Ac-86 build - RC Groups
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May 07, 2013, 07:01 PM
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John Xman's Avatar

Ac-86 build

OK I am a new member and thought I would start a new Thread on my new Project.

I am building a 1/10th scale America's Cup Catamaran.
This is going to be really big and fast!

Length: 86 inches
Width: 55 inches
Wing mast: 12'-0"
Displacement: 15 lbs.

I am currently working on the Hull(s) mold and hope to mold the first hulls by August. Molds are alot of work and must be done with patients.
I will be building the following molds:
Hull(s), forward cross member, rear cross member, Center RC control module, and five leading edge sections for wing mast.
All molds will be split down a centerline and be designed for vacume bag molding. Everything will be molded in Carbon Fiber. Working with some specialist for the Layup schedule.
It will have 6 Channels:
Rudders, Wing, Jib, Centerboard/foil lift, Foil cant, Wing let-off trim.
This is an ambitious project and will require the use of a small trailer to transport.
I will be purchasing a Yakima Rock & Roll trailer for my chase Kayak and the cat.
I am working up a KIckstarter project and am having a 3D model specialist create a short 2-3 min animation. Will post when it's up on Youtube.

Enjoy- John X
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May 07, 2013, 10:16 PM
Thomas Armstrong
Nice build project, John! You are clearly aiming higher than me with carbon hulls... I will just use plastic on mine...

I got just one comment at this point: do you really need separate jib control? Maybe you know something about wings that I don't know about... but there are lots of experience on using just one servo for both sails on a lot of models... If you need different geometry for wing vs. jib, you can use a combination of the following:
  • Movable points on the hull and/or booms, giving different turn ratio for each sail
  • Multi diameter barrel for the winch (or different lenghts of servo arm) for each line, giving different travel lenghts
Just wondering... maybe I learn something from you...
May 07, 2013, 11:24 PM
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John Xman's Avatar



Reasons for the double winches.
1. The huge size of the wing 12 feet tall 29" wide at base
2. the jib is the size of a Wheeler or AC main.
2. RMG (Sailwinches, AZ) recomends this set up (surface area)

Great question.

Was setting up my new Airtronics SD-10G today for Dual Rates on the rudders and foil cant. The most critical components will be the Wing, foils and rudders.
I will most likely go through several versions to get the cat foiling

John X
May 07, 2013, 11:45 PM
Thomas Armstrong
Wow! That's a big cat! Makes sense to have double winch for doubling the power...

Just and idea then: Maybe you can simplify controls a lot by moving the two winches with a single channel. I've seen this done on RC airplaines...

Same may apply to rudders (I plan to use two twin servos located on the hulls), and maybe also foil canting. This reduces mechanical complexity by increasing electric complexity, but with the benefit of being able to locate servos where they make most sense...

My motivation for doing this is that I will not have a center cockpit. I am forced to fit everything on the hulls... And I do not want mechanical connections between hulls...
May 08, 2013, 10:30 AM
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John Xman's Avatar


Yes the main and jib will most likely be on the same channel. I will use a servo splitter. All of the electronics will be in the Center Pod. The two hulls will have no openings (yes- a drain plug) I am designing the Cat to float in the tipped over position without any of the electronics in the water. It will float on one hull and the upper 2 feet of wing. When she goes over I will be using a Kayak to go right her so it will need to be stable in the "over" position. This also means the wing will need to be built to handle a cartwheel at 20 mph! Yes Velocity Predictions show 20 mph on a reach (25 max)

I think I need to rethink the Kayak righting? How can I get enough leverage to right the cat when my butt is basically in the water. Walk my hands down the wing and then a little toss?

John X
May 08, 2013, 10:55 AM

Once you right it . . .

I hope your transmitter is water proof so you can control the beast from your kayak once she's righted.

This is an awesome project. Cudos!!
May 08, 2013, 10:58 AM
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John Xman's Avatar


Rethinking the Kayak as a chase boat!

John X
May 08, 2013, 12:26 PM
Registered User
Dr. John.

You must have a lot of patients!

Watching this build with great interest.
May 08, 2013, 12:31 PM
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Dick L.'s Avatar
Consider keeping wing and jib on separate channels. You can then use the jib to hold and be back-winded to help push the bows over during a tack, then be able to release, let jib tack itself, and then re-trim. Just a suggestion.
May 08, 2013, 02:06 PM
Thomas Armstrong
Originally Posted by Dick L.
Consider keeping wing and jib on separate channels. You can then use the jib to hold and be back-winded to help push the bows over during a tack, then be able to release, let jib tack itself, and then re-trim. Just a suggestion.
I knew I could learn something from this discussion! Great advice, specially if you consider cats are really difficult to tack...

