Reno Air Race Crash

It struck concrete. I'm certain that it has been repaired. There would be no reason not to.

 

The windscreen that blew out was not due to the fasteners being too short, although they claim that a few of them that were the right diameter were too short by 2.5mm which is about one thread and absolutely no factor. Minimum thread protrusion out the back side of a nut plate is generally 2 threads.

The rest of them they claim were the wrong diameter which makes me wonder how thy measured them with the window gone who knows where leaving only empty holes. I cannot understand how they could have torqued those screws properly if they were indeed the wrong diameter. The holes must have been slap full of butyl sealant to give them any grab at all.

When you install those they have to be torqued in a certain pattern and in 3 or 4 different torque setting stages so I don't really buy the "chinese blueprint" excuse that they put in the same size that came out which must have been wrong. I bet they used the same screws which should have been replaced with new ones in reference to the MM. That is jack leg maintenance and one damned lucky pilot.

 

THAT! is for sure.

 

I conducted a course to train new hire engineers at Boeing a hundred years ago, really in 1960-61, and the emphasis in one lesson was on the proper design of fasteners and edge margin in the material. This gets into flange width, bearing loads in the material, and fastener diameter. This is something that a mechanic can not ignore because hopefully a good engineer calculated what fasteners had to be installed in that particular connection. "What comes out must go back in" if you are working on a removal and re-installation. Inexcusable procedure if you put a fastener into a hole that that is of a larger diameter than the bolt or screw or rivet. I recall that 2+threads should be exposed beyond the nut and 2.5 X the diameter of the fastener should be the edge margin on a flange.. Spasso correct me if I'm wrong. Thinking back on some of the new engineers in the class I remember some of them were appalled that they were "lowered" to design brackets and bolts and they thought that they would have a desk from which they could hand-wave crucial design decisions. They soon learned.

 

The standard edge distance (which is what Boeing calls edge margin) is usually 2d +.03 in metal and at least 2.5d in composites (where d is the fastener diameter). Thus for the common #10 (.190) diameter fasteners, we usually show .41 edge distance in aluminum and .47 (or .50) in composites.

And the standard for thread protrusion is 2 threads minimum. The grip length shown on engineering drawings is often ignored, since the shop will grip each fastener before installation and choose the appropriate grip length. When fasteners are ordered, it is common to order one and two grip lengths above and below the nominal specified on the drawing.

 

Thanks for your very knowledgeable input. I was digging back to 50years ago and I couldn't remember all of it. The engineer students that I had then were fresh out of college and full of theories and graphs. Only those from Purdue, Texas A & M, a few eastern schools knew what the standards manuals were and how to use them. Many of the students had no exposure to actually designing anything. "Nuts and bolts were something the mechanics did"

 

That's why aerospace engineering departments in universities should insist that at least one of their faculty members is a veteran of working in the industry. Too often the universities only hire PhDs who invariably spend much of their time in lab coats doing research when they aren't teaching class. They may be able to teach theory very well, but they know nothing about the practical aspects of designing and building aircraft.

When I was studying at the University of Florida in the early '70s, we were fortunate to have such a man in the department. His name was John Hoover and he was the only non-PhD on the faculty roster. He had spent many years as a structures engineer in industry and taught both the structures and aircraft design courses at UF. He often told us about happenings in his industrial career when it helped illuminate the course material, including his time at Globe aircraft where he worked on the famous Swift.

I was lucky enough to have Mr. Hoover assigned as my faculty advisor, and he is the main reason that I became a structural design engineer. I seriously doubt if I had been as well prepared for what I found when I got my first job at Grumman if it had not been for John Hoover. I suggested to the school that they name the main aerospace engineering at UF for John, but they declined to do so. (In fact, that building remains unnamed to this day!) R.I.P. John Hoover, and thanks for the memories.

 

We were assigned to do a emergency exit path lighting mod on some existing 727's when that became mandated.
One of the competitors used our facility to do the first prototype installation.
While doing it per the instructions (measuring off of each individual seat structure) I noticed that "it didnt look right". As one of the engineers walked through he cabin I suggested he measure off of the fixed seat track rails. He looked down at me (literally as I was on the floor drilling) and said "Who is the Engineer here ?"

When the FAA came on board to test and approve the system they turned it on and it looked as if some drunk had wondered down the aisle marking the light locations as he zig-zagged down the aisle. They literally turned around and walked out.
Turns out the seat structure the lighting guys chose to use as a reference point was a variably installed part.

I dont know how much was invested in that start up but it all went down the drain.

 

IIRC the BAC111 used a different set of tools hence fastener types than standard Metric or SAE. Perhaps the wrong fasterer types were used as well.

 

Trim tab balancing on these planes is CRITICAL.
If not done exactly they will induce vibration which could work a nut off of a bolt, even if self locking, if not secured with safety wire or a cotter pin.
With 20/20 hindsight if short bolts were found in one critical location it could be assumed they were installed elsewhere as well.
In any case the competance of the installer who should have known better should have been questioned. Not saying he was but the question begs to be asked.
Many of the mechanics are well meaning volunteers.

 

Loose screws, probably no new restrictions on the race itself... age (of pilot) not a factor, alcohol not a factor... etc.



http://news.yahoo.com/ntsb-findings-2011-reno-air-races-crash-071719507.html

 

http://www.msnbc.msn.com/id/48801527/ns/us_news-life/

A news report just out on nbc.com, oops, same report as above

 

I was looking back on my Reno photos from last year. I can see in one of my pictures the "oil canning" of the fuselage in the lap prior to the failure. Its not as clear of a shot as some of the others ive seen, but its definitely there.

 

I just got the latest issue of "Warbirds International" magazine, which is one of their periodic issues devoted entirely to the P-51. It has an article that includes the following:

"The crash of..... N79111..... was caused by deteriorated locknut inserts in the elevator trim tab. These deteriorated locknut inserts allowed the elevator trim tab attachment screws to become loose and caused fatigue cracking in one screw. This condition, which resulted in reduced stiffness in the elevator trim system, ultimately led to aerodynamic flutter at racing speed that broke the trim tab linkages, resulting in loss of control and the eventual crash.

As the racer rounded pylon eight in the third lap of the six-lap race, the aircraft experienced a left roll upset and high-G pitchup at approximately 512 mph. During the upset sequence, the racer's vertical acceleration peaked at 17.3 G, incapacitating the pilot. Seconds later, a section of the left elevator trim tab separated in flight. The racer descended and impacted the ramp in the spectator box seating area."

The article includes reference to a new May 2013 Service Bulletin correcting a 1952 maintenance instruction that erroneously called out #8 thread structural screws to be installed in #10 spline nuts. I don't see the connection to the above narrative, and, besides, this maintenance instruction referred specifically to the aileron trim tabs and not those for the elevator.

A photo with the article shows the Mustang in its final dive, with no sign of the pilot visible in the canopy.

Hopefully all owners of P-51s, whether racers or otherwise, have since checked the integrity of all of their trim-tab attachments.