the pull-up,causing roll,as the controls have become free,and as the aircraft starts downhill,it will try to go to a trim speed,controls free again.

On another subject,I have searched for the NTSB archive for the definitive results of the investigation into the tail failure of Miss Ashley` in `99`,but only find the standard report,which give no real structural results..Anyone got anything more definitive..?

PS.GG was reported at 495 mph; that equates to M.645 at 5500ft at an assumed *T of 20*C; M.75 would be 579 mph in the same conditions.

Other P-51 racers are saying the oil canning is normal, and transitory, though I'd think they'd eliminate that from a drag standpoint since they're meticulous on maintaining smoothness. The deflection of the port tab with the strbd in trail caught my eye as an engineer.

Placard is 0.75M, but they've tested to 0.85M where the Mach buffet shakes the scoop loose and causes rivets to pop. The aircraft was unairworthy on return. As such, MD will be 0.75M as opposed to the 0.80M Mach misspeak from earlier. This would mean demonstrating the Reno q's during the dive test would have been more unlikely even using an adjusted VEAS for 5,000 ft instead of SL. The structural engineers would have compensated to 5,000 ft q's, but it wouldn't have been demonstrated.

The conversion to metal from fabric was to limit the PIO on dive recovery at high Mach numbers for reason you've noted.

Currently the quick push, post left roll you noted, would have further increased the loads on the right elevator and that might have been what did it. The pitch change occurs immediately after the left roll. This would assume a natural disturbance to cause the roll.

Loads weren't understood as well in the forty's so the engineers overbiult everything. That's why DC-3's are still in service, and the reason these airplanes are lasting so long. But the tails are getting beaten up from the horsepower increase to 4,000 and they are in direct influence of the vibrations caused by the blade pass frequency, and are getting bombarded by the blade tip vortices.


Going to a single tab will put undue loads on the tab free side, and maybe it all just added up. Or the tab actuator rod just had enough since it was supporting double the load.