The first Gebhardt Lecture of the 2014-15 academic year gave listeners valuable insight into some of the most dramatic aeronautic disasters of our time.

On Aug. 21, Dr. Henry "Harry" McDonald, a former director of NASA's Ames Research Center, spoke candidly about his experience as a forensic engineer investigating the 1991 Titan IV booster rocket explosion and the 2000 crash of a Marine Corps V-22 helicopter. McDonald also spoke about his work investigating the Challenger and Columbia crashes.

"The investigation teams all came from science and engineering fields, so we knew about the systems involved in these vehicles. But none of us were compromised by having worked on these particular vehicles," he said.

"All of us worked collegially because we wanted our findings to withstand future scrutiny."

Check out this Powerpoint from his Aug. 21 talk.

An immediate analysis of the 1991 Titan explosion revealed an upper motor case breach and overpressure in the first segment solid rocket. McDonald was a part of a team of scientists and engineers that Lockheed Martin brought in to go beyond these findings to pinpoint the precise reason for failure.

Among their findings:

• The core pressure following ignition was underestimated in region of first-second segment joint;
• The design computer code used to make core pressure estimate (BLIMP+) had been incorrectly run;
• The propellant grain modulus of elasticity was borderline given initial material specs;
• Later specs had been tightened by designers but predictions had not been re-run;
• The core collapsed at first and second segment joint.

Future firings of the Titan incorporated the team's findings and were trouble-free.

McDonald said the Department of Defense (DoD) was very interested in rehabilitating the engineering flaws that led to the deadly April 2000 crash of the V-22 Osprey.

"The Marine Corps loved the specs of this vehicle. They thought it showed tremendous promise, so if we could make it do what it was supposed to do -- and do it safely -- they didn't care if it took some money. It was worth it," McDonald said.

Ultimately, the forensic engineering team brought in by the DoD determined that the accident had been caused by vortex ring state, a concept well-known among rotorcraft engineers but possibly overlooked by some of the fixed wing engineers who designed the V-22.

"The V-22 is a hybrid vehicle, so there were airplane and helicopter engineers working on it," said McDonald. "Engineering failures often occur at the interface of related disciplines, where important information from one field is not fully interpreted by the other."

A native of Glasgow, Scotland Dr. McDonald holds a B.Sc.(Hons.) and a D.Sc. in aeronautical engineering from the University of Glasgow. He is a member of the NAE, and the UK Royal Academy of Engineering and is a Fellow and Honorary Member of the American Society of Mechanical Engineers and is a Fellow of Royal Aeronautical Society.

At United Technologies Research Center, he became a department head and concentrated on what became known as Computational Fluid Dynamics. McDonald held a number of academic posts at Penn State University and Mississippi State before 1996, when he was appointed Center Director at NASA Ames Research.  He is currently the chair of Excellence in Computational Engineering at the University of Tennessee in Chattanooga 

Mark your calendars!

The next Gebhardt Lecture is Thursday, October 9 and will feature Dr. Richard M. Murray from CalTech.