TSR of PVC blades

[loumart]

Hi all

I've finally got my little 5" genny to produce a fair amount of power after a lot of tinkering. The results are as follows for those interested:

results @ 525RPM (from drill press)

open voltage = 18.25V

current = 13A (approx)

resistance = approx 1.4 ohms

This gives the following data:

12V cutin = 350RPM

Power @ 350RPM = 0 Watts

Power @ 700RPM = 8.57A into a 12V battery = 103 Watts : Power lost = 103 Watts : Blade power = 206 Watts

Power @ 1050RPM = 17.14A into a 12V battery = 206 Watts : Power lost = 411.3 Watts : Blade power = 618 Watts

I've used Alton's wind calculator to find that a 3 foot prop with a TSR of 3 gives a pretty good match although it wont cutin until around 13.5MPH winds.

I'm looking for a PVC rotor design to fit the specs of my genny but I can find much info on them. Does anyone know how to calculate the TSR of PVC props? Would the calculations from alton's calculator work for PVC (I mean will I need a PVC prop with measures 3 feet and has a TSR of 3)? If so then how do I get a TSR of 3 on a PVC pipe? I will be using 3 or 4" pipe for this.

Any help would be gratfully received.

Thanks in advance

Martin

[Flux]

I know absolutely nothing about PVC blades, but I think you can assume that with highly curved blades the effect will be to increase lift for a given setting angle.

The thing the calculator gives is based on the mean line ( the line joining the centre of the leading edge to the trailing edge).

For aerofoils of the conventional type made from wood or fibreglass, the lift will be low when the flow is along the mean line. Angles of attack of about 4deg give a good compromise between lift and early stall. With something with a highly concave mean line you will have a much higher lift for the same setting angle. This means that you will run at a lower tsr based on the pitch angle. The ideal chord for this same pitch angle will be significantly wider, so if you just copy the dimensions of a wooden prop the proportions are all wrong.

Tsr 3 is very low so you will be looking at probably 6 blades to get the solidity with reasonable pipe size.

If you try the blade calculator I believe you can alter the default value of Cl. Try using a considerably higher value then the angles that it predicts will more reasonably suit what you will need based on the leading and trailing edge( the only thing you can measure).

Flux

[ghurd]

TSR.  How about between 3 and 5.5.

It must be more than 3, if your numbers are correct.

A decent 4 blade, 3 foot diameter PVC prop, made from 4" diameter pipe, will hit 350 RPM well before 13.5 MPH.

It is less than 5.5, because I have 5.5 TSR CNC cut blades, and they are quite a bit faster than PVC blades of the same diameter.  

Plus the CNC blades were intended to use 3 blades and I used 4.  I expect that slowed them down a bit.

G-

[bluefox]

I have

PVC 10cm

4 blade

diameter 1m

RPM 106  min-1/(m/s)

TSR 5.5

[loumart]

Hi there Flux

Thanks for your comments but unfortunately you have lost me a little as I'm new to blade design and construction (thats why I want to go down the PVC pipe route for my first genny).

I do understand a little of what you are saying and I had a feeling the calculator would be no good for pipe blades

I was planning on only 3 blades but you are probably correct in saying go with 6 as the pipe will have a lot of flex - will more blade reduce the stress present on each blade?

Thanks again

Martin

[loumart]

Hi guys

Thanks for the posts

I was hoping for 3 blades but 4 will be ok. Does this mean that the standard TSR of PVC blades is 5.5?

I used Altons calculator to find the size of blades I need but this is for wooden blades - I'm totally lost with pipe blades and cant find and useful infomation on the internet about design.

I dont suppose I could see your designs for the blades (please!) Also, what size alternator are they fastened to?

Thanks a million

Martin

[Flux]

Probably you can do it with 3 blades if you start with large diameter pipe. You will need quite a large chord at the root and I think you may need 6 or 8" diameter pipe for 3 blades. The larger diameter will result in less curvature and if the pipe is nice and thick you can work a simple aerofoil profile on it, but it is a lot more work than the thin pipe.

For smaller diameter pipe I think you will do far better with 5 or 6 blades and not taper them very much.

As Ghurd said you should easily reach your alternator cut in speed with a 3ft rotor.

