A brief comment on the probable trim tab failure in the Reno P-51 crash

[GliderGuider]

It's clear by now that the elevator trim tab failed in flight.

According to a friend's sources in the sport aviation world, a P-51 normally trimmed will cruise nicely in neutral trim at 300 MPH; at 500 MPH the trim is full down and the stick is pushed forward past neutral. Lose the elevator trim and you get 11 positive Gs instantly (enough to fail the tail wheel up locks). 11 Gs at 74 years old (and that may be irrelevant) = pilot incapacitation.

That probably explains whey there was no sign of Lakewood in the cockpit in the last photo before impact - he'd blacked out and been forced down below the canopy rail, out of sight, by the excessive g-forces. In that same picture you can see that the tail wheel, which is normally retracted, has been forced down.

Lakewood was most likely unconscious at the time of the crash. what appeared to be a last-minute piece of heroics to miss the stands was probably random.

[leveymg]

1. It was impossible for his head to fall below the cockpit surround in that aircraft.

Conscious or not, his head would be visible in any profile or even the 3/4 approach shots in the crash sequence. We had a long exchange about this here yesterday. http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=439x1956733 Here are some relevant photos.

It's immediately apparent, there is simply nowhere the pilot could go strapped inside that small cockpit:

[GliderGuider]

3. OK, so what happened to it? It's missing from the photo after all.

I don't buy the argument that it was obscured by reflections.

I suspect there is enough room in that cockpit for a head that suddenly weighs 120 pounds to be bent far enough forward on a 74 year old neck to be forced out of sight. A sudden hit of 11g can do a lot of damage.

[leveymg]

4. No way he could bend that far forward wearing a five-point harness. Here's the profile and 3/4 shot

I don't buy the obscured by reflections argument, either.

There is no good answer that I have seen. It's been suggested the photos were faked or photoshopped. I don't buy that, either.

Here are the crash photos. Judge for yourself:

[malaise]

7. I actually hope he was unconscious before that

aircraft hit the ground

[leveymg]

25. Here's the photo of the plane as it flew inverted - pilot's head not visible

back or center of the cockpit, where it should be. The lighter rounded area at the very front of the cockpit is, I believe the top cowling over the instrument panel. If that is his helmet (it doesn't look large enough, though), the pilot's shoulder restraints may have failed and he's slouched all the way forward. To enlarge: SHIFT+



Here's a photo of the plane in normal flight, pilot's head slightly forward:



The question now is: how far back does the instrument panel extend on this particular aircraft? Is that the helmet or the top of the forward cowling? It would appear that the top of the instrument panel, which is silver, is in that area, as one can see from a photo taken from this angle:

[leveymg]

27. I think we have to conclude the restraints failed, and

the pilot slammed forward into the instrument panel, and is slouched forward, motionless, his head just below the level of the cockpit surround.

10Gs is well within the ratings of the harnesses that are used, and it does not appear that the pre-crash G force was enough in itself to cause severe neck injury due to impact of the kind that killed Dale Earnhardt (42Gs). Still, a requirement for a Han restraint device might not be a bad idea in Unlimited air racing, as it is now in many forms of auto racing.

Restraint failure is very improbable, but it's the only explanation that makes sense.

[RUMMYisFROSTED]

2. I'm leaning towards murder.

:tinfoilhat:

[Motown_Johnny]

17. maybe an alien abduction

:sarcasm:

[dtexdem]

18. Raptured!

;-)

[RUMMYisFROSTED]

28. Trim tab shenanigans!

:tinfoilhat:

[AngryAmish]

5. As someone who really does not know much about this field, having a crowd nearby really seems stupid

There have been multiple crashes over the years. The activity is not safe, especially with the modifications on this plane.

It just seems like a terrible idea.

Put out in the desert and on tv. If the pilots want to kill themselves, fine. Just no spectators.

[Kolesar]

10. And a waste of limited resources

Oil and vintage airplanes

[bvar22]

6. I really question this information from your friend.

"According to a friend's sources in the sport aviation world, a P-51 normally trimmed will cruise nicely in neutral trim at 300 MPH; at 500 MPH the trim is full down and the stick is pushed forward past neutral."

This may be true for a stock P-51 rigged to escort bombers at 300 mph,
but would be unacceptable rigging for an Unlimited Racer.
Full trim down and stick forward would produce so much drag that anything flying in this configuration would not be competitive.

I am NOT an Unlimited Class Racing Pilot, but I will have to see some other support for this claim.
My best guess is that anyone who wanted to be competitive in this class would be Trim Neutral for 450 MPH.
ANY "trim" deflection causes drag, and these guys are so OCD about drag that they will freak out about a fingerprint.
The thought of trying to race with Full Down Trim seems highly unlikely.

The only credible information I could find from someone who actually flies Unlimited P-51 Racers seems to contradict the information you posted.
He says THIS about the trim needed to fly the highly modified P-51 "VooDoo",
very similar to the one that crashed at Reno.

