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

MPX Test Model

MPX Test Model Specifications

A) Name- Fire Arrow

B) LOA-79" (6.58')-including bowsprit

1. mainhull-60.75in.(5.06')

2. mainhull+ rudder and gantry(no bowsprit)- 69.125" (5.76')

3.planing portion of ama=34in. (2.83')

4.ama LOA=50.75in.(4.23')

C) Beam-81.6"(6.8')

D) Mast 103in. (2"chord wing mast / 8.58')

E) Sail Area:

1. Main+ Mast + Jib= 3454sq.in.( 24 sq.ft.)

2. Main+ Mast + Code Zero=4244sq.in.(29.5 sq.ft.)

F) Foils:

1. Mainfoil(wand controlled flap)-Span=23.75in., Area=39sq.in.

2. Rudder foil-Span=19in., Area=29sq.in.

3. Ama foil(one used at a time)-Span(from bottom of ama- a surface piercing, soft "L" configuration)=16.5in., Area(from bottom of ama)=45sq.in.; varies with speed and load.(Inspired by the TNZ AC 72 main foil with refinements that allow it to behave as a surface piercing foil with a wide speed range that- hopefully- won't require manual angle of incidence adjustment while sailing.)

G) Weight-Estimate 19lb.

H) Foil loading at takeoff(19lb)=.186lb/sq.in.(F3-.188)(lighter=better)

I) SA/Lb(19lb displ.est) with Code Zero=223sq.in.(F3-208.5)(more=better)

J) SA(incl Code Zero) per sq.in. of mainfoil group area(102sq.in) at takeoff=41.6 sq.in./per sq.in.(F3-49 sq.in/per sq.in)(higher=better)

K) SA/WS(with Code Zero)= better than F3 at takeoff(even with the wide planing hull)--7/1 seahugging, 16.5/1 foiling.

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MPX FOIL SYSTEM
--added #6 below 12/8/13 and modified 12/9/13
--added to #3 below on 12/13/13

Here is a brief summary of what makes the MPX foil system unique and why that is important:
1) The boat has four foils total. On the fullsize version, only three foils are used at any one time. On the model, since the ama foils will not be retractable(at least initially), they both contribute to vertical lift at take off with the majority of lift coming from the main wand controlled foil and the lee ama foil.
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2) Here are the unique characteristics of the ama foil:


See page 73, post 1090 for much more on the theory that applies to the unique ama foil. It has just been updated with a link to Dario Valenza's experiments on A Class cats with "uptip" foils where he found that the foil will function w/o leeway coupling for heave stability --using the breaching of the inboard tip for altitude control when leeway is low.


