Back when I was an engineer, we were doing development work on a small military aero engine. Small, well it still had a 5 foot twin blade wooden propeller. Because we were a small company with many projects on the go, we lacked anywhere to run the engine, so we got permission to use a small wood beside a grass landing strip near the village in which we were based.
Now for the part where H&S should look away.
We had this mounted on an old four-wheel motorcycle trailer (um, wobbly, too), and we lacked any kind of prop cage, even though we were using carburettors, and, due to the lack of manpower, I ran it on my own, plus since our sole half-brick mobile phone contract had run out I had no way of calling for help either.
The day came when I had to adjust the engine at full throttle, 7000 rpm with a prop speed of 2500 rpm. I should have gone and got the support of a technician, but it was a long way back and I might lose half a day's testing. So, there I was, lying over the intakes, 6 inches of steel carburettor adjusting tool in one hand, prop whirring by about 12 inches away, when the engine stuttered.
Ho ho...
When any engine stutters it jumps a bit in its mounts, more so with a propeller attached. Since I was precariously balanced on the side of the trailer, I kind of lost grip of the tool as I grabbed hold of a carb to stop myself from falling into the prop.
I can still see the tool tumbling down the gap between the propeller and the radiator, turning end over end.
And then it wasn't there.
If a propeller breaks, it just explodes. I know, I had seen it happen. Without a load, the engine would then attempt to leap out of its mounts, into my lap. I smacked the throttle lever shut, the engine subsided, and I saw that the propeller was still there, in one piece. Later, after I had switched the engine off and hugged a tree for a bit, I found a small dent in the tip of one of the prob blades, and my tool some distance away through the trees.
We built a prop cage the next day.
trevor