Dynarig system

Whilst I follow your exmaple, a plane wing in the upright position wouldnt twist with the wind as mentioned below concerning MF´s rig would it?

I dont have a solution but I do admire the problem.

 

I starting a thread asking the question "can a boat beat the wind downwind" and was assured that it is indeed possible and is done, though perhaps not an everyday event.

A boat of the advanced technology and size of MF should have no problem doing that. The trick, as I understand, is to tack when going downwind so the apparent wind has an off-the-beam component. As the boat accelerates the wind shifts from off the quarter to off the bow and thrust is always there until the limit of rig efficiency and hull drag is reached. Tacking should resolve the problem of masking.

I would like to see the MF doing that.

 

Actually, a plane wing has twist already built into it. If you look really closely at an airplane wing, the angle of attack near the root of the wing at the fuselage is greater than at the tip. This is so that the portion of the wing closest to the fuselage will stall before the outboard portion. Therefore, the pilot senses vibration and loss of lift on the inner portion, but he still has good airflow and aerodynamic control on the outer portion. He can safely recover the plane from an unsafe attitude. This is a built-in safety measure to prevent total stall of the wing all at once. Pilots are trained regularly to notice the signs of premature stall and to practice recovery from a stall.

This kind of aerodynamic twist built into the wing is called "washout." If the twist were reversed so that the tip was at a higher angle of attack than the root, it is called "washin". Washin is very dangerous, washout is very safe.

Eric

 

This is called tacking downwind, and lightweight multihulls have the ability to sail so fast that even when sailing away from the wind, the apparent wind is still coming from ahead of the beam. Boat speed can exceed wind speed. This is called "making your own wind." It is a common phenomenon on the large racing multihulls. Maltese Falcon would never be able to do that, I don't think, she is simply too heavy. But I don't know that for a fact because I have never seen her in real life, let alone been aboard her. But such is my estimate of her performance.

Eric

 

Eric's comments about washin and washout are absolutely correct.

Twist in an airplane wing is there for quite different reasons to twist in a sail, though.

The wingsail with controller vane is very nice, an example of force multiplying mechanisms.

There is another reason for fitting wingsails with it apart from force multiplying and oscillation prevention;

Rigid sails are notoriously difficult to operate compared to soft sails because there is no visual indication of approaching insufficient angle of attack (luffing). With the controller vane it is always at the angle of attack set by the operator, and immediately reacting to slight changes in apparent wind due to gusts and wind turbulence.

The twist thing -

As Ancient K says the wing made up of separate sections, each with its own controller vane would twist correctly. It was not entirely clear to me however if this point was understood or not, and that is that the controller vane would be set to the same angle on all the sections, so there is not really a need for separate controls. One master control setting the same angle for all the vanes would work fine. The apparent wind itself is twisted and would take care of twisting the sail, each vane would make sure each section of sail is at the same angle of attack.

If that was understood i'm sorry to be pedantic, i just feel it is important to really understand what is going on with a sail's twist.

Furthermore i think a very elegant solution (for a wingsail) would be a wing sail which has low twist stiffness and one continuous controller vane attached at numerous points (many 'booms' sticking out of the sails trailing edge if you will) . It would be the same but analog instead of digital.

 

Since a rigid wing can be allowed to feather with very little drag, is it generally necessary to reef it? Certainly for a hurricane or in port but one gets notice if such events.

Cant speak for a ridgid wing , but with a fully battened mainsail handeling is a delight.

At anchor , the main can be hoisted and it does not flog , just pop from battens curved one way to the other way.

When sailing in rivers and confined waters the sail is very docile , and does not flog , as you wait for bridges to open.

At sea it is easier (for me ) to reef 1 or 2 x with the aid of a boom gallows.

Again no flogging, IF you have sufficient battens.

And yes with good use of a boom vang the proper twist can be generated aloft for proper windward work.

FF

 

Eric: thanks for the washin/out explanation, I heard of the term years ago in my model aircraft days but never understood it until now. As you say, the existing MF might not be able to "make her own wind" but a long boat would at least have the hull speed if designed for it, without needing foils.

T3: good point about the single controller. With such a long mast mechanical connections to each stabiliser would be unwieldy. A single control could be used for each mast but a separate actuator would be preferable for each stabiliser, probably a simple electric servo of modest power. Electric wiring would be lighter and more flexible than a mechanical arrangement. It could easily be made fail safe so any failed wing segments simply turn themselves off and feather. With an electrical system, it would also be easy to arrange redundant power, controls and wiring so repairs up the mast could be deferred in heavy weather.

