142 replies to this topic

[Suppenkelle]

Impressive as it is, this is just one short video. I'd recommend to collect some more experimental data before chopping the tips of your foils and replacing them.

Burkh

[2005]

[I have a tilting mainfoil, no flap. When I ventilate, it loses lift, like every other foil. My compensating mechanism instantly throws the foil into a negative AOA as the foil re-enters the water. Rather than crash, the foil frequently simply reattaches instantly and establishes lift again - before the hull touches the water. It was not a designed feature of the system, but it has saved me many times. It is not universally effective but it illustrates the point that lowering the angle of attack gets rid of bubbles - quickly even, presumably by increasing the pressure on the low pressure side of the foil. But anyone who has ever done a quick tiller jab to reattach a vented rudder knows that.

Shedding bubbles may happen more quickly on a foil without a hinge gap regardless of AOA though. They are no surface irregularities at all and no gap at the foot of the vertical.

[/quote]

I would be very interested in hearing about your tilting main foil. How is it constructed and how is it working in practice, seems to me that you would have a lot of movement compared to a little flap moving?

[Phil S]

OK I got the videos confused. The one from post 1 is the mainfoil with flap, and the one in post 47 is the rudder without flap.
The ventilation near the tip we are discussing is on the first video.
I think the std M2 foil Bora is using has a full span flap, Bora confirm?

So why is the bubble retained inboard of the tip? I think pcraig is getting closest. Something about the section or change in leading edge profile as the foil tapers. Or maybe outboard of that point the sweep aft is enough to shed the bubble.

pcraig's recommendations for twist is as used in aircraft to prevent stall initiation near the wing tips, which makes for instability at low speed. It would seem valid here for similar but not completely related reasons. The problem with twist at high speeds is the torque loads applied to the section, and the higher drag at the tips if the AoA is reduced below the section optimal angle locally.

For the rudder twist is a no no as it operates at various times in both negative and positive AoA depending on where the skipper is located fore and aft.

[now_what]

So why is the bubble retained inboard of the tip? I think pcraig is getting closest. Something about the section or change in leading edge profile as the foil tapers. Or maybe outboard of that point the sweep aft is enough to shed the bubble.

I'm thinking the conversation needs Bora to eliminate some variables:
- how clean was the foil?
- how is port different from starboard end of foil ( the few tacks shown in post 1 display no vortex on starboard span)
- Is Bora suggesting "there ain't no sunshine when she's gone..." ( the tune)
- Bora's next video to tune of "dirty deeds done dirt cheap" suggests he may be vigorously yanking our collective chains...
-- vid 2 "goofing off" http://www.youtube.c...h?v=CHWLk6JQ-DE
-- http://www.goof-off.com/

Perhaps time for Bora to stop laughing and come clean....

..NW

[atg]

I would be very interested in hearing about your tilting main foil. How is it constructed and how is it working in practice, seems to me that you would have a lot of movement compared to a little flap moving?

I have posted about it here before so no need to rehash. Basically it tilts, pivoting at the hull exit. When I do it again it will be different, but this seems to work well in a certain set of conditions, which frankly is more than I expected from a first attempt.

Need to dial on some height here, but you get the general idea:
 China_Girl_flyby.JPG   208.07K   37 downloads

The ski is not kind to wavelets, esp. since I slowed the foil action down:
 China_Girl_Flyby2.JPG   197.35K   47 downloads

But the boat doesn't seem to mind the added drag much, and (mostly) neither do I:
 ChinaGirl_Flyby3.JPG   327.81K   42 downloads

all photos courtesy The Black Pearl & co (many thanks Richard)

Sorry for hijack - back to ventilation now.

[The Black Pearl]

Liz (the photog) always commented "That thing at the front caused lots of spray". Think she is confirming your comment about the ski and chop. Although must say when we sailed in +20s, didnt see it so pronounced. May be twist offsetting or the general mayhem of foiling when windy, but man it was fast!

[atg]

Liz (the photog) always commented "That thing at the front caused lots of spray". Think she is confirming your comment about the ski and chop. Although must say when we sailed in +20s, didnt see it so pronounced. May be twist offsetting or the general mayhem of foiling when windy, but man it was fast!

The faster it goes, the less the ski digs in, and the less spray. I could use a bigger one and put a step in it but it's kind of fun making all that spray! Learned lots about planing surfaces sailing with that thing; it will get small again soon.

[viva la figa]

Liz (the photog) always commented "That thing at the front caused lots of spray". Think she is confirming your comment about the ski and chop. Although must say when we sailed in +20s, didnt see it so pronounced. May be twist offsetting or the general mayhem of foiling when windy, but man it was fast!

The faster it goes, the less the ski digs in, and the less spray. I could use a bigger one and put a step in it but it's kind of fun making all that spray! Learned lots about planing surfaces sailing with that thing; it will get small again soon.

hay there Carl glad to see the boat coming along nicely. Thanks again for that fantastic sail a while back at abyc with the mckey bros et al...just let me know any time you need a test pilot hahaha

phil

Attached Files

•  phil_moth_sailing.JPG   393.34K   21 downloads

[bgulari]

that is an impressive wave behind your ski.


on a side note anyone notice that Douglas might have either missed a patent opportunity or has actually got someone qualified to build something. Around page 6 of latest Sea Horse. Looks like a drawing similar to his rotating hull with keel to cant to more that 90 degree, in something about 18 ft long but that is just a guess.

[FIGJAM]

Do you guys think cavitation will be a problem in Dubaiii? I am amazed when I go overseas to race, the problems that you guys face and talk about everyday, we never ever have them, does that mean im not flying high enough ??

[wind_apparent]

on a side note anyone notice that Douglas

WHO? ...........

[bgulari]

So why is the bubble retained inboard of the tip? I think pcraig is getting closest. Something about the section or change in leading edge profile as the foil tapers. Or maybe outboard of that point the sweep aft is enough to shed the bubble.

I'm thinking the conversation needs Bora to eliminate some variables:
- how clean was the foil?
- how is port different from starboard end of foil ( the few tacks shown in post 1 display no vortex on starboard span)
- Is Bora suggesting "there ain't no sunshine when she's gone..." ( the tune)
- Bora's next video to tune of "dirty deeds done dirt cheap" suggests he may be vigorously yanking our collective chains...
-- vid 2 "goofing off" http://www.youtube.c...h?v=CHWLk6JQ-DE
-- http://www.goof-off.com/

Perhaps time for Bora to stop laughing and come clean....

..NW

Well I am really laughing now besides you are reading way too much into the music selection. Try putting videos on you tube there is a lot of copyrighted music that the you tube police wont let you use. I have used both