Wings!

Hi all,

I have been hunting through the forum so realize wings have been discussed in great detail already but am struggling to find any info on some control systems.

Basically I wanted to work out how to adjust the camber on a wing, similar to say the Object2 Skiffworks wing built for Charlie McKee.

I have found the patient lady pdf but can't see how the camber 'self tacks' and adjusts..

The explanation im looking for then is really how the camber adjusts and self tacks through blocks and rope etc, like a rigging diagram...

Thanks!
Hughph

 

wings

Have you been thru this thread?
http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/understanding-wing-technology-34697.html
Both Steve Clark and Magnus Clarke(high on carbon) are members here and would probably be willing to help you out after you read that thread. Good Luck!

 

Yes I have definitely read that thread!

Whilst it was incredibly useful to understand the theory and effects, i couldn't find effectively a 'rigging guide' as to how the camber adjustment etc actually worked in practice... and auto tacked etc...

Cheers
PHS

 

Hugh, I know you said you've seen this but it sure seems pretty detailed to me:
Both these by Steve Clark:
Patient lady control system,
Open Wing

 

Right, I should probably explain myself more clearly!

I understand that to control the camber you have a 'boom' attached to the rear element that goes forward to a pivot...

Basically what I don't understand and haven't found so far is exactly how the boom is rigged to be self tacking- it is very simple if you have individual port/starboard controls (Then it is just a delta on the bottom of the wing either pulling it on the left or right....) But with the boom I cant' see how the camber is autmatically put into the wing without air pressure and also how the wing camber is reduced and stays self tacking without it crashing into the blocks as it 'crosses'

It is probably something very simple and I will kick myself when i see it, but a diagram including rope and tackle systems would be perfect.

Also will re-scan that thread to see whether I can find anything on how the boom box works....

As you can tell I am a rookie at Wings, but I have to start somewhere! (This is an A-Level design project- albeit a complicated one. )

 

N.B I should add I am planning on building this wing WITHOUT twist. So does that make the Boom Box irellevant?

 

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I think I could answer your question but since I have zero experience actually sailing a wing you'd be a lot better off to ask the question directing to Steve or Magnus via e-mail or PM.

 

Ok will do tomorrow morning,

Any input would be greatly appreciated though so please fire away!

 

If you subscribe the The Daily Sail you can check out a series of videos done with Steve Clark demonstrating the controls on the Cogito wing. Watching those videos will go a long way toward answering your questions.

 

The Hubbard style of wing control depends on the air pressure on the wing. There's a line to the port & starboard hulls (called the "traveler" by AC teams, but it could just as well have been called a "sheet") to control the rotation of the wing about the pivot. The traveler is attached to the clew of the flap. With the wing restrained forward by the pivot and aft by the traveler, air pressure on the wing makes it want to fold in half about the flap pivot axis.

The amount of folding - camber - is simply limited by the arm projecting forward from the flap, under the foot of the main element. There's a line from centerline on the wing main element to the camber control arm. A cleat on the main element allows it to be adjusted. Because the camber control line goes to the centerline and is slack when the camber is being reversed in a tack, the system is self-tacking. No blocks are needed at all, unless one would want to reduce the camber while the wing is under load. The tackle can be inside the main element upstream of where the camber control line leaves the main element to go to the camber control arm projecting from the flap. I suspect the bit you were missing was this physical manhandling of the wing to get the control system to work.

The force on the traveler is transmitted up the wing by control lines that slave the upper flap arms to the bottom flap position. Thus, the bottom flap camber control line controls the camber along the entire span.

You're right that it takes pressure on the wing to make it work. Friction in the system means there may not be enough force in light winds to reverse the camber, or to increase the camber when the camber control line is slack. That's why you'll see the wing trimmer on an AC45 physically pushing on the wing at times in order to get it to move the right position.

Twist is controlled similarly, with a twist quadrant that is allowed to rotate relative to the bottom flap, and limited by the twist control line - also led to centerline on the flap to make it self-tacking. So the positions of the upper flap control arms depend on the rotation of the bottom flap plus the rotation of the twist quadrant relative to the bottom flap. Changing the camber control will move all the flaps together while maintaining the same twist along the span.

 

You can build the wing without twist, and then add twist later. The control system would remain almost unchanged. The only difference is the upper flap control lines would dead end at the bottom flap structure (after having passed over the bottom flap control arms) instead of on the twist control quadrant.

Control of twist is very important, as induced drag is far and away the biggest source of aerodynamic drag on the boat, and the parasite drag of the wing is only a small proportion.

If heeling moment is not the limiting factor, minimizing the induced drag leads to a comparatively high center of effort. Once there is enough wind to reach maximum righting moment, then the center of effort is lowered through twist control so increasing amounts of lift can be generated with more wind, while maintaining the same righting moment. Without twist, you would have to go with either the high center of effort for low drag in light winds but sacrificing drive in high winds, or optimize for high winds and suffer more drag in light winds plus have a much higher threshold wind speed for being able to fly a hull.

 

Thats is perfect, cheers for clearing that up for me.



The reason I am staying off twist is that it seemed much harder to build into the wing, and seeing that the moth guys decided not to use it persuaded me that it would work well without it. Please feel free to prove me wrong!

With the CofE I understood that you used the same section profile all the way up, but it tapered as you got towards the top. So would keeping it wider for longer move the CofE upwards? I don't have access to any CAD Testing software so will have to do alot of this off theory..

Thanks for your help.

NB It is also worth saying this has a high chance of going on a monohull.