Author Topic: Blades 3.0 suggestions (Read 5150 times)

bigrockcandymountain · « **on:** February 09, 2021, 04:43:47 PM »

It is -30 here and windy and so i decided to do a basement project and build some blades. They will be 2x8 spruce again, since that is what i have. When i perfect them, maybe i will build a nice set out of cedar or fir.

My plan is to do goe288 airfoil with 3 degrees at the tip 6 degrees midway and as steep as a 2x8 will allow at the root. The degrees measured across the bottom imaginary flat line, not the chord line of the airfoil.

The tips are 120mm and taper to the full 180mm.

The diameter will be 4m / 13'. Cut in is 160 rpm

Are there any suggestions or comments? I would like better start up, quiter, and better protected from erosion. Is there anything wrong with goe288 for a turbine? Is my angle close? I'm not sure how under cambered airfoils act compared to flat bottomed ones.

MattM · « **Reply #1 on:** February 09, 2021, 07:21:05 PM »

How available is matching chunks of spruce to get extra steep at your roots?

Adriaan Kragten · « **Reply #2 on:** February 10, 2021, 03:47:05 AM »

There are many airfoils which you can use (see report R443D at the bottom of the list with KD-reports on my website). I prefer the Gö 623 (12 %) or the Gö 624 (16 %) because these airfoils have a flat lower side which is also the zero line of the airfoil. Aerodynamic characteristics of these airfoils are given in my report KD 463. Another nice airfoil is the Gö 711 or the Gö 711-12% airfoil because these airfoils are flat over 97.5 % of the chord and so only the curved side of the airfoil has to be machined. The aerodynamic characteristics of these airfoils are given in report KD 333. A disadvantage of this airfoil is that measurements are only given for a rather high Reynolds value of 4 * 10^5. Any rotor should have been designed for a certain airfoil using the Cl-alfa curve of that airfoil. The original airfoil can only be changed by another airfoil if this other airfoil has about the same Cl-alfa curve.

What I don't understand is why people still make tapered and twisted wooden blades which is a lot of work and uses a lot of wood. Wind tunnel tests have proven that blades with a constant chord and no twist can have a maximum Cp of at least 0.4 if they are designed according to the aerodynamic theory but these blades are much easier to make. The starting torque coefficient is only a little lower (see KD 697). In chapter 5.4 of my report KD 35, I give the design calculations for two rotors with the same diameter and design tip speed ratio. One rotor is designed with the optimum lift coefficient and the other with a constant chord. On my website there are several design reports like KD 484 for rotors with constant chord blades so it isn't necessary to design one yourself. The report numbers can be found in the note: "Sequence of KD-reports for self-study". The most recent report is KD 710 about the 3-bladed VIRYA-5B3 rotor.

mbouwer · « **Reply #3 on:** February 10, 2021, 12:04:18 PM »

With this motor/generator conversion of yours.
I thought of mounting an extra drive shaft in front with a coupling to the generator shaft.
In that axle a slotted hole to enable blade pitching.

bigrockcandymountain · « **Reply #4 on:** February 10, 2021, 12:27:23 PM »

Mattm i have some spruce around that would work for extensions at the root. I hadn't thought seriously about that but maybe i should. I would need to get some decent glue.

Adriaan you gave me some good suggestions there. I think the goe711 are very similar to what i have now. Looking at the cl-alpha curve it looks like it stalls at a bit lower angle than the rest. That could contribute to poorer startup if i am looking at it correctly.

The goe624 looks pretty good. I favour the thicker ones for stiffness, since my first set hit the tower. Is there any drawback to thicker airfoils in low wind? They have more drag at high speeds compared to thinner airfoils. Or that is how i understand it. I don't know a lot about aerodynamics.

I use tapered twisted blades for 2 reasons.
1. Strength/stiffness. The poor quality spruce i use needs all the help it can get.

