made pvc blades & stress tested

[Trivo]

today I bought an old coventry victor 1 pot deisel with 5 kva 250 vac running well for $450

Also went to the dump and picked up 2 lenghts of 300mm dia pvc pipe for $6

made the small ones, 1 meter as a test, took 2 hours including stress test

this pipe is 20years old  10mm thick and very strong.



this is the original pipe

the big ones



ready to cut in half



Profile marked



Blade cut

Stress test









try and do that with wood just sprung back when load was off

[wdyasq]

Trivo,

The problem with turbine blades is not will it take a hard flex once - or fifty times, the problem is will it do it a million or billion times?  At 1000 rpm, that is about 17 hours per million, 2 years per billion.

I can't properly gauge the thickness frome here but, I'd think it is near 10mm.  A 100mm piece of wood will indeed flex and return like that.  And wood has a very long - as yet to be determined, fatigue life.  

Go back through the old stories.  Figure out how many plastic props were made.  Then figure out what percentage are still running and making power.  That will be the test that matters.

Ron

[pyrocasto]

Unless you're working with the greenest of wood, then it wont flex quite like that at 100mm thick. Think about it. Take a 4"x4"(less that 100mm thick), and try and bend it like that. It would snap. Wood doesnt bend as much as shown in the picture, unless very thin or very green. If it's green, it will dry, so then you are still back to stiffness.

I think the blades should do fine because I know it takes alot of push the bend the blades back that far, and I dont think the wind will do it(normal wind) anyway. Next time you test something, make sure the piece is straight up and down. That way, you can bend it back, put something on the end, and cut the rope. Temporary catapult(sp?).

[wdyasq]

10. mm - not 100mm - fat fingers trying to type.
    
100. mm might have taken the post out or stopped the car.
     
     

Ron

[domwild]

Thanks for that. Novel testing method!! I am using 9" or 220mm pipe nine and 12 mm thick and will have to use a PVC primer and silver paint to stop UV damage. UV will make PVC brittle and then it will snap. Most posts give PVC props about 2 years. If you can get your hands on ABS, I think that's what it is called, then that plastic is best. Jerry sells those blades.

Beauty with PVC and ABS is that you get a bit of autofurling as the tip will bend back. However, use furling as a safeguard.

[DanB]

Im a bit skeptical also of PVC blades.

How will it hold up over time in the sun?

It would be interesting to perform the same tests at -20 deg F and at 100 deg F.

And as Ron said there...  it will go through millions of fatigue cycles.

As with all things though... time will definitely tell.

[LEXX]

I'm not entirely sure about stress ing the blades at very low temps but i Know that in high temp it is fine, as long as it's not too high (140 F or more) it will hold up just fine.  As for the life cycle in the sun it is also fine, when you are using it for irragation(it's intended purpose) it is speced for a 15 year life cycle.  I also like wood but probably because you can customise it a little more.

LEXX

[electricsquirrel]

I think you are on to something here. PVC can be slowly heated and it stays in its new shape. There are bend limits but it looks like that is not an issue. You can rent PVC blanket heaters to slowly heat the PVC so you can mold it. A mold out of wood in the shape of your blade will make it very easy. Remember if you make a mistake just re-heat it.

[DBGenerator]

For the cost of PVC, and the time to make it, I think I would make 2 or 3 extra sets of blades just for the fun of it in case you needed it.  It couldn't have taken more than 15 minutes to lay out a pattern and cut that out.  It beats spending hours with a chisle, saw, sandpaper, paint, and whatever else.  Although.....I know that some people build their wooden blades because they look neat and it's a craft.  I've seen some PVC around my house get brittle after a while.  It wouldn't hurt to put some UV protectant on it.

I'm going to have to try that on a smaller scale.  I like it.