a. The ama foil is designed to only lift vertically(no downforce),
b. The ama foil is targeted to perform throughout the speed range with no adjustment. It is anticipated that the angle of incidence may have to be changed once if it is changed at all.
c. The ama foil is designed to carry 80% of the weight of the boat with the rudder foil carrying 20%. The ama foil loads up as the mainfoil unloads.
d. The ride angle of the ama foil is controlled by the action of the main foil and rudder foil together.
e. The ama foil was inspired by the new type of foil designed by Morrelli and Melvin for TNZ except that this foil has a wider range of speed before angle of incidence adjustment might be required.
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3) The main foil has a flap and the flap angle is controlled by a wand*. This allows the boat to fly the main hull in very light air which is a big advantage for an oversquare trimaran-particularly a tri under 20' which would, likely, not be able to fly the main hull in these conditions. As soon as the main hull lifts off, the boat accelerates to roughly twice windspeed in a 5mph wind. As the boat speeds up and heels, the mainfoil unloads as the wand causes the flap to rise. At a certain point the flap causes the main foil to not produce any lift with all the load automatically shifted to the ama foil. If the main hull rises above this point(about 10 degrees angle of heel initially), the flap will continue to rise causing the main foil to create down force(unless this facility is disabled). When the main foil is developing downforce it is also developing lift to weather, similarly to the lift to weather when a Moth is using Veal Heel(except on this boat it is a function of the "normal" heel of the boat and the downforce on the mainfoil). See post 532 for an illustration of how this works.
* The boat actually has dual wands but they act on a single axle acting as a single wand.The reason for that is to allow the wand to work when the boat is heeled. The lee wand is nearly vertical when the boat is heeled 10 degrees and acts to maintain an angle of heel of about 10 degrees and an altitude of the main hull of about 6". See the sketch below showing the heeled waterlines. Also see posts 512 and 514 for more on the wand system. See page 40, post 597 for a video of the MPX wand activating the main foil flap.
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4) The rudder foil is a trailing foil that automatically develops 20% of the lift required at takeoff, then gradually unloads until it begins,again automatically, to pull down.
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5) As best I can tell there is no other trimaran in the world using a foil system like the MPX system. Having a wand controlled mainfoil on the main hull and an ama foil that flies the ama(nominally a few inches above the water) with no control input other than that of the surface piercing component of the foil and the effect of leeway on the "L" portion of the foil(however small) will be significant if it works. The whole foil concept will be significant if it works because:
a. it allows an oversquare tri to fly the main hull in light air,
b. it unloads the mainfoil allowing it to become,with the rudder, primarily a pitch control system which controls the running angle of the ama foil.
c. it allows the mainfoil to contribute to righting moment with downforce,
d. it allows the mainfoil to develop lift to weather when it is developing downforce.
e. the deep main foils acting to control pitch prevent the main hull from bottoming out and allow the angle of heel to be varied between approximately 10 degrees and 17 degrees by adjusting the wand length.
f. the planing ama design serves as back up in rough and/or gusty conditions when the foil might be momentarily overpowered.
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6) Speed- Top end speed is NOT the priority of the MPX Foil System-light air speed resulting from the unique ability to fly the main hull in light air is. The MPX Foil System's main claim to relevance are the two lifting foils on the main hull which allow an oversquare platform to fly the main hull when a wide trimaran,particularly 20' or under, w/o these foils would not. To make a 1.2-1.3 oversquare tri fly the main hull requires excessive sail area(or wind) for the ability of such a boat to control it's pitch stability. The two main foils work together to provide pitch stability way in excess of any "normal" trimaran and control the running angle of the planing ama and ama foil. The system should work well with a planing ama using foil assist and/or using an ama foil that allows the ama to fly when the main hull does(the current test model configuration).
Top end speed is enhanced by the initial configuration being tested which has the light air advantage intrinsic to the system with the added speed potential in heavy air due to the reduced ama wetted surface and the fact that the main foil will develop downforce adding to the righting moment. Further, the foil that flys the ama is designed to support 100% of the boats weight as the boat speeds up, unloading the mainfoil and reducing drag substantially.

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>Preliminary testing has encompassed testing all foils to 3 times their calculated maximum load(estimated 150% reserve above that before breaking)

> Boat is designed as a scale test model of an 18 footer based on a full size hull I used to have(donated to a friend).

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...

Frankly Doug, it would be much of an improvement if you would just post a LINK TO MY EXPECTATIONS every day, instead of reposting the entire book.

This is the thread which by a factor of 2.5 is the most clicked on in the forum, which I think is perhaps because of new readers seeing the high view count.

I think it would be cooler if you avoided these long redundant posts, and went back and replaced them with something very brief, instead.

...

and here's the windguru for tomorrow and Friday:



...

That was pretty funny, HighonCarbon, about parking in Doug's couch and drinking beer until he splashed the model.



But how long a vacation would it require?

 

MPX Test Model

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I couldn't disagree more.......see the pm I sent.

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I'll let you know how accurate that is-the local forcast is much higher. Whats the reputation of "wind guru"?

 

Unsubscribe

 

Doug, are you scared of this thing you made ?

 

In my usual couth Kiwi vernacular, stop fargo trucking around, Douglas old mate.
I can exactly understand Fanie's question but, fargo truck ... you're not going to be aboard this spiky foiled contraption, not going to get hurt if it cartwheels.
Now if you were piloting aboard Sid in 15-20 knots wind, would understand - because that is a savage and vicious little ******* ... but you, Doug; most that can happen is you'd get your feet wet.

