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

you may not have itended washout, but foils move through the water with 5 degrees of freedom, one more than airplane foils and you tip is washed out from a spanwise flow perspective, and since spanwise flow is heave control, this is significant. If you prefer to think of it in just static 3D, its tip droop, but given the complex shape you have there I would not guarantee that its free of washout if I were ypu

 

Re post 946
Amazing to see it all put together - gorgeous indeed!
Can't wait to see just how the rig works - and the little 'gaff' at the top.

Looking at the overall proportions now, am wondering what the primary purpose is for the draft of the main board & rudder foils being so much deeper that the draft of the ama foils?

Thanks,

 

Tom, its because Doug's vision is that it sails canted eventually flying on the leeward foil and the main foil, this requires the weather foil to cheat out of the water sooner.

As to the sail - frankly it looks like the gaff is going to not work very well at all as even at rest it is showing a tension wrinkle from the tack to the gaff outhaul. Which as I explained above, is going to play havoc with draft positioning at the top of the sail.

even windsurfers with sails this size use full battens for draft control at speed, there is no reason why this sail should be different.

One of the interesting things about a model this size vs. the one in the recent video is that Reynolds number is a power function. thus the relative scale of windspeeds and power is dramatically different. the model in the video was sailing in "scale" windspeeds of between force 6 and Force 8 winds (strong breeze to gale).

And it struggled to foil in the low wind range. so just looking at SA/wt doesn't tell us all that much about models. Looking at Curtis' model vs. the "mpx" we see that Curtis' is roughly 1/2 the LOA and 1/8 the SA. which suggests that the efficiency of the rigs differ by at least a factor of 4. This suggests that the liftoff speed of the MPX is going to be substantially higher than that of the F3



as to the washout boat lifting foils have 5 axis of freedom vs 4 for aircraft, thus the spanwise profile also needs to be looked at, in which case the tip droop appears as washout. furthermore given the complexity of the surfaces involved, I remain to be convinced that they got shaped with no washout.

 

MPX Test Model

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Thanks,Tom! The boat is designed to sail at an angle of heel of between 10 and 17 degrees-10 degrees for the initial set up. The main foil wand* is set for that
angle. Should the boat heel more, the wand will automatically generate downforce until the designed angle of heel is achieved again.
The depth of the main and rudder foil is because, once the designed sailing angle is achieved, the main foil is unloaded and the primary purpose of the main and rudder foil together then is to provide pitch control. To do that reliably in waves and at the design angles requires the foils to be deep to assure that they continue to work. The primary purpose of the wand controlled main foil on the daggerboard is to allow the boat to fly the main hull in very light air, with the secondary purpose to control pitch well in stronger winds. Note that the depth of the foils is almost directly proportional to the depth of Moth foils for its length.
The fact that the main foil can produce downforce can allow a substantial increase in righting moment as well as provide a windward component of lift (similar to Veal Heel in a Moth but caused by downforce instead of vertical lift) but the downforce can be "turned off" by a simple adjustment of the wand system.
*surface sensor controlling the mainfoil flap angle.
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Tom, take a look at post 926 for the extensive series of RC boats I produced a few years ago-almost all used a variation of a gaff rig that was proven superior in extensive testing in all wind conditions but particularly in light to moderate air. One of the biggest advantages is the "upper outhaul" that allows far more control of sail shape than would otherwise be possible.

Illustration-Left=windward lift due to downforce, Right=MPX gaff+ GDC(gaff control device) + upper outhaul:
click-

 

My boat

Hi Doug, the loading is the same for each AMA foil at takeoff , once the boat is out of the water the windward foil is 100% unloaded.

Here's my wetted surface area its fairly accurate but not exact. I didn't know weather to have both sides of the daggerboards/ foils so I posted both...

TO:

Main hull: 0.075m^2

Float hull (leward), windward is out of water:0.04m^2

Foils (1 side of each foil) 325cm^2

Daggerboards, 324.5cm^2

Total TO (1 side of foils/daggers),

1799.5cm^2
278.9in^2

Total TO, 2 sides of daggers/foils:
2449cm^2
379in^2

2349cm^2 (with more accurate float hull)
364in^2


Total Foiling: 1 side of foils/daggers:

242.6cm^2
37.6in^2

2 sides:
484cm^2
75in^2

I think that's everything, the hull W/S is a bit exaggerated mainly the float hull (maybe closer to 0.03), the foil is exact.

