High Performance MPX Foil/Self-righting Trimaran-The Test Model

Srt/mpx

The fantastic 2.4ghz radio arrived today with specially selected servos and a carrying case.
Also went to Fiberglass Florida and bought $160 worth of brushes cups , acetone, sandpaper and Adtech P-14 Ultra white filler to assemble and cosmeticize the boat and foils.
Tomorrow, I may be able to order the woven carbon and uni from Aircraft Spruce and miscel items from McMaster-Carr.
Thursday, I'll get the resin from Resin Research.
And as soon as the mast comes in and I make a bend test(and talk to Eric) I'll take the sail plan to Scott at Morgan sails.

 

MPX test model

As I've developed the SRT concept using the MPX foil system, the foil system has taken priority in terms of testing over the self-righting concept for the time being. I think the foil system has a lot to offer, particularly on small tri's. Thats what this model is all about.
This is a post I wrote on SA to, once again, try to describe the system and its advantages in this thread http://forums.sailinganarchy.com/index.php?showtopic=144099#entry4028748

I always hear that foils are too complicated, cost too much etc, etc. I always hear that a high performance tri wouldn't interest the target market because(see 1st sentence).
1) There are reasons I suggested using small amas: they weigh less and they cost less,
2) With the savings from the small amas foils would not be a problem,
3) Since I have yet to see an under 20' high performance tri designed to fly the main hull with ama foils and foils on the main hull-how in the hell can anyone say it wouldn't be attractive to the target market?
----a. Speed is fun
----b. Foils aren't just for speed- they dramatically improve handling if designed and implemented correctly. The system I described earlier with ama foils and foils on the main hull is different than any tri I have ever seen. Most tri's have a single daggerboard and single rudder-the only difference with mine is the addition of a foil on the bottom of each. And single ama foils. All the foils would be easily retractable fascillitating saling off a beach. Since the amas are small and light why not have plugin cross arms? Or use a variation of Gary's single cross arm.
----c. Modern foil systems can be almost automatic-they aren't complicated and offer too much to be shelved.
----d. The RM(righting moment) of a an 18X 18 or 18X 16 tri is too great to allow the main hull to fly even with a single person sitting in the center until the wind is 15knots or above. Many sailing areas in the US have 10knots or less year round. To make it fly earlier you have to add enough SA that you'll have to reef early and the enormous SA will cost more and be difficult to handle. Thats probably why you don't see small tri's that can fly the main hull-and are also fast.
But the solution is simple and elegant:
---by using the two foils on the main hull the boat can be designed to lift the main hull in a 5 knot breeze!
---This is important: the main foils begin to unload as soon as the main hull lifts off and the ama foil begins to take more and more of the load untill at speed "X" the ama foil supports 100% of the load(not the 70 or 80% of the Mod 70's) and there is little to no ama or main hull wetted surface-all automatically. More than that, the induced drag(drag due to lift) is reduced dramatically on the two main foils which are relegated, nearly 100%, to controlling pitch of the whole boat-not lifting the whole boat.(Much better pitch control than a "normal" tri.)
--- And most importantly the sailing angle of the whole boat(angle of heel) is automatically controlled and maintained.
---This allows the crew(1 or more) to sit comfortably in the center of the boat while the boat sails at a max heel angle of 10-13 degrees. No running side to side. No pitchpole. Dry, not sitting in a fire hose spray(main hull is in the air). More comfort, much more speed and able to perform like this in very light or heavy air. No chit.

 

MPX tri test model

Just heard from Forte-the wing mast has been shipped! Also, the carbon and some miscel. items shipped yesterday from Aircraft Spruce in Georgia. Coming together.....

 

Keep going I want to see in action.

Who's going to capsize her

 

MPX test model

============
Fanie, I'm giving it hell! What does "capsize" mean? (!)

 

LOL Dough, that's where you sail with your feet up in the air...

 

MPX test model

Just ordered the finest winch made in the world-the RMG sailwinch-380H, proudly made in Australia by Rob Guyatt-who was there for me 17+ years ago when I built RC models professionally:
https://www.rmgsailwinch.com.au/rmg/products/380EH.html

features: https://www.rmgsailwinch.com.au/rmg/pages/Features.html

specifications: https://www.rmgsailwinch.com.au/rmg/pages/Specifications.html
=================
Bec Switch/power management system: https://www.rmgsailwinch.com.au/rmg/products/RMGSwitch%2dBEC.html

click-winch, wiring diagram using the BEC switch--

 

MPX test model

I don't know how to post larger pictures so you'll have to click on the picture to see this. It's a sketch of the crossarm angles and the fore and aft tubes on each side of the "cockpit" that support the bucket seats on the full size version. One or two on each side -easily removable.

 

SRT/mpx test model

The mast is here! Take a look at the container it was shipped in. I'll open it tomorrow but these guys are great-I wanted it well protected and it sure is.
=============
Couldn't wait. The mast is simply perfect! Stiff and very light: 10.3 oz which corresponds to a 7" chord X 2.7" wing mast full size weighing 30lb. Can't get better than that!
Can't take pictures tonight.....

 

SRT/MPX test model

Here are a couple pictures of the mast: (Note-it's a bit shorter than the full size mast will be but the sail plan is matched to the model righting moment)

click--

 

Hey Doug,

I did not catch the details on the mast (cord, thickness, length).

