Questions about "Zubwoofer" blades

[valterra]

I built my mill ( http://www.fieldlines.com/story/2007/2/19/173948/328 ) and people mentioned that my blades were mounted too close to the center of the pipe.  They also mentioned that the angle looked too steep.  So I changed it, and remounted them right on the edge.  

Now, of course, they're even steeper.  I want to make a set of the "Zubwoofer" blades, but I have the following questions.  Thanks!

  Using Zubwoofer method, you measure 7 degrees and 25 degrees from a point on the outside of the pipe.  Since we're measuring angles from the outside rather than an invisible point in the center of the pipe, you only really have 180 degrees of available angles.  So I figured out the circumference of the pipe (pi x diameter) and divided it by 180, then multiplied it by 7 or 25 as appropriate.  I mention this so you can follow my math (and tell me where I'm wrong?)

That would result in the following measurements of the root and tip of the blades (multiply the root by 2 if you make a double blade out of a single piece like zubbly and wooferhound describe):

6. inch pipe = 0.733 inches wide at tip.  2.618 inches wide at root
   
8. inch pipe = 0.977 inches wide at tip.  3.48 inches wide at root
   
10. inch pipe = 1.22 inches wide at tip.  4.36 inches wide at root
    
    

My current blades are made from 3 inch diameter pipe.  And using that same math as in the zubwoofers, my 2 inch tip is 38 degrees, and my 4 inch base is 76 degrees.  So I see why you guys said they look too steep!

Question 1:  I am surmising that to get blades that aren't teeny, I need to use a 10 inch or larger pipe.  Is that correct?

Question 2: My current blades use what I'm calling "thick" PVC.  Maybe 1/4 inch thick.  Do I need to get the "thin" stuff to make these blades?  I like the thick stuff because the blades do not bend much (and therefore catch more wind?) if at all.  They are very tough.

Question 3:I've read in other posts that 4 foot diameter is preferred on these Ameteks.  What about width.  If my math is correct above, should I go with 6, 8, or 10 (or even bigger?) pipe?  As you can see, the base gets pretty big.

Thanks for your help!  And if you are one of the non-PVC believers, and say that wood is the best, please post a simple guide to wood blades, or email them to me at mobile(at)jeharper.com

Once again, thank you guys!  Wind power is awesome!  Even when I don't THINK the wind is blowing, my voltmeter tells me otherwise!

[Norm]

Here is the calculator for Zubwoofer blades

http://www.fieldlines.com/story/2005/4/17/6437/83378

This oughta work.

               ( :>) Norm

[valterra]

according to the subsequent posts, that program gives incorrect results because it doesn't measure the angles from the outside.  

Does my math look okay to everyone?

[RP]

"Now, of course, they're even steeper. "

I wonder if perhaps you moved the screw holes to the wrong edge.  The pitch should be very steep near the center (at the root) and "almost" dead flat to the wind out at the tip.

If I'm seeing it right on your webpage, in the image with your daugter, the screw holes in the blade holding the helicopter should be right next the edge closest to her.

This would explain the poor performance and why the pitch got steeper when you moved the holes out to the edge.

[wooferhound]

#1 - The larger the pipe diameter the better, there will be less arc to the blade and the tips won't end up being so thin or narrow

#2 - Thicker is better. Thin blades will bend back in the wind and hit the tower. They also warp faster in the weather

#3 - Sounds like the same question as #1 to me.

Some notes about your comments . . .

You say that a pipe prop can have a maximum angle of 180º, that would be a half round piece of pipe. The maximum angle that you can have from a pipe is 45º which will be a quarter round piece of pipe. If you try to make the angle greater than 45º the pipe will curve around on itself and divert the airflow away from the prop.

There is not any kind of simple math that will calculate your angle points.