Thanks a lot.
May 08, 2013, 03:00 PM
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John Xman's Avatar


Dick L,
Great idea, now how to make it work on the transmitter? With a two stick transmitter this become tricky! I do have side rotational Aux channels on my 10 channel transmitter. I could put the jib on one. I am using the other for lifting the centerboards. Then during a tack I can leave the jib full in and ease the wing? until up to speed. Apparent wind is going to make sailing this size of RC cat very challenging.

I am also planning on using a 2D(3D) aircraft stabilizer to control the wing as the cat lifts the windward hull the upper three rear wing sections will ease out (reduced lift) until the flying hull comes down then the wing section will draw back in to standard position.

John X
May 09, 2013, 12:46 PM
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John Xman's Avatar


I would like to see the mechanicals for the F3 Tri-foiler foil control.
I am thinking of using a Wand in place of the center servo for the foil angle control?
Anyone have a image or a drawing of the Wand system?

New updated AC-86 PDF drawing loaded below

John X
May 09, 2013, 02:55 PM
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Dick L.'s Avatar
I have a few photos of a local MicroSAIL boat that I took back in the early 2000's. They are on my backup hard drive, but essentially use a small round wand hanging down off each foil support.

Over the wand/tube there is a sliding plastic tube that when adjusted sets the height of the hull off the water surface. A lightweight spring provides a method of return to the wand. The faster you sail, the more the water pushes the wand back which in turn regulates the amount of up/down attitude to the foil.

The concept was pretty simply, but clever and it worked. Probably still has current patent active, but was offering info for free for anyone wanting to build back then. I am no longer in contact with the individual, but you might search "Doug Lord" and he lived in/near Orlando, Florida and owned MicroSAIL. May even be some folks who are still in contact with him. You will notice that the amas were almost twice as wide and the main hull length which help it achieve it's great stability.

Will see if I can find and dig them out, although I "think" they were posted in the multihull's section of the forum.
May 09, 2013, 03:25 PM
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Dick L.'s Avatar
John - found this in my data files and provides a more complete detail on the "wand system".


Height Control for sailing Hydrofoils by Dr. Sam Bradfield

Foil Height Control
The following is a description of the altitude control system on the Microsail F3; it uses the same principle as on the RAVE and, most important,Dr. Sam Bradfield has given permission for me to disclose this for the multiONE Class;

"Dr.Sam Bradfield , the father of the modern foiler,reserves all rights as to the manufacture of this system on any size boat or use of this system on full size(manned) boats: I would not write about this without his gracious permission; this is his contribution to the multiONE Class"

An altitude control system for a foiler must sense the water level and feedback that information to the flaps on the main foils. But first you have to decide on how high you want the boat to fly:One factor in that decision is the need to see to it that the main foil is operating at least 2 chords below the surface. Another factor is the expected waves you want to fly over. The height above the water of a fully submerged foil system is not a major concern in a model because the system develops it's own righting moment and the extra distance between the CLR and CE is not too much of a concern; just keep in mind that the higher it is the more the foils are loaded earlier in the takeoff process.....

