how protect vane in a windvane

[roverhi]

Made a corrugated plastic 8" x 48" light air vane for the WindPilot. The mfg supplied plywood vane just wasn't able to deflect quickly and enough to steer in light air. The servo steering part of the vane worked even down to .001 knots of boatspeed if it had the steering input from the wind vane. The much larger corrugated vane solved the problem. It steered the boat to Hawaii DDW with a relative windspeed almost never above 8k. The plastic vane is still in use despite getting a very rough work out on the passage. It was often going stop to stop to steer the boat with the confused 4'-8' seas slewing the stern around. The vane bent but never broke and I still use it here in light air Kona. Did have four backups if the original pretzeled.

As far as a preservative for a wood vane, any good UV protective finish works, varnish or paint.

Yes, the weight of the vane has to work with the counter weight. Too light a vane and the counter weight will keep it straight up in winds too light to counteract the weight not giving steering input to the servo rudder. If too heavy, it will have a tendency to fall over and stay over giving the wrong or very slow steering input. Don't know if there is a magic number you can calculate but the vane should self center rather quickly in no wind condition yet not take too much force to move in light air. Know the 8" x 48" corrugated plastic vane seemed to have the same balanced steering effect as the wooden vane in lighter air. FWIW, Monitor sells a light air vane that is identical to the one I had made up. Believe they still supply their system with a plywood vane to be used for most condtions.

One last thing, if you fabricate a corrugated plastic vane be sure the corrugations run vertical not horizontal.

[Snowpetrel]

Originally Posted by JeffH

Doesn’t the weight of the vane have to match the weight of the counterweight?

It has to match it, but by moments about the pivot rather than weight, so if the vane is taller it's total weight needs to far lighter than a shorter vane.

I usually balance it by experiment, I want it to return to upright, but slightly slowed due to air drag. My first set of vanes where far too light and in light airs lost sensitivity. I drilled a small hole and put a heavy shackle through it near the top of the vane, and suddenly it started steering in a whisper of wind.

[a64pilot]

Originally Posted by Snowpetrel

Sounds like the same stuff as the solarfilm we used as kids to cover the wings of our RC airplanes and gliders. Shrink it with an iron (not to hot...) I wonder how it holds up to UV long term. Might also help keep the water out.

There are several competing versions of Monokote.
No idea about UV, I’d be surprised if it were real resistant though.
Dope and silk ought to go ten years though, if using fabric be sure to use several costs of silver, the silver block the UV from penetrating to the fabric.
While I know next to nothing about a wind vane, I was wondering how a fully symmetrical airfoil would work, I’d think better than a flat blade?

A lot of model airplane wings have been built with balsa coating a foam core, and you can use carbon fiber arrow shafts for spars. I use to shoot Easton I think ACC shaft, aluminum covered by carbon, and they were extremely strong, and lightweight. I’d think a bundle of say three carbon fiber arrow shafts for both a main and rear spar ought to be pretty strong?

[model 10]

The stock plywood vane for the Aries works better than any I've come up with and it too steers the boat in 8 knots downwind. I made a big one from super thin fiberglass and foam once and it weighed more than the stock plywood vane.
I'm still using the plywood vane that came with the unit and it's ready for another spray bomb varnish job any day now. It's the lightest way to do it.

[Ramona]

Originally Posted by JeffH

Doesn’t the weight of the vane have to match the weight of the counterweight?

The weight lead is slid up or down to match the chosen blade. Some systems use different sized blades.
On my unit The blade is made of cedar and tapers from the leading edge of 3mm to 10 mm at the rear. It's finished with a couple of coats of spray enamel. I have tried epoxy on other blades but this adds too much weight. When not in use it resides on the quarter berth.

[Ramona]

Originally Posted by a64pilot

There are several competing versions of Monokote.
No idea about UV, I’d be surprised if it were real resistant though.
Dope and silk ought to go ten years though, if using fabric be sure to use several costs of silver, the silver block the UV from penetrating to the fabric.
While I know next to nothing about a wind vane, I was wondering how a fully symmetrical airfoil would work, I’d think better than a flat blade?

A lot of model airplane wings have been built with balsa coating a foam core, and you can use carbon fiber arrow shafts for spars. I use to shoot Easton I think ACC shaft, aluminum covered by carbon, and they were extremely strong, and lightweight. I’d think a bundle of say three carbon fiber arrow shafts for both a main and rear spar ought to be pretty strong?

