Moth on Foils: 31.1 knots (35.8 mph)

[gggGuest]

Originally Posted by Chris Ostlind

Have any of the Moth Class rules been altered to reflect the use of foils and rudder gantries which didn't exist before the foil thing happened on the scene?

No. None.

Originally Posted by tspeer

It would be helpful to have a flap on the aft foil that could be used to adjust the pitch trim. This would not have to be actively controlled. It would be used to fine tune for performance.

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Tom, both the Bladerider and Prowlers use rudder foil flap adjustment(Prowler) or an adjustment thru moving the whole rudder/foil assembly(Bladerider). I've read comments from Moth foilers that some frequently use the adjustment and from others that they hardly ever do. On the Rave multifoiler you could special order rudder flap adjustment from a lever in the cockpit.On the F³ rc models the boat was initially supplied with servo control of the rudder flap but it proved completely unnecesary.
On my new boat I'm going to spend a lot of initial time experimenting with manual control of just the mainfoil flap and of the mainfoil flap and rudder flap simultaneously.
I still see potential advantages to using manual main foil flap adjustment-perhaps tied in to the rudder foil flap at some particular ratio- in the Moth class. And from my limited experience using manual mainfoil flap control(with separately adjustable rudder foil flap) on a bigger boat I'd say the advantages would be substantial in heavy conditions where I've read that the Moth wand has some trouble particularly downwind in big waves.
But it would take committment and some time to fully develop a good manual system in that class....
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From the Fastacraft site today:

"The current hydrofoil configuration we build for the International Moth is an inverted "T" style on each of the rudder and centreboard. The rudder foil has a trailing edge flap controlled by twisting the single tiller extension to operate a nylon worm type adjusting screw."
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Bladerider X8 as of today:
"The entire rudder assembly can be rotated by the tiller twist grip to manually adjust the angle of attack. Manual lift control on rudder hydrofoil by tiller twist grip. All control mechanisms are stainless steel and therefore will resist any force."
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OUESTION FOR ANYONE WHO HAS SAILED EITHER ONE OF THESE SETUPS :
With a single extension tiller ,it would seem that the direction to adjust the rudder flap would reverse with each tack or gybe; is it hard to keep track of which direction to rotate the twist grip for flap UP or DOWN ? Or is it easy to just remember clockwise or counter clockwise?

[Phil Stevo]

Originally Posted by gggGuest

No. None.

Yes there have. In 2005 we added a maximum length for bow and stern outriggers of 500mm. There were other clarifications without changing any parameters.

[Phil Stevo]

Originally Posted by Doug Lord

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QUESTION FOR ANYONE WHO HAS SAILED EITHER ONE OF THESE SETUPS :
With a single extension tiller ,it would seem that the direction to adjust the rudder flap would reverse with each tack or gybe; is it hard to keep track of which direction to rotate the twist grip for flap UP or DOWN ? Or is it easy to just remember clockwise or counter clockwise?

We all have a note on the boom to show which way is bow up and which is bow down. This is particularly important when changing boats because the Prowler and Bladerider systems work in opposite directions.

[frosh]

Doug, some of the variables in flap trim angles, both front and rear that you suggest might be overidden by a skipper working with manual twistgrips or similar in heavy winds could be tackled differently. Talk with the medical genetic specialists to find out the possibility of evolving a human sailor with two brains and a third arm.
I am being very serious about this suggestion, as I cannot see even a sailor of higher calibre than Rohan Veal managing a 12 inch max. beam boat with this much input and biomechanical function required, to control foil attitudes and keep the Moth sailing at max speed under racing conditions, without going for a big swim.
Doug, I realize that you are tryng to push the performance envelope a little beyond what is currently achievable, but come on, often you expect the near Impossible!

Frosh, didn't you read the previous posts? Moth foilers are ALREADY EQUIPPED WITH A TWIST GRIP HIKING STIK ! Granted my suggestion would increase the importance of the twist grip which as best as I can tell now is used infrequently by many foilers. But since it is already there it's not like introducing something completely foreign
to the crew-a new skill to go along with a new function for the twist grip-yes. Something even remotely impossible-hell no. Only a little difficult to learn.
Potential gain: less drag,less weight= slightly more speed.

