Wild Goose Flies

[Laurie Forbes]

Raised my flyweight blade pitch control mill today. Have it set to go into stall at a fairly low speed and seems to be working as it does not over-speed or loose speed even with no load on the alternator. Waiting for stronger winds to test further. Max prop RPM so far is 150. Pics below.

Had a slight setback when a blade hit a guy wire - good thing I had a spare :rolleyes:

No trying to figure out best way of enclosing the hub mechanism, in particular sealing at the pitch shafts (can't make the seal too tight or it will interfere with shaft rotation).

BTW, this is my first two blader and I have not noticed any instances of yaw juddering - maybe at higher RPMs or stronger winds but nothing yet. Might be related to the top-end weight which is about 150 lbs so there is quite a bit of inertia there.

[Mark Parsons]

Greetings Laurie,

Great pics! Nice work. Variable pitch is the way to go.:)

I think I see how the weights are thrown with increasing centrifugal force and feather the blades. I assume there must be a spring to offset the weights and return them to starting position. Is this spring driving the center rod and linkage?

If clock (torsion) springs were used to offset the weights directly on the pitch shafts, do you think the linkage between the blades would still be required? Would it be too dificult to tune the weights to keep the blades feathering in sync? I assume out of sync feathering would cause a significant amount of unbalanced forces.

Regards,
Mark

[Laurie Forbes]

Greetings Laurie,
Great pics! Nice work. Variable pitch is the way to go.:)
Thanks Mark. Variable pitch _is_ the way to go (especially for larger turbines).I think I see how the weights are thrown with increasing centrifugal force and feather the blades. I assume there must be a spring to offset the weights and return them to starting position. Is this spring driving the center rod and linkage?Actually the weights in this setup push the blades towards stall (feather may be better but that would, I think, require a considerably larger range of motion which, I think, would be more difficult to achieve as the fly weights aren't that effective over a swing of much more than 40 deg or so. Pitching towards stall also has the advantage of allowing a steeper pitch at low RPMs, (going then through the "normal" position and then to stall as speed picks up) which should improve start-up ability.

I started with a compression return spring on the centre rod but that introduced additional friction into the "spider" bearings which resulted in jerky & erratic motion. If you look closely, you can see single coil torsion spring(s) directly inside of the fly weight hubs (which seem to work considerably better).

There is still however friction in the spider bearings as they are only steel bolts on bronze bushings with washers for side friction. Ball bearings would have worked much better but I have a still better plan, I think, for my next effort which will have a central bevel gear, free to rotate on the main shaft, and a satellite bevel gear, for each blade, on the end of the pitch shafts. This should have very little friction and won't require a centre rod hole through the main shaft.If clock (torsion) springs were used to offset the weights directly on the pitch shafts, do you think the linkage between the blades would still be required? Would it be too difficult to tune the weights to keep the blades feathering in sync? I assume out of sync feathering would cause a significant amount of unbalanced forces.
Yes, a linkage is probably required as gravity acting on the fly weights will tend to pull the blades to feather on one side of the rotation and to stall on the other side which I imagine would result in a lot of roughness & oscillation (I'm tempted to try it however just to see how much badness results). As you point out, I don't think the blades would feather otherwise in sync very well anyhow. All pitch control mechanisms I have seen have linkage to keep the blades synced.

Now, if I can just get a nice Chinook blowing here I can carry on testing....:D

[Tony Savage]

Laurie,

That's awesome, I sure wish I was at the stage you're at. You should have been in Ontario today. We had lots of strong winds today and you would have been making some pretty good power I'm sure. Good luck with the testing. Anxiously waiting for power output results.

[Laurie Forbes]

Laurie,

That's awesome, I sure wish I was at the stage you're at. You should have been in Ontario today. We had lots of strong winds today and you would have been making some pretty good power I'm sure. Good luck with the testing. Anxiously waiting for power output results.

Thank you Tony. No testing today (little wind, and rain coming tomorrow). As far as power output, I'm really not focusing on that as I'm running two blades only from an original four blade prop - don't know exactly what to expect (maybe 500W compared to the original 1000W?). In any case am concentrating on getting the pitch control working properly and, if successful, will be happy.

My next iteration will likely be a three blade prop, with pitch control (of course) as the current one, and maybe purchased blades from the guy selling the fibreglass units on ebay (they had 10 foot dia prop blades going for a bit over $100). I dunno, I'd also like to try something bigger but that would require a larger alternator and taller pole etc.

