Foiler Design

i think it ruins any notion of a good spanwise lift distribution!

 

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You're right but they work very well.

 

cool, does it fly? what boat is it?

 

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As I said it is an experimental design. On the F3 model the boat takes off in very light air(5 knots) and will go 2.5 times wind speed in those conditions.
I used almost the same foil planform on my 16' bi-foiler and the boat foiled but had other problems so I have no clue whether that foil planform is successfull on a full size boat. I will learn a lot more before long since I'm using those foils on my new boat BUT I will have new foils with full span flaps to compare them with.
F3 :

 

if your flap is soft, no bind, at least with the membrane flap

 

New Moth Control System

I'd sure like to hear Tom Speers and Alan Smiths opinion of this new Moth control system: the dual bow wands control the RUDDER flap and the mainfoil flap is controlled by the twist grip extension tiller.

 

What do YOU think Doug?

As you've said, you made the first pioneering foiler with twist grip tiller extension control ten years ago. Do you think this will have the same level of success you did?

With all your experience on the aeroSKIFF mark 1 and the F3, you are probably better qualified to respond to this as you have practical on-the-water "time in the saddle".

The Moth certainly looks good, and I'm sure they had good reasons to try this configuration, as they could have followed the crowd but chose not to.

This may just be vindication for your manual control theory - where they adjust ride height by the twist grip, and allow automatic pitch control via the dual wands. Who knows, they may even be decoupling the two sides of the rudder foils - one to each wand!

On another note, shouldn't you be giving your lawyer a ring-a-ding? I'm sure this may breach one or more of your patents, and this may be your lottery ticket.

--
Bill

 

New moth control system

Doug Lord has requested my response
I am sorry I have not been following the foiler and moth threads of late and certainly do not understand “two wands and man in the loop twist grip control of main foil flap”. As a side issue it would be convenient to refer to the main foil control surface as flap and the rudder one as elevator.
There are two control loops involved in stable level “flight”. The first is pitch attitude, the second is height itself. A bow mounted wand achieves both, from a control system point of view, very robustly. The other aspect of “flying” if take off and for this low induced drag is critical and best achieved by the largest span practical. Too much foil area increases form drag and lowers “flight” speed. Stability at the moment of take off is not that important. Hence for take off high camber of both foils (mainly achieved by trailing edge down of both flap and elevator) and near as you can get equal pressure loading of both foils is necessary. Once airborne stability is paramount. This necessitates unloading the rudder foil by moving crew weight forward or sail thrust or both. Using a “wand to flap” control and tiller twist trim of the elevator the boat can set the up with an optimum pitch attitude at the height the wand force the boat to fly at. The higher the speed the less flap required and the boat flies higher as the speed increases unless an adjustment of the wand to flap linkage is introduce, either mechanically or by pressure on the wand to force it deeper into the water, the later increasing drag and being difficult at elevated speeds.
Now to hold near constant height over waves; this is greatly assisted by quick changes in attitude augmenting the flap attempting to lift the boats total mass. Control through the elevator is the best way of achieving a fast attitude change. Hence a configuration worth considering is wands to both flap and elevator and tiller twist height trim by changing the linkage length between wand and flap. There are two problems in controlling the elevator from a bow mounted wand and that is with an on coming wave the elevator needs to be trailing edge up but for takeoff trailing edge down. The wand cannot tell the difference! Secondly if the elevator wand is set to aid lift (TE down when height is low) when in “flight” the elevator will pitch the bow down as the flap tries to lift the boat and careful selection of gearing is necessary. It would be better to place a wand pivot near the rudder and use the difference in bow and stern wand positions to control attitude only via the elevator; and have a mechanical trimmer for that linkage to aid takeoff.
All this gets complicated and when the chips are down there is no substitute for simplicity.

 

Ahhh, yes. The eternal sweetness of simplicity.

Some of us have been pushing that concept from day one, while others seem to find the excessively complicated to be their Siren Song.


A Siren’s Song

In Greek mythology, the Sirens were nymphs that lived on an island called Sirenum Scopuli. They would sing their spellbinding song and lure the passing sailors into the rocks where their ships would be destroyed and they would be devoured.

Odysseus escaped the Sirens by having all his sailors plug their ears with beeswax and tie him to the mast. He was curious as to what the Sirens sounded like. When he heard their beautiful song, he ordered the sailors to untie him but they ignored him. When they had passed out of earshot, Odysseus stopped thrashing about and calmed down, and was released (Odyssey XII, 39).

 

(There is always the Siren's side of things, so here is a poem for your amusement-)

'maggie and millie and molly and may'

maggie amd millie and molly and may
went down to the beach (to play one day)

and maggie discovered a shell that sang
so sweetly she couldn't remember her troubles, and

milly befriended a stranded star
whose rays five languid fingers were;

and molly was chased by a horrible thing
which raced sideways while blowing bubbles: and

may came home with a smooth round stone
as small as a world and as large as alone.

For whatever we lose (like a you or a me)
it's always ourselves we find in the sea

-ee cummings

(emoticon added by your humble poster)

 

Practical experience is always the best teacher but these days validated science can usually assist

 

If I understand what you're describing, the boat is using the rudder foil for height control and the main foil for trim. The drawback I can see in this scheme is the phase lag between the wand and the rudder foil.

I'm not sure what the sign of the gearing is between the wand and the rudder foil. If upward movement of the wand produces trailing edge down deflection of the rudder foil flap, then as the boat starts to pitch down, the rudder foil will make the boat want to pitch down more, and the system will be unstable. If upward movement of the wand deflects the rudder foil flap up, then the feedback will help stabilize the boat in pitch.

However, for the latter case, if a wave hits the wand, that will deflect the flap upward and cause the boat to pitch up. But there's a lag in this response. The flap deflection will accelerate the stern downward, followed by the lift on the main foil flying the boat up. In the mean time, the wave has been progressing past the boat. Depending on the speed, wave length, and direction of travel relative to the wave, the boat may be flying up just as the trough arrives. Or it may be flying up just as the next crest arrives. Or the waves may be arriving so quickly that the boat doesn't have time to react appreciably to the waves, and they just average out.

Height feedback from the wand to the main foil produces an immediate upward acceleration of the boat. But as the upward velocity picks up, the pitch stability will pitch the boat up. I've sometimes thought that linking the two flaps together might produce a combination that would provide a smoother ride than either control separately. Trim control can be mechanically summed with either one.

 

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Thanks ,Tom. I'm going to use a system linking the two flaps together on the new boat in a version controlled with a twist grip tiller extension -and a version controlled with a midship wand.
I want to have the mixing between the two flaps fully adjustable so that ,for instance, it is variable between the rudder flap moving the same amount as the mainfoil flap to 50% or less- adjustable incrementally.
Do you have any suggestions for implementing this?
Here is a sketch you did a while back:

 

Doug
Yes, linking both flap and elevator to the one wand is workable profided their motion is opposite to one another. However you really need both flap and elevator trailing down for earliest possible lift out. It is possible for your trim adjustment to achieve this but you may have difficult adjusting the trim quickly enough for the "in flight"condition.

Movinng the wand to the centre of the boat looses valuable rate of climb information that enhances height stability. So be prepared to move it back if you run into difficulties.

Setting the system up to best travis waves is a big challenge, a gear ratio (flap angle as a function of height) that suites one wave frequency may be diabolical in another. You could go from hobby horsing at one setting to 180 degrees out of phase. I did significant analysis in this area for Ian Ward about 3 years ago and could brush the dust off it if you are interested.

alans