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DaveP68
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Posted: 15 June 2018 at 10:34am | IP Logged Quote DaveP68

*** ding ding *** nothing about winning here in my view. Concentrate on that outer 3rd of the blades when it comes to all of the above...

Edited by DaveP68 on 15 June 2018 at 10:36am


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Warpspeed
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Posted: 15 June 2018 at 10:49am | IP Logged Quote Warpspeed

Oh I think a successful project can be viewed as a personal win.

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Madness
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Posted: 15 June 2018 at 11:07am | IP Logged Quote Madness

This Calculator from Warlock Engineering is very comprehensive and should give you correct angles and cross section.

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yahoo2
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Posted: 15 June 2018 at 1:24pm | IP Logged Quote yahoo2

BarkyJ wrote:

@Yahoo2 do you happen to have a picture of what you did with the whipper snapper cord? Really curious to see.





no photos. Usually the line would be forward of the arrow I have marked. I would superglue it on, test it, when we were happy with the diameter of the filament and the position add a bit of filler and tape it down.

It is kind of hard to explain, you are trying to max the lift and minimize the drag, sometimes a very thin layer of turbulent air gives a lower drag number than trying to "stick" a laminar flow right to the tail. Think golf ball, car rear boot lip, vortex generators.

The shape of the leading edge dictates the % split of air going over and under the blade, plus the natural turbulence in the air the wind turbine is running in plus the load on the generator slowing the rpm, that all changes the position of the line.
I had prop tape with me most times because insect impacts would damage the edge of some blades and it was a quick fix.

I might have a photo of a really nice Chinese blade with the line molded in, it is probably archived, I am not keen to dig it out unless you really need it.


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DaveP68
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Posted: 15 June 2018 at 5:45pm | IP Logged Quote DaveP68

Can anyone shed light on blade weight to help out James?

Most of what I've posted over the last 2 days mostly reflates to this important fact.

A "personal win" for me if we want to focus on these (not my intention) is how accurate my guess of 5 kg's was for the blade weight, as it ending up being 4.5 kg's.

At a current "per blade" weight of 4.5 kg's the Centrifugal force acting on the hub will be 1887 kg's at 500 RPM. That's A LOT of force!!

If the blades go into runaway and they reach 750 RPM that force "per blade" goes up to 4250 kg's!! At 1000 RPM it climes to a whopping 7550 kg's and that's "PER BLADE"!!

Blot them down carefully, as a blade coming off has the potential to travel some distance before it comes to a sudden stop! Heaven forbid through the windscreen of unsuspecting car travelling nearby...

My intention here is not to scare James at all as I'm right behind him. Everyone to date has made equally valued contributions.

Just hoping someone out there can give some advice on this one as I could be over thinking this one and James will be fine with what he's put together so far.
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BarkyJ
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Posted: 15 June 2018 at 7:05pm | IP Logged Quote BarkyJ

Yep those are certainly scary numbers.

500RPM already scares me a bit, so I likely won't let it get even that speed, to start with at least. I will just turn it out of the wind earlier with my turret control. But yes, if that fails for whatever reason and things go pear-shaped, it's certainly something to be well aware of and figure out what to do about.

Each blade is bolted with 3 bolts in a triangle pattern, to the main steel hub, as well as having steel runners going out 400mm or so, so there are 7 bolts in total. At this stage they are 8mm, is what the plan is for.

I do need to think of a backup plan if the motor fails and what to do to get the windmill out of the wind and disabled, in case of an emergency.

The plan though is to turn it out of the wind as the speed increases, so I can then run it at say 20 degrees or 45 degrees etc to the wind, as I see fit, or 90 degrees if required. Leaving it up to the mercy of self direction by tail/wind does scare me, but at the same time relying on mechanical also is also somewhat scary. I have more thinking to do, but I am still going with a motor driven turret, and no tail.

At least so far.
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Madness
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Posted: 15 June 2018 at 9:34pm | IP Logged Quote Madness

Are you calculating the centrifugal force at the tip? It will much less as you get closer to the centre.

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yahoo2
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Posted: 15 June 2018 at 10:20pm | IP Logged Quote yahoo2

I think it is more likely to flutter and flex the blade close to the root above the clamp plates which could form a crack.

If the turbine will hold with the phases shorted it should be fine.

the general direction of the wind doesn't change much, it should be quite easy to park it out of the wind.

my rough calculations at 70 m/s (250 kph and 445 rpm) tip speed on a 3 m diameter fan spreading the 4.5 kg evenly gives me 7300 newtons per blade (740 Kg roughly) I could well be wrong, its been a while since I had to do any of this stuff.

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DaveP68
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Posted: 16 June 2018 at 8:16am | IP Logged Quote DaveP68

Yes Yahoo2's numbers are closer to the mark as missed some minor details, it's still 1000 kg's of blade force at 500 RPM! That's a lot of force in the grander scheme of things...

As I stated before profiling the Airfoil shape of the blades trailing edge more on the outer half section will get the weight down in the region that matters most.

The inner half of the blades can still have plenty of meat on them to maintain strength.
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