[Tony Savage]

Hi Laurie,

I was looking a little closer at your pictures today and I see the broken blade in the top one. What a shame!! I bet that must of been a bit of a pi$$ off. I'm not sure I've seen how your blades are made. I would like to know if you don't mind sharing. Your bevel gear idea sounds like a good one. I still think that there would be a big benefit if you were to change the flyweight orientation so that it moved parallel to the blade axis. Smoother operation, easier to tune and greater range of movement. In regards to power output, from what little that I have read, the two blades should work almost as good as four. It will be interesting to see when the wind picks up out your way.

[Laurie Forbes]

Hi Laurie,

I was looking a little closer at your pictures today and I see the broken blade in the top one. What a shame!! I bet that must of been a bit of a pi$$ off.

Mostly because it was a stupid mistake (I though I had allowed enough for the longer blade reach and reduction on top end height from removal of the original tilt-back mechanism but was about 1 cm too long). Wasn't a big problem however as I have four blades and will not be going back to that configuration.
I'm not sure I've seen how your blades are made. I would like to know if you don't mind sharing.

They are constructed of finger jointed & laminated 1x6 that the home improvement stores sell for baseboard (bought it because it is not too expensive and straight with no knots). Joined lengths together to give 1 1/2" thick at base and marked the curves using Hugh Piggot's spreadsheet. Rather than hand carve the blades, I built a jig and cut the forward surface using a radial arm saw with repeated cuts across the face at the right angle and depth which works because the forward surface is flat in the width direction. The back surface was then curved out using a belt sander. It takes a while but works well. The only problem was the wood evntually began to separate in a few places at the finger joints so I don't think I would use that material again. The problem is getting straight wood with few if any knots. I've seen blades made of laminated 2x2 clear cedar which look great but I'm not sure cedar is strong enough for larger blades.Your bevel gear idea sounds like a good one. I still think that there would be a big benefit if you were to change the flyweight orientation so that it moved parallel to the blade axis. Smoother operation, easier to tune and greater range of movement.
Perhaps so but additional linkage would be required. I'm not sure the benefits would outweigh the additional complexity however. I don't think there is any inherant reason why my current setup will not work satisfactorily as there are commercial pitch control systems which operate with the same fly-weight arrangement. I guess time will tell!
In regards to power output, from what little that I have read, the two blades should work almost as good as four. It will be interesting to see when the wind picks up out your way.
Two blades will produce as much power as four but they have to be sized & carved a little differently. As well, they have to turn faster to "see" all the wind passing through - my four blader was set to top out at about 300 RPM and I don't think I would want to go much above that with wood blades (at least wood blades like mine). I think I may buy the fibergalss blades on ebay for the next iteration.

[Mark Parsons]

Hi Laurie,

You have my mind thinking. Can you smell the wood burning??;)

I tend to agree with Tony on an axial flyweight arrangement. I quickly sketched up an idea in Visio.

Each flyweight is connected to a control arm. The control arm rotates around a pivot point. A torsion spring at the pivot point biases the weight against centrifugal force. The control arm forces rotation to the freely rotating bevel bull gear (your idea, a great one) by a finger / dog. The bevel bull gear drives the 3 bevel spur gears. Only tricky part is pivot points and control arm geometry to attain the required stroke to get the pitch rotation.

How much pitch rotation do you think you need - 45 degrees enough? the full 90 degrees?

Your thoughts?

Mark

[Laurie Forbes]

Hi Laurie,

You have my mind thinking. Can you smell the wood burning??;)

Yes, and I can see the smoke :D

I tend to agree with Tony on an axial flyweight arrangement. I quickly sketched up an idea in Visio.

Each flyweight is connected to a control arm. The control arm rotates around a pivot point. A torsion spring at the pivot point biases the weight against centrifugal force. The control arm forces rotation to the freely rotating bevel bull gear (your idea, a great one) by a finger / dog. The bevel bull gear drives the 3 bevel spur gears. Only tricky part is pivot points and control arm geometry to attain the required stroke to get the pitch rotation.

How much pitch rotation do you think you need - 45 degrees enough? the full 90 degrees?

Your thoughts?

