Aerodynamic Stress

By Ted Tryba

Transcribed from “BAD News – Journal of the BAD 2 Association” Vol. 10, No. 3, July 1987

© 1987 BAD2 Association

Although I had checked several B-17Gs as they were introduced to Warton, my first “big look” intimately involved devising a test to ascertain the extent of the fuselage rippling on the sides, just aft of the cockpit. The thinking at the time was that the added weight and protrusion of the nose was damaged due to enemy action.

I picked a B-17G I knew was going up that day, although I didn’t know who would be the pilot. As it turned out, it was Col. Moore, the base commander. I introduced myself to him and told him I was going to check some things, not specifying just what I was going to check.

I settled myself on the bottom of the fuselage, just after of the co-pilot’s seat. Picking out five stringers, I attached a dial micrometer in a descending stagger to each one, pre-loading each to .020”.

Everything went fine during the take-off roll, with the needles bouncing back and forth until the aircraft rotated. At this point there were five loud reports, like a .45 calibre weapon would make. It started from the forward clamped on micrometer and preceded individually aft, each a singular (loud) report.

The colonel at the controls at that point was calling out, wanting to know what was going on!

I went up to him, and explained what the noise was, and what had caused it. It took me a while to come up with “why”. This was due to the stress wave organizing itself to accommodate the re-alignment of stress in an airborne condition. I was embarrassed, to say the least.

So that the test would not be a total loss, I transferred the micrometers to the left side and checked them during landing. Nothing happened except I got good readings from each unit as the area undulated during landing and braking. After the flight I showed the colonel one of the micrometers and its attached clamp and explained further what had happened. Each stringer was cracked and I had left them that was, allowing this area to act as damage inflicted by enemy action.

Col. Moor didn’t chew me out… he just said “keep up the good work”, whatever that meant, under the circumstances!

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