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gotwind
Forum Admin
United Kingdom
1067 Posts |
 Posted - 16/03/2008 : 16:06:15
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I have been considering some way of adding a flat front section to the P.V.C blades we make, still not a true airfoil but it may improve performance??
I've not tried it, but what if you carefully wrapped strong duct tape down the length of each blade and painted over the top to seal.
The ends may need blocking off also.
If anyone fancies trying it, it wouldn't take too long to do.
Ben.
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gholt
Junior Member
USA
107 Posts |
Posted - 16/03/2008 : 18:29:59
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Hello Ben,
The addition of the duct tape flat front is very interesting and you're correct, the round tube can only approach an airfoil. It's not clear how much the flat front would assist the lift-drag ratio, but it's an interesting idea with some good potential. If there is any perceived or measured improvement in lift, one can make this more permanent by applying a layer of fiberglass over the duct tape and allowing this to cure. The fiberglass would then be removed from the duct tape (it's a natural separator) and after removing the duct tape as well, the glass sections could be easily "glued" to the blades using the same epoxy used to lay them up. Another approach would be to "fill" the concave area of the blades with polyurethane expandable foam - the kind used to seal for air leaks in homes and construction (comes in an aerosol can). After filling the hollow, the cured foam can be "flattened" using a rasp, file and/or saw. This type of foam sticks to just about everything it touches and the expansion is relatively random but when cured is very light weight and can be easily shaped. Covering this foam with fiberglass would be an option.
I'm about to cut my first set of PVC blades today if it gets warm enough. I plan to add several layers of carbon fiber along the full length of the trailing edge area with the intention of increasing the strength at the point of attachment which is the weakest part of the design and is a fairly straight forward materials issue.
Thanks for the great thinking - where would be all be without the PVC blade concept?
Garland |
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gotwind
Forum Admin
United Kingdom
1067 Posts |
Posted - 16/03/2008 : 22:03:25
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Good reply gholt, appreciated.
I like the polyurethane expandable foam idea, maybe something for member 'superwindy' to try, I know he can get it free, as he is in the building trade.
Balancing the blades afterwards would be a good idea - probably not by much. I have also read about people using a stitched fabric (Nylon) sock and fiberglassing over the whole lot, just another idea to toss in.
Ben.
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ghurd
Junior Member
USA
337 Posts |
Posted - 16/03/2008 : 22:31:00
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I half-heartedly tried something like that. Mine got worse.
I can't test with any accuracy, so "I Think" mine got worse. They weren't very good to start with and the modifications weren't very great either. Plus it wasn't very big.
I believe the concave area is important for PVC type blades. Kind of makes them split the difference between real airfoils and drag blades. Gives them some good torque in low wind!
Would be great if someone could get some decent figures.
G-
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BushWhacker
Junior Member
Canada
339 Posts |
Posted - 16/03/2008 : 23:27:35
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If someone is going to test the theory, perhaps using a 'heat shrink' wrap used as a wing covering on flying model aircraft might be worth a try???
Just a thought,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
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MattM
Junior Member
USA
137 Posts |
Posted - 17/03/2008 : 01:45:32
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You want rigidity in the span whatever you use.
Go Huskers! |
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DENNIS A
Starting Member
United Kingdom
19 Posts |
Posted - 21/03/2008 : 00:00:52
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Hi Ben
I think that a flat side added to the curved blades will not work. To gain any real improvement in performance, the flat side will need to be a true helex on a pitch angle and this would not fit in with simply filling in the blade curve.
The curved PVC blades if made from 3 mm material give a unbeatable perfomance for the amount of work, cost of manufacture and spin really fast.
Dennis a |
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Sundowner
New Member
Ireland
58 Posts |
Posted - 11/04/2008 : 13:03:38
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Hi Ben and all the Gotwind readers and lurkers :)
Ben raised the question about improving the design of the pvc blades.
I haven't made pvc blades yet so it might not be right for me to speculate.
I was looking around the tangled web today and found articles on this stuff "Depron foam sheet" do a google search.
If its as good as it sounds and as flexable as it appears would pvc blades covered in this be an improvement.
Sundowner
P.S I built a micro micro turbine and put it up in the garden it worked so well I burnt out the windings (I think)it was lighting up 2 leds but it stopped generating after a particularly long spell of spinning.
I've also just been given a hub dynamo (sturmey archer) dated september 65 its lighting the bike lamp with a little spin of the wheel :) :)
Sundowner....huh.........thats what they call us.......Sundowners |
Edited by - Sundowner on 11/04/2008 13:05:00 |
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BushWhacker
Junior Member
Canada
339 Posts |
Posted - 12/04/2008 : 05:14:14
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I'm sure I can get some large diameter pipe. I have some 12" pipe and know I can get 18" and 24", but unfortunately the material starts getting pretty thick. (12mm or 1/2" for 12" pipe)
Any thoughts on if one chose to cut say a 3" to 4" wide section of that pipe and made a blade? I know it's going to weigh like a brick but I'm curious about the aerodynamics end of it. I could round the leading edge with a router and angle the trailing edge to 45 degrees as well. HMMM? Just pure speculation on my part.
Now that the first spring blizzard is over the garage is looking more inviting. http://preview.tinyurl.com/4n9lu9
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
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Victor
Average Member
United Kingdom
522 Posts |
Posted - 13/04/2008 : 11:05:28
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After making around 15 pairs of blades over a 18 month period this is what I have to say.
It would not make much of a difference with the pvc blades.
You have extra weight on them if you try to modify them.I have made over 15 pairs now with modifications and I think they are better kept the way they are.(except for modifiying for ametek motors)
However they do tend to reach a maximum speed in high winds.Over 40 miles an hour. I have tested these blades on a hill with 250 meters above sea level in total open space. The amount of force produced on these blades can be a lot,but adding more modifications to these blades will make them unsafe for urban turbines.
These blades are more than good enough for use on an ametek and dynohub. If you have low winds then by all means play about with the blades,but remember that when you have stormy and windy conditions your going to have problems.Bits might fly off and endager houses nearby.
You also have a lot of torque running on the blades in high winds and I`m not going to modify anything on the pvc blades except the shape!!!!
Anyone ever tried to hold an ametek or dynohub in their hands in a 30+ mile wind will know how much pressure the wind can create on the blades.It`s like somone try to push you off your feet.
The wind can bend the blades as much as 10 cm and this will cause the modificatrions to come loose and make the turbine a hazard.
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Sundowner
New Member
Ireland
58 Posts |
Posted - 13/04/2008 : 13:42:34
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anybody have any ideas on the depron foam sheet as per my earlier post.
Its used for building wings of model aircraft.
Sundowner....huh.........thats what they call us.......Sundowners |
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Topic |
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PVC blade improvements - ideas.