Mark

Mark, driving the bevel bull gear is certainly an approach worth considering. As for how much rotation is needed, it looks to me that roughly 10 deg would be enough if one wanted only to go from "normal" pitch to stall (as an experiment, I rotated my blades about 10 deg into stall as the rest position and the turbine did not move at all ,at least in moderate winds). If however, one wanted to go from a somewhat feathered position (to improve low speed performance) to stall, then I guess you would ideally want maybe 50 or 55 degrees. In any case, a compromise could be made depending on how much pitch rotation the mechanism allows.

However, looking at your diagram I see that the "finger/dog" may have trouble maintaining contact with the bevel bull gear over an appreciable rotation (maybe a sliding finger could act on a pin or somesuch). Another way though might be to add a spur gear behind and attached to the bull bevel gear and drive that spur gear with another gear with a fly-weight attached to it. That should give a pretty large rotation capability, especially if the fly-weight spur gear(s) was larger than the driven spur gear, and, only two fly-weights would be required (spaced at 180 deg) if they are mounted far enough behind the bevel gears to clear them and the pitch shafts.

This gets more and more interesting.....!

[Stewart Corman]

Nice handwork Laurie,
Been following your project since you first posted.
Keep us posted on how the chain drives work out w/r to noise, stretch/slop, wear, oiling, and reliability

I envision the term "feather" to mean that at rest, the blades are at high pitch angle to get started ie 15 degrees, then at optimum shallow pitch angle at rated WS ie 4 degrees, then start to furl at too high a WS ie 25 degrees max to approach stall ...this is not a trivial mechanical mechanism

Stew Corman from sunny Endicott

[Laurie Forbes]

Nice handwork Laurie,
Been following your project since you first posted.
Keep us posted on how the chain drives work out w/r to noise, stretch/slop, wear, oiling, and reliability
Thanks Stewart. I already have some of the above info as I ran a similar setup for a couple of years (not continously though by any means) and have noticed little chain drive noise (a soft whirring noise not very audible above the wind noise), stretch or wear so far. Have only applied oil occasionally when the mill was lowered for some reason. My only problem with reliability is the blades for which the factory finger joints are separating at a couple of locations and paint cracking/blistering.
I envision the term "feather" to mean that at rest, the blades are at high pitch angle to get started ie 15 degrees, then at optimum shallow pitch angle at rated WS ie 4 degrees, then start to furl at too high a WS ie 25 degrees max to approach stall ...this is not a trivial mechanical mechanism

I'm thinking the ideal situation would be somewhat more than 15 deg at rest (it seems to me that max slow speed torque would result at an average pitch of 45 deg). Yes, then going to 4 deg or so at rated speed but I've found that only about 10 deg into stall may be required (as I mentioned in a previous post).

[Mark Parsons]

Another way though might be to add a spur gear behind and attached to the bull bevel gear and drive that spur gear with another gear with a fly-weight attached to it. That should give a pretty large rotation capability, especially if the fly-weight spur gear(s) was larger than the driven spur gear, and, only two fly-weights would be required (spaced at 180 deg) if they are mounted far enough behind the bevel gears to clear them and the pitch shafts.

This gets more and more interesting.....!

Like this?

Mark

[Laurie Forbes]

Like this?

Mark

Yes - pretty close. I would make the fly-weight gear(s) a bit larger though to rotate the bull bevel further.

I would also make the blades the same length :D

Mark, I definately think you should build one like that and we'll see how it compares with my current arrangement.

Edit: Just noticed you are driving the bull bevel directly with a bevel fly-weight gear - that's a good improvement.

[Mark Parsons]

Mark, I definately think you should build one like that and we'll see how it compares with my current arrangement.


I was afraid you might say this. :eek:

Will add to my long list of "to do's". First thing for a mechanism like this, is getting the geometry right. I will see if I can recruit one of my mechanical designers for some pro-bono solid modelling sketching and material and merchandise selection.

Starting design constraints: (Advise comments and additions.)
- up to 50 degrees of blade spar rotation, if possible.
- hub diameter minimize.
- weight minimize but strength and operation must be robust.
- easily adjusted for testing.
- use readily available gears, bearings, bushings, springs.
- weather and water intrusion and corrosion resistance.
- size for 12' - 15' diameter swept area for initial working model.
- Any others?

Mark

[Laurie Forbes]

I was afraid you might say this. :eek:

Will add to my long list of "to do's". First thing for a mechanism like this, is getting the geometry right. I will see if I can recruit one of my mechanical designers for some pro-bono solid modelling sketching and material and merchandise selection.