If you can get a good look at a Marlec or LVM turbine rotor and copy it best you can it should work well. The early Marlec blades would be better to copy than the modern ones which are more aerofoil shaped and not directly copyable with pipe sections.

Flux

[ghurd]

I believe the `standard TSR of PVC blades' is a crap shoot, and the best versions could only reach past 5.5 unloaded.

I started with total junk PVC blades.  Then moved on to Wooferhound and Zubbly's PVC blades.  I understand they intended them for use as a 4 blade rotor, and I tend to make more 4 blade props.  I do some 3 and 6 blade stuff though not too often, and the results were the same.  I find 4 blades easier to get properly mounted and balanced.

I changed the length, root angles, the tip angles, both, all, etc.  

The more I deviated from Woof's published angles, the worse performance became.

The closer the blades match each other the better. It is audible if one is very off spec to the others.

Here is what I use.  (I sure wouldn't try it with 1-1/4" pipe!  4" is my minimum pipe, 3' the max prop dia)

http://www.fieldlines.com/story/2003/11/11/172721/53

Here are a couple (related) old and basic sketches I did long ago.  Maybe they will help.

http://www.otherpower.com/images/scimages/2050/ValPVC.gif

http://www.otherpower.com/images/scimages/2050/ValPVC2.gif

This monstrosity actually did quite well.  The flexible blades started to fold back in good wind.  It made some amazing power for it's small diameter and low TSR.  Even this one had a TSR over 3.  

It had some high solidity, but still moved right along, even when loaded.  It was most probably underloaded.  Another antique.  Made completely from junk.

http://www.otherpower.com/images/scimages/2050/ugly30efkabuckt.jpg

If you have a decent alternator (you do), it is pretty easy to get some power out of it.  I'm not saying it is hard to ruin.

Hope something here helps, at least with inspiration!

G-

[CG]

Martin,

Here's a design I have experimented with: http://www.fieldlines.com/story/2005/10/17/1228/6385

I'm in the UK, and they are made from standard PVC guttering that is used here. Flux has mentioned Marlec's turbine, and that is the size that interests me. Don't worry if you can't get PVC guttering where you are, because the curvature is about the same as 110mm soil pipe. But the guttering is of a thinner wall thickness, so you may have to adapt the pipe design.

[loumart]

Hi CG

I've seen your post recently when I was trying to research PVC blade. They look great but do they produce much power? Have you tested them with a genny yet? I'm also from the UK (Durham)

I would be very interested in the design of these blade and the power they can produce

Best regards

Martin

[loumart]

Hi again Ghurd

I thought 5.5 seemed too good to be true. I'm not bothered though as I want a smaller diameter blade so a lower TSR would be better (more power for the same RPM)

I've seen woofers description (your first link) but the 10 to 12" diameter pipe put me off. It may work with 4" - I'll have to give it a try I guess

I like the wind genny made from junk - well done mate.

I'm going to experiment with the blades soon. I'm using 10mm ID bearings and a 10mm bolt for the main shaft. There is play (about 0.2mm!) and wobble which I need to get rid of before I attach blades!

I'll keep you all upto date

Thanks for the help - its always appriciated

Best regards

Martin

[loumart]

Hi again Flux

The 3 blade design sounds like a lot more work. I may have to build a CNC router to cut wooden blades for me

I know the 3ft rotor would easily meet the cutin but I also need more power at the higher revs to match the alternator. This is why I need a TSR of around 3.

I've done a lot of searching of the Marlec turbines but havent been able to get a good look at any of the rotors

I think it may be time to experiment

Thanks for all the advice

Best regards

Martin

[CG]

Martin,

I'm affraid I haven't produced a watt, the electical side of wind turbines is definitely my weak point. I have thought about using the same cycle hub as I used in the photo to build a generator, but I haven't done anything about it yet. So all the power I have produced so far is spinning the weights in the photo. That is not a fair test because all the energy goes into a flywheel effect and smoothes out the turning of the blades. But I am sure that my blades would power your generator.