 

Like 6 years ago I bought a Hobie 16, happily took it out for its first sail in 25 knots solid, 3 spectacular cart wheels and maybe 4 hours on the water sailing fast!!! I was hooked (although to be honest i've been hooked on this gig for like 23 years now i.e. my age)

So lets do it!

At some point I'm going to fly over to... wherever you are, bring my radio kit from my models, and steal it, and take it for a sail if it doesn't get on the water soon enough.

 

How close ?

Hey Doug, is this AMA attachment problem the last box to tick or are there other things that are in the way to do. If there isn't much I would suggest just to use whatever string/ rope (I don't quite understand the size string your using) you have that is strong and reliable. You could always change it after if it was stretching or not behaving.

I'm not much use when it comes to what type of string to use (I'm using 25lbs fishing braid) and tying everything off with a bowline/ reef knot. But the fact is my rig is now done and if it doesn't work then I'll just try something else.

Maybe the best approach to this is just give it a go, even if its blowing 15 knots it should be fine (?) if you just point it into the wind.


Good luck with the rest of it and I hope my suggestions help in some way.....

Regards,
Curtis

P.S All that's left for me is mounting radio gear and joining the hulls together!!

 

I hope he remembers to detach it from the stand when he finally takes to the drink...

Hoyte is in Florida too, maybe he can pick Doug up and throw him off a ways from the solid stuff, and as he pulls off just shout SHARK ! SHARK ! and charge back to land. It's the quickest Doug will learn to sail that fish bone with the already bent pieces on it

Reminds me of a friend who went to South-West Africa with some friends, one took a hand glider along. The friends all tried to fly in this thing, none could get it off the ground. Finally frustrated because he could see what every one else does wrong from observation, he took over and did what he saw should work. It did. He said a gust took him up and everyone else down below looked like ants. He says it's the fastest he learned anything in his life. He managed to do a bit of gliding and steering to some extent while everyone below ran around hysterically, fearing for his life. Long story short, the landing was something else. He said he tried to come in on a sand dune (what ever that means) to make a soft landing, he ended up splatting the sand flat from the front (apparently saved his life), looked like a sand storm on that dune. He couldn't breath and everyone else thought he was dead.
I guess surviving an emergency crash landing LOL like that kinda makes him an expert on hand gliders... right

Come on Doug, go make the thing wet ! Hoyte is on his way to pick you up. Being old and full of crap he's not going to take no for an answer

 

MPX Test Model

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Curtis, basically all thats left is to install the retainer lines, the radio and set the rig up. Her Majesty will sail when shes ready....... Good luck with your boat!

 

What's the radio for... ? To call for help if it sinks or is someone radio controlling it from the shore ?

 

She looks ready. Shall I bring my camera?

 

MPX Test Model

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Sure, in about a month or so......

 

MPX Test Model

Got the ama retainer system installed. Loops in the center and on the starboard side are made of 150lb spectra because of its "slipperiness". The other line is 50lb dacron. The snaps are regular fishing snaps and the bowsies are left over pekabe.

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MPX Test Model--Reference post

Interesting Posts for reference:

---See page 45, posts 669-674 for a pictorial history of this project from the idea to now!

---See page 46, post 687 a bit on the MPX deep main foils compared with the Moth(Dgrbd. area as a % of SA) and an example of another foiler with deep foils designed to be beach sailed.

---See page 48, posts 711 & 714 for updates on the rudder servo and sail winch and transmitter.

---See page 50, post 750 for an historical reference illustrating the boat that inspired the test model and represents the probable smallest effective application of the MPX Foil System.

---See page 62, post 926 for pictures and commentary on the extensive use of modern "gaff" rigs("Wing Tip Rig") that I made on a series of production and experimental RC models 12-14 years ago. The modern gaff has tremendous advantages most especially the upper outhaul.

--- See page 65, bottom of page(post 975) for comparisons of the MPX and other RC foilers specifications and a couple of ratios.

---See post 1052, page 71 for the new main hull for the full size version of the Test Model.

---For future reference: Tom Speer on the effect of leeway on a T foil from a question I asked in 2011:
http://www.boatdesign.net/forums/hy.../effect-leeway-lift-drag-hydrofoil-37398.html