It’s been a bit warm of late, here on the East Coast. I was on vacation in an un-air-conditioned house – and although I live in an un-air-conditioned house, my usual modus operandi involves box fans and ceiling fans. In the vacation house, I had an oscillating fan in my bedroom, and I noticed that the effect of the fan was noticeably different when it was moving in one direction.
Facing the fan, the blades were moving clockwise. When the fan was moving left to right (again, from the POV of someone standing facing the fan), I could feel the sweep of the breeze moving across me. When it was moving right to left – not so much.
Hmmm… could be a gyroscopic thing; if you hold a gyroscope horizontally and try to turn it, it will be deflected upwards if you turn in one direction and deflected downwards if you try to turn in the other. Given that there’s a fair bit of flexibility in the construction of a typical oscillating fan, I think it’s possible that this sort of deflection could have caused the main thrust of the draught to be higher up on one stroke and lower on the opposite stroke.
Couple this with the fact that you, the observer, are not uniformly sensitive to cool breezes across the entire surface of your body (for a variety of reasons including density of nerve endings, density and activity of sweat glands, and parts of your body being obscured by clothing), It seems entirely possible that it was shifting the same amount of air in either direction, but only in one of the directions was the main stream hitting you somewhere that you could appreciate it.
Another possible factor though, is that the oscillating mechanism may not be symmetrical in operation; it might move quicker on the return stroke than the forward one; this would mean that not only was less air shifted in the case of the faster stroke, but even more deflection (see above) would occur.
This is kind of what I was thinking – is it because the movement of the blades and the movement of the whole fan head is in the same direction that it has that “oomph”? The motor is kind of fighting the movement of the blades on the backstroke.
I don’t know about that, because whatever is true for the blades on one side on one stroke should be true of the others on the return stroke, assuming that this is a propeller-type fan and not a tangential one. I was thinking (in the second paragraph) more along the lines of the actual mechanics of the oscillating components; if it is driven by a rotary pin and follower mechanism, then it could be that one action is faster than the other because of the working length of the follower arm; if it is driven by a cam vs spring, then the blades might actually be turning slower on the outward action, if power is being taken off to drive the cam against the spring.
But I still like the gyroscopic effect explanation better, even though it might be a bit fanciful.