Starting design constraints: (Advise comments and additions.)
- up to 50 degrees of blade spar rotation, if possible.
- hub diameter minimize.
- weight minimize but strength and operation must be robust.
- easily adjusted for testing.
- use readily available gears, bearings, bushings, springs.
- weather and water intrusion and corrosion resistance.
- size for 12' - 15' diameter swept area for initial working model.
- Any others?

Mark

Mark, looks like a good start! I would add if I could:

I wouldn't go too hard on the weight minimization, especially the fly weights, as you want the mechanism to be able to easily overcome bearing friction and any unbalanced forces that may result from turbulance etc on the blades (my fly weights are 2 1/2 lbs ea which seems about the right range). Ball bearings for the bull bevel bearing and flyweight bearings would be best but my "spider" sync mechanism uses just bronze bushings which also seem OK (avoid steel on steel). One could also use bronze bushings for the blade shaft bearings which may in fact be better than ball bearings (which I am using) as they are apparently not as prone to the "rocking" type of wear they will see (may be more friction thought - I would use ball bearings I think).

The weather proof enclosure is something I'm wrestling with now, the problem being how to seal the blade shafts adequately w/o introducing excessive friction. I'm contemplating just coating everything that cannot be painted (such as the shafts and bearings) with a water resistant grease or somesuch (suggestions wanted) and leaving everything exposed. Nickel plated ball bearings are available but maybe cheaper ones could be used and replaced once a year or two(?).

It may be possible to procure plastic (nylon?) bevel gears at lower cost which may work if large enough (I priced out a steel set for a three blader and it came to about $100 US)- maybe go with plastic to start and replace with metal if everything works out?

I must tell you though that my particular mechanism seems to be working very well - we had some strong winds yesterday and it seems to keep rotation speed nicely limited, even with no load on the gen (which is v nice insurance in case of an electrical disconnect or chain break). If further testing goes OK, my next step will likely be a third blade and bevel gears (but probably with the flyweights still attached directly to the blade shafts).

Anyhow, I encourage you to go for it - no matter what the details more experience with pitch control will be beneficial to all.

[Mark Parsons]

I wouldn't go too hard on the weight minimization, especially the fly weights, as you want the mechanism to be able to easily overcome bearing friction and any unbalanced forces that may result from turbulance etc on the blades (my fly weights are 2 1/2 lbs ea which seems about the right range)

Hi Laurie,

There are more questions I want to ask.

Have you noticed any forces working for or against the pitch rotation? Do the blades themselves help pitching to stall, or hinder, or no observable effect? Put another way. If the blades were free to rotate about the spar pipe, would they want to roll to feather or stall or unknown? If to feather, is this only because the spar pipe is not located in center of blade chord but in middle of thickest blade area nearer leading edge giving the trailing edge a deflection torque?

More questions: In your case you are throwing a 2.5 lb flyweight on what looks to be about a 8" moment to center of blade spar rotation? What would you say the angle of your flyweight arm is to horizontal at start position? 5 degrees? Flyweight distance from center of hub rotation? 8"? Trying to figure out the anticipated centrifugal forces operating on your blade spar.

As I try to further constrain and design this mechanism I'm sure more questions will arise. Thank you for supplying some details.

I was thinking about using automotive ring and pinion gears for bull bevel and blade spur. Cheap and plentiful. Your thoughts? Flyweight bull drive gears are a little trickier unless I change the concept somehow to use more pinion gears.
http://www.motivegear.com/

Regards,
Mark

[Laurie Forbes]

Hi Laurie,

There are more questions I want to ask.

Have you noticed any forces working for or against the pitch rotation? Do the blades themselves help pitching to stall, or hinder, or no observable effect? Put another way. If the blades were free to rotate about the spar pipe, would they want to roll to feather or stall or unknown? If to feather, is this only because the spar pipe is not located in center of blade chord but in middle of thickest blade area nearer leading edge giving the trailing edge a deflection torque?

That's a v good question Mark and one to which I do not have a good answer (I posed it a while ago, not sure on what forum, and received no reply). All I did was guestimate a good neutral position for the blade shaft (spar pipe) and that was in the middle of the blade root. The shaft also turned out to be pretty much flush behind the root due to the way I attached the blade to the shaft. Anyhow, I haven't noticed any unfavourable effects insofar as helping or hindering blade pitch rotation

More questions: In your case you are throwing a 2.5 lb flyweight on what looks to be about a 8" moment to center of blade spar rotation? What would you say the angle of your flyweight arm is to horizontal at start position? 5 degrees? Flyweight distance from center of hub rotation? 8"? Trying to figure out the anticipated centrifugal forces operating on your blade spar.

