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Critiquing PVC Props
By Baling Wire, Section Wind Posted on Sat Sep 13th, 2008 at 07:40:20 PM MST
Here are pics of 2 props that I've started, but Not finished.

The smaller one is 4 ft. in diameter and hopefully was for useage on an Ametek 40 whose 12v cut-in is 345 rpm. The larger prop is 5.5 ft. in diameter and I was planning to try it on a treadmill motor whose 12v cut-in is 265 rpms. Neither prop has the leading or trailing edges completed. I realize that pvc props do Not perform as good as a well designed wooden one. I really don't have the tools and skills to build a wooden one! I have wondered if the "dagger style", "TLG metal ones" or the "Chinese fiberglass" would be any better than what I've got started?
My pvc ones may not "run" fast enough? My main concern, before I go any further, is whether I've Left too much width in the root area of these. This causes too large an angle and may cause more drag than lift, pulling the rpm down? I hope that I got the setting angle pitch close when I mounted them? There's not much angle at the tips. I'm eager to hear from "the experienced"! Oh! Average wind
is 8.7 mph.

BW

Critiquing PVC Props | 22 comments (22 topical, 0 editorial)

Re: Critiquing PVC Props (3.00 / 0) (#1)
by luckeydog (bryan@coloradowindpower.com) on Sat Sep 13th, 2008 at 03:28:49 PM MST
(User Info) http://www.coloradowindpower.com

Bailing wire

I have owned both tlg blades and the cheap chinese blades.
this is what my experience has been with both.

the TLG blades work well in low wind.
they are ready to use right out of the box.
they are quiet.
Terry the owner of TLG has great customer support.

the chinese fiberglass blades
they have poor low wind start up
in good wind 8+ mph they are very fast.
they are not ready to use out of the box.
plan on spending some time sanding painting and balancing them.

if you don't want to carve you own wood blades then you may not want to
mess with the chinese blades.

I believe the host of this Forum do sell finished wood blades.
ask DanB
they have great support for their customers and for the people on this Forum.

Luckeydog
.
wind gens are much funner to watch than solar panels. Broomfield,Colorado

Re: Critiquing PVC Props (3.00 / 0) (#2)
by Basil (basil(spamblock)key@bellsouth.net) on Sat Sep 13th, 2008 at 04:27:48 PM MST
(User Info)

What luckeydog said is what I found out also. You will have to work with the pvc blades to get them the way they work the best for you. Me, I use air master fan blades on my 38 volt motor. and it does great for me. I put 36 in metal fan blades on one at my fathers and it works great to keep the battery up on his tractor. I did not have any luck with pvc blades. And yes the root is a little wide for me. It will start better but lower rmp on top.
Bad luck or none at all.

Re: Critiquing PVC Props (3.00 / 0) (#3)
by Basil (basil(spamblock)key@bellsouth.net) on Sat Sep 13th, 2008 at 04:34:08 PM MST
(User Info)

After you post you see the miss spelled words. By the way the blades look very good. Hope they work out. Read my post about the luck I had with fiber glass and PVC blades.
Bad luck or none at all.

Re: Critiquing PVC Props (3.00 / 0) (#4)
by bob g on Sat Sep 13th, 2008 at 05:30:19 PM MST
(User Info)

don't look bad to me, but
they are pitched backwards
the root part of the blade should be pitched back instead of forward
in order for them to work properly.

unless i am missing something

bob g

Re: Critiquing PVC Props (3.00 / 0) (#6)
by ghurd on Sat Sep 13th, 2008 at 05:39:08 PM MST
(User Info)

Sorry Bob,
My trail edge remark was not aimed at you. We were typing at the same time.
I thought that too, but decided it was the camera angle.
Photo #5 shows the tip shadowed, but the leading edge with sunlight.
G-

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#7)
by bob g on Sat Sep 13th, 2008 at 11:09:53 PM MST
(User Info)

the root of the blades look for all the world to be pitched outward toward the wind
instead of pitched back downwind as they should be.

the mounting supports this conclusion, there is no angularity on the mounting ears/tabs.

i can see how they would turn in the wind no problem, but making power due to blade lift i cannot see how that is going to happen because the blades will turn backward.

thats how i see it :)

maybe tomorrow after i have had some sleep i will take another look at the pics, these old eyes are tired!

bob g

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#8)
by veewee77 on Sat Sep 13th, 2008 at 11:41:01 PM MST
(User Info)

Actually, they are pitched the correct way for PVC blades. It looks wrong, but it is actually correct. Those should fly pretty fast and should run fairly quiet. Smooth the leading and trailing edges for a bit more efficiency and a bit less noise. . .

Doug

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#5)
by ghurd on Sat Sep 13th, 2008 at 05:35:07 PM MST
(User Info)

There is not a lot to go on with PVC blades. "Try it and see" is what I do.

