Zub Woofer blade calculator

[stevesteve]

Hi,

I have been wanting to make some plastic blades for a while but I did not know how I could do it with out molding. Now with the plans that have been posted here I have been able to make a set for my 'pilot' or P.O.C. system.

The only thing is that I can't strap a protractor on every pipe I see to work out how wide the blades will be.

I wrote this little program to help me quickly do the calculations for tip and root width. Although it is labelled as 'Chord' on the program it is actually the dimension that would be used on a flat paper template which can be stuck on to the curved surface of the pipe.

Download here

Any comments or suggestions welcome.

Cheers, Steve

[Norm]

   Tried it ...doesn't work on my computer ...

says Class not registered. You need the following file to be installed on your machine.

Msstdfmt.dll

   I only have mainly at my disposal 5 gal buckets

so I'm limited in length anyway, but I'm sure

this will be helpful to others and hoping they

don't have the same problem as I did..thanks

for sharing.

                  Have Fun!

               ( :>) Norm.

[stevesteve]

Doh!

Thanks Bill G.!

Download DLL here

Save file in c:windowssystem32

Start

Run

then type:

regsvr32.exe msstdfmt.dll

This is good for buckets as you can work out the distance around the bucket for various tip angles and can recalculate for the narrower diameter further down (presuming it's a tapering pail type thingy).

[wooferhound]

Works fine on my computer

I'm not real clear on what the answers mean

is it the distance around the pipe to the centerline

or

is it the distance measured straight from the centerline to the calculated point

A amall paragraph of instructions would help the newbies

another coupla observations

You shouldnt be able to enter a value over 45 degrees, as trying to cut the pipe for this is not really possable

Also you may want to put a check in there to make sure that the tip angle is always equal to or smaller than the hub angle or you will end up with a really funky set of blades.

[ghurd]

I am going to use it!

Thanks

G-

[stevesteve]

Hi Woof,

Here is a pic of the results of my calculations:

The dimensions given are the dimensions on the flat paper template which are then wrapped over the curved surface of the pipe. Clicking on the two buttons highlights where the dimensions go on the paper.

Just in case you are wondering I thought that the pipe I bought was a one metre section... it turned out to be slightly less but I kept to the central point so its just a bit short both ends.

I take your points about the limits that might be set in the software. I will add them in to a later version. It started out as a quick and dirty reckoner for my own use.

[wooferhound]

I will use it for sure !

I have an 18.5 inch plastic barral that I've already used the program for. I'll use the default settings of 25 deg. hub and 7 deg. tips. I end up with nice big numbers like 8.5 inch hub width and 2.25 inch tip width. I'll be working on these blades within the next coupla weeks, so stay tuned . . .

[ghurd]

Should the tip angle (7') vary by the length of the blades?

G-

[Norm]

 Okay Steve ...finally got around to it ...and it works fine now...

              thanks a Lot!

              ( :>) Norm

[windyknight]

Steve

Found some strong 8 inch dia plastic pipe about 9 ft long and am thinking of replacing the three 4ft blades on my pmg cos its output is too low.  Whats the longest i can cut from this pipe and would it be better to go for 4 blades (thinking maybe 2 of the  'double'type like shown in some of the photos easier to fix)

Spreadsheet works fine but dont know what angles to input.

Am i right in thinking i just then cut out a paper template using dimensions given and bingo?

k

[stevesteve]

Mmmm... that's begining to become more technical. I am currently starting out and am at the stage where I have my 1m pilot two blade machine up and I say "Hey kids it's going round again!" each time the wind blows.

The angle of the tip (and root) is dependant on the final rotational speed that you are looking for in certain wind speeds. I have Hugh Pigott's book and am begining to get an understanding of this but I cannot give you a good answer yet! I set the defaults as 25 and 7 degrees as that was what had been quoted before.

The blade length is also mixed into the calculations. The maximum length partly depends on the strength of the plastic. The longer the blade the greater the centripetal (centrifugal?) forces on the root and the greater the risk of failure. Someone (Zubby?) has also mentioned that very long, narrow blades may flutter. I think that happens when laminar flow is lost over part of the blade length and the blade twists leading to resonance (that could be a load of cobblers but I think it is along those lines.

Whatever angle you choose for your blade length the values given are the dimensions across the blade when drawn flat on the paper. This is then wrapped onto the curved surface. It is calculated as a proportion of the circumference.

I have not progressed beyond a two blade system yet. It is easy to mount but I am going to go for a three blade unit with a hub next.

Other folk have more experience with these pipe-blades. Anyone else want to comment?

Cheers, Steve

P.S. Where did you get hold of the pipe? Was it for drainage?

[windyknight]

Thanks steve

I'll give it a go. Pity I havent mastered a quick way of getting photos from camera onto site to show you - i'm a bit of a techno dinosaur!

Pipe was found in a skip ages ago and i kept it for a ditch crossing which never materialised - it looks like thick walled sewer pipe (underground upvc) but seems more plasticy (durable)and is really tough to cut so should do the biz

keith

[stevesteve]

Sounds like a typical Welsh farm situation!

That's speaking as someone who rented an old Welsh farm house while a student. Big house, double garage, workshop, greenhouse, veg patch... basically loads of space for someone like me who sees a bit of metal etc and thinks "that might come in handy sometime".

If you looked carefully you could read the numbers off the fighter pilots helmets as they screamed up the valley below.

Happy Days!

[wooferhound]

This program is not accurate because it measures from the center of the hole in the pipe, and not from the centerline of the outside diameter, as the diagrams show.

[ghurd]

I thought I was doing something wrong!

Thanks

G-

[stevesteve]

Ah... see what you mean now.

It works if you measure the outside diameter of the pipe and then cut straight through the plastic.

If you make angled cuts you end up with a slightly wider blade... Mmm could re-write some bits depending on the angle of cut and the thickness of the pipe. Or you could make straight cuts and try a power plane to shape the edges (not tried this so not sure how practical it would be).

Well heck I'll either make the blades as they come or reduce the angle to compensate. The blades I made still spun dangerously fast when hand held and on my test genny (stepper motor) I made the mistake of stopping a simple two blade (ie one piece) blade from the pipe above with my hand. BANG... oooh that smarts :-O

[amiklic1]

How to determine prop diameter. I don't see such info to input into the calculator.

 

[wooferhound]

No you are still misunderstanding

To get your angle points you need to measure from a point that is on the outside of the pipe that is on the centerline. Your program uses a point that is in the middle of the space that is inside of the pipe and uses that angle

for example

to get the proper 7º angle as posted in the diagram, you will end up with a fairly wide piece at the tips of the blade. But using your calculator the tips end up being very thin and almost pointed because the angle points are calculated from inside of the pipe at the imaginary point in the center.

[wooferhound]