The Wand

This system relies on a piece of material like a carbon or aluminum rod or tube dragging in the water to sense altitude. On the full size boats it has been found that if,in the foilborne position, the wand is bent so that it tends to plain across the surface rather than just drag they achieve better results; a straight tube works well in a model but we have not experimented with bending the tube; it might(and probably would) be an improvement. The upper wand on the F3 is a bent piece of stainless steel rod 5/32nds in diameter it is bent in about a 1" radius with about 2" of rod straight past the 90 degree radius either side. The upper part is run thru ball bearings and hooked to a lever that is in turn attached to the vertical pushrod coming from the flap; the distance from the centerline of the stainless wand rod to the centerline of the pushrod is 7/16ths(.4375")inch; the lever sticks out from the rod CL 1.5" so the ratio between the lever length and the distance from CL to pushrod is 3.4/ 1. We know this works although a longer lever could be used up to about 7/1 . The top of the lever is connected to a line running to a block that turns the line parallel to the cross arm and is then hooked to a spring. The spring is attached to a longer line that is run in toward the main hull around another block attached to a bowsie for adjustment and attached back on the outboard end of the crossarm near the shroud attachment point.We'll come back to this in a minute. The bottom of the stainless portion of the wand can have a brass tube about 1 1/2" long attached to it with cyano and a .157 carbon tube can be slid into place to comprise the bottom of the wand. To set the altitude: mark on the vertical fin 2 chords up from the top of the horizontal hydrofoil. Set the wand angle at approximately 45 degrees back from vertical referenced to your designed flying altitude waterline. Make sure the wand connection to the pushrod allows the flap to be in neutral (parallel to the foil) at this point. Cut the carbon tube so that approximately 3/4" of the wand will be below the altitude mark on the fin with the wand set up as described. Now we go back to the line+ spring +line coming from the wand lever. The wand should pivot freely and the flap should go + or minus 25 to 30 degrees. Tension the spring so that when you pull the wand all the way back(flap down 25 degrees=max lift) that it wants to gently spring forward. The idea is that when the boat is in the water the wand will be pulled all the way aft because of the water flow which is covering a lot of the wand before it gets on foils.As the boat begins to lift the wand will come forward until the flap reaches its neutral point.. If a force is applied to the hull to which the wand is connected ; either up or down -the wand will move either forward or aft from it's neutral point to bring the boat back to its correct altitude. In stronger winds it can be advantageous to have the windward spring a little tighter than the leeward spring; this can be done with servos or automatically by hooking the wand control line to the main boom about halfway....The main foils are set at plus 2.5 degrees relative to the design flying waterline and the rear foil at zero degrees... Note: this is an excellent system for foiling but in very lite air the wands cause the foil flaps to be max down -wanting to take off-this creates a lot of drag when it is too light to foil; in a race you may want to remove the foils (or at least the wands) in lite air--this is one of the few disadvantages of a foiler against a "normal" tri or cat
May 09, 2013, 03:27 PM
Registered User
Dick L.'s Avatar
One more article on foilers. This one by Doug Lord ......

Basic R/C sailing hydrofoil design

Thanks to Doug Lord or Microsail, designer of the F3 and Monofoiler for sharing this information with MultiOne
Rave ,F3, Dancer and aeroSkiff use a loading that is 80-85% on main foil and 15-20% on rear foil until point X in wind/speed is reached when 100% of the load is on the main foil and the rudder is actually pulling down.Point X on the Rave is about 20knts...
In foil discussions, angle of incidence is usually referred to as the angle of the foil relative to the design flying waterline and the main foil(symetrical section) is set at +2.5 and the rudder foil at 0 degress.On fully submerged foil systems with wand or other "active" altitude control the rear foil flap is seldom adjusted; on surface piercing foil systems and on some fully submergerd systems with skipper controlled altitude the rear flap is used to actively control pitch attitude...

Surface piercing foiler stability is limited to weight times .5 X the distance between the center of lift of the foils; fully submerged foils with active altitude control have no theoretical limit to righting moment-just a practical one: at some point something will break if sail is not reduced!Some Raves have warnings in the cockpit saying:" Warning: do not exceed 30knots" The main cross arm can break at 35..... Some facts:Area of F3 foils(both mainfoils together) is equal to 2% of sail area; rudder foil is 1% sail area. Rave mainfoils:1.8% SA; rudder foil 1/2 that.

F3 sail area per pound: 208sq. inches So a simple design guide for a fully submerged foil system corresponding to the Multione class is: Design and build hulls, crossarm etc; weigh and add estimate for mast, sails and foils. Multiply weight in pounds by 208 to get Sail Area; multiply sail area by .02 to get combined mainfoil area(each mainfoil is one half that figure); use 1/2 of combined mainfoil area for rudder foil area..all three foills are same area.

For instance a 4.8lb multiONE should have(4.8 X 208=998) 998 or 1000 sq.inches of sail; Foil area is (.02X 1000=20) 20 sq.inches for both main foils; 10 sq.inches for each main foil and 10 sq. inches for rudder foil.Angle of incidence (12% symetrical section)measured relative to designed flying waterline should be : main foil:+2.5 degrees; rear foil: 0 degrees. Load should be arranged so that 80%--85% of load is on two main foils at static(so CB of main hull is slightly aft of center of lift of foils) and 15%-20% on rear foil; this will change in dynamic conditions...

Center of effort(actual not geometric) should be just aft of the quarter chord point of the vertical fin supporting the mainfoils. Thats it! How to design a foiler in 2 paragraphs!

--Doug Lord

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