2. Startup. This motor conversion has lots of iron loss on account of a large stator. It also has very large grease filled bearings that drag especially when cold.

Mbouwer variable pitch is very interesting and might be something i will play with once i get some machining tools set up. For now i will keep trying to improve my fixed pitch setup.

SparWeb · « **Reply #5 on:** February 10, 2021, 09:08:40 PM »

You may have looked at sites like this one already:
http://airfoiltools.com/search/index

I find them handy for making comparisons.

I proportion my blades with about 12:1 span/chord. Meaning your 14 foot diameter will have 14 inches chord at the root.

Do you have Hugh Piggott's spreadsheet?
If not, I can share my copy with you (it has some tweaks).

I am not as concerned about airfoil shapes as others, which I've said before. I pay more attention to surface finish and overall geometry to get good performance. So far so good.

MattM · « **Reply #6 on:** February 10, 2021, 09:42:05 PM »

bigrockcandymountain-

If you just want easy start-up then grab some rectangles of sheet metal and add leading edge flaps. Overall much less weight and no need to do variable pitch for easy start-up.

Adriaan Kragten · « **Reply #7 on:** February 11, 2021, 05:11:23 AM »

Quote from: bigrockcandymountain on February 10, 2021, 12:27:23 PM

Mattm i have some spruce around that would work for extensions at the root. I hadn't thought seriously about that but maybe i should. I would need to get some decent glue.

Adriaan you gave me some good suggestions there. I think the goe711 are very similar to what i have now. Looking at the cl-alpha curve it looks like it stalls at a bit lower angle than the rest. That could contribute to poorer startup if i am looking at it correctly.

Generally the angle at which an airfoil starts stalling is larger as the airfoil is thicker. So if you compare airfoils for which the thickness is 12 % of the chord, you will find about the same angle if both airfoils are measured for the same Reynolds number. Increase of the Reynolds number also results in increase of the stalling angle. But it depends also on the turbulence of the wind tunnel in which the airfoil was measured. A higher turbulence has about the same effect as increase of the Reynolds number. For the measurements of Göttingen it is known that the wind tunnel had a low turbulence. For some NACA measurements the turbulence was much higher. So comparing NACA and Göttingen measurements may give differences which are not caused by the difference of the airfoil.

In my report KD 697, I have found that the starting torque coefficient for a constant chord blade is somewhat lower than for a tapered and twisted blade which is designed with the optimum lift coefficient if both blades have the same design tip speed ratio and if both blades use the same airfoil. There is a certain radius rc for the tapered blade where the chord and the blade angle are the same as for the constant chord blade. The part of the constant chord blade for which r is larger than rc contributes more to the starting torque coefficient than that part of the tapered blade. The part of the constant chord blade for which r is smaller than rc contributes less to the starting torque coefficient than that part of the tapered blade. It appears that the negative effect of the inner part is somewhat larger than the positive effect of the outer part.

bigrockcandymountain · « **Reply #8 on:** October 28, 2021, 10:52:19 AM »

Well, this has been put off for a very long time. I finally got back at it and carved these out. They aren't a whole lot different than the ones i have, which is ok because the current ones have worked for 2 years.

I wanted better leading edge protection, better balance, and quieter more than anything else. I'm contemplating epoxy gluing some formed steel leading edges on in about 6" sections. Otherwise i might just get some good expensive 3m tape.

The better balance should be easier. My last set had 1 blade made out of wood that was about half the density if the other 2. It didn't balance well. These are all close.

I'll try tapered tips and a better surface smoothness for quieter operation. I'm thinking hoerner shaped tips deserve a try. Epoxy primer might help smoothness. I just used water based house stain last time. It swells the grain and makes them quite rough.

The airfoil has a slight concave which was mostly just for the challenge.

kitestrings · « **Reply #9 on:** October 28, 2021, 03:51:32 PM »

Your shop and mine have remarkable similarities, including the Sear's radial-arm.

