Bruntons flying wires

SockeyeUS119

Super Anarchist
I was turned on to a soursce for lenticular rod riging yesterday. Steenaero.com see the page for bruntons wires. They can thread either direction and leave round sections for the spreader tips. 316 SS and aircraft forks it that is what you want. No prices, but if they are competitive, is this a good thing? i know some of the old sixes had this stuff. It looks fast.

 

Moonduster

Super Anarchist
4,823
231
Not just fast, but cool, too. But it vibrates in the slightest of breezes, even at the dock, and the vibrations led to metal fatigue and that led to masts falling down, which is neither fast nor cool.

I'd love to get a length for the internal tie rod from the partners to the mast step just to raise some eyebrows, but lenticular rod has no place on a boat. Stay well clear.

Good luck!

 

Moonduster

Super Anarchist
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231
To quote from Richard Henderson's "Understanding Rigs and Rigging" - "Rod shrouds come in two basic sectional forms: round or lenticular, a biconvexed, streamlined shape. The latter affords somewhat less windage when sailing close-hauled, but in certain conditions it may develop a severe high-speed vibration, causing a hum or singing sound and sometimes leading to a rapid fatigue."

I doubt that the "string and shock cord" approach can stop the tendency to vibrate. At best it might raise the frequency to the point that it's not distressing to the human ear. The fatigue will still accumulate at a much faster rate than happens with round rod.

 

Moonduster

Super Anarchist
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Rod is used as structural cross links in some airplane types. I don't think you'd find it in any sort of exposed area - always inside the fuselage or within the covering of the wing. Since there's no air flow over those areas, it's not much of a problem.

It certainly wouldn't be a good application for the exposed cross links that brace the wings of a bi-plane!

On the flip side, airplanes are subject to much more rigorous inspection and replacement schedules than are yachts ...

 

European Bloke

Super Anarchist
3,407
826
The tendency to resonate is dependent on the windspeed and the length of the rod. Both will be very different on a plane than on your boat, that could be why they work for them not you.

Wrapping a line around them interferes with the vortexes that tend to form off the leeward side of the rod. That stops the vortex shedding and stops the humming. Have a look at a chimney on a cooling tower, you’ll often see a helix shaped wrap around some point of it. That is there to stop the same problem occurring there.

At uni I saw a video clip of two identical flag masts, neither had flags up and they were side by side. One had the halyard wrapped around it about 3 times, the other didn’t. The one with the wrapped halyard was perfectly still, the other was going nuts, an excellent demonstration of vortex shedding and how to control it.

Not saying the stuff is good for you…

 

longy

Overlord of Anarchy
6,821
1,154
San Diego
IIRC - and this is REALLY old memory - lenticular rod only had better wind resistance thru a very narrow angle of AP flow across the rod. So it was slightly better going straight upwind, but as soon as you came off that close-hauled course it had more resistance than round rod. So only of benefit if you only race upwind/downwind courses.

On a biplane wing, wind direction is constant, and at a much lower Reynolds number, so benefit is constant. I also seem to remember that the rods were lashed to each other at crossing points to stop vibration, but that you'll have to check with the flyboys. Biggest concern is how the threads were formed on the ends, and whether it's been load tested. Threaded rods ends caused more failures than shape of rod, as much of the strength is on the surface of the rod.

Tuning threaded rod is a HUGE pain, as you have to evenly rotate the entire piece of rod, which can only be done under no load.

 

Moonduster

Super Anarchist
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My boat had threaded rod for the first 22 years of its life. It was all aircraft rod and tuning was no hassle. The rod was threaded to fit into turnbuckle bodies. The other end of the body had a standard rigging fitting that ended with a toggle. Tuning was no different than with Navtec terminals.

The key to threading rod is to "upset thread" rather than "cut thread". Upset threading is a cold-working process that presses the thread into the rod causing some material to get "upset" and rise above the surface of the piece and form the threads. In other words, an upset thread has half of it's thread depth above the working surface and half below. All aircraft rod is upset-thread.

Cut threads are really bad in stainless because they invite crevass corrosion a the bottom of the cut thread due to the high internal stress that remains from the cutting process. Additionally, because they reduce the cross sectional area, they reduce the ultimate strength of the rod.

I have xray photos (in storage in California somewhere) of the upset-threaded rod. It looks as good as new after 22 years and lots and lots of ocean miles. To be honest, I'm not entirely certain why I replaced it with cold-headed Navtec rods and fittings, but what's done is done.

 

P_Wop

Super Anarchist
6,919
3,978
Bay Area, CA
I remember using this stuff on 12-meters, and as above, it was a bitch to tune, as you had to rotate the entire rod. One guy up the rig, and one at deck. Bloody stuff.

And there were many divergent theories on orientation. Some said align the long axis fore-and-aft. Some said twiddle it to point outwards at 20° or so on both sides, which seems to be the apparent wind direction at the shrouds when you're hard on the breeze. Nobody could agree on this.

Looks good. Very expensive. Marginal gains. Horrible to maintain.

Hey, anyone remember vortex stimulator strips which you glued on the mast to promote turbulent flow breakaway on the lee side? Same sort of stuff.

Much better, IMHO, to spend the time and money on things you KNOW will make the boat faster. Crew. Sails. Tuning. Practice. Beer. Lots of beer....

 

bammiller

Super Anarchist
1,111
16
The lenticular rod rigging that I have seen was only nitronic 50 rod, as is usually used, then rolled flatter. The ends are left round because any kind of threading, turned or rolled, was drastically reduce the lifespan of the rod, then a traditional heading process would be done using a nosepiece. 316 SS, diameter for diameter, is about half as strong as nitronic 50. You would need to drastically increase the size of the rigging to get the same strength and stretch properties.

The only time I have seem rod rigging threaded, they would press a head onto the end that was double the original diameter, then thread that. Adding threads reduces the cross sectional size of the rigging at a very highly stresses area.

If lenticular rod rigging was such a huge improvement, or even a modest improvement, then it would still be used. Currently, Navtec (at least they used to) would roll your rigging for your mega yacht, making it long enough to cut the old head fittings off and replace the fitting without losing any length of the panel.

Bam Miller

 




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