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blade comments requested
By jacquesm, Section Wind Posted on Sun Oct 17th, 2004 at 10:18:49 PM MST
have made our first blade, looking for feedback

We have completed our first blade (RonB and myself), and we would like to sollicit feedback regarding the blade.

It's of a slightly unusual design in that it has the 'tip' portion of the blade centered with respect to the root in the 'y' (width) and 'z' (thickness) axis. This allows us to produce the blade from a much thinner blank than would otherwise be possible.

Pictures of the blade in my latest diary entry, they'll say more about what the blade looks like than I can do with words and measurements.

A little bit of hard data: the profile is 'regular' NACA4412, the blade tip is 6" wide, the root is 10" 3/8 wide. It weighs roughly 3 kilograms (7 pounds or so), including the stub that is still attached to the root.

The blade will be covered with a fibreglass skin.

This one (a trial version) is made out of laminated spruce (cheap!), and will be covered with fibreglass to increase stiffness and to protect the wood from the weather.

blade comments requested | 11 comments (11 topical, 0 editorial)

Re: blade comments requested (3.00 / 0) (#1)
by gibsonfvse on Sun Oct 17th, 2004 at 11:09:51 PM MST
(User Info)

I suspect you mean "radical" in the construction method. It is a beautiful blade. My only thought, based on my (limited) knowledge of rotary wing aerodynamics, is that it will perform best at low RPM because the twist is "so" small (it seems so, visually, at least). The startup performance should be great, but at higher RPM, the tips will stall sooner than they would if the blade had more twist.

Re: blade comments requested (3.00 / 0) (#2)
by Flux on Mon Oct 18th, 2004 at 01:15:31 AM MST
(User Info)

Nice work, I admire your determination and your computer skils.

I have never tried covering blades with fibreglass, I don't know how easy it is to get a good surface finish that way round, normally the mould provides the surface finish.

How do you intend to fix it to the shafts on your pitch mechanism, that is the bit I am doubtful about, but it seems that Jacobs didn't do anything very sophisticated.

I am sure the aerodynamics of it will be fine.

Flux

[ Parent ]

Re: blade comments requested (3.00 / 0) (#3)
by troy on Mon Oct 18th, 2004 at 10:31:38 AM MST
(User Info)

Amazing technology and lovely blade. My only comment would be about the fiberglass. If it's absolutely watertight, you may do well. But I have a modest amount of experience with fiberglass over wood in a boat application. The fiberglass may actually work against you if you totally sheath the blade. Moisture will somehow manage to get into the wood. Centrifical forces will cause the water to migrate to the outer portions of the blades. The fiberglass will prevent the moisture from leaving the blade by evaporation causing soggy tips.

Other alternatives that I have considered are:

fiberglassing just the inner third of the blade for the strength, or
in a built up blank, laminating fiberglass or carbon fiber on the inside of the blank (between layers of wood) to provide the strength without mitigating the ability of moisture to leave the blade.

This is about 95% theoretical pondering on my part and 5% hands on real world information, so take it all with a grain of salt.

Again, first class amazing work you are doing there. Can't wait to see the outcome.

Best regards,

troy

Re: blade comments requested (3.00 / 0) (#4)
by hvirtane (hannu_markus_virtanen(at)yahoo(dot)com) on Mon Oct 18th, 2004 at 12:25:17 PM MST
(User Info) http://web.archive.org/web/20050404022706/www.cc.jyu.fi/~hvirtane/cooker/

In my opinion they look great.
I think that they will work
really well.

Troy: The fiberglass may actually
work against you if you totally
sheath the blade.
Moisture will somehow manage
to get into the wood.

My opinion is the same.
There is always moisture
in the wood and at least
with wooden boats
fiberglass coating
doesn't work well.

I think that it would
be better to use linseed oil
as it is or varnish.

- Hannu

Re: blade comments requested (3.00 / 0) (#7)
by DanB (danb@*no spam*otherpower.com) on Tue Oct 19th, 2004 at 07:33:04 AM MST
(User Info) http://www.otherpower.com/

I tend to agree...
Im not sure what the point of the fiberglass would be. It would certainly add a lot of weight and Im not sure that the xtra strength would outweight the added forces on the blades from all that weight. Laminated up the way you have them - I suspect the blades are plenty strong as they are.