Flyweight angle at start is now about 10 deg (as I'm sure you know, it has to be > 0 or it won't move). It's an interesting exercise to calculate rotation angle as the flyweight torque, acting against the torsion spring, will increase rapidly with RPM to some point and then level off as the angle approaches 90 deg. The flyweight distance is about 7" and I've made it adjustable for experimentation (with multiple bolt holes along the arm).

As I try to further constrain and design this mechanism I'm sure more questions will arise. Thank you for supplying some details.
No problem - I'll be v interested to watch your results.
I was thinking about using automotive ring and pinion gears for bull bevel and blade spur. Cheap and plentiful. Your thoughts? Flyweight bull drive gears are a little trickier unless I change the concept somehow to use more pinion gears.
http://www.motivegear.com/
The ring & pinion gears sound like a v good idea esp if they can be had in used condition (any wear is not likely to be a big factor here). There would obviously be some machining required, for one a centre shaft would have to be fitted to the ring gear.

Not sure why the flyweight gears would be trickier - could you not just use five pinions in all (three for the blades and two for the flyweights (assuming they would all fit at once around the ring gear)? One problem might be buying five pinions with only one ring gear though.

Edit: Just realized the blade shaft pinions will fit the ring gear but the flyweight ones won't as they are at the wrong angle to the ring (and the same applies to straight bevel gears, I think). You may have to go with the spur gear attached to the ring gear method, driven by spur gears on the flyweight arms.

[Rob Beckers]

That's a v good question Mark and one to which I do not have a good answer (I posed it a while ago, not sure on what forum, and received no reply). All I did was guestimate a good neutral position for the blade shaft (spar pipe) and that was in the middle of the blade root. The shaft also turned out to be pretty much flush behind the root due to the way I attached the blade to the shaft. Anyhow, I haven't noticed any unfavourable effects insofar as helping or hindering blade pitch rotation


I can speculate a bit regarding this: From airplane airfoils I know most of the lift (by far) is generated by the leading edge. So, if one hinges the blade around its chord center, that would mean it'll try to rotate towards stall angle if left to its own devices. If one would get the lift distribution for a profile vs. wind speed then one could even calculate the torque it'll produce on the blade hinge, since the arm is known.

My $0.02...:cool:

-Rob-

[Laurie Forbes]

I can speculate a bit regarding this: From airplane airfoils I know most of the lift (by far) is generated by the leading edge. So, if one hinges the blade around its chord center, that would mean it'll try to rotate towards stall angle if left to its own devices. If one would get the lift distribution for a profile vs. wind speed then one could even calculate the torque it'll produce on the blade hinge, since the arm is known.

My $0.02...:cool:

-Rob-

I don't think this is a critical issue vis a vis pitch control though as one should be able to easily adjust it out, or make use of it, by changing the flyweights' size or moving their postion on the arm.

BTW, is their any way of changing the thread's title (I just realized it should read "Wild Goose Flies" :o )

Also BTW, I just noticed my "Rep Power" has advanced from 0! How does one receive this prestigious accolade? :)

[Rob Beckers]

I wasn't suggesting that the blade aerodynamics had much (if any) effect on pitch control. My reply was just meant to try and answer Mark's question on what force works on those free-moving blades. Since there are many pitch controlled gennies out there that work very well it clearly is not a problem.:)

Not entirely sure, but I believe I can change the thread title. I'll do it tomorrow, since it involves rebuilding all the database indices (things like search terms, similar threads and all that are actually stored in tables, so a change means it's a good idea to rebuild). Right now it's just about 22:30 here and that's my time to snooze!

Reputation is based on feedback from other members, they can give away 'points'. You can do the same for others, oh great one! ;)

-Rob-

[Mark Parsons]

Flyweight angle at start is now about 10 deg (as I'm sure you know, it has to be > 0 or it won't move). It's an interesting exercise to calculate rotation angle as the flyweight torque, acting against the torsion spring, will increase rapidly with RPM to some point and then level off as the angle approaches 90 deg. The flyweight distance is about 7" and I've made it adjustable for experimentation (with multiple bolt holes along the arm).


