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Post by gingerbeer62 on Feb 28, 2015 21:52:15 GMT
Does anyone know why there is such a strange mechanical fan (now removed from my car) fitted to the Rover V8 - did they all have such a strange out of balance object. Don't understand it myself.
Cheers
Colin
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Post by Phil Nottingham on Feb 28, 2015 22:14:19 GMT
Rover Co had their little ways so I am sure they knew what they were doing even if they had 2 varients of their common theme - which one do you have? Straight or bent tips?
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Post by gingerbeer62 on Mar 1, 2015 12:28:40 GMT
Rover Co had their little ways so I am sure they knew what they were doing even if they had 2 varients of their common theme - which one do you have? Straight or bent tips? The one with the blades are not equidistant. I thought it was bent out of shape. Then realised that it was made that way  ?? Cheers Colin |
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Post by Simon H on Mar 1, 2015 19:45:23 GMT
Made that way and perfectly balanced. I have no idea why Rover chose the asymmetrical design...
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Post by gingerbeer62 on Mar 2, 2015 13:56:53 GMT
Made that way and perfectly balanced. I have no idea why Rover chose the asymmetrical design... I've been an engineer for many a day and year and it is the strangest choice of fan design I have ever seen. I will leave it at that.  I can see the balance weights on it but all the same, why not start off with something that is at least tidy looking ?   Cheers Colin |
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Post by Simon H on Mar 2, 2015 15:44:59 GMT
The wider spacing on those 'odd' blades certainly helps when fitting a fan belt...
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Post by richardlamsdale on Mar 2, 2015 16:15:22 GMT
I believe it's to reduce noise - with equal spacing the fan will tend to resonate and be louder at certain speeds. Unequal spacing causes multiple frequencies to be generated which reduces the occurrence of a strong resonant frequency, and with careful tuning can create frequencies that destructively interfere with each other to reduce noise levels.
Some other cars had this as well apparently - Cadillacs and Mercedes and a few others. Most others tended not to bother.
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Post by Warwick on Mar 3, 2015 2:34:34 GMT
I believe it's to reduce noise - with equal spacing the fan will tend to resonate and be louder at certain speeds. Unequal spacing causes multiple frequencies to be generated which reduces the occurrence of a strong resonant frequency, and with careful tuning can create frequencies that destructively interfere with each other to reduce noise levels. Some other cars had this as well apparently - Cadillacs and Mercedes and a few others. Most others tended not to bother. Correct. |
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Post by djm16 on Mar 3, 2015 2:37:28 GMT
Reduce number of resonant frequencies was my guess too.
The P4 also has an asymmetrical 4 blade fan.
While you have the fan off you may as well check the balance to help with water pump bearing life.
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Post by gingerbeer62 on Mar 3, 2015 11:04:54 GMT
Reduce number of resonant frequencies was my guess too. The P4 also has an asymmetrical 4 blade fan. While you have the fan off you may as well check the balance to help with water pump bearing life. Thanks for all the input. I have removed the fan anyway and installed an electric one. May have to put the mechanical one back on in the summer if the electric one can't keep up !! Cheers Colin |
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Post by wrexhamrover on Mar 8, 2015 13:22:49 GMT
My local garage claimed that an equidistant 4 blade fan has a tendency to act like a propeller and this wears a pump bearing by moving it forward and back leading to eventual bearing failure. I think this is a great story even if incorrect!
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Deleted
Deleted Member
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Post by Deleted on Mar 8, 2015 18:39:01 GMT
Surely the idea of the fan is to act like a propellor.
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Post by gingerbeer62 on Mar 8, 2015 21:59:08 GMT
Surely the idea of the fan is to act like a propellor. Indeed sir, it is a propeller but I am still interested in why the offset. I am inclined to think about harmonics - nodes and antinodes. I do remember when I was at sea that some large marine engines that had a node at certain established revs that was to avoided and reved through as quickly as possible so damage to the engine did not occur. Even so, that is mainly a vibration (nodes and antinodes) thing, so it's probably a noise reduction thing as someone has already suggested. This is a link to a Jeep fitting of a fan which is also an offset fan, we don't, it seems have the only ones. The guy says that it helps with fitting it. ?? www.jeepsunlimited.com/forums/showthread.php?496635-Mechanical-fan-upgradeAlso some stuff about air flow noise and assess www.madsci.org/posts/archives/aug98/899326517.Eg.r.htmlAlso www.chevelles.com/forums/showthread.php?t=311327Cheers Colin |
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Post by enigmas on Mar 8, 2015 22:43:15 GMT
If you want the Rover V8 to cool efficiently offset fan or not, fit a well designed fan shroud. A correctly designed shroud pulls air through the entire surface area of the radiator. There's a bit of science to correct shroud design and fan positioning. Better still use a flex fan either after market or from an American V8 from the 60s - 80s. The aircon types move the most air and work very effectively.
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Post by Warwick on Mar 9, 2015 12:20:57 GMT
I believe it's to reduce noise - with equal spacing the fan will tend to resonate and be louder at certain speeds. Unequal spacing causes multiple frequencies to be generated which reduces the occurrence of a strong resonant frequency, and with careful tuning can create frequencies that destructively interfere with each other to reduce noise levels. Some other cars had this as well apparently - Cadillacs and Mercedes and a few others. Most others tended not to bother. Correct. Range Rover 3.5L engines have unevenly spaced blades on their plastic fans, for the same reason. |
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