Variable camber double skin

[sigurd]

Hello there, this here mechanism is intended to vary the camber, if desired the camber can twist along the span also.

It might work on either battens and cloth, or a semi rigid material.

The red line goes through pulleys at the aft shear web, as shown, and can go from there down through the mast, or up to a control surface at the mast head.

Please let me know what you think.

[ancient kayaker]

Can you modify it to take the wind from either side?

[sigurd]

Yes, just mirror the red actuation rope and use a symmetrical leading edge section. I made the drawing thinking of an aircraft, that's why it's asym.

I assume the small glitch in the TE will not affect performance considerably?

[ancient kayaker]

I suppose the panels could be tapered to minimize airflow disruption at the TE.

I think it might be of interest to the ice/land sailer community where the wingsail is set up for the prevailing conditions, and possibly short-distance sailboat racing. The main body of sailors would want to be able to reef and furl the sail, and for boats weight might be a problem.

I mention these as challenges to be overcome rather than obstacles to the use of this idea, which I think is a good one. There are several other threads proposing ideas for wingsails.

What would be really great would be to have an aerodynamicist offer a critique.

Oops, just noticed in another thread you are experimenting with Javafoil.

[ancient kayaker]

In another variation on this theme it was proposed that the two panels be attached to each other at the TE and made to bend by moving them diferentially fore-aft at their leading edges, sliding over the LE section. I prefer your concept, but you could attach them at the TE by a sliding joint and cause them to slide one against the other by two block and tackle systems. This would tend to keep the edges in contact and reduce the rope tension. One rope could operate several such systems at intervals along the TE.

[sigurd]

Yes but I am by no means an aerodymamicist!

Myself I'm not interested so much in masted rigs as in kites, so this was for an ornithopter with the ability to reverse camber, but I thought it might be interesting for masts as well.

For reefing boats the mast would be the front section, and then use battens and sail on the rear section, with tracks for them. Haven't put much thought into that, it might be complicated. Too keep the bare pole drag low, a short trailing edge section could be added to the mast.

Another option is to pull the battens forward till they meet inside the mast behind the leading edge.

If only for furling and not reefing while sailing, the battens could be rotated up or down so they laid along the mast.

[sigurd]

I realise camber and twist control are already quite well functioning on single skin sails (outhaul, sheet, kick, aft stay etc) and this here drawing relies on those and thus is quite unrelated to the above. But since I was onto the subject of reefing... Look up winggrids, supposed to increase span efficiency (vultures are said to have e of 2.69 with their spread tip feathers).

[sigurd]

Back to the double skin sails:
"but you could attach them at the TE by a sliding joint and cause them to slide one against the other by two block and tackle systems. "

As far as I can see (tested with two battens and a rope) keeping the battens together at the TE happens naturally when the rope is tight. Especially with the thickness limiter ropes (maybe not necessary depending on batten stiffness and the way they attach to the mast) and the wind pressure...
But if not, yours would be a nice way to pull them together.

[sigurd]

I just came to think of this one, also unrelated to the subject.

The rotating mast is a very cambered fore aft symmetrical section, functioning as a slat for the mainsail, reducing separation on the lee surface, increasing stall angle. much like what jibs do for the main. Have not simulated it.

[ancient kayaker]

The last one is particularly interesting, I assume the sail LE of luff is attached to, or consists of a tensioned line which I think is called a horse in marine parlance, though it's a very old term. It hinges on whether an efficient slat can be symmetrical.

I was intrigued by the tip feathers; I believe the plane industry is working on that concept.