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

[Doug Lord]

Fire Arrow Foiling System Testing and Development

This is a heads up for anyone considering the use of ama foils, particularly uptip foils. The picture below says it all. Fire Arrow has a lot of crossarm dihedral for a number of reasons but one of the most important is that when foiling at the designed heel angle of 10 degrees the windward ama foil is well clear of the water. That means that the foil doesn't have to be raised and lowered every tack and every gybe like it does on the AC cats or GC32 or others using uptip foils including the new Morrelli and Melvin foiling tri. So you can have the advantages of an uptip foil with none of the disadvantages! The same will be true on the fullsize WOLF.


Note clearance of the uptip ama foil:

 

[Doug Lord]

New Foiling tri

See the story here about the TH 10 a 32 ' foiling tri that is using A Class/Nacra type foils with four in the water all the time(two surface piercing main foils +two rudder T-foils) :
http://www.boatdesign.net/forums/multihulls/new-trimaran-foilers-55834-5.html post 62

Boy, would I like to see a 32' Fire Arrow go up against it!

 

[Doug Lord]

Fire Arrow Foiling System Testing and Development--Mainfoil/Wand

It's hard for some to get the physics of the Fire Arrow because the mainfoil and dual wands work differently than they do on any other foiler. Immediately after mainhull lift off, the main foil begins to unload until the foil is NOT LIFTING at all. Thats because as the pressure increases in the rig the boat heels causing the main hull to lift and eliminating the requirement for vertical lift from the main foil. If the wind lets up the angle of heel will lessen, directly affecting the wand which then causes the flap to go down and the foil to lift until the 10 degree angle of heel is restored. If, at that point, there is a gust or if the wind substantially increases, the angle of heel will want to increase and the instant it does the wand causes the flap to go up causing downforce until the 10 degree angle of heel is restored. It's automatic and virtually instantaneous.
The big difference compared to other multihull foilers that use wands is that when the mainhull reaches its designed angle of heel, lift is no longer required from the main foil so it is 100% unloaded. Whereas on a Whisper, S9, Rave, Osprey, when the boat reaches its designed flight altitude the main foils still have to lift the weight of the boat. Again, when the Fire Arrow main hull reaches its designed flight angle of heel lift is no longer required from the main foil!
This substantially reduces the drag of the foil.

Illustration: note that flap is slightly up because the symmetrical mainfoil is installed with a 2.5 degree angle of incidence--

 

[Doug Lord]

Fire Arrow Foiling System Testing and Development / WOLF

Making progress on the WOLF concept model. Had to order 3/8" carbon tubes for the crossarms(equivalent to 3" diameter). Laid up the "curved pieces" for the two stage amas*. Remodeled the hull. Slow progress- fit in between other projects- but progress nonetheless.....

*"Curved piece" is Stage Two of the two stage ama-see page 160, post 2387 for picture

 

[Doug Lord]

Fire Arrow Foil System/ Fire Arrow 70

UPDATE-12/9/16--This is a rough comparison of the Fire Arrow advantages scaled up to 70' as compared to the Gitana MOD 70. Its a rough comparison because no design work or engineering has been done for a 70' version but, as will be seen below, many of the advantages of the small boat(post 2297, above) would likely translate to a larger version. This was done before anything was known about Maserati!
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What would be different than the Test Model:
1) the amas would not be a "Two Stage" ama(page 129, post 1922) as described in the previous post and the crossarm dihedral would not be as high. However, the ama would not be the same as Gitana(for instance) but would have about 150-200% total buoyancy(about 85% ama + curved piece on the small version of the Fire Arrow). If you've seen the latest(last few years) version of the Hydroptere amas you will have noticed(maybe) that they are stepped planing hulls designed for incidental contact with the surface at high speed. The Fire Arrow 70 Amas would be a stretched out version of the Hydroptere amas in that they would have lots of buoyancy but would also have stepped planing hulls designed specifically for low drag incidental contact with the water at high speed. They would not be designed to be at their optimum at slow speed but since the boat would foil in light air it won't matter.
--
2) the main hull would not be the same as the small Fire Arrow either-it would have a much higher L/B ratio but consideration would be given to reducing drag due to incidental contact with the water at speed while retaining relatively low drag at low speeds.
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Comparision of FA70 to Gitana MOD 70 Foiler:
1) Gitana LOA=21.3m(69.8') X 17m wide(55.76')
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2) Fire Arrow 70=21.3m(69.8') X 25.9m(85') wide.
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Now, if you consider that boats like MOD 70's and other large tri's want to be able to fly the main hull or, at least, have it just skimming they have to juggle maximum sail area, weight and overall beam to be able to do that.
If they get the beam too wide for the sail area then it will be difficult to fly the main hull. So they have to strike a compromise that will allow the hull to fly/skim in the widest range of wind possible. And, of course, foilers want the main hull clear as much as possible.
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The Fire Arrow 70 would start out with a wider beam than the Gitana type(similar proportions to Hydroptere, except that the center of lift of the ama foils is substantially further outboard than it is on Hydroptere). The wider beam is possible because of the unique features of the Fire Arrow foil system.
1) the boat would have a T-foil on the daggerboard utilizing an all moving foil/board combination or a flap on the main foil. The foil would control the altitude of the main hull and the angle of heel of the whole boat. A wand type surface sensor, electronic sensor or manual/hydraulic control of the foil and/or flap would be used to actuate the foil.*
Electronic or surface sensor systems would probably be best because they would automatically control altitude and could be simply adjusted for different conditions.
At any rate, since the foil would be designed to lift at least 80% of the boats weight at relatively low speed ,it could be easily designed to provide 40-60% of the boats weight in downforce which translates to much greater righting moment than possible with the Gitana type. Whats more this force would be created automatically making the boat much more stable in gusty conditions. Further, the amount of downforce , if any, could be completely adjustable. Structural analysis and engineering would determine how wide the boat can be and how much downforce can be allowed. But there is no doubt that the RM of the FA70 would be substantially greater than the Gitana type tri. And, again, the foil lift makes it possible to precisely design when* the main hull will fly which will ,undoubtedly , be in much lighter air than the Gitana type trimaran.
*what wind speed
--
2) the Fire Arrow 70 would have a single rudder T-foil(vs two +a single main rudder on Gitana). This rudder foil would work with the main foil to control pitch for the whole boat. And since the mainfoil unloads as the flap approaches neutral, the pitch control authority would be greater than on a "normal" tri.
--
3) A great advantage of the Gitana(and potentially Macif and Exocet) trimaran systems with an uptip foil and rudder t-foil on each ama is that in just the right conditions those boats should be capable of flying on just two foils. However, because of the nature of the Fire Arrow foil system it is likely to be faster because it allows greater power to carry sail from the get go, flies earlier and produces far more righting moment in stronger wind. And it can keep the main hull clear of waves in conditions where Gitana and Macif(Ultime-100') have shown that they will face frequent main hull wave contact.
At least that's what it looks like to me.