The math that you are trying to apply is exactly the same as trying to measure the pipe from the imaginary center point, that is incorrect. The correct way to get this angle is to lay the pipe down with the center line on the bottom, then set a protractor down at the end of the pipe with it's centerpoint aligned with the pipes centerline. Find your angle points and mark the pipe. Now you can measure the pipe and mark the other end.

[wooferhound]

Here's a little Zubwoofer History . . .

http://www.fieldlines.com/story/2005/4/19/161431/811

[wooferhound]

Oh ,  and one more thing

make sure the prop spins Clockwise when you face the front, or the prop will unscrew it's self and fall off.

http://www.fieldlines.com/story/2005/12/29/1513/3449

[valterra]

I think I see your point.  And that sucks bwcause it means I made counter-clockwise blades.  

 

[valterra]

Zubb,

   Let me clarify - I am NOT saying that the max prop angle is 180 degrees.  I'm saying the maximum angle measureable with your method is 180.  Referring to the diagrams you posted, I say, "My Thoughts Exactly!"  

   As you can see, the lines on both diagrams intersect the circle at the exact same points.  However</u>, on the one on the right, the angles are incorrectly labled.  They should be 0, 30, 60, and 90 which are exactly double the values on the left.  Of course, you know that a horizontal line that intersects a vertical line is 90 degrees.  You have that labeled 45.  Looks like the software guy fixed it his math.

   What I meant by 180 degrees is this.  Please carefully consider what I'm saying.  A Zubwoofer 45 degrees is the same thing as 90 degrees measured from the center, according to the diagrams (when the numbers are fixed).  

   Using zubwoofer method, where would your 90 degree mark be?  Straight up - that's 180 degrees measured from the middle.  

   If you lay your protractor flat on the table, it IS a half-circle, right?  :-)  There is only 180 degrees' worth of range, lines, measurements, whatever.  

  So if you have a 10 inch diameter (31.4 inch circumference) pipe and you put your protractor on the table, using the zubwoofer method, and measure (for example) 90 degrees (straight up), you'd end up with a 15.7 inch arc of pipe, correct?  

   Well, 31.4 divided by 180 times 90 (my math) is 15.7.  Same result.

   Am I making  sense?  I'm not trying to upset anyone or start an argument.  I'm just being mis-read here.  :-)

>

[valterra]

And, unless I am truly all wet here, it means if you measure from the center (impossible - your method is MUCH SIMPLER) you are getting blades that are 50 degrees at the base and 14 at the tip.

[Capt Slog]

I'm not making any comment about the Zubwoofer blades in posting this; I'm sure that they are excellent.

But I used this when I made a set for my last project....

http://www.velacreations.com/chispito.html

I didn't follow the instructions, more the idea.  I think I used 6" pipe cut into 1/3s along the length and then cut each 1/3 in two lengthways to give two blades.  So I got 6 from my bit of pipe.

What I ended up looked a lot like the Chispito blades and worked very well, and spun fast enough to pull the little mill apart!

[valterra]

Thanks!  I think I can see why you didn't follow their instructions.  They were a little confusing!  :-)  Zub's plans are pretty simple.  Just a circle and a couple straight lines.

Most of these blade concepts revolve around the same idea I followed for my current blades.  That is, to make a single blade, cut the pipe so that it is X inches on one side and 2X or 3X on the other side.

I'm not sure where the 7 degrees and 25 degrees in the zubwoofers came from, but I've read many times not to vary much from that design.  His blades would be X on one side and about 3.57X on the other side.

[valterra]

Sorry for calling you "zub."  I have zubwoofers on the brain.

[Jerry]

High Valterra.

Here are a few pictures that show a wooden triangular hub I made. I then used a Roto Zip router to cut the circular slot for the blades to insert into.

Nice thing about the slot. You can slide the blade in the slot to adjust blade angle.

These blades start out prety steep at the root but are fairly flat at the tip.

The dome nose cone thing comes from Lowes pluming dept. Its a plastic roof vent pipe cover. It has 3 mounting spots on the outside and comes with the screws.

                         JK TAS Jerry