Those look great. In my experience, though not extensive, the single biggest change that makes for quieter blades, is to take the trailing edge to as shark an edge as possible, especially nearest the tips. Looks like you've got that covered here.

SparWeb · « **Reply #10 on:** October 30, 2021, 12:51:47 AM »

You've probably seen enough of my stuff to know what I prefer already.

If thinking about metal on leading edges, consider brass. It is used on aircraft props, is both formable and stiff enough to hold a shape. Can buy sheets of it in rolls called "shim stock". But the 3M tape will then look more like a bargain.

Sharp TE's are great but don't last long. A few hail storms and they start to look like... well... like that shark chewed on them.

Finishing...
https://www.canadiantire.ca/en/pdp/varathane-diamond-wood-finish-for-exterior-water-based-0489857p.html

bigrockcandymountain · « **Reply #11 on:** November 01, 2021, 09:06:21 PM »

Yep, I have seen your blades sparweb and i think they are fantastic. I can't just do what you do though. For the sake of science or just being contrary i have to try something different. So far you win hands down though.

I sanded what i would call Hoerner tips. They look cool and should be quieter than the square ones i have been doing.

I'm going to work really hard at getting a glass smooth paint finish. Then I'll apply the cheap leading edge tape that i have been using. It actually works ok, but doesn't stick to the really rough spots and when it peels off, then they wear like crazy. Maybe I'll do 2 layers or maybe I'll shell out the $100 for good 3m tape. I haven't decided for sure yet.

If they do wear out, i think I'll do epoxy with metal powder on the leading edges. A friend has a small plane with a wooden prop like this and it is holding up great.

The trailing edges are pretty thin. We don't get much hail here so hopefully no problem there.

bigrockcandymountain · « **Reply #12 on:** November 01, 2021, 09:08:35 PM »

Here is a tip. I loaded the wrong picture last time.

SparWeb · « **Reply #13 on:** November 02, 2021, 12:21:55 AM »

It's not a competition (officially). They look good already. What wood is that? Spruce?

I didn't know Hoerner was given credit for that tip shape. In his book Hoerner calls them "raked" tips which works as a description too.
Then again, I notice a whole bunch of references point back to Hoerner's own work in the '40's on tip shape.

bigrockcandymountain · « **Reply #14 on:** November 02, 2021, 08:38:19 AM »

Yes it is just spruce 2x8 lumber again. 2 are perfectly clear and 1 has 5 knots that i filled with epoxy. They are about the size of a dime down to the size of a pencil.

Thanks for info on Hoerner. I have always heard them called that but never looked up the history.

kitestrings · « **Reply #15 on:** November 02, 2021, 02:49:42 PM »

Interesting treatment at the tip. I've seen them rounded in various ways, but not this way. I like that it maintains the airfoil profile, though reduced size, to the tip. I'll be interested to hear how they work; and sound.

bigrockcandymountain · « **Reply #16 on:** November 30, 2021, 07:57:58 AM »

This is why I was asking clockman about his mounting plate diameter. I'm building a new hub, and now that it is done, I'm second guessing the size. The sprocket is 14" diameter, but i lose some bearing surface to the middle hub. I'm pretty sure i will just run it and see how it goes.

On a positive note, the lathe works pretty nice. Still some details to work out and some more tooling to buy, but it is coming in handy pretty often it seems.

The wind is howling here, so my lathe work was 100% wind powered, which is pretty cool i think.

kitestrings · « **Reply #17 on:** November 30, 2021, 11:42:27 AM »

Looks heavy-duty... and just plain heavy.

I'd meant to ask, is this a new rotor for your existing turbine, or a new one?

bigrockcandymountain · « **Reply #18 on:** November 30, 2021, 01:03:25 PM »

This is for the existing turbine. I hope to have two hubs and rotors, then when I tip it, the rotors can be swapped fully assembled and balanced.

