Improved ZubWoofer Design

[ghurd]

Hi all,

Looking at some blade designs and a program, it occurred to me...

That the root section of carved blades should be very thick.

The ZubWoofer PVC blades are a lift design.

And the section near the root has a very poor angle of attack.

Looking at a drawing of the ZubWoofers would be helpfull here.

The numbers I will be using are just pulled out of thin air.

What I thought was to increase the root angle to maybe 30 degrees.

Then, for the trailing edge from the root to maybe 20% out toward the tip,

at the root mark 5 degrees into the blade, at 20% out mark the trailing edge,

and remove that material.

Visualize the cross section about 5 or 10% out from the root.

The angle of attack and lift should be improved.

The surface area would not change drastically, but the same idea as like starting with a very thick piece of wood for a carved blade to get a good angle of attack.

While the center 1/3 is only 11% of the power produced, I read,

It would also maybe increase the power from the rest of the blade,

because it would not be dragging the dead areas through the air.

That dragging and induced interferance in the air flow could be why they stall at a certain RPM?

The leading edge would be changed considerably, and may need adjusted accordingly.

Is this way off base?

I am not a blade guy. Does it show. LOL.

G-

[nothing to lose]

I wonder if we are a little on the same track in a small way.

I was going to try 2 shorter blades at one angle, 2 longer blades at a different angle.

Sort of try for more start up in lower winds with 4 blades, higher speed in faster winds with a 2 blade.

[Experimental]

      Well guys, again, I,m getting into an area I haven,t explored much as yet, but I can share a few truths with you !! (I Hope!!)

     Highly cambered props, without a true airfoil shape, will start at lower wind speeds and probably be fairly powerful -- but, they will stall out quickly at higher speeds due to the fact that the wind "breaks" loose from the back side of the airfoil, turbulates and generally destroys all efficency !!

    Highly cambered, with a true airfoil shape, will work better, but due to it,s highly cambered feature, the wind at higher speeds, can not stay attached to the back side,again causing turbulance..

    Flat thrust face, small rounded leading edge and thickest point of cord, about 25% from the leading edge is about the best bet-- tapered toward the tip and angle of attack , washing out toward the tip !!

    The wash out is because the angle of attack, at the approx base of the propeller in one revolution -- (we  will say) would travel foreward 30 inches, in one rovolution at it,s set angle -- the tip, due to it,s diameter, needs less angle, to arrive at the same 30 inches in that same one revolution!!

   One thing that destroys efficency in propellers, is bending in high winds as

Bending also changes the pitch at the tip -- that is why aircraft propellers are made of several laminations -- it makes them stiffer and less bending !!

   If the leading edge is to sharp, it will erode quickly, espically in rain -- if you flatten the leading edge and put a bead of polyeurathane "putty", or epoxy resin on it, then sand it to conture, it will last, years longer...

    It sounds like what you are trying to do Ghurd, is actually, getting the pitch of the tip, more correctly in line with the root angles -- thus makeing it more efficent !!  That should also, reduce bending !!

    There are a lot of highly efficent prop profiles, but they are also, fairly critical to construct and profile -- that is why I recommend the flat thrust face and profiles, Hugh Piggott and many others use --They are easy to work with, and fairly efficent !!

     Most of my experience is with raceing props, for aircraft -- and wind generators are similar but operate more like a wing than a propeller in my estimation -- but, both share some of the same principles !!

    I hope, something I have said here, is helpful-- Keep inventing guys..Bill H..

[ghurd]

""It sounds like what you are trying to do Ghurd, is actually, getting the pitch of the tip, more correctly in line with the root angles -- thus makeing it more efficent !!  That should also, reduce bending !!""

I was thinking the tip is OK.

Was trying to get the root more in line with the tip.

Played with tip angles, and 7' or 8' seems best.

It just looks like the angle of attack at the root is way off.

The blade programs show the root area leading edge almost facing into the wind.

So the PVC blades root is way off.

Instead of 0' (?) and 25'for the root,

More like 5' and 30'.

That should bring the angle of attack closer to perfect.

How far off is my reasoning?

But from 25% of the length, out to the tip would not change.

Not sure how it would effect the flexing.

Kind of figure the tip would go negative.

Really thought this would get more interest.

At least 'good idea' or 'thats totally wrong.'

G-

[Experimental]

      Well Ghurd, like I said, I,m a little out of my element as I,m still learning at this point-- If it were a prop for aircraft, I could tell you a lot more -- but wind driven props are a different animal..

     In the instance of PVC, and a constant changing angle, because of the high camber and lack of a true airfoil, you,re in "no mans land" -- It looks like one of those areas where it,s -- Try it , and see !!   BUT, what your trying to do, is more in line with the the basic rules (if there are any rules !!??)

    The biggest problem I see with PVC and other types of plastics, is the flex in the blades -- that flex , changes everything !!  The trick, is to make the prop become more efficent, when it flexes ---BUT, when you have changing wind speeds how do you do that

    With the raceplanes, we had engines that were red lined at 2750 RPM -- but we ran them at about 4300 RPM, at the races -- we only had one thought -- go fast, and accelerate out of the turns !!

    Here we have props DRIVEN by changing winds !!  Believe it or not, it,s more complicated because of ever changing conditions !!!

    In a lot of ways, You are a pioneer, and although a lot of testing was done thru the years, by companies like -- Boeing aircraft -- they weren,t designing props for guys like us -- they wanted megawatts !!