[Phil Stevo]

The rudder twist grip is used as a gear change not as a real time height controller.
Response time between eyes, brain, wrist, and foil are too slow to react to pot holes in the water surface.

Originally Posted by Phil Stevo

The rudder twist grip is used as a gear change not as a real time height controller.
Response time between eyes, brain, wrist, and foil are too slow to react to pot holes in the water surface.

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In my posts I mentioned modifying the rudder twist grip as to function-I didn't mean to imply(and don't think I did) that it could be used- as is- in place of a wand unless it was hooked up to the flap on the main foil. Again, it would have to be hooked up to the flap on the main foil for the manual system I'm describing.
According to the people who have actually done it(including me) the response time is not outside what a person is capable of. Of course, those results were on a Rave(where the system controlled Altitude,Righting Moment and Pitch Attitude-one more function than required on a Moth),an I14 foiler and a 16' monofoiler and do not predict whether or not a manual system would be faster than a wand. But there is little doubt that the boat could be flown manually based on the real world experience with other foilers.
Would manual control result in a speed gain in the Moth class? Impossible to say for sure at this point- but just maybe.
============edit 6/7/07===================
Manual Control Summary
1) at least two Rave 16' multifoilers where a joystik allowed altitude,pitch and RM to be controlled manually.
2)16' bi-foil monofoiler: manual control of the mainfoil flap/21 foot bi-foiler under development: manual control of main foil and rudder foil simultaneously or separately/interchangeable with wand system.
3) David Luggs I14-first two person bi-foiler to sail: manual control of rudder flap only(small main foil largeer rudder foil)
4)John Slatebo's Slatts 22 and 16: proa's utilizing manual control of righting moment with single main foil.
5) Rush Randle(and others)foilboard: manual altitude control with weight movement /sail movement.

[frosh]

Please don't assume that I know little about the wand system and twist grip on the tiller of the Moth as in the Fastacraft Version.
Give me a little credit please!
Furthermore I once raced scow Moths in big winds and seas in Perth Western Australia, and this much more stable craft is still an absolute handful, particularly for the lighter sailor. How many Int Moths have you raced in demanding conditions? Therefore I will put it politely: most of what say is coming thru your hat.
Also you have an infuriating quality of often denying what you clearly stated a few posts back. I will quote one from you, but there other quotes also, I just can't be bothered to collect them all, and copy and paste. Try this one anyway!

I still see potential advantages to using manual main foil flap adjustment-perhaps tied in to the rudder foil flap at some particular ratio- in the Moth class. And from my limited experience using manual mainfoil flap control(with separately adjustable rudder foil flap) on a bigger boat I'd say the advantages would be substantial in heavy conditions where I've read that the Moth wand has some trouble particularly downwind in big waves.
But it would take committment and some time to fully develop a good manual system in that class.... QUOTE - Doug Lord - Post #527

Try to get some integrity into your own arguments, that means admit to what you have already said, and above all, take responsibility for your own actions.

[frosh]

If it is possible but just a bit more difficult to learn according to you;

to the crew-a new skill to go along with a new function for the twist grip-yes. Something even remotely impossible-hell no. Only a little difficult to learn.
QUOTE - Doug Lord - Post# 531

Maybe we can solve the argument regarding all these great ideas you invent to improve the Int. Moth. Only you assume that it is in desperate need of improvement.
Buy one, modify it to reflect the improvements you suggest, test the new version yourself, and learn to sail the Moth reasonably well yourself with your new mods fitted, then tell us on the Forum if it did, or did not work as well as John Ilett's production version. If you can't (and most of us already know the answer) HAVE SOME HUMILITY and keep a much lower profile. You might think that your postings are helping the class develop into a higher performing sailing machine, and that you are responsible for large advances about to occur in hydrofoil sailing, but come on; neither is remotely close to being true!

[sigurd]

It's actually a requirement for stable pitch-heave coupling that the forward foil react faster to heave than the aft foil. The forward foil should control heave and the aft foil should control the pitch attitude.

Not sure I understand what you ment here: Are you saying the wand should definately be coupled to the front foil?

