A frame mast concept

[Norman Brown]

Amoco Procyon was a interesting experiment. But as a new concept was not the best or common sence answer for a 'A' frame mast system. The spars were not to correct beam theory so were over weight. On a correctly sparred system they would taper at both ends of each mast (windage down). No heavy system is neaded for chainplates for lower shrouds as they are gone. Lighter compression plates under the masts. No mast compression post (all weight !)The 'A' frame is scantled lighter as it is stiffer as 2 beems are cross joined. If you count it all up with loosing so much steel wire (sg. of 7.2). With a more efficient main I would like to know what's bad !?
Norman

[tspeer]

Originally Posted by Norman Brown

Amoco Procyon was a interesting experiment. But as a new concept was not the best or common sence answer for a 'A' frame mast system. The spars were not to correct beam theory so were over weight. On a correctly sparred system they would taper at both ends of each mast (windage down). No heavy system is neaded for chainplates for lower shrouds as they are gone. Lighter compression plates under the masts. No mast compression post (all weight !)The 'A' frame is scantled lighter as it is stiffer as 2 beems are cross joined. If you count it all up with loosing so much steel wire (sg. of 7.2). With a more efficient main I would like to know what's bad !?
Norman

The main and jib help to reduce the drag of the mast. A Karman vortex street cannot form behind the mast because the sail acts like a splitter plate. The jib reduces the angle of attack of the mast, changing the apparent wind direction to coming more from ahead, and there can be a favorable pressure gradient toward the jib leech that helps to stabilize and reduce the lee-side separation bubble behind the mast. The rounded leading edge of the mast also provides a generous front-facing area for leading edge suction.

The exposed A-frame mast gets none of these benefits. The mast legs are totally bluff bodies that get more of the full variation in apparent wind direction. The mainsail has a thin leading edge with very little area for leading edge suction. These factors more than make up for the reduction in windage from not having shrouds.

[alan white]

I think the A frame has a chance with a rig where the main working plan is in the mains'l. The two shorter masts angle back enough to allow a vertical mains'l luff to backstay the jibstay.
This allows the omission of any backstay to the stern. Now you can carry a full roach main on a foil gunter yard, so there's a clean leading edge all the way to the top.
The two masts are now far shorter (about 33%, say) and the overall rig windage is improved, as the "center of parasitic drag" is far lower.
If a rig like that performed well enough, it might well be the perfect rig for lowering in minutes for bridges, maintainence, or hauling.

[Norman Brown]

Tom Speer's coment on the sail acting as a splitter plate behind the mast is right. But only part of the answer as vortice's are induced and do spoil the entry of the wind.
The mast legs must be small foil shaped. Circular section will induce drag. Too large a foil and she will sail to windward and have problems in high winds. So correct calc's on the beams and shapes is critical.
I have found a small article on a yacht called 'Kolika' Unfortunatly little info on her sailing capabilities. Does any one know more about this ?
Norman Brown

[Squidly-Diddly]

googling the name didn't bring up anything.

[Paul Scott]

http://www.tspeer.com/landyachts/twin/top.jpg

One direction the A frame idea could lead for sailboats, at least, would be something like Tom's sketch (link above), and designing the A frame for (say) 2 single foiled 3' chords for 20+ K, then use the 2 3' chords as wingmasts for fully battened mainsails (hoisted on them) for 8-20K, and then put a free flying jib in between them (in front of them?) for the light stuff, and a variety of (certainly interesting) downwind sails when needed. The tension for code zeroes might be a bit easier to achieve?
Might be a bit of a nightmare at mooring, but hey, no pain, no gain...

Paul

[Fanie]

got any pics of this A-frame?

Look under aft mast.

[Norman Brown]

For a look at a new type 'A'frame. (Double wishbone 'A' frame) Go to the boat design gallery and put. Lionhart. (Lionhart of Hartlepool). It takes some working out !

[gggGuest]

Originally Posted by Norman Brown

Tom Speer's coment on the sail acting as a splitter plate behind the mast is right. But only part of the answer as vortice's are induced and do spoil the entry of the wind.

Have you read Mikko Brummers CFD piece on rig behaviour here? You probably should.

http://www.wb-sails.fi/news/Ad_aerodynamics

It seems to me that the more we learn about what's going on the better a conventional round spar looks, and the advantage to be gained by using anything less conventional looks smaller and smaller. As a long standing enthusiast for the idea of using over-rotating wing masts I'm not entirely comfortable with this, but it does help explain why they've so rarely seemed to work as well in practice as I've thought they ought to.

[Paul Scott]

I was obsessing about this a while ago- some stuff I found interesting

"Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods" Mahmbub, Sakamoto and Moriya

"Flat plate drag reduction by turbulence manipulation" Narasimha and Sreenivasan

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest

Paul

[fishwics]

Originally Posted by Paul Scott

some stuff I found interesting

"Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods" Mahmbub, Sakamoto and Moriya

"Flat plate drag reduction by turbulence manipulation" Narasimha and Sreenivasan

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest

URLs? or are they paper-only
Cheers
Simon

[Paul Scott]

[quote=Paul Scott;259603]I was obsessing about this a while ago- some stuff I found interesting

"Reduction of fluid forces acting on a single circular cylinder and two circular cylinders by using tripping rods" Mahmbub, Sakamoto and Moriya

http://cat.inist.fr?/aModele=afficheN&cpsidt=15272519

"Flat plate drag reduction by turbulence manipulation" Narasimha and Sreenivasan

http://www.springerlink.com/content/a7514400p341477g/

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest

my printout of this one does not have the web address on it, but I'll try to get it.



Paul

[Paul Scott]

"fluid mechanical issues of the flow around a bluff body" Akhilesh - this one is a power point presentation, so easiest to look at


http://www.leb.eei.uni-erlangen.de/w...1/pdf/0116.pdf

[Norman Brown]

The unstable vortice's of a round body are avoided by having a egg or slight wing form set of masts. This drops the unstable element. Cross spars are made smaller and flatter. It has to be remembered that a standard rig has all the wire holding it up that has exactly this problem. Listen to the rigs of yachts in harbour during a strong wind, Oscilating. With a 'A' frame most of this is gone.

[Russell_Miller]

It'd be interesting to conduct the experiment again with a skin around the frame to help the aerodynamics out. When people home build carbon spars they'll build round sections (cause its easiest) and then add a better leading edge from a less expensive material that won't affect the spars bend characteristics.