Otherpower 10' Amperage Limit

[watermanhfl]

This weekend we had heavy wind and I saw 50 mph on my weather station twice.  My 10' was furling late with the new tail I put on it and I was seeing 1,500 to 1,800 watt peak a lot.  This is the 48 volt version and amperage was in the 30 to 35 amp range during peaks with about 15 amps as the base.  I had the mill shut down during the worst of it but these numbers were when the wind was in the 40 gust, 25 steady range.  Mill was furling a bit but not much.  Two weeks ago I had added 1 square foot or about 2 lbs to the end of tail to improving it's tracking.  I have now put the old tail back on and added a thin washer to space out the magnet rotor to stop rubbing.  As you can see from pictures the stator was hot but is still functional now with a slight warp.  So set your furl before this point.  Anyone have any thoughts on a good tail material so I can up the size but not the weight?  I am using fiberglass from a tub wall surround.  I bit lighter than plywood.

[Norm]

  How about a fiberglas frame with an aluminum

panel... I started to suggest a foamboard panel,

but maybe that's going a little too much...still

as long as the frame was sturdy enough the rest

don't have to be bulletproof?

(split frame 2 halves bolted together with the aluminum sheet or foamboard sandwiched between)

             ( :>) Norm

[Ungrounded Lightning Rod]

I'd make the tail longer and shrink the vane rather than trying to find an exotic light material.  Doubling the length of the tail doubles the tracking force from a given vane area.  It also doubles the effective furling force by doubling the lever arm on which it's applied.

The weight of the tail strut also goes up in proportion.  But the reduced weight of the smaller vane should more than compensate for the added weight of the longer strut.  That will result in earlier furling, which you can then tune away as desired by adding weights at the vane end.

[tecker]

The blade wash turbulence and the back pressure bubble as the blades exceed the wind speed make for an area  of pressure that you have to measure to make the tail more reactive .If your in that pressure bubble the tail has a tendency to move side to side in the wash that is a good indicator.

 

[watermanhfl]

Tks for comments guys.  I knew that longer tail mount would help tracking but thought that longer tail with same weight would furl later.  Then Tecker brought up the blade wash issue which I had not thought about.  So I want to go longer but is weight the only issue for furling change or does length and the leverage come into play, if angles all stay the same?  I even thought about tilting the tail 10 degrees so that as wind hits it the wind pushes tail up.

[Flux]

The thing that matters for furling is the moment about the tail hinge. If you make the tail boom longer you need to reduce the weight of the vane, but you can partly compensate by not needing such a large vane for the same tracking.

For years I have used sheet aluminium for tail vanes. As long as you bend the top and bottom edges at right angles and use some strips of steel to stiffen it it will be ok, otherwise it will rattle off.

Plywood is heavy but if you use the correct angle for the hinge it will be ok. If it is too heavy then you need a smaller angle for the hinge but once welded on that is not adjustable so you need to reduce the weight of the vane.

If it tracks the wind ok you can probably make the vane smaller to reduce weight.

It is the product of weight at the c of g x radius at c of g that determines furling.  Stability and ability to point into the wind below furling is determined by vane area and length of boom from pivot to centre of pressure.

To some extent you can use a smaller vane and offset the boom away from furling direction so the prop stays normal to the wind but the tail will run at an angle. If the vane is seriously too small the angle will make it look silly.

Flux

[Flux]

Having read your comments again, I think you are furling seriously late, It should be well furled during the 40 mph gusts.

I think you are relying more on stall limiting than furling. The odd peak during a gust to 1500W will not probably hurt, but you will not survive long if you don't restrict the continuous power to not much over 1kW.

I suspect technically your coils are already burnt out, but they will work for a long time with the decomposed wire insulation between turns at low voltage. Failure will probably come when due to distortion they rub the magnets.

It may be that for use with a decent sized plywood tail, the tail pivot angle needs reducing below the suggested angle ( 20 deg?). Everyone uses different weight tail boom and vane materials so what is safe for one may not be so for another. It would be useful on one that furls properly if someone weighed the tail at a convenient point ( say 3ft from the hinge) and gave a figure for the moment ( weight times this distance) that would be a guide to others.

Flux

[scoraigwind]

As Flux has pointed out, it is not the weight of the tail so much as the moment of weight that matters.

The way to measure the moment of weight is to lie the machine down sideways on the ground so tht the furling hinge is horizontal.  then measure the weight of the tail at a certain point.  Moment of weight is the weight you measure times the distance from the hinge of the measurement point.  If you measure at 3 feet away, and the weight is 10 pounds then the moment of weight is 30 foot-pounds.  Personally I would use metres and kilograms but it is not hard to convert between them.

The angle of the tail hinge is also an important variable.  A better way to measure the effect of the tail is actually to put the macine back up vertical (truly vertical yaw bearing) and measure the amont of horizontal force on th evane at a certain point that makes it move.  The amount of force to hold it there will be less due to friction.  The average restoring moment of the tail will be the average of these two forces times the distance from the hinge.

When you measure the distance from the hinge, This must be done at right angles to the hinge line.  If the measurement point is beyond the top of the hinge then extend the hinge line up to the point where you can throw a right angle off the line to the point of measurement.

As Dan points out the machine is probably heavily stalled anyway so you could be getting a lot more current out of it if the voltage were allowed to rise and it sped up.  In which case the tail would need to be lighter to prevent burn-out.

[Seaspray0]

I don't know anything about tail design, but I do know about sails on a boat and thier design.  What I've seen so far on tail design here suggests improvement in tracking can be made by shortening the length and increasing the height of the fin (increased aspect ratio) and using an airfoil design over flat material.  I've considered creating a simple airfoil by taking a 1 inch tube and wrapping the middle of two foot wide sheet metal around it (creates the leading edge) and riviting the edges together (trailing edge).  The tube will also provide support for the fin.  The airfoil shape will provide superior performance over flat material.

[TomW]

Sea;

Well, I understand what you are implying on airfoil shaped tail but do not see how it would improve things? The taller tail actually makes sense to me tho.

Could you maybe make a story post on your thoughts on this so we could see some discussion on it?

Cheers.

TomW