Did not know that, Claudio! Well, you are clearly the man!
The downside to the yellow sail-plan is the aspect-ratio of the foils and the strong tapering of the triangular planform vs. the more elliptical standard rig.
I don’t see any reason you couldn’t use a higher aspect-ratio sail planform with the double stay-sail rig (?).
Cheers,
Geoff S.
Hi Geoff,
nothing against an higher aspect ratio, it is worth to try. Of course the CE will move up !
The question is : which will be the better choice between a better sail efficiency and a better righting moment ?
Rotating mast ! was considered on a larger model while I assume will be too heavy for the RG65 …
Cheers
CD
You have already lowered the CE by splitting the rig into two sails.
Remember that the induced-drag goes as the square of the span.
Also, a triangular wing has a span-efficiency of about 0.72 (vs. nearly 1 for a rectangular planform).
Maybe. I would think that a carbon-fiber wing could be similar in weight to a circular mast.
The rigging for a wing shouldn’t be much heavier than for a round mast. One down-side is that you can’t use spreaders, lower stays, or a backstay, although you can get some of the same benefits by locating the side-stays aft and using diamond stays.
Cheers,
Geoff S.
Just an idea: a carbon fiber mast shaped like a wing, but with a circular section base. Mount into the hull like a swing rig, allowing for rotation. The actual wing will be to narrow to self-support the sideforce, but you can add a spreader at mid-height to make it stiffer. Yes, this would add some drag, so it calls for very thin wires for the spreaders.
Does this make sense? I may try it on my RG65 swing rig!
I kows that aspect ratio increase the sail efficency !
A normal round carbon mast composed of 10mm and 8mm tube, will weight about 43g, spreaders escluded.
If a Mast wing could be made avalable with the same weight, why not !!
As I said before, OK for a class M where out of 4.5kg there is still a margin to buil a mast wing…I sceptic for a RG65 !
CD
Sounds like a challenge. And I like challenges!!! Ok, I got plenty of updates pending for my RG65, will put this one in the queue!
In the meantime I will think how to build it… Any ideas on the proper profile it should have? I think it should rotate with the boom only… Or is a must that it rotates with the leading angle of the sail?
You may watch what it is done with the RC Land Sailing.
Just an example but heavy : http://www.rcsailing.net/forum1/showthread.php?7039-Wingmast-for-Marblehead&highlight=wing+mast
CD
Excellent suggestion!
Some sites:
http://www.iceboat.org/RCBoats/rciceboats.html
http://geoff-s.net/ice/K-1/index.html
These are all larger rigs than the RG-65.
I see this has all be discussed here before: http://www.rcsailing.net/forum1/showthread.php?5397-Wing-Masts-Rotating-Rigs-and-Solid-Wing-Sails
I found this image via a Google search. It was part of the above thread but seems to have been deleted from its original location.
This may be the best/only way to create a light enough wing-mast for the RG-65. The fiberglass would have to be very thin, or perhaps just stiff mylar with some ribs to form the shape:
BTW, most wing-masts sit on a ball-and-socket system so the mast can rotate freely even if the rake changes (ex. due to the rig stretching or changes in tuning).
Thanks Geoff… But theres is a problem: RG65 rules mandate the spars fit inside a 12mm circle. This means a big foil-masts are out of the question…
Now I’m thinking there are 3 general ways to solve the “mast interfecence problem” as explained by Claudio (turbulence behind mast), for a RG65:
- Put mast behind sail, where the turbulence does not influence airflow around sail (but there is turbulence/drag anyway)
- Build a 12mm long foil as mast, but needs enough lateral support for a 120cm hight sail! May seem impossible… but just keeps the challenge up! Still thinking around this one… Rotating a 12mm long foil may be needed after all, as it will interfere with the sail more than a round mast!
- Build the sail around the mast altogether. This may done in three ways I think:
3a. Build an envelope into the sail, and put the round mast inside (some people have done this, with no real benefit as leading edge is still 6mm wide)
3b. Build a wingsail (in general to heavy for a RG65)
3c. Build an hibrid sail, wing+cloth in different proportions (maybe a good performance/weight compromise?)