* Remember this was written before it was known that Maserati had used a manual/hydraulic system to control mainfoil AOI!


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This description will be frequently updated(5th-4/27/16) as the conception of a larger version of the Fire Arrow System becomes more clear.
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“There’s a full-on revolution going on in sailing, and more specifically ocean racing. We’re in the process of writing a new alphabet and we’re on letter A”
Baron Benjamin de Rothschild
http://www.gitana-team.com/en/b-9/multi70-edmond-de-rothschild


Fire Arrow Test Model, July 24, 2014, 5mph wind :

 

[Doug Lord]

Midship wand / Forward wand

This is from Tom Speer on another forum:

The pitch attitude of the boat is the sum of the angle of attack of the foil and the flight path angle of the foil through the water. The slower dynamics of the boat play out at almost a constant angle of attack, and changes in the pitch attitude of the boat reflect changes to the flight path angle. If you multiply the flight path angle by the velocity, you get the rate of change of the flying height. So the pitch attitude times the speed also corresponds to the rate of change of the height.

Putting the wand ahead of the foil means the feedback signal is a combination of both height and the rate of change in height. This adds lead to the control system and improves the damping. If you consider that, at constant speed a change in angle of attack is needed to change the flight path angle, then pitch attitude feedback adds even more lead because it anticipates the change in the flight path angle as well as the flight path angle's effect on height.

If you make a feedback system that has only position feedback (like pure height measurement), what you create is an oscillator. The feedback will make the system correct back toward the set point, and the feedback goes to zero at the set point, but the trajectory is already passing through the set point and headed toward the opposite extreme. As error accumulates in the opposite direction, the system will reverse and correct back, but it will overshoot again in the original direction.

When you add rate feedback, the reaction of the control system is stronger when it is headed away from the set point, and the feedback goes to zero before it gets back to the set point. The control system will already be applying control to slow things down as it gets to the set point, so any overshoot the other way is less than for the pure position feedback design. This makes the response settle down and converge to the set value. If you have enough rate feedback, there won't be any overshoot at all and the system will be heavily damped.

That's why putting the wand forward helps to make the boat easier to sail. It's not so much that it anticipates the waves, but more that it anticipates what the boat will do, even in flat water. Sure, you can put the wand at the foil and get damping from other sources. But moving the wand forward is a powerful way to add damping, and pitch attitude feedback is especially effective when the boat is going fast.

 

[petereng]

Hi All - More can be learned about this sort of thing by looking at PID control systems which were originally developed for autohelms by the way. see https://en.wikipedia.org/wiki/PID_controller Peter

 

[Doug Lord]

Wands

Thanks for that Peter. I think it may be over my head but I'm going to try to understand it. Dr. Sam Bradfield was a great believer in a midship wand for foilers and had a terrific way of explaining things-I wish I could ask him about what Tom wrote.......