The whole idea of the vane is to indicate a change in the wind direction. A symmetrical airfoil would delay the change. The best shape is a taper followed by a flat section with a symmetrical shape a distant third. Commercially made vanes are flat because that's the cheapest and easiest to make. I have also seen twin flat sheets of thin alloy separated by 30mm spacers that apparently worked well.

[a64pilot]

Too bad, cause it’s a whole lot easier to make a thick airfoil light and strong than a blade.

[model 10]

Originally Posted by a64pilot

Too bad, cause it’s a whole lot easier to make a thick airfoil light and strong than a blade.

A symmetrical airfoil would work fine but it's hard to make one and maybe you don't need too. At the speed my boat is going with 8 knots downwind, there isn't enough rudder to do much anyway.

[Snowpetrel]

I think the biggest advantages of the foil over the flat plate are reduced drag (not really an issue for us), so much better lift to drag ratios, and higher stall angles. I'd love to experiment with foil shaped vanes, but it seems like the simple flat plate works very well when sized correctly. Maybe a foil would be marginally better, but probably not by enough to justify the extra work.

[Alan Mighty]

Hmm ... thanks to all for the ideas.

Seems I only need wait for the next election in Aus.

Corflute signage (corrugated plastic structures, similar in structure to double-sided cardboard - see: https://signarama.com.au/products/corflute-signs or https://www.campusreview.com.au/2014/02/corflute/ - and much used in Aus and NZ for election campaigns) may be worth trying.

Cost is low, especially the morning after an election.

And the screenprinted ink likely acts as protection against UV.

Now I just need a political party using the right colour ...

[Snowpetrel]

^^ I wouldn't use coreflute, its far too flexible on its own, maybe with a strong spar up the guts, but not as a unsuported single skin.

They often use twin wall polycarbonate roofing sheets. It's much stronger and stiffer than the coreflute, but still needs reinforcing to handle stronger winds.

[Siberian Sea]

I have a Monitor wind vane and they use a plastic material that seems to not only hold up against the UV rays but is uneffected by weather. Maybe you can modify one of their plastic blades to fit your unit. They come in two sizes. A larger one for light airs and a smaller one for heavy winds. Call Suzy Savage at Scanmar International at 510-215-2010

[Ramona]

Originally Posted by Siberian Sea

I have a Monitor wind vane and they use a plastic material that seems to not only hold up against the UV rays but is uneffected by weather. Maybe you can modify one of their plastic blades to fit your unit. They come in two sizes. A larger one for light airs and a smaller one for heavy winds. Call Suzy Savage at Scanmar International at 510-215-2010

Monitor uses the polycarbonate sheets about 6mm thick. These only seem to be available in 12mm thickness from Bunnings in Australia. I have tried the sign coreflute and it is not strong enough. When epoxy and cloth is added it becomes a bit too heavy but I have one like this as a spare. All the major windvane manufacturers seem to use the same dimensions, 800 x 200mm. There is plenty of technical info online about windvane blades and explanations on what is the best shape. The windvane section on this site also has plenty of good info from people who build and experiment with vanes.
Windvane

[Snowpetrel]

Originally Posted by a64pilot

Too bad, cause it’s a whole lot easier to make a thick airfoil light and strong than a blade.

From Bill belcher's book. Looks like the AR5 flat plate has a lot less maximum lift than the AR5 foil but the lift is similar at the lower angles of attack that our wind vanes normally work in.

It would be facinating to do a test. I guess the challenge would be to make a foil shaped vane that is light enough. Maybe a typical model aircraft wing with a film covering. It may work better in the light downwind where the apparent wind can shift dramatically.

[a64pilot]

Many years ago, as in WWI era aircraft wings were very thin, pretty much plates. The idea was thin wings have less resistance and you can go faster. However being thin they are very weak and flexible, necessitating a lot of struts and wires and other braces to keep your wings from disintegrating. then I’d guess about the 20’s or maybe as late as the 30’s it was discovered that thicker airfoils performed much, much better allowing higher angles of attack etc before stalling and being thicker, it was easy to internally brace them and make them strong and speeds went way up, without the external bracing they were much less resistance too.

I don’t know about size, but this Viper 500 wing has zero dihedral, is fully symmetric and is stronger than you can imagine and very lightweight.
https://www.towerhobbies.com/cgi-bin...BoCkjYQAvD_BwE

Comes in Read or white, already prebuilt, covered etc. it does have thin strip ailerons though that you would need to install.

The Viper 500 is a very, very fast little racing airplane