Technical asymmetrical (unevenly spaced) bladed engine fans

Have you noticed that the tread on your tires isn't evenly spaced for the same reason?

 

What tread?

 

@twenty8
If you measured the sound of a really quiet night it would be between 72- 75db
Dead silence to the human ear is different to absolute silence.

I had this major problem [I didn't, but the sanctioning body did] with my BB Corvette being 3db over our limits
It was 93db vs 90db limit.
The extra 3db coming out of side-pipes made a huge difference that could be heard over other race cars.

The fix was quite simple! I knew where they measured sound levels at the track, so I lifted off the throttle when I passed that place

 

We had a few anechoic chambers at my former employer. Very few people could remain in them, while closed, for more that a few minutes.

 

I think that's the white sticker that says what size they are, country of origin, etc.

 

dont tread my tires...

 

The decibel measurement system of sound level is scaled around the human hearing range. Zero decibels is actually the level where the the human ear can't hear any sound. There are still sounds and sound waves happening at 0 dB, but we can't hear them.
@Kerrynzl is correct, 20 dB is 100 times louder than the minimum level of sound audible to the human ear. I just enjoyed the way he made the statement...

 

The hospital where I spent my last 5 working years had a couple "dead silent" rooms used for testing hearing. I sat in them a couple of times just to listen to the noises my body makes. For those of you getting ready to respond to my comment: NO, I never farted in one of them.

 

This. Don't forget, the decibel ratio to measure volume is not linear.

You have to have a huge amount of energy to double the volume at high (80+ dB) volume.

 

If I were to put a six bladed fan on my vehicle, I figure it would just give me a higher percentage of chance to take the end of a finger off.

 

Or the opposite. The more blades it has, the less time you have between each blade passes to get a finger in before the next blade arrives. Less chance to get a finger in there long enough to make significant damage.

 

WWII Messershmitt BF109 used an assymetrical 5 blade prop; ME109 did not.
The Bayerische engineers (BMW) followed thru with the engine upgrade, including the prop.

 

Don't know about that. I managed to get my right hand ring finger down to the second joint and the pinky before I could get my hand back out of there.

 

First let me say that I agree with you that the way the American system is set up, there is often a much better way. Case in point is "drill bits".........why call a .013 drill bit a #80...........just call it a .013......seems pretty obvious to me. Also I don't understand why we use different gauge thicknesses for different metals......there again, why don't we just call a .020 thk sheet of metal 20 gauge?

Are you sure about that ? If thats the diameter of the wire, it would seem to me that doubling the diameter would more than double the area......kinda like using a larger diameter exhaust pipe has a lot more area.

 

Yep.Weird feeling. Been in a few for EMI/EMC testing.

 

The cable is rated by the cross section area of the conductor, the 1.5mm² cable has 1,5 square millimeters of copper.
If it was diameter it would indeed have 4x the area if diameter doubled.

If you also happen to remember that the resistivity of copper is 0.0175, i.e that one meter of 1mm² copper has 0.0175 ohm resistance, you can easily calculate the resistance of a wire. Say we want to power a headlight through 3 meters of wire including ground, and the 12V lamp uses 5A.
3m of 0.75mm² cable would have a resistance of 3* 0.0175/0.75 = 0.07 ohms
3m of 1.5mm² cable would have a resistance of 3* 0.0175/1.5 = 0.035 ohms

5A through 0.07 ohms mean a voltage loss across the wiring of 5*0.07= 0.35V, while it's 5*0.035= 0.175V for the bigger cable.

Then we come to the step of determining how big a voltage loss is acceptable, but that's probably not part of a fan blade discussion. I'm not quite sure how I even got this far off topic, but I think it may be time to stop rambling now.

 

Want to keep this as a discussion

What you initially said was :

The drill bit comparison is a "diameter".

A 1.5 mm wire has a 9.68 mm diameter............

Dang, the metic system is just as confusing as our American Standard System..........


To me, the logical thing would be to call any electrical wire by the ampherage it can carry over a specified distance. So instead of cross section which requires computation, or the American system that assigns an arbitrary "gauge" number .............Why didn't they just call it what it was......a 30 amp wire or a 100 amp wire (based on a standard distance)? Would that not have been a lot easier when you are buying wire for a 30 amp breaker or a 100 amp panel? Seems logical .....guess thats why they didn't do it.

 

As long as the thread starter or the moderators don't get upset...

...which makes the most sense, because diameter is how holes are rated, most of the time. Especially while making them.

You lost me there. A single, solid round 1.5mm² wire has just under 1.4mm diameter. Don't know how to get to 9.68mm from there. Thicker insulation than on ignition wires perhaps?

Well, I'm sure confused by your attempt of using it! Might not be the metric systems fault this time, though.

I've got a good reason for that. You want it standardized around one situation, one specific use. Great when that's exactly what you do all day, every day. When you need to do something else, on the other hand, it would confuse a lot of people as they try to use 30 amp wire in situations when it perhaps only can handle 20 amp. It says right on the box it can handle 30 amp, but it's actually only able to handle 20, or 5, or 50, or... You'd still need some sort of datasheet telling you what it can handle in different situations, and you're better off forcing people to go straight there, then to give them a half-truth on the box because you know just as well as anyone that people are incredibly lazy and once they think they know what they need they sure won't spend another second researching it. They're going by what it says on the box (if anything at all).

Rating the cable by the crossection area gives you the most basic data about it, no interpretation of how it's expected to be used, no unintended confusion.