Hi Laurie,

Start position of flyweight 10 degrees from horizontal 7" out on torque arm from spar rotation center. How far from hub rotation center? Flyweight torque will increase to 90 degrees of angle. However, since the weight twists at a tangent to hub rotation in your configuration, the centrifugal force only increases by the radius change due to this tangent.

For a 2.5 pound weight at 9" (scaled the photo) to 11" (hypoteneuse when weight twisted 90 degrees) hub radius, centrifugal force Fc = mv^2/r = 1.14kg * (2*pi*0.23m/s)^2 / 0.23m = 10.4 Newtons per RPS (60RPM) = 2.3 pounds force * 2 weights = 4.6 pounds force per 60RPM at minimum to Fc = 1.14kg * (2 * pi * 0.29m/s)^2 / 0.29m = 13.1 * 2 = 26.2 Newtons = 5.9 pounds per 60RPM maximum. At 150RPM the total force is 14.7 pounds max.

This force is applied to rotate the spar as a moment vector function of the sin of the angle in your configuration created by hub offset distance and torque arm length. If 9" from hub center and 7" torque arm then 77% of the above force is used to create the spar rotate torque. As above this would be 14.7 pounds at 7" * 77% = 1.6 in-lbs max. Seems light.

This small torque required to rotate the blades is perhaps explained by Rob indicating that the blades lift force is assisting in pitching to the stall position.

The math is much simpler for an axial configuration. The forces available for an axial configuration are also much more since this vector is in line with the plane of rotation. Smaller flyweights with shorter torque arms may suffice, or just more safety margin.

Not sure why the flyweight gears would be trickier - could you not just use five pinions in all (three for the blades and two for the flyweights (assuming they would all fit at once around the ring gear)? One problem might be buying five pinions with only one ring gear though.

The pinion gears are made to interact with the ring gear in plane of rotation. The flyweight gears need to interact at right angles to the ring gear in my concept.

Has my calculator (or brain) malfunctioned in any of the above?
Mark

[Laurie Forbes]

For those of you interested in carving your own blades, I've attached a pic of a jig I built to facilitate the process using a radial arm saw to form the front blade surface (assuming it's flat chord-wise) and hog out the back side (after which the edges can be rounded off with a plane or belt sander).

The jig is moved one blade(s) width at a time in the lateral direction while the screw adjustment sets the chord angle to be cut. It takes a while to move across the length of a blade but IMO is a lot easier than true carving with a plane, chisel etc.

I've placed an already cut and painted blade in the jig just to demonstrate how it works. The blade height is set to begin cutting at the leading edge and deeper from there depending on the jig angle set. As the cuts move from the hub to the tip, the angle is reduced to provide the blade twist called for by the spreadsheet (provided by Hugh Piggot's web site). The screw adjustment came from a metal chop saw clamp.

[Laurie Forbes]

Have stepped up my mill RPM (by moving the flyweights a notch inwards) and it is now maxing at about 230 RPM with no load. Had a good stiff wind today and everything worked well. Under load the RPM peaks at about 200 so regulation is not real tight but not that bad. The blades get a little noisier when into stall but not really too noticable.

Since the two blades I'm using now are cut for a four blade turbine, to get a better test situation, I think I will make two more this time designed for a two blade machine (the chords will be twice as wide for same performance as the four blader).

Since it's hard to find good wood here, I'm contemplating trying laminating 1 by 6 or 8 spruce construction lumber, cutting out the knots and joining the pieces to hopefully get something pretty close to clear straight stock. Am not sure what would be the best joining method however (box, dovetail, lap etc,). Any suggestions would be appreciated.

I've also been observing the two blade mill in operation and it doesn't seem all that much different than the four blade configuration (the tail jiggles a bit when yawing but not enough to cause concern). Rob, I was wondering if you have any info as to why the Scirroco manufacturer decided to go with two instead of the more common three blades (I seem to recall asking this question before so apologies if I did)?

[Ralph Day]

Hi Laurie

From past woodworking experience, maximize your surface area in the glue joint. If you have a shaper, great, or a good router and table, ok. Your best bet would be a finger joint. Check out Busy Bee (or Lee Valley if you can afford it) for the bits. I think it's the maximum surface area for joining. For glue...you can't beat West System epoxy. Never had any joints fail in 15 years of use. There's different additives to custom mix the type of glue to the type of job/stresses the joint will be exposed to.