    I think the guys, building wood blades, are on the right track -- but, getting all the blades at the proper profiles, is somewhat a problem for all of us ..

I also think they should be using laminated blades as well --( for stiffness) BUT, when you are building a one off project, on a limited budget and limited tooling -- it gets real difficult !!

     Keep experimenting, and thinking "outside the box", that is where the best ideas come from, and from your posts on this forum, I haven,t seen you come up with a bad idea yet Ghurd !!    Keep inventing guys, Bill H....

[ghurd]

Thanks!

My stuff is all very small.

Like tiny, but not quite that big!

Flexing doesn't look like much of a problem even with the extra thin green PVC.

I am going to try it.

But don't have any way to get any accurate comparisons.

Unless it is very good or very bad, I won't know any difference.

My next ones will be a thick wall PVC.

With an attempt to get a little airfoil in the last half or so.

(I don't expect it to go well)

The 1/2" EMT tower will snap before that stuff flexes!

G-

[Experimental]

         Just happened to think, You could cut a simple wood form, cut your PVC, put it in an oven,about 200 Degrees (250) If you have troble holding the PVC in place -- drill a couple small holes to slip over cut off nails, in your wood form-- it will mold to the exact shape you want, and retain that shape when cool !!

       You can have all the blades you want, at the shape you want -- if your oven is big enough (and the wife isen,t home !!)

      I have also used a wooden box and a heat gun, blowing hot air, to shape plastics--- keep the heat from blowing directly on the plastic, and don,t exceed about 250 degrees -- I got elaborate,and used an old oven thermostat control to control the heat gun, but for something small you just need a thermometer stuck thru a hole -- candy type, (again, maybe when the wife isen,t home )

   I lined the box, with aluminum foil  and you need to give the plastic time to soak up the heat, to be uniform !!   It, s easier than it sounds !!   Bill H...

      ( NOT responsible, for burned down houses or domestic disputes )

[ghurd]

I have bent PVC and plexiglass with a torch or a heat gun.

Heat gun was easier to control.

Slow is the key, for anyones first try.

G-

[Experimental]

     The more we talk about it, the more I want

to try it myself Ghurd !!  BUT, the last thing I

need right now, is a new project...

     I,m looking foreward to seeing this tied

up to that $10 motor you just bought, and it sounds

like you have a good start on it -- I,m looking foreward

to some pictures !!   Bill H.......

[ghurd]

That $10 motor was long ago.

Actually, it's the one Norm has now!

Got another for my friends excersise bike.

May try a high torque 24" fan blade on it,

but I do not expect it to work with anything

under 30" or 36".

Unless I make a lighter hub than that flywheel

(and I don't want to!).

Don't have a place to fly something that big anyway.

[Experimental]

      Hi Mr G ,  After looking at that $10 motor-- I decided I have to have one, but have no idea what I,ll do with it -- it,s just to neat to pass up !!

    But going back to your blades, I,m sure anything you do to bring it more in line as far as pitch goes -- should be an improvement -- other than that it will probably have a definite speed range, where it will stall out !!

As long as it does what you want it to, in it,s range, it dosen,t matter what happens in a 20 knot wind as you will probably have it furled anyway !!

     At my cabin, i,m going to have to put a furling tail on my Hornet mill, as I don,t know what to do with the extra power -- 20 knot wind and 90 Degrees weather, how much hot water can you use !!??

     AND, if you want an aluminum hub for that motor -- and it is a simple one, I,ll be happy to make you one and send it to you --For just the cost of shipping,

 Catch me this week though, or you will have to wait untill I return from my cabin --my email address is above ....

     Why are you so imited to size on your mill -- neighbors, I expect !!

    Bill H...........

[ghurd]

Furl?

If it gets fast enough to explode here I'll have been in the basement for hours!

My neighbors.

Open windows...

One can read this as I type it.

The other is asking if I want a cup of coffee.

Well. Almost.

G-

[ghurd]

Hey Bill!

I would love a hub.

But it is some goofy left hand thread.

And pretty large too.

You'll see when you get your motor.

There are nuts available, somebody found them, with a part number even.

We just figured on using a belt to the bike parts.

But where the 'extra-size' bike is we could put up a 4'-er. I think.

A Hornet at a cabin?

Yup.  Sounds like overkill.

[Experimental]

       Hey Mr, G -- That hub is not a problem, nor the left hand threads as I have two lathes that I can cut threads with !!   I do however , need a sample , so it fits tight -- If you are not in a hurry I can do that in a couple of weeks, when I return --- another thought, would be to machine down the existing hub and drill holes for a prop !!

      On the exercise bike, that heavy flywheel would help keep the speed constant, so it would be helpful there !!

      The Hornet is a good rig -- the problem lies, at the cabin site -- Three things worry me there,    The lightning storms , Unbelivable winds and rattle snakes !!!

      Have only seen one rattler on my property in three years, but killed 6 last summer, in the valley below !!

     Wind , sometimes seems like a gale --- summer lightning is scarry, and cost one gen, three days after putting it up !!

    BUT, I love it down there, and the lake is within walking distance -- lots of fish ....."DON,T get any better than that !!   Bill H.......

[ghurd]

Hurry?

Jeeze. I had the motors for like 3 months. Still shiny.

My sister and hubby moved to Missouri 15 years ago.

Copperheads, scorpions, black widows, tarantulas...

don't seem to bother her anymore.

Maybe you get used to it?

I won't!