The PVC blades I make come down to a guess on the first set.
The 2nd set is a guess at fixing the problems the 1st set had.
The 3rd and 4th sets are trys at getting a little better.
Longer/shorter and/or wider/thinner.

The smaller ones look OK. Root may be a little wide.

I don't like the big ones.
The huge root looks like it will just cause drag.
Plus I think 4' is about the limit on PVC. Loaded, in a strong wind, they bend back more than most people would expect. It would not surprise me if the 5.5'-er hit the tower.
Most reports show PVC blades will break. Maybe not today, but it will happen.
That's a big chunk to go off at high speed.

Might find a 4' that is a little wider than the 1st 4' set will drive the treadmill motor OK. I believe PVC can somewhat 'drag past stall'.
Might make a decent low wind machine, with less danger.

On the bright side, the trailing edge is in the right place. :-)
G-

why reverse pitch/twist on pvc blades (3.00 / 0) (#9)
by bob g on Sun Sep 14th, 2008 at 12:28:58 AM MST
(User Info)

three questions

if as you say they are pitched right for pvc blades, then they are pitched opposite of carved blades?
why would a pvc blade require being pitched opposite of a carved blade?
if the tip of the root is pitched toward the wind, then when met with the wind this tip of the root is the bottom end of the leading edge of the blade?

respectfully, this goes against everything i have studied about proper profile design, so i would like to understand the reasoning behind it.

ok a couple more questions if i may :)

why couldn't a pvc blade be cut so that the root of the blade is pitched back away from the wind and then twist toward the tip at a flatter angle as do carved blades?
what advantage does this reverse twist present or rather how is it better than the conventional design?

hmmmm
i really would like to know answers to these questions :)

bob g

Re: why reverse pitch/twist on pvc blades (3.00 / 0) (#10)
by Flux on Sun Sep 14th, 2008 at 02:44:42 AM MST
(User Info)

The pitching thing is just an illusion.They are the same, it just looks odd when the blade mounting is at the trailing edge.

They are coarse pitch at the root and fine pitch at the tips. It doesn't matter how they are supported. With wooden ones the mounting is the original board and it is natural to cut back the trailing edge so that the TE drops behind the mounting point.

For curved sheet blades you can mount either way. TLG use the method shown and it probably has some advantages in terms of strength and clearance.

It is probably necessary with pvc to use these large coarse pitched sections at the root to get sufficient strength. They probably suit low speed operation where large starting torques are required such as "draggy" dc motors.

I am sure that if you keep them to low tsr ( below 5 or perhaps better below 4) they will work fine. The result is that you need a slower larger and considerably more costly alternator for the same power out. I don't think they are interchangeable with the Dan type projects intended for wooden blades.

I have not had any real experience with them, the only blades I ever tried to make from pvc were more trouble than dealing with wood which I find easy.

I have recently had a chance to compare an early Freelite prop made from sheet aluminium alloy with the later wooden one. This is a fast prop by modern standards and the aluminium ones has significant less pitch than the replacement wooden one at the tips and is tapered and twisted. The wooden one has little taper and no twist. On the Freelite the wooden one is way better faster and quieter than the aluminium one and I suspect that the aluminium one would need a slower and larger dynamo for equal results.

I think the curved sheet things behave far more liked cambered aerofoils. We tend to think of the pitch in relation to the front surface of the wooden ones and that is reasonably justified with the Clark Y type profile that they approximate to.

The pitch should be related to the line joining leading edge to trailing edge and with the cambered sections the lift will always be higher for the same pitch angle. For high speed the pitch of the single surface things ( pvc etc) will probably have to be negative to be equivalent to the wooden types. If you do this I am sure you can get the speed up ( Suspect drag will be a lot higher). The snag is that you will not have enough strength at the centre to support a high tsr type.

For normal operation except for the dc motors and possibly some conversions with bad iron loss and cogging I am convinced that this large chord and pitch at the centre predicted by calculators is not beneficial and is probably detrimental with the constant speed loading as approximated to by battery chargers.

Even with mppt loading I still am not convinced about this large coarse pitch middle section, in fact I am not convinced that the middle third of the prop is other than a hindrance and I suspect the wind flow through it is not as predicted.

Anyway this is mostly speculation based on my own findings, everyone to their own choice, I couldn't be bothered with pcv but as I have been carving wooden ones since I was 10 I find it easy and can't see any point in doing otherwise.

Flux

[ Parent ]

Re: why reverse pitch/twist on pvc blades (3.00 / 0) (#14)
by TheCasualTraveler (a.miklos@yahoo.com) on Sun Sep 14th, 2008 at 02:49:26 PM MST
(User Info) http://thecasualtraveler.com/wind.htm

Sorry to go off topic but...