[ Parent ]

Re: blade comments requested (3.00 / 0) (#5)
by iFred (ifred2006@yahoo.com) on Mon Oct 18th, 2004 at 07:42:39 PM MST
(User Info)

Test and see the result. Then you will know for sure. But by the looks, it's OK! NICE JOB GUYS!
>> all energy used to produce this comment or post came from solar and wind energy! It works!

Re: blade comments requested (3.00 / 0) (#6)
by devoncloud on Mon Oct 18th, 2004 at 10:57:26 PM MST
(User Info)

That looks awesome! It looks like it may be kind of skinny by the root, but that could just be the twist making it look like that in the picture. It looks like you will have one hell of a generator. Congrats on all the hard work panning out for you!!!!
Devon

Re: blade comments requested (3.00 / 0) (#8)
by Wa on Tue Oct 19th, 2004 at 10:40:25 AM MST
(User Info)

hi,

beautiful work -

i have tracked several laminating materials over several years, and found that specifically, fiberglass (cabon, kevlar etc.) when covering completely, in an outdoor or marine environment, actually comprimises the structure of the wood rather than strengthens - many critters live in the pores of the wood, kept in check by air and temp. - sealing up the wood causes it to rot fairly quickly - it also causes the fibers of the wood to remain continually wet, and actually allows the fibers to slip against each other - similar to when you steam sides on a guitar

it would be better to laminate synthetics in between the layers (between wood layers) (i have successfully done this) but this may complicate tooling - choosing the right reinforcement is also important - kevlar in this situation would be ideal because it has a modulus of elasticity similar to the wood surrounding it - carbon in flex tends to separate itself at the bonding layer in extreme conditions of repetitive loading - i have personally found kevlar,wood, and vinylesters, or high quality epoxies the best match - complete wetting, with vacuum bagging or high pressure clamping, and a slightly elavated cure temp (as per resin) would result in a very adequate, rugged blade

hope this is useful,
cheers,

warren

Re: blade comments requested (3.00 / 0) (#9)
by jimovonz (username at matata dot co dot nz) on Tue Oct 19th, 2004 at 02:27:01 PM MST
(User Info)

I too plan to use fiberglass over wood for my blades. The reason being I have a ready supply of easily worked softwood(redwood) that would certainly not hold up on it own in a blade of any description. Would the problem of water penetration you describe also apply to any non-permeable coating - such as varnish, paint etc? Could this be mitigated to some degree by providing a small exit hole at/near the tip? I certainly do not want to go to the trouble of producing a blade set only to have it rot out on me!

[ Parent ]

Re: blade comments requested (3.00 / 0) (#10)
by Wa on Wed Oct 20th, 2004 at 12:27:59 PM MST
(User Info)

hi,

unfortunately, no commercial coating at present is truly non-permeable - varishes, poly's and oils are suprisingly permeable - this is a good thing - flexibilty is everything in this game with respect to weather resistance - the best speadable coating with a high permeability is parrifin - melted wax, brushed thick - everything else breathes to a certain extent - sealing up anything organic with no path for draining at the endgrain, will eventually loosen up - ever try to put a band-ade on wet skin? - not to mention pressure build up - i have seen plenty of ballooned out hulls in the sun with bad glass jobs that didn't pay attention to the moisture content of the wood - wood needs to breathe

FRP (fibre reinf. plastic) over foam works because the foams stabilizes with respect to moisture content (slow in slow out) - stryrofoam actually takes on quite a bit of water over time as compared to polyurethane - after many years, the styro insulation in your refridgerator actually becomes waterlogged and ceases to have a the R factor it once had - poly is vastly superior - foam also excels because the laminations are not twisting in respect to the core - wood wants to deform in very specific ways, quite unlike the frp skin - foam lets the skin do what you have designed the skin to do - as in an I-beam or any stress-skin shape, the core is of small contribution to the total strength

hope this helps,
cheers,

warren

[ Parent ]

Re: blade comments requested (3.00 / 0) (#11)
by troy on Wed Oct 20th, 2004 at 06:35:12 PM MST
(User Info)

If you're concerned about strength using softwoods, I think a composite stucture is still possible. But much better to laminate the kevlar or what have you inside the blade between layers, using an appropriate epoxy, like the West system. Fabulously strong in wing spars, yet still allows for moisture control/migration. I would be very hesitant to use fiberglass over the outside of a wooden blade.

Good luck and have fun!

troy

[ Parent ]

blade comments requested | 11 comments (11 topical, 0 editorial)

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