 

[petereng]

What Tom is saying is analogous to trail on a bicycle/motorbike or castor on a car wheel. The larger the trail/caster the less sensitive it is to rapid changes, ie the more stable it is because the effect of the input is slower, so it filters out the fast inputs and sort of reacts to the mean input. A PID circuit does this electronically and you can adjust parameters to predict the overshoot so the input stops before/at the set point rather than overshoot etc. Peter

Using a wand for flight leveling is sort of a wrong way to do it in some ways. ie if the foils are deep enough the surface shape does not affect them. It would be better to have a mechanical level or electronic level on board that controls the flap not the wand. The current assumption is that you want the boat to follow the surface shape - the problem with that is filtering the small waves (noise) out yet be able to follow the long waves. But I'd expect if we had a boat levelling system the crew could easily trim for long waves, its the small stuff that creates issues at present. That's why the wand out front works as it provides a long trail(lead) for the system. As the boat pitches the effect of the wand is less the further fwd the wand is. This is like balancing a broom stick in your hand. If the stick is long its easy to balance, if its short its hard to balance because the cause and effect are close together. When the broom is long the cause effect is long enough apart for the person to compensate the balance. Cheers Peter S

Moths are very light and short so need high damping or very fast control. As boats get bigger like the Rave they have more mass (are damper) and are bigger (the foils are further apart) so are more stable. With most systems adding mass helps make it more stable/damper but on a race boat we don't want to add mass so we need to improve control. Peter

 

[Doug Lord]

Wands

Thanks Peter. I've sailed a Rave with midship wand and talked a lot to Dr. Sam about it. He once told me words to the effect that the wand ought to control altitude and the rudder t-foil should control pitch. Of course he was a great American foiling pioneer ,professor and engineer. Thats why I'm having so much trouble with this. I designed and built the first production RC sailing foiler ,the F3, 16 years ago on the basis of the things I learned from Dr. Sam. It worked perfectly-never any problems with flight altitude, pitching etc. Same with the limited testing on the Fire Arrow-the midship foil works perfectly.
And then there is Ron Price who designed the Whisper foiling catamaran and the F101 foiling trimaran both of which seem to work perfectly.
He says this about the trailing midship wands that both boats use: (He or one of his people are very experienced instructors in the Moth at a sailing school)

WHY IS THE WAND ON THE TRAILING EDGE OF THE MAIN FOIL?

The F101 has its control wand fixed to the back of the trailing edge of the main foil, as opposed to the mounted at the bow which is where Moth’s mount the foil. There are a number of advantages to the trailing edge position, the most important of which is that the wand measures the ride height of the boat irrespective of pitch. This important factor can help to eliminate the porpoise effect which many beginners experience when learning to sail a Moth.

Whisper foiling cat with midship trailing wands:
https://www.youtube.com/watch?v=7wRka-zf5VM


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F101 Foiling Trimaran with trailing midship wand:
https://www.youtube.com/watch?v=UU7ROtmSfUA

 

[petereng]

Hi Doug - There are many ways to solve this problem and Tom says this as well and yes the conventional way is for the board to control lift/height and the rudder to control pitch. If it works then its "perfect" for the situation no matter how it looks and I'm sure we will see other solutions over the next few years, its all changing fast. Peter

 

[Doug Lord]

Wands + Foils

Thanks for your input, Peter. I want to increase my understanding as much as possible. If it weren't for Dr. Sam, though, I sure would have missed a lot.
Actually designing and building boats using this stuff is a heck of a learning experience- that he inspired......

 

[petereng]

Doug - When are you going to go METRIC? Peter

 

[Doug Lord]

Fire Arrow Foiling System Testing and Development

Probably not in this lifetime. However, many times I've posted both and probably should have in the last post but I didn't think about it.

UPDATE-fixed

 

[David Cooper]

Interesting argument from Tom, although it looks as if putting the wand next to the foil works fine on many boats on flat water at all speeds, so I don't know how significant the effect actually is. The argument I've heard about the advantage of a forward wand on the Moth was to do with how well it goes over waves, the wand picking up the change in terrain earlier than it would if it was at the foil, thereby pushing the flap down sooner as a wave approaches (which should actually happen on the way down into the bottom of a trough) and changing the boat pitch sooner (with the rudder foil holding the back end down as the centre rises), thereby generating more lift over a long distance so that the boat stays higher and is less likely to touch down - the guys who had central wands on their Moths were, I was led to believe, being slowed by more uncomfortable impacts with waves.

Having looked carefully at his Tom's argument, most of it appears to be a diversion away from the relevant part, and when the relevant part is described it's done in a very unclear way. The key place where you get a difference between a front wand and a central one in relation to damping of porpoising is what happens when the boat comes back to the right height having been too high or too low. If it's coming down to the correct flight altitude from above, the hull will still be pitched down (more than it should be) and it will be moving down too, and in this situation a wand at the front will add lift to counter that sooner because it thinks the boat is too low before it actually is too low, whereas a central wand is only just getting to the point where it thinks it's back at the right flight altitude. Similarly, when the boat is coming back up from too low, it will be pitched up (more than it should be) and moving up too, but again the front wand counters that sooner because it detects the boat as being too high while a central wand is reading the height as being the correct flight altitude. In both cases (moving downwards or upwards), the movement is not arrested at the point when the central wand detects that it's back at the correct flight altitude, but a front wand thinks the boat's overshot the correct flight altitude before it reaches it, leading to it arresting the movement earlier, hopefully stopping at or near to the correct height.