That line about carving blades since you were 10 made me think, if you ever write a book I want it. But then I thought, maybe Flux HAS written a book on this stuff, so I'm asking Flux, Have you?
Andy
[ Parent ]

Re: why reverse pitch/twist on pvc blades (3.00 / 0) (#15)
by Flux on Sun Sep 14th, 2008 at 04:50:11 PM MST
(User Info)

No the only things I have ever written about wind power are on this site.

Flux

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#11)
by spinningmagnets (velmis1450bc(at)aol(dot)com) on Sun Sep 14th, 2008 at 11:21:45 AM MST
(User Info)

I "think" the benefit of mounting PVC props this way is that you can use a flat mounting disc, and you want the gen to spin in a particular direction. Plus, maybe the blade twist protrusion is farther away from the pole?

When mounting home-made wooden blades, you can of course carve them to mount and spin any way you want.

The way I understand it, PVC can be a very fast and easy way to get a gen up in the air and spinning. But with UV weakening, and stress cracks growing, it means as soon as you get it spinning, you should start working on some long-lasting wooden blades.

In spite of the "less than optimum" curve in PVC, it may give you some useful blade length data before carving wood?

Re: Critiquing PVC Props (3.00 / 0) (#12)
by Stonebrain on Sun Sep 14th, 2008 at 02:11:40 PM MST
(User Info)

Hi,balingwire

The chord line is perpendicular to the shaft.
Imagine a circle with the shaft as centerpoint.Perpendicular on the shaft means a circle around the shaft.In fact this is the relative air movement.If you don't get this approach,you won't understand what I'm talking about.
If you make this circle intersect your blades close to the shaft you get a weird profile,also because of the 'muffle'(is this the right word?) of the pvc-pipe.

In my opinion the parts pointing forward near the center (on the broad side of the 'muffle')will be counterproductive.Cut them off.
Only follow my advise if you understand what I mean and if you agree.

cheers,
stonebrain

Re: Critiquing PVC Props (3.00 / 0) (#13)
by Stonebrain on Sun Sep 14th, 2008 at 02:49:15 PM MST
(User Info)

This is what -in my opinion!- have to be taken away to get rid as much as possible of the negative effect of the 'muffle'

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#16)
by Jerry on Sun Sep 14th, 2008 at 09:16:35 PM MST
(User Info) http://www.dplusv.com/Photo-03.html

This is a picture of my foam type PVC blades. They are quite strong with the foam fill between the 2 thin skins.

The blade looks a littel more like a conventional blade?

These are 4ft. I'm working on 5 and 8 ft versions. These 4ft are cut from 6" foam pipe.

My next hubs are made from Choice deck. Its that plastic wood stuff. It lasts forever and its not effected by watter.

JK TAS Jerry

Airheads Page

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#17)
by Jerry on Sun Sep 14th, 2008 at 09:21:03 PM MST
(User Info) http://www.dplusv.com/Photo-03.html

PS. This foam pipe material is about 5/16" thick. I'm makeing the larger blades from 8" diameter foam pipe.

JK TAS Jerry

Airheads Page

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#19)
by Slingshot on Mon Sep 15th, 2008 at 01:18:16 PM MST
(User Info)

OK, I'll bite - how do you cut that curved slot in your wooden hub?

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#20)
by Tritium on Mon Sep 15th, 2008 at 02:07:22 PM MST
(User Info)

Here is his original thread.

http://www.fieldlines.com/story/2007/2/2/41629/53700

Thurmond

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#22)
by Slingshot on Mon Oct 6th, 2008 at 11:15:05 AM MST
(User Info)

Aaah .... the trusty "roto-zip", as seen on late-night TV!

[ Parent ]

Re: Critiquing PVC Props (3.00 / 0) (#18)
by Baling Wire on Mon Sep 15th, 2008 at 10:13:44 AM MST
(User Info)

THANKS! to ALL who commented. IT seems as if I have No major errors to this point?
I will probably take the "charoit horns" off the larger prop and work-up the leading and trailing edges and "try them" as Ghurd would say. Maybe a Boost Converter with These would make a decent setup? Any way, thanks ALL!

BW
73 de ke5yd

Re: Critiquing PVC Props (3.00 / 0) (#21)
by ruddycrazy on Tue Sep 16th, 2008 at 03:41:38 AM MST
(User Info)

One thing no-one has commented on, all the photo's in the top post SHOW the wind genny AT ground level, one can see a house in the background, trees everywhere etc. I don't mean to detract but some of the guys posts in here are good advise if you must go the pvc prop route. Just remember to get your genny UP in the air away from obstructions when you want the thing to work.

A comment from an Ozzie after a
few homebrews

Cheers Bryan

Critiquing PVC Props | 22 comments (22 topical, 0 editorial)

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