On another note, Alans & Co's 14ft in the pic on the prev page, was controlled manually by rudder flap, or rudder incidence?

[Phil Stevo]

The other advantage of the wand operated main flap is that at low speed and low height the wand pushes the flap down, increasing foil camber and lift coefficient and assists early take off.
When normal ride height is achieved the flap is up near neutral, reducing lift and reducing drag so that the boat can now go faster.
This does not occur with a fixed sytem like Dave Lugg used, nor with the all moving main foil as used by Ian Ward on his present moth.

Conversley the flapped rudder foil works in reverse, and is probably detrimental in this aspect.
Up flap and low drag is used to raise the bow and increase incidence on the main foil for take off and consequently this reduces lift coeff of the rudder foil when more lift would be useful,
and down flap to lower the bow and reduce the incidence on the main foil at high speed, at the same time increasing drag on the rudder foil because of the increase in camber.

The all moving AStevo system used on the bladerider does not have the disadvantage of the rudder flap's increased drag at high speed but also does not have the low drag advantage like the wand operated main flap at high speed.

As Tom said earlier there is some advantage in having both flap and variable incidence on the rudder foil to get the best of both worlds.
An intersteing mechanical challenge to build.

Sigurd, David Lugg/Alan S's 14 used a flap on the rudder foil for altitude control connected to the ext. tillers and activated by twisting except that I think they had two tillers.
On the 14 the main foil was quite small and the rudder foil was larger....
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Phil, somewhere in this thread(edit- wrong: in the "Foiler Design" thread) is an illustration by Tom of an interconnection system between the mainfoil, rudder foil and wand. I'll try to find it later.
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Comments Tom Speer made in "Foiler Design" post 324 about the difference between an all-moving foil and a foil with a flap:

Originally Posted by tspeer

The ideal would be to still be operating in the drag bucket. Looking at the data, it looks like flaps rather than incidence are the way to go.

The Fastacraft foils are a NACA 63412 section with a 120mm chord - Reynolds number of 66,000 per kt; say Re = 500,000 for takeoff. The profile drag is pretty constant from a lift coefficient of 0.1 to 0.7. This is where you want to operate. Say you designed the foil to take off at a lift coefficient of 1.2. The profile drag coefficient there is 0.01894, but at a lift coefficient of 0.6, the profile drag coefficient is 0.00816. So it would be better to double the area of the foil - that would cut the profile drag at takeoff by 14%.

With flap you can extend that to a coefficient of 1.0 or better. But with the bigger flaps and bigger flap deflections, there's such a strong suction peak at the hinge line that I wonder how good the predictions are. The hickup in the lift curve occurs when the transition (via laminar separation bubble) jumps from the flap to just behind the leading edge. The larger flaps extend the drag bucket a bit more. The best section lift/drag ratio looks to be with a 30% chord flap, operating near zero angle of attack.

I rather suspect XFOIL tends to overpredict the maximum lift. But the max lift doesn't seem to be very sensitive to the size of the flap. Flaps definitely increase the max lift, however.

To use the previous example, you could use a 30% chord flap to take off at a lift coefficient of 0.9. That would be a foil 1/3 larger than the unflapped foil that used incidence to take off at a lift coefficient of 1.2. But the drag coefficient would be 0.00872, saving 40% in profile drag once you took the different foil sizes into account. Using the flap to take off at a lift coefficient of 0.9 vice using incidence and no flap to take off at the same lift coefficient (same sized foils) would save 35% in profile drag.

Of course, the induced drag will be big contribution. But if you use full span flaps, the induced drag of the flapped and incidence cases will be pretty much the same.

Judging by the photos I've seen, the pitch attitude seems to be high. So I suspect the main foil is undersized. A bigger stern foil won't help because the load is being taken by the forward foil, and it has to trim at the same angle of attack to carry the load. Increasing the span would significantly reduce the induced drag at takeoff, too. So you might try a longer main foil and see if that is a worthwhile trade of takeoff performance versus extra drag at high speed or when hullborne.