Best of luck.
Ralph

[Stewart Corman]

Laurie,
quick comment on woodworking


Since it's hard to find good wood here, I'm contemplating trying laminating 1 by 6 or 8 spruce construction lumber, cutting out the knots and joining the pieces to hopefully get something pretty close to clear straight stock.
I used some 2x4 spruce in middle my blades .... big mistake ...grain/knots makes sanding to shape difficult ..will NOT do that again

it is easier to glue thicker sections on edge rather than 1x6 flat planks
http://s145.photobucket.com/albums/r203/scorman1/Turbine%20project/blade%20construction/?action=view&current=4200.jpg
try to find 6/4 or 8/4 poplar from local sawmills ...straight grain, no knots, strong and lightweight

and while you are glueing ..look at the trick to add a diagonal trailing edge (hardwood? maple or cherry, not oak) for better grain control (this was one of the best ideas I have come up with in this project)
http://i145.photobucket.com/albums/r203/scorman1/Turbine%20project/blade%20construction/4251.jpg

in 15+ years glues have improved significantly ...I use the waterproof Titebond III ....did a test where I glued sample together and left submerged in pail of water for a week ..intact! confirm for yourself
http://www.titebond.com/WNTitebondIIITB.asp

Stew Corman from sunny Endicott

BTW, I complement you on the radial saw fixture for roughing out the blade contours ...good thinking + implementation

[Laurie Forbes]

Hi Laurie

From past woodworking experience, maximize your surface area in the glue joint. If you have a shaper, great, or a good router and table, ok. Your best bet would be a finger joint. Check out Busy Bee (or Lee Valley if you can afford it) for the bits. I think it's the maximum surface area for joining. For glue...you can't beat West System epoxy. Never had any joints fail in 15 years of use. There's different additives to custom mix the type of glue to the type of job/stresses the joint will be exposed to.

Best of luck.
Ralph

Ralph, I did look at finger joint router bits (didn't know they were even available) but all I saw were only about 1 1/2" long so I don't know how well they would work with wider stock (how do you maintain the registration with multiple cuts?).

Also checked out the Western System epoxy - sounds excellent but at about $150 per gallon, a little pricey for experimentation stuff IMO - maybe for later iterations.

[Laurie Forbes]

Laurie,
quick comment on woodworking

I used some 2x4 spruce in middle my blades .... big mistake ...grain/knots makes sanding to shape difficult ..will NOT do that again
I hear you - that's why my plan to remove the nasties and join the pieces together.
it is easier to glue thicker sections on edge rather than 1x6 flat planks
I'm also looking a that - would still be able to remove knots etc.
http://s145.photobucket.com/albums/r203/scorman1/Turbine%20project/blade%20construction/?action=view&current=4200.jpg
try to find 6/4 or 8/4 poplar from local sawmills ...straight grain, no knots, strong and lightweight
That's the problem, the only product produced by saw mills around here is spruce lumber.
and while you are glueing ..look at the trick to add a diagonal trailing edge (hardwood? maple or cherry, not oak) for better grain control (this was one of the best ideas I have come up with in this project)
http://i145.photobucket.com/albums/r203/scorman1/Turbine%20project/blade%20construction/4251.jpg
Interesting idea - I might just do that.
in 15+ years glues have improved significantly ...I use the waterproof Titebond III ....did a test where I glued sample together and left submerged in pail of water for a week ..intact! confirm for yourself
http://www.titebond.com/WNTitebondIIITB.asp
Looks like a good choice & likely a lot cheaper than epoxy. BTW, my currently used blades are lamed together with the ordinary yellow, indoors carpenter glue (I had it onhand & figured the paint would protect it). It seems to be holding up pretty well so far - the only problem I've had is with the finger joints, that were in the wood stock ,separating.

BTW, I complement you on the radial saw fixture for roughing out the blade contours ...good thinking + implementation

Thank you. I'd recommend this method as it seems a lot easier than the traditional manual methods (I borrowed a neighbour's draw plane a while ago and it seemed much too much like work esp for larger blades plus the ever present danger of chipping or accidently going too deep).

[Laurie Forbes]

Visited the WW2 Air Museum in Nanton, AB today and was struck by one thing in particular in regards to blade pitch control. A Harvard trainer was one of the aircraft on display and guess what it had attached to the sides of the propeller hub - fly weights! I guess there's not much new under the sun.