Yes, it is heavy for it's intended purpose, but it was all free out of a scrap pile so i can live with the extra weight. The hub that is on there now is heavier yet. It was built in a hurry and is lopsided, so adds to my balance issues.

kitestrings · « **Reply #19 on:** November 30, 2021, 03:46:46 PM »

Oh, I meant the lathe

SparWeb · « **Reply #20 on:** November 30, 2021, 08:52:27 PM »

Quote

Still some details to work out and some more tooling to buy...

Yeah. "just one more boring bar" they say. Right...
Now that I have one of these myself, it is amazing how often I think "...if I had a # tool for my lathe I could do #..."

bigrockcandymountain · « **Reply #21 on:** December 01, 2021, 08:28:47 AM »

I just finished a restoration on an old Atlas driil press. I'm quite happy with how it turned out so I thought I would share. I have never had a proper drill press, so I couldn't be happier with it.

My list for the lathe right now....
Drill chuck for the tailstock
Live centre
Boring bars
4 jaw chuck

Bruce S · « **Reply #22 on:** December 01, 2021, 08:47:48 AM »

Hope you don't mind an old mechanic noticing

, the cylinder head in the background looks to be a bit "carbonized"

Great restoration !!

Congrats!
Bruce S

bigrockcandymountain · « **Reply #23 on:** December 01, 2021, 09:12:48 AM »

Wow, you've got a keen eye Bruce. It is a 2006 5.9L cummins diesel. It had broken top rings on all but 1 cylinder so ya, lots of carbon. The block is in town getting bored .040" It will be my first proper rebuild so I'm quite excited to see how it goes.

SparWeb · « **Reply #24 on:** December 01, 2021, 07:09:24 PM »

Looks nice now.
The broken knob doesn't bother you?

SparWeb · « **Reply #25 on:** December 02, 2021, 12:55:34 AM »

Bruce noticed the engine block - I'm noticing the cherry-picker. Convenient WT test stand? You can be up close and personal as it furls and the blades come around...

bigrockcandymountain · « **Reply #26 on:** December 02, 2021, 08:50:22 AM »

You just had to notice the knobs... ya they are on my ebay watchlist, but not ordered yet.

I never thought of going up in the picker and watching the turbine furl. That would be pretty wild I would think. I'll lend it to you and you can try it.

I think it goes up 46 feet.

SparWeb · « **Reply #27 on:** December 02, 2021, 11:18:46 AM »

That's taller than my last tower!

With that lathe, your next tool could be a tool-post swivel bearing for making spheres.

bigrockcandymountain · « **Reply #28 on:** February 18, 2022, 04:16:12 PM »

This is a little lathe project that has been on my mind for quite awhile. Its just a bushing for balancing my rotors.

I got the new hub and blades assembled and balanced. They are WAY better than the last set for balance. I'm not sure when this will get installed. The old ones are still working and I might wait until fall to save them a summer of weathering before I need them.

SparWeb · « **Reply #29 on:** February 19, 2022, 06:35:11 PM »

Looks great!

Why am I craving steak all of a sudden?

bigrockcandymountain · « **Reply #30 on:** February 20, 2022, 07:38:48 AM »

The quarter of beef in the background is for...scale?

It's my first home butchering other than deer. It went well so far and the weather is cooperating for hanging. I should have a steak ready for you sometime this week.

This rotor balanced with less than 2 cu in of steel weights. The one on there now has about 25 cu in and still isn't very balanced. I'm hopeful that this will run smoother with less vibration.

JW · « **Reply #31 on:** February 20, 2022, 08:09:13 AM »

Got some really nice ground round from the butcher the other day, they were setting out some really nice stuff.

JW · « **Reply #32 on:** February 20, 2022, 08:19:02 AM »

https://www.fieldlines.com/index.php/topic,129125.msg835995.html#msg835995

News:

Author Topic: Blades 3.0 suggestions (Read 5150 times)