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Ed Anderson wrote:
Here is a story failure mode of an alternative engine on another list that I found interesting. I rather doubt that stuck belts would cause a rotary to stop - although if at idle rpm, it just might. I recall one of rotary flyer who had a bolt jam the water pump pulley, but this caused both belts to jump off the water pump pulley. No coolant circulating, but pilot made it back to the airfield, had to make a go-a-round due to conflicting traffic, but landed safely. Engine was toast but still running when he shut it down.
Ed
The cause and subsequent sequence of events has now been established.
Alternator bearing seizure initiated dual rubber v-belt slip at the
crankshaft
pulley.
In 2-3 seconds 50 cruise hp turned both rubber belts into smoke and
vulcanised
them instead of driving the now freewheeling prop (no flywheel effect to
snap
belts).
The alternator was switched off immediately but to no benefit since its
load was
not the issue.
So instead of the crankshaft pulley driving the alternator, the alternator
now
seized was now driving the engine to a stop! A relatively minor accessory
failure
had initiated a cascade of events equivalent or even worse than a major
engine
failure.
This sounds strange, Ed. A couple of slipping belts stopped the engine? Is that possible?
Ernest, I would not have thought so myself. I would assume the belt would jump the cleave or break. But perhaps with a lower HP/Torque engine or especially at low engine rpm - two stopped belts might be sufficient additional load to cause the engine to die. But, it sounded like the engine kept turning (at least for a while) as it caused the heat and smoke cited. Perhaps that was sufficient to cause the pilot to shut down the engine himself. Giving the smoke, vibration, etc,. not an unreasonable action. But, apparently, the pilot did not. The load appeared to cause the engine to die. But, did he throttle back when the crap hit the fan - I'll bet he did, perhaps reducing the power from the 50 HP he cited to something considerably lower.
It sounds like part of the reason this turned out worst, is the Sprague clutch referred to permitted the prop to windmill (spin freely) which considerably changed the drag and descent path. Inoperative trim and the fact that apparently lowering the gear also extended the flaps (not necessarily what you want when trying to clear a hedgerow {:>)).
Luckily no one was injured.
Ed
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