For house wiring you need certification etc. here so average Joe shouldn't be messing with that, and the electricians should know what to use and when to use it.
For a 12V system for example, normal people (unlike me, that is ) generally use a nomogram like this to figure out what cable size to use. As the demo line shows, you draw a line from the 5A/60W point on the left (when you intend to feed a 5A load) and the 10m point to the right for cable length, and it crosses the cable area graph in the middle between the standard sizes 2.5 and 4mm². You round it up and go with the 4mm² cable. Different nomograms apply to different situations.



Now, let's say that 4mm² cable is rated for example 20A according to your system, someone is going to mess up royally when coosing a much smaller one only rated for 5A, because they just account for what the cable can handle, not how big voltage drop will be acceptable - a very important factor in low voltage systems.

 

How did you manage to arrive at that answer ???

 

Very simple.......I looked it up on the internet, which is what 99% of us dummies do.
The quote below and one at another website BOTH said the diameter of 1.5mm wire is 9.68

"People also ask"
What diameter is 1.5 mm cable?
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"The size 1.5mm refers to the cross-sectional diameter of the cores so the overall diameter is 9.68mm."

So its not something I calculated. The point I'm trying to make is that many people build shops and wire them themselves. They aren't interested in learning electrical theories and doing mathematical calculations. They don't care about cross sectional areas........AND.........when they try to look things up on the internet...they get conflicting information and confusion. They simply want to know what size breaker they need and what size wire they must use. Myself, I always use a larger amp wire than what the breaker will trip at. In some cases, I get a much larger wire when working with the larger cables to the panel or a piece of machinery.
I'm simply saying that if you can call an 8mm drill an 8 mm drill and everyone will know exactly what to get whether they know anything about the metric system or not. But lets take it one step further and simply both the American Standard and the Metric. Convert both to "thousandths" and then you know exactly what you are getting..... When someone wants to Tap a hole, they get the correct size tap (for either system) and the first thing they must do is look at a chart that tells them what size drill bit to use. So look at the chart below.....the American system uses fractions,letters, and numbers to identify the drill bits . The Metric system gives you a millimeter ......extended into decimal places. The only thing anyone needs to know in either system is "how many thousandths the diameter of the drill is. Why call it something that requires you to convert to something. Lots of times when machining, a machinist may not use the specified drill bit but something slightly larger if one is available......in order to adjust the fit of the thread for some purpose. Its all about "thousandths" for us Americans. I have some Metric micrometers......never use them.


Think about it, what does the "F" tell anyone in the chart above. Nothing........

So look at the electrical wire sizes. There are charts available that are essentially the same as the drill charts, and they tell you the amp rating for the wire. What does telling someone the Metric size or the Gauge size accomplish? Ultimately the person (especially an amatuer like me) wants to know "how many amps can the wire handle". Here are charts that do that, and if you go to any building supply center you will see charts like these and hear amatuers talking to the salesman about what ampherage he needs. You will not hear anyone asking about cross sections and such.




With all due respect, my confusion over using arbitrary conversion information actually demonstrates that a lot can be lost in the process when you get the average electrically illiterate (like me) trying to do a bunch of calculations and conversions rather than using a straight forward chart. I've wired my own home (with directions from a friend) 40 years ago. Since then I have added a large 40x60 building and 3 other small buildings. There are 4 large 80 gallon compressors wired up as well as several large machines. Even have a homemade 3 phase converter for my mill. Added a professional 3 phase converter in the pole barn to operate a 10 gage shear. I just always make sure I use a larger wire than what the breaker will trip and never had any problem. I think thats what most amatuers do.
Anyway, not trying to knock your expertise..........just saying that its too easy to make a mistake using complicated information.

 

Well this thread went to garbage.
Subsequent off, off topic posts.
Looks like valuable information but is completely LOST as it resides in a topic subject that has nothing to do with wire sizes.

 

I got lost at the part about harmonicas

 

They are the ones made on a Monday morning or a Friday afternoon.......

 

When I was working at the news paper our press room averaged 110. When all 9 presses were running we hit 147 (louder if there was a problem). On a common press run we ran 5 presses. When we were running all 9 (Thanks Giving was normally when we ran them all) you used sign language, you literally could not shout and be heard 5 feet away.

Very little in this world is linear. We use linear because most people cannot think abstract. The only way that we can be extremely accurate in most situations, is to think abstract. An example in our world, I had my 355 in an OT pickup in 1998. The way the truck was geared if you use an online calculator the truck was capable of about 180. I know the truck would never hit that mark, so should anyone reading this and I actually hit the red line on the highway. No where near 180. The algorithm is linear, that is the way that most people think and understand.

 

You can inverse square that all the way to the bank!

 

Not sure I could hear an 11db sound over my tailpipes?

 

I think the one thing we did learn was that they make them assymetrical in order to dampen harmonic noise............(Can I say that on here....did they have Assymetrical fans in 65? Does it only dampen noises measured with the metric system? If you had two mules that were twins.....would they be Ass symetrical?
I think I'm loosin it

 

I guess we could have stopped there...
After all, it wasn't a question. More an admission of guilt. Statement of fact.

I'm glad they didn't.
Sure... they could have stopped there and just liked it, but boys being boys who could resist offering a comment or question to that admission?

Cavitation. Just the mention of that word and it syllables had me asking Google.

Post CES 2013: Silverstone's new fan reduces cavitation noise. - YouTube

I'll say this much for the conversation, automotive fans will be looked at differently from now on.

I think a posting is much like a forest fire. Either fueled to keep burning or they starve and go out.
I'd say yours did good.

 

I put a 5 blade oem clutch fan on my BBC truck. Much quieter. Alum 6 blade is officially a wall hanger.

 

I don't have much info on fans. However I am a fan of The Who and they were recorded at 126 decibels, 100 feet from the speakers in 1976. That is all I have to say about this subject.