I went up to the field lunch wagon to get a cup of coffee while the mechanics warmed up the ship.
I went back down to the hangar and crawled into the ship to do the first two of the next set of five dives. These were to demonstrate pull-outs instead of speed. Here was where I found out what the accelerometer was for.
I knew that the accelerometer was to indicate the force of the pull-outs. I knew that it indicated them in terms of _g_, or gravity. I knew that in level flight it registered one _g_, which meant, among other things, that I was being pulled into my seat with a force equal to my own weight, or one hundred and fifty pounds. I knew that when I pulled out of a dive, the centrifugal force of the pull-out would push the _g_ reading up in exactly the same proportion that it would pull me down into my seat. I knew that I had to pull out of a ten-thousand-foot dive hard enough to push the _g_ reading up to nine, and pull me down into my seat with a force equal to nine times my own weight, or thirteen hundred and fifty pounds. I knew that that would put a considerable stress on the airplane, and that that was the reason the Navy wanted me to do it; they wanted to see if it could take it. But what I didn’t know was that it would put such a terrific stress on me. I had no idea what a nine _g_ pull-out meant to the pilot.
I decided to start the dives out at three hundred miles an hour and increase each succeeding dive in increments of twenty miles an hour for the first four dives, as I had in the speed dives. I decided to pull out of the first dive to five and a half _g_, and pull out of each succeedingly faster dive one _g_ harder, until I had pulled out of the fourth dive of three hundred and sixty miles an hour to eight and a half _g_. Then I would do the grand dive of ten thousand feet to terminal velocity and pull out to nine _g_.
I took off and went up to fifteen thousand feet and stuck her down to three hundred miles an hour. I horsed back on the stick and watched the accelerometer. Up she went, and down into my seat I went. Centrifugal force, like some huge invisible monster, pushed my head down into my shoulders and squashed me into that seat so that my backbone bent and I groaned with the force of it. It drained the blood from my head and started to blind me. I watched the accelerometer through a deepening haze. I dimly saw it reach five and a half. I eased up on the stick, and the last thing I saw was the needle starting back to one. I was blind as a bat. I was dizzy as a coot. I looked out at my wings on both sides. I couldn’t see them. I couldn’t see anything. I watched where the ground ought to be. Pretty soon it began to show up like something looming out of a morning mist. My sight was returning, due to the eased pressure from letting up on the stick. Soon I could see clearly again. I was level, and probably had been for some time. But my head was hot with a queer sort of burning sensation, and my heart was pounding like a water ram.