If I had to guess, I would say it looks a lot like a NACA 24 with a fat rounded TE.

How are you planning to attach the sail to mast? Will you try to get a smooth transition from hard surface to soft surface?

FYI, I did some playing around with wingmast performance in XFLR5 as discussed over in:

http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/what-significance-wing-thickness-45383-new-post.html

I am not really considering any wingmast efforts, but it looks like Petros is. Do you have any reference material that would help us to understand what are the advantages of a given foil section for use as a wingmast?

 

=============
Mr. Flados(sorry, don't know or remember your first name!) The model mast is 2" X .625" X 86". It weighs 10.3 oz and will support a 2500sq.in.(changeable and reefable) rig.
I have no idea what the section is(see below). I was searching, since these things are not generally available, and I found a spreader section on the Forte site that looked close enough for jazz. It is ,nominally, 7% of the chord of the main halfway down. I talked it over with Eric Sponberg and sent him the section drawing and he thought it was fine. I had to talk Clint at Forte into laying this up at about half the spreader wall thickness-but he was amenable and did a first class job. I'm going to attach the sail by gluing a series of very small tubes in the center of the back of the mast spaced about 6" apart. The luff of the main will have about a 3/8" pocket in it and little notched out rectangles and a wire will run up the pocket and thru the glued on tubes to hold the sail on. I've used this system for many years on rc models and it works well. As far as a smooth transition from mast to sail-it won't be-it will be more like Sponbergs system which is like the system described here by Tom Speer:

trimming a wing mast to the sail-new theory-9-4-12

I used to think the lee side should have a smooth, unbroken contour, too. But the more I've looked at the aerodynamics of wingmast/sail combinations, the more I'm thinking the mast trim should be somewhat different.

If you trim the mast so the lee side is a smooth contour, then it's highly likely there will be a large separation bubble on the windward side, with the flow separating from the mast and reattaching some distance back on the sail. From the CFD simulations I've run, there is less drag if the mast is trimmed to create a small separation bubble on both the windward and leeward sides. This means there will be a concave kink in the leeward side at the mast/sail junction.

I now think the best way to trim the mast is to position the stagnation point just to windward of the leading edge. This can be seen by putting a dense row of short telltales around the mast. The stagnation point will be at the dividing point, where the telltales point in opposite directions. An alternate method is to mount a small dinghy wind vane on the mast centerline, with the tail just barely clearing the mast. The tail will go to the leeward side and stay there when the stagnation point is on the windward side. If the tail is mostly to leeward but flicking occasionally to windward, then you've got the mast trim about right.

Frank Bethwaite found that it was good to have a blunt, flat base to a wingmast, which you can see in his section for the Tasar dinghy. I think it depends on the thickness ratio of the mast. From the maximum thickness, there's a limit to the angle at which the sides of the mast can be brought together without the flow separating. If you don't have enough mast chord to bring the sides all the way together at that angle, it's better to just truncate the mast at the design chord with a flat base rather than to increase the curvature to achieve the closure at the design chord. If the angle is too steep, the flow is going to separate anyway, so you haven't reduced the wake of the mast by making it more curved. It's better to keep the flow attached all the way to the backward facing staep and accept the separation bubbles that will lie behind it. The angle will depend on the size of the mast and the speed range for which you want to design it, so it's not possible to name a single value for it.

(BTW, "laminar flow" and "attached flow" mean two different things, as do "turbulent flow" and "separated flow". I think you meant the flow should be attached as it flows from the mast to the sail. The transition between laminar flow and turbulent flow is likely to have occurred earlier on the mast, although it could still be laminar at the point where it separates to form the windward separation bubble. The flow in the boundary layer will definitely be turbulent but attached where the telltales are laying flat on the sail.)
__________________
Tom Speer

 

It seems to me if you are trying to get maximum lift, such as in low wind conditions, than the lee side shape is more critical since that is the low pressure side, where most of the lift is generated. So it seems it would be more desirable in this case to allow for a larger separation bubble on the windward side so you have better lift on the lee side. Beside the separation bubble should be correspondingly smaller since the flow should reattach faster to the windward surface since it is on the high pressure side.

If you are trying to optimize L/D than I would expect what Tom Speer wrote would be correct, allowing for two smaller separation bubbles split between the lee and windward side (low pressure and high pressure sides). Usually most designers feel that for higher speeds in higher wind conditions, best L/D performs better than simply best lift.

Question is can a shape be developed that allows transition from mast TE to sail surface that can minimize this separation and still yield good low speed lift, and good L/D at higher speeds.

Several ideas I had to accomplish this is to put a sleeve on the LE of the sail and have the mast inside of it, like many sailboard rigs. Or to have a "D" shaped mast with two fabric surfaces coming off each of the mast's rear corners (with two set of tracks on the flat of the mast and two sets of battens), and these two surfaces can be cambered to give a smooth curve yet allows the TE to meet to allow attached flow all the way to the TE of the assembly. It seems to me than you can get both high lift in light wind conditions, and good L/D for high speed conditions.

 

Petros,
It has been done already, see the Wing Mast Practice thread and
www.advancedwingsystems.com or www.scoop.it/t/soft-wing-sails

 

Now we can say we've goggled a noggle !