NTSB Releases some Reports on GG Reno Crash from 2011

51fixer · **Posted:** Wed Aug 22, 2012 8:40 pm

http://dms.ntsb.gov/pubdms/search/hi...TOKEN=82086778
For those who are interested in the nuts and bolts of NTSB imvestigations and internal workings of P-51 and Racing systems.

JohnTerrell · **Posted:** Wed Aug 22, 2012 9:03 pm

The link in Rich's post is broken, here is the full link: http://dms.ntsb.gov/pubdms/search/hitli ... N=82086778

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11330

Primary cause seems to be elevator trim tab flutter from worn parts. It may have been excited at that moment from a gust or wake turbulence.

The speculation that the aircraft was going the fastest it ever had is bogus. The aircraft had actually slowed a bit from the previous lap and the power had been pulled back.

From what I infer, the modifications to the trim system probably didn't help the situation.

JDK · **Posted:** Thu Aug 23, 2012 3:28 am

Very interesting, thanks.

bdk wrote:

It may have been excited at that moment from a gust or wake turbulence.

Serious question - is 'excited' in this context a technical engineering term (like 'stress')?

How much is aerodynamic flutter fully understood these days? (I'm thinking back in the 1920s onwards where it was not fully understood, so otherwise sound designs might be compromised and destroyed by previously unexpected flutter.)

Regards,

51fixer · **Posted:** Thu Aug 23, 2012 7:44 am

JDK wrote:

Serious question - is 'excited' in this context a technical engineering term (like 'stress')?

Regards,

More like induced or it was an additional load different than the loads it was experiencing at that moment.
I believe the wake theory has to do with why GG banked so far or was upset from from the path that was intended.
The recovery was underway by aileron deflection when the pull up to 17gs occurred.
The trim tab as an issue was already in play in the turn prior to these events it seems.

JDK · **Posted:** Thu Aug 23, 2012 7:48 am

Thanks Rich, it was really a question on the term bdk used, rather than the 'what happened'. (I'm sure 'bogus' isn't something bdk uses on official forms in the day job, but I do collect odd sounding terms with specific technical meanings...)

Regards,

CDF · **Posted:** Thu Aug 23, 2012 8:06 am

JDK wrote:

Thanks Rich, it was really a question on the term bdk used, rather than the 'what happened'. (I'm sure 'bogus' isn't something bdk uses on official forms in the day job, but I do collect odd sounding terms with specific technical meanings...)Regards,

There you go. I just did a google search under "reno crash flutter" and this came up

Quote:

flutter is described as a self-feeding and potentially destructive vibration where aerodynamic forces on an object couple with a structure's natural mode of vibration to produce rapid periodic motion.
Submitted by John Carpenter on September 20, 2011.

http://www.flyingmag.com/news/reno-cras ... ta-emerges

51fixer · **Posted:** Thu Aug 23, 2012 8:13 am

JDK wrote:

Thanks Rich, it was really a question on the term bdk used, rather than the 'what happened'. (I'm sure 'bogus' isn't something bdk uses on official forms in the day job, but I do collect odd sounding terms with specific technical meanings...)

Regards,

As far as "Excited" for most in Warbirds the context I was thinking was in the bar after the airshow is over with the women but I'll accept your and BDKs context as well :wink:

In Southern Calif "Bogus" might very well be an official term

I know when I was there "Super Bitchin" was. :supz:

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11330

Normally one uses a coefficient of bogosity. I didn't want to get too technical though. :wink:

Excitation in this case means that in a steady state condition something might not occur, but a small spike in load, force or pressure might cause the system to trip into an unstable condition.

There may have been multiple conditions that needed to be satisfied for the system to become unstable, but the influence of each is difficult to predict. This could have been just as likely to occur ten seconds later or never. There is more to the equation than just speed.

JohnTerrell · **Posted:** Thu Aug 23, 2012 1:46 pm

Looking at the photo-by-photo study (as seen in the last photos/pages here: http://dms.ntsb.gov/public%2F51500-5199 ... 501402.pdf) of the aircraft turning around the final pylon, the roll correction, and the pitch up, I was amazed to see how crinkled/dented the bottom aft cowl panel becomes (seemingly more so as the photos/time plays out, though that may just be my imagination), just as the forces also bring about the breaking of the tail wheel lock. This of course besides the metal denting/oil canning that has been brought up before, and in the report, in the mid-aft section of the fuselage.

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11330

Looking at the photos, you can also see the upper skin of the wing oil canning. I don't see this as abnormal. There were some photos circulating a few years back showing oil canning on the fuselage of Rare Bear.

Look at a B-52 sitting stationary on the ground and count the wrinkles.

JDK, flutter is well understood, but full scale flight testing is still performed. It is not an exact science. Keep in mind that full scale structural tests are still performed on new designs.

P51Mstg · **Joined:** Tue Jan 25, 2005 11:36 am **Posts:** 1202

As far as a I know B-52 wrinkles were put in at the factory to allow for some stretching as the wings flapped in flight..... Still the basic idea is there.

Mark H

51fixer · **Posted:** Thu Aug 23, 2012 4:22 pm

JohnTerrell wrote:

Looking at the photo-by-photo study (as seen in the last photos/pages here: http://dms.ntsb.gov/public%2F51500-5199 ... 501402.pdf) of the aircraft turning around the final pylon, the roll correction, and the pitch up, I was amazed to see how crinkled/dented the bottom aft cowl panel becomes (seemingly more so as the photos/time plays out, though that may just be my imagination), just as the forces also bring about the breaking of the tail wheel lock. This of course besides the metal denting/oil canning that has been brought up before, and in the report, in the mid-aft section of the fuselage.

IMHO the fuselage wrinkles show the work the tail is doing to keep it going straight. It could have been in some unstable air and the bob weight was reacting to the chop or at that moment the pilot was implementing some slight control input. Some aircraft are flexible. P-63's had the Ventral fin added as slight rudder inputs could actually cause the tail to act like a trim tab and the result would be the opposite effect as desired. A hair of right rudder could result in a slight L/H heading change. At least that is what I remember.
The cowling wrinkle could show pitch up effects, sorta like it took extra nose high pitch as it slid around the turn with extra impact of air on the cowling skin. It could also be a shape or fitment of the cowling caused this to happen as unsupported skin moved around by turbulent airflow. The carb ducting on this was new composite rather than the original which fits real close to the skin of the lower cowling. Dunno if the lack of the orig carb elbow duct allowed the skin to pucker that much.

N3Njeff · **Posted:** Thu Aug 23, 2012 5:11 pm

Looking at the report and the construction pics only makes me wonder what GG was really capable of when Jimmy finally decided to "Show that last hand" has he would probably put it.

Anyone in the racing community thinking about following his lead on modifying a P-51 design or you think its too much?

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11330

P51Mstg wrote:

As far as a I know B-52 wrinkles were put in at the factory to allow for some stretching as the wings flapped in flight..... Still the basic idea is there.

Never seen wrinkles designed into a plane. How would you do that?

I suggest that the fuselage was built straight in a jig, and the wrinkles came when it got some weight on it. I suspect that the wrinkles go the other direction in flight.

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NTSB Releases some Reports on GG Reno Crash from 2011

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