I hope it compares well

-Curtis

 

Doug you do realize that the size of the vector to weather is going to be tiny given both the angle and frequency you are going to be operating with "Negative lift/increased RM". Unike Veel Heel which reduces projected SA and increases vertical lift generated by the sail, your approach will increase heeling forces as you increase RM. this sounds like an equation for a driven oscialltory rather than damped oscialltory system

 

RC Hydrofoil Stats

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Thanks, Curtis. When calculating the lift of a hydrofoil(daggerboard and or lifting foil) you only use one side for the foil area. For wetted surface, you have to use both sides. Thanks for doing it the way you did-especially for "translating" the metric values! I'll add the results to the "Master" shortly.
PS- do you think that, initially, the boat might heel to the point that the lee ama touches the water until speed builds enough to tend to level the boat somewhat?
With the windward foil lifting it seems like the boat will be hard pressed not to heel some initially. Depending on wind strength the F3 did just a bit but it had a wand on the windward foil that developed downforce as soon as the thing heeled a little. Your boat and the MPX don't have that prior to and right at takeoff-unless you use the mainfoil by radio to create downforce? It will be interesting to see how it actually works....
======
A) Does this replace the measurement above for the float hull or is it the float +daggerboard? Not clear to me...
B) How come two sides of dagger/foils is not twice one side of dagger/foils? Make sure you've included only the immersed portions of the daggerboards(both sides).
=============================
So we need:
1) Wetted Surface-not foiling:
a. main hull
b. daggerboard+ main foil-both sides
c. rudder + foil, if on main hull-bothsides
d. lee ama
e. lee ama foils-both sides
f. windward ama
g. windward ama foils(only the immersed part-both sides)
h. rudder + foil, if on amas( only the immersed part-both sides)
2) Wetted Surface-Foiling:
a. immersed part of lifting foils and daggerboards-both sides.

 

If the gaff allows such good control of the shape, why is there such an ugly Gaff To Tack crinkle? Seems to me the Gaff - because it is straight and stiff inhibits shaping of the sail in the regions of the sail near it

That's why square headed jibs in full scale boats - also called "Jib Top Reachers" or "blast reachers" use battens for the over-roached section - to allow for tunable flexibility.

But what do I know, I've sailed only about 1/2 dozen high performance boats that take advantage of full battens for sail shape. Must be that I didn't understand how those sail controls worked.

 

Hi Doug, ThatIs more than 16 in^2, the 16.2 is just the main foil, with both AMA foils there is a total area of:

245cm^2 (37in^2)

which puts the foil to sail area ratio back to 1:15,

Both ama foils are fully immersed until the main hull leaves the water.

Also for the wetted surface area, you asked if the loading for the ama foils is the same, yes at takeoff it is the same only when the boat has taken off does the windward ama foil become 100% unloaded.

The float hull WS that you high lighed is the total take off WS with the revised and more accurate version of the float hull. There is 1 AMA and the main hull in the water at take off. There are about 3 degrees heel here the windward AMA clear of the water by 4cm and the leeward in the water (I expect that it will be in the water the whole time till the boat takes off).

The reason the numbers aren't double is because only the dagger boards and foils were doubled not the hull W/S. The last Take-Off W/S is the correct one , the one with the better float hull data. I'll delete the wrong one from my other post to make it clearer.

Sorry for the confusion there.

Your main looks really good! and the picture with the door in it really puts it in perspective!!!, is there much left from the rig point of view to go?

Good luck
Regards,
Curtis

 

MPX Test Model

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Thanks, Curtis! No, not at all but I'm not likely to be able to do much on the boat for the next month and a half-two months, unfortunately. Things could change, though.

 

Ok so that means Early April at the latest. Lookiing forward to seeing the videos.

 

No, and I don't intend to. There is a high loading on the top of the foil (the water pressure trying to push it forward) and whilst I guess I could change servo position as I tack the boat, right now my focus is on foil concepts and shapes, combined with rig balance. I want to end up with a foiling multihull that can also race round a windward/leeward race course. I haven't got this yet. I like the "V" foil setup as it is self-compensating by reducing area as it goes faster. I can only cope with so many issues at a time . . . . The boat is working, and I want to make small refinements right now. To convert to wands, or servos would almost be back-to-the-drawing-board.

 

Full length battens in the top section of the sail are bad news for light winds. The modern-looking "Fat-head" mainsails are more often than not a real pain. The purpose of the fat-head is either to gain unmeasured sail area (depends on the class rules as to how the mainsail is measured) or to give more sail area with a lower centre of effort. The problem is that the top full length batten is usually under considerable compression. If it isn't then the mainsail will have too much twist in a breeze. So if the batten is under a compression load then it is quite possible that the batten itself will not "tack" or flick across to the new tack. It is amazing how this slows down a boat!

The mainsails in the attached photos are all by Heinz Bohn. He makes good sails, with a moderate roach that works in light winds. 44 is my Nightmare, 46 and 49 are both Shinobis from Mike Cooke

 

Where full length battens are good is in a breeze when they help to hold the shape of the sail. So on smaller rigs which are only used in a breeze, they are excellent. But you have to watch how the batten is attached to the sail. If they are stuck on, it is amazing how a flapping sail can unstick a batten! In the photos here - which is a #3 rig - the battens are in pockets in the sail which is by far the best way to fit them, but is much more complicated for the sailmaker to construct

 

Ian, check your last YouTube page.