On Handling

"Voodoo requires very little trim change for change in airspeed..."

http://www.teamsteadfast.com/voodoo.html

This whole article at the above link is extremely interesting,
and should be read by anyone with a passing interest in the accident at Reno.

[GliderGuider]

8. Excellent contribution. Thanks!

I have no idea of his source, so I'm agnostic about the validity of the info.

You're right about the drag, of course. Still, the evidence does seem to point to a very high-G excursion.

[bvar22]

9. I had heard yesterday that the accident occurred shortly after take-off.

I haven't bothered to check other sources, only what has been posted on DU.
I haven't seen the YouTube, or the TV reports.

I really should check those before commenting,
but I still feel that losing the trim tab in and of itself would not be catastrophic.
The Trim Tab departure is more likely a symptom of a deeper structural or design failure.

Disclaimer:
I am NOT an Unlimited Class Racing Pilot,
engineer, designer, or builder of these types of aircraft.
I did obtain my Commercial License on my 19th birthday (1969),
am a life long Sport Aviation enthusiast
with many hours in High Performance Aerobatic Experimental aircraft,
even an hour in the jump seat of a modified P-51,
and WHAT an experience THAT was!

[Auntie Bush]

11. Good for you!!!! Must have been an exciting life!

[bvar22]

14. In some ways it was.

It was a different World back then.
GOOD Jobs were plentiful,
and the Working Class had some Disposable Income.

In many other ways my life now,
living in The Woods, building everything by hand,
and producing our own food, is more exciting.
It is certainly more fulfilling than looking for the next extreme adrenalin high.
There is definitely a problem when motorcycles are too tame.

[guitar man]

21. I'm wondering about balance

Control surface balance can be critical to prevent control surface flutter, especially at high speeds. I'm scratching my head wondering if the departure of the trim tab and subsequent loss of its weight didn't throw the elevator far enough out of balance to induce a high speed flutter?

[bvar22]

23. That is a good question,

...and way above my ability to answer.

I would tend to believe that High Speed Flutter would cause the Trim Tab to depart,
rather than to other sequence.


Chicken...Egg...Splat. :shrug:

[guitar man]

26. Yeah might have

High speed flutter sets in, kicks the trim tab off, elevator put of balance begins to shake even more violently , very low altitude, hauling ass, end of story...

[BobbyBoring]

24. I've heard that too

But on some of the videos, someone says they are entering the 3rd lap so that would not be right after take off.

[leveymg]

20. Here's a video that captures the last few seconds - he went inverted, and then straight down.

See seconds 11-14. http://www.youtube.com/watch?v=xF72nzr1Ixc

[hunter]

13. The answer is in your own question...

Air is hard and unforgiving at high speeds. That's why racers are so concerned about it.

I remember riding motorcycles well past 140 miles per hour when I was young, stupid, single, and thus immortal. The nature of air itself was pretty damned scary at those speeds.

I also remember the folded steering wheel and the seatbelt bruises on my chest from a much lower speed car wreck I was in. (I was beginning to feel a little less immortal after that...)

At very high g forces it's not difficult to imagine that Mr. Leeward's seat and restraint system failed such that he was squashed down out of view toward the floor.

We'll wait and see what the final consensus is, but I think g-forces will be part of it.

[bvar22]

16. The information I "questioned" was that...

...an Unlimited Class P-51 in racing configuration is flown with Full Down Trim and Stick Forward.
Anyone familiar with Drag, or "Air is hard" as you put it, would also have this question.

I have never questioned the "hardness" of air, or the power of "G" forces.
I DO question whether the loss of a Trim Tab in and of itself would have catastrophic consequences.
The departure of the Trim Tab in this incident would seem to be a symptom of a deeper structural or design problem.

[hunter]

19. Reply to wrong post...

Sorry.

[leveymg]

22. Watch the video. He went inverted, waggled, and then looped straight down.

The dive looked like it would generate a lot of Gs, but not enough to compress the pilot below the cockpit surround. Seconds 11-13.

http://www.youtube.com/watch?v=xF72nzr1Ixc

But, I wouldn't be too surprised if the G-s being pulled by the pilot in another P-51 doing aerobatics in this video are about the same (see, minute 3:11): http://www.youtube.com/watch?v=WE0sr4vmZtU

[bullwinkle428]

12. Just to give DUers an idea of relative speeds, look at this video of racing planes

traveling at around 220 mph. This is from the Red Bull Air Race series, in which the aircraft race in individual trials through a series of pylons, performing acrobatic maneuvers while timed.

http://www.redbullairrace.com/cs/Satellite/en_air/Video/Final-4-Highlights,-Windsor-021242858371762

Now consider the speeds of planes at the Reno event, where they approach 500 mph!

[Posteritatis]

15. An unexpected 11 Gs for a young person in perfect health would probably be incapacitating

That kind of shock isn't something most people would be able to withstand without being thoroughly prepared for it, no?