Oxnard Montalvo Posted September 7, 2004 Share Posted September 7, 2004 This is keeping me up at night. Why are some auto cooling fans asymetrical? Every other fan I can think of has the blades spaced evenly around the hub. What purpose does uneven spacing serve? Where can I get a life? Link to comment Share on other sites More sharing options...
Guest De Soto Frank Posted September 7, 2004 Share Posted September 7, 2004 So the machine gun doesn't shoot-off the blades ? (I really don't have the faintest notion why... ) Link to comment Share on other sites More sharing options...
Jay Wolf Posted September 8, 2004 Share Posted September 8, 2004 I think it has something to do with harmonics, the uneven spacing makes the fan make less noise. Link to comment Share on other sites More sharing options...
Guest Ken G Posted September 8, 2004 Share Posted September 8, 2004 I think Jay has touched on the reason. I should say here that I am a mere audio engineer, not a mechanical engineer designing fans, so the following is a guess.Think of the passing of each blade as delivering a puff of air. If the blades are uniformly spaced, then the puffs come at regular intervals of time. Thus the spectrum of air movement consists of a fundamental, the frequency of blades passing, and harmonics of that frequency. The result is a distinct pitch, which may be clearly audible at some engine (or fan, if it is electric) speeds and which I suppose might set up resonance within the engine compartment.If instead the blades are not uniformly spaced, there is no one fundamental frequency. Instead the spectrum is spread out, with less energy at any one frequency and no distinct pitch. This is likely to be less audible and much less likely to set up resonance.The blades must still be balanced, so there is a limit to how non-uniformly they can be spaced.Ken G, 1925 Rover 16/50 (San Francisco) Link to comment Share on other sites More sharing options...
Oxnard Montalvo Posted September 8, 2004 Author Share Posted September 8, 2004 Ahhh...Puffs of air, machine guns and harmonicas. Works for me. I can sleep now. Link to comment Share on other sites More sharing options...
Guest De Soto Frank Posted September 9, 2004 Share Posted September 9, 2004 Oxnard,I remembered reading somewhere that one automaker developed an fan with alternating long and short blades (in a symetrical pattern?), that was intended to cut down on fan noise?Makers of household fans (another hobby of mine) around the 1930's began to looks for ways to quiet the operation of so-called desk fans; the pre-Depression models just had tear-drop blades and pretty much sounded like early aero-planes when running. The new generation of "quiet-blade" fans featured larger blades that overlapped one another, so the the leading edges of the blades "would sneak into" the slip-stream of the preceeding blade...Such fans are known as "elephant ear" fans (Emerson), as well variations from G.E. - the "Quiet Blade" and "Vortalex".For more info about fans and their history, take a look at the Antique Fan Collectors website: www.fancollectors.org ; they have a wonderful photo gallery which allows you to browse the development of household fans from the late 1890's to the late 1950's...Enjoy ! Link to comment Share on other sites More sharing options...
Mrbuick714 Posted September 11, 2004 Share Posted September 11, 2004 Harmonics.Buick had some fans on their 320" engines that had,I believe three,regular blades on one side.then a heavy blade across from those. Worked fine ! Link to comment Share on other sites More sharing options...
Harry Van Arsdale jr. Posted September 12, 2004 Share Posted September 12, 2004 Balance,balance it was explained to me combined with a configuration that would make the least noise with the most air volume.I guess maybe different engineers came up with different solutions ?The machine gun firing thru the propeller used to bug me no end until I was told there is a cam on the motor which blocks the firing pin release until the propeller passes the gun barrel,simple. Link to comment Share on other sites More sharing options...
Guest De Soto Frank Posted September 13, 2004 Share Posted September 13, 2004 I always liked the early protoype Morraine-Saulnier (?) planes from WWI with the "deflector blocks" on the propellor blades...had to wonder just WHERE those "deflected" bullets went...Then the Germans captured one of those French Morraines, and a clever Dutch engineer by the name of Fokker got a look at things, and figured out how to make that interrupter gear work...Didn't Ford or Lincoln use alternating long & short blades on their fans during the flathead era? Link to comment Share on other sites More sharing options...
Guest Hal Davis (MODEL A HAL) Posted September 14, 2004 Share Posted September 14, 2004 I remember reading about the first attempt at firing throught the prop. The theory was that the prop is in front of the muzzle such a short period of time that the chances of hitting it were soooooooo slim that..........Well, luckily they tried it on the ground first. Deflectors were quickly developed after this. Link to comment Share on other sites More sharing options...
61-63 Posted September 16, 2004 Share Posted September 16, 2004 Actually it was because the guy in purchasing didn't order enough blades. Link to comment Share on other sites More sharing options...
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