I am glad that you are in the UK (I am in Norfolk)because it seems we are about the only country that uses PVC in guttering. For small turbines I see no need to go to the expense of soil pipe. I have used the Deep Flow brand also; this type of guttering is the same as standard guttering, but with a higher side (more a U shape). When this is cut down the middle the two blanks are asymetrical, and they look like the top of and aerofoil. Being wider I was able to make a longer blade (.75mm). I made two blades and put them on in place of the ones in the photo. Like everyone here says: as soon as you test something the wind drops. So it was like that for days. But then late one day the wind picked up and I went to bed with the wind rising strongly. The next day I found my turbine off the mast with a broken blade (it had struck the mast). I then made a .5mm bladed three blade rotor. But it doesn't run smoothly, so I think the standard guttering is best, and it is a lot cheeper. You can buy 170mm diameter industrial PVC guttering, but this is very expensive and hard to find.

The rotor I have on the mast now is almost the full Monty except for one thing - no alternator. But it has a generator fixing mount, a yaw mount, and it furls. All the parts can be sourced from B&Q (I still shop there, even though they are misselling the Windsave tubine). But all this, of course, is academic if I have not produced any electricity yet, but being on grid, even though I live in a rural setting, it is just a hobby with me.

PVC guttering is cheap, it won't cost you much to experiment with it, so my advice is to have a go at it. If you do, let me know and I will pass on any tips on cutting and such, that I have learnt - generally the hard way.

[loumart]

Hi again CG

A bicycle hub is a good idea for the bearings - I'm using 2 ball races and milled MDF to accept them. The rotors currently dont run true which I'm hoping is a problem with the MDF being weak or maybe that my mill is 0.1mm out over 150mm (I'll have to fix that!)

Yes, I have a B&Q close to me so I'll give the guttering a try I actually found a piece of yellow plastic gas pipe lying about a couple of years back. I got it to build a tesla coil but I later changed my mind (too dngerous for me!) and got rid of the pipe - I really wish I'de kept it now - it had a very thick wall and the diameter was large (10 to 12")

I may start to sell these alternators as they are very neat and produce usable power. I'll send you one at cost if you can help me with the blade design For a start what is the best shape to use? Do you have any drawing on the PC?

I'm also on the grid but I love experimenting with things such as this

Best regards

Martin

[CG]

Martin,

I can't help you much with the design of the blades because I designed them with one of these: http://www.drobe.co.uk/features/artifact1467.html It's a crying shame that a great little computer has been reduced to this, but that's IT for you. As you may know it's not compatable with a PC so I can't swap files. Also I do all my internet stuff from Cromer Public Library - I'm not even on the phone at home. If you have an arts package on your PC, just take a look at my photos and copy them; Asia has built up a huge manufaturing industry doing just that. But you will need two root reinforcers on each blade; I ran a six bladed turbine with three blades having one root reinforcer and three having two, after about a year I got failings with the ones having one root reinforcer.

If you have not got any graphics software on your PC you could look around for an old Acorn machine, that could be cheaper than buying a software package for a PC. Draw, the vectored arts software I used to design the blades is built into the roms, so it comes with every computer. But you would have to make sure that you had the applications disc for you printer drivers. It would also mean having to learn a new GUI and Draw itself, which would all take time.

Once you have made one blade for a profile it's easy. I have no idea of whether wide blades or thin blades are best; I think all this theory is ok, but the best way is to test the two designs side by side with the same alternator on each turbine. My whole idea was to produce cheap, small turbine blades; the last time I looked Marlec's 913 blades, which are the same size as mine, cost £15 a set of six, and they don't look too special to me.

I'll keep an eye on this post, and if you have any questions I'll do my best to answer them, but bear in mind there can be days when I can't get on the computer.

Best of luck with your project,

Colin

[thefinis]

You know I think that many of us get too caught up in trying to get everything just right instead of jumping in building and learning from the experience. I know that I did. I spent years researching and reading doing all the math trying to come up with the perfect match. Once I started building blades things didn't always go like on paper and some of my ideas were just junk no matter how well thought out.

I like Ghurd's ugly turbine and it is a good example of "Just build it" and see if it will fly. Some of the blades that don't look very good put out a lot of power and they almost seem to adapt to the genny put behind them. Some sets of fancy blades never deliver what you expect and get real picky about what genny/load you put on them. The biggest problem with the pvc is how long it lasts and the flex but for the price they are hard to beat.

Have fun

Finis