I think that the following represents a great idea with a wand system-at least as an experiment. I also believe that it would be ideal to try a manual setup with manual inputs where Tom shows "wand input" in the sketch below. Anybody that's ever sailed a wand system knows there are conditions where the wand puts in too much input to the flap-a manual system would eliminate this-among its other potential advantages.
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From Tom Speer page 23, post 35 of Foiler Design:

Originally Posted by tspeer

I don't think the flap deflection has anything to do with whether the boat is in a steady-state condition or not. The flap deflection is controlled by the wand, and is only determined by the flying height. In the photo, if the flap was deflected upwards, it was because the boat was trying to fly out of the water!

There's only an indirect correlation between flap angle and speed. Let's assume that the wand is set so the flap angle is zero when the boat is at its design flying height. With, say, a level pitch attitude, the lift on the foil will only be correct at one speed. At higher speed, that same angle of attack will produce more lift, which is more than the weight being carried by the foil. As the boat rises up, the wand will deflect the flap up to counter the rise. The boat will trim out at the height that corresponds to the flap deflection that brings the lift back down to equal the weight.

The problem with this is speed and height become coupled, and the flap is not powerful enough to counter substantial changes in angle of attack due to changes in pitch attitude. The wand does a good job of regulating the height once the boat is trimmed, but asking it to do the trim function, too, is using up a lot of its control power.

Adjusting the incidence of the main foil would be an option. For example, the incidence and flap deflection could be linked together like an antiservo tab. This would reduce the incidence at the same time it deflected the flap up. One problem with this is it increases the hinge moment compared to just using incidence control alone.

I think the answer is to start controlling pitch as well as heave. The aft foil could be given a flap of its own that the pilot could use to adjust the pitch trim, and thus the flying height and main foil flap deflection. Just what a Moth sailor needs - another thing to operate! Or maybe the aft foil could be run with a wand of its own.

I think a more promising solution is to add a forward/aft foil interconnect. The aft flap would be linked to the forward flap so that they moved in opposite directions. As the boat rose up, the wand would deflect the forward flap up to reduce the lift on the main foil. But it would also deflect the aft flap down which would reduce the pitch attitude and also reduce the lift on the main foil. The flap acts immediately, but the rudder foil takes effect a little later because it's not until the pitch attitude has changed that change in lift is seen. However, in the long term, the net effect is much more powerful.

It would be possible to sum a manual trim input with the interconnect to the aft flap. The attached sketch shows a schematic of how it can be done. When the trim input is fixed, the two flaps move in opposite directions in response to the wand movement. If one considers the wand to be fixed in position, the trim input moves the rudder flap. Adjusting the ratio of aft flap to forward flap movement provides a means to tune the system for best performance. Naturally, Morse cables are probably a better way of mechanizing the system, rather than the pushrods shown. But the action would be the same.

Friction and having two surfaces instead of one may be tough for a wand to drive. After all, the energy to activate the controls comes from drag on the wand and you don't want any more of that than absolutely necessary. So it maybe desirable to put some kind of hydrodynamic balance on the flaps.

I wouldn't rule out external flap foils, either. It's a lot easier to arrange the pivot on the flap to make it balanced and it can form a slotted flap for high lift on takeoff if that's desired. At low flap angles, the main difference between an external flap and a single element section of the same total area is the drag of the brackets needed to support the flap. There may be enough other advantages to make the bracket drag worthwhile.

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Sketch of Toms idea:

[sigurd]

Hello Jon, I had stopped reading this thread for a while until now (no sleeping):

A tentative question:

This is not my area, but having been induced to look around this forum this thread is getting interesting. It occurs to me that conventional, ie, non-foiling monohulls with moth-like performance could be sailed entirely without the provision of rudder surface below the aft foil if a yawl-like rig is used, ie, the mizzen becomes the (aerodynamic) rudder and, as long as the boat is slippery enough to travel at a good fraction of the wind speed no water rudder is needed.

If this is applied to a foiler with a submerged foil on the daggerplate/centreboard and the rudder horizontal surface is made into a planing surface, ie, a ventilated foil running on the water surface so that it does not create sideforce then this principle may work here as well. This should give slightly lower trim drag, even if it doesn't it would at least be fun to play with; blasting around the harbour with only a couple of sheets in hand and no tiller. It's not a Moth, is it an interesting possibility?


Jon.

Then I read this, and thought you might find this one sheet kite proa funny?