I thought about the twistable wing after reading a previous post but was not sure how it could be constructed. However, FastFred's post about battened sails provided food for thought. Lunatic started a thread about an experimental sail consisting of a fabric sail with a hard leading edge; the LE is divided into several independently pivoted sections. The sail has a pocket that slides over the LE for reefing and furling. It's at:-

http://www.boatdesign.net/forums/boat-design/experimental-sail-2-needs-analysis-25038.html


All these ideas seem to be calling out for some genius (or gathering of plain folks like ourselves) to put together. A battened version of Lunatic's sail with stabilisers on the battens might work, but it needs a way to camber the sail correctly. If that can be done it would probably be more efficient than the hard wing which necessarily has to have a symmetrical profile. I will mention this thread to Lunatic.

FF: The single continuous vane would save a lot of complexity if it could be made to work but I don't see a design solution at present.

 

At the risk of a slight digression from the topic, let me add a little more info about twist in airplane wings.

In sailplanes flying fast at low angles of attack, the tips start to lift downwards and it gets to a point of being a structural concern.

So what is done is the camber is slightly increased towards the tips. This is combined with the washout to create a foil with no twist with respect to the zero lift angle of attack, but with twist with respect to the stalling angle of attack.

The last model glider i designed and built had a wing like this. The foil section morphed from a less cambered 9.5% root section to a slightly more cambered 8.5% tip section, with chord taper and geometrically spaced ribs (rib spacing increasing towards tips).....Very tedious to work out the individual plots for each pair of ribs. Flew a charm though.


I don't see any feasibility problems with a continuous vane at all.

The main problem with vane controlled wingsails is they forego (as far as i can see) any reefing posssibilities

 

If initial flow is critical ( what is LE on MF ) LE form change could use leverage of aft section of conventionally trimmed sail as controller all within envelope of a partial double skin. I have sailed a crude mast rotated version and about to build self-regulating segmented one for twist. Full size 2' section X 4' chord shows promise, amazing how strong tip vortices are with such low aspect. Cutting full size sail,75 sq ft a challange,could use feedback

 

Loony's sail can be reefed and furled.

 

Ancient K. Loony reefing with a controller vane?

Where do i find out more?

Lunatic i have trouble understanding your last post.

 

http://www.boatdesign.net/forums/boat-design/best-leading-edge-25142.htmlhttp://www.boatdesign.net/forums/boat-design/experimental-sail-2-needs-analysis-25038.htmlhttp://www.boatdesign.net/forums/boat-design/experimental-sail-needs-analysis-24894.htmlhttp://www.boatdesign.net/forums/boat-design/sail-design-trim-camber-twist-leading-edge-23524.html[/url]
A rather messy design process as above postings will indicate, and may not lead to a practical rig; but in context of controller vane orienting main foil, I am trying to create a twisted drooping D section LE by the leverage of local sail pressure further downstream. Somewhat of a similar puzzle. One advantage of posting is clarity of thought and expression, but does not always work.

 

T3: Loony has an idea for a fabric sail with a leading edge pocket that can be raised over a sectional leading edge, each section is independently pivoting on the mast. For the full details see hiis thread. In effect, he has created a concept for a semi-hard sail that can twist, as per your suggestion.

The idea of adding battens with stabiliser foils to that was mine, in an attempt to have all the advantages of a stabilised hard wing and a reefable soft sail. Hope I haven't confused everybody by trying to bring these separate concepts together. I have sketched what it might perhaps look like using flexible battens bent by the stabiliser foils; not sure how many of the battnsn would need stabilisers.

 

To prevent sail hanging up on segments, light connective nylon ribbon needs to run along LE and TE of D section, which, if turned by battens, will twist but not droop. Partial mock-up has shown me fabric alone will do the trick and the gaff with modern tuning devises has potential of high performance battenless sail, and allows tuning at the top of the rig where it is needed most.

 

I omitted the ribbons for simplicity i my sketch but you are probably correct that some kind of device will be necessary to keep the segments line up when raising the sail. We may not be speaking of your own battenless sail here, at this point it seems the battens are needed as a place to mount the stabiliser foils used for automatic control of the angle of attack.