These are my thoughs of today…
That would be a problem. I saw the rigid-wing boats and thought there wasn’t a limitation…
From the comment above, it appears that all that is limited is the spar itself, fairings around the spar are allowed (?)
As you’ve noted, one key parameter is the leading-edge radius. To get any improvement that needs to be somewhat smaller than the max width of the mast/wing (i.e. the leading edge of the rig needs to look “wing like”).
One way to do this is with ribs or some other non-structural support that shapes the sail envelope in front of the (structural) mast. That gives you all be benefit of the wing-mast but still retains the 12mm dia. tubular mast. Most classes that allow sails made from more than one layer prohibit this for exactly that reason.
A much simpler alternative is to choose a non-rotating mast shape that generates the least interference.
Arvel Gentry did quite a bit of work in this area:
http://arvelgentry.jimdo.com/articles/
In particular there are three articles that discuss this problem:
[ul]
[li]Design of the Courageous Mast
[/li][li]Studies of Mast Section Aerodynamics
[/li][li]Low Drag Star Mast
[/li][/ul]
One “take home” from the Gentry articles is that an elliptical mast gives you much of the benefit of the more tailored sections.
I believe Frank Bethwaite also talks about this issue in the section on designing the mast for the Tasar in “High Performance Sailing”.
Cheers,
Geoff S.
Mmmm… looks we are hijacking Claudio’s thread about narrow-deck RG65’s… but you started teh experimentar rigs discussion, Claudio! Do you prefer we move to a new thread?
in the meantime… my feedback on Geoff’s:
Rigid wings are allowed in RG65’s, but their whole lateral area is to be counted as sail area. The 12mm diameter rule applies to the mast when it’s not counted as part of the sail area… If I use a 30mm chord wing-mast, and count it’s area towards total sail area, then it’s not illegal… Just read about this!
Not a bad idea at all! May be tricky to get it to move freely around the mast when wind is pressing the sail… worth a second though. Oh, 12mm. dia is the maximum allowed. Typical RG65,s masts are 6mm dia.
Today you can buy a stiff 6mm dia. carbon fiber tube. I’ve never seen a different shape. A non rotating 12mm chord airfoil was what I was thinking of in the first place… 
I think that would be a good idea!
I think me too !
And going back to : “Wingmast for Marblehead” discussion in this forum
http://www.rcsailing.net/forum1/showthread.php?7039-Wingmast-for-Marblehead&highlight=wing+mast
CD
ok, I moved last thoughrs to here: http://www.rcsailing.net/forum1/showthread.php?7039-Wingmast-for-Marblehead&p=71045#post71045
I’m very sorry!
Don’t mind it was better for the readers to reconize a “mast issue” more then a “hull design”
BTW you should also delete your posts about mast design from this tread as I done it myself, thank you !
CD
About Hull form and Rules.
I have a question : is it allowed hollows below 3mm in the hull as depicted in the drawing ?
Note:
When the hull is upright no hollows exist underwater.
CD
Just compared various Hull Forms with same Main immersed surface and displacement :
CD
The analysis of the hull main section shape is gone a little further.
All immersed areas are the same, here at 21cm²
Still starting from the Narrow deck concept, I pushed for a narrow water beam.
Obviously narrowing the water beam the draft is increasing, but not so much when the hull is heeling.
Certainly a deep hull will produce a deeper wave when “running” and therefore producing higher drag!
The narrow “all together” is nevertheless an interesting option that deserves the full hull drawing.
Another remark concern the main servo since in the narrow hull only a drum servo can be used.
I suggest watching the various dimensions and see the evolution !
For sure at glance the hull ‘C’ appears to be the smallest section … will be the overall hull surface also ? … wait and see !
ClaudioD
Claudio: Have you seen this way of using a sail servo sideways? May fit in your design…
Ref: http://rg-andy.blogspot.com/2014/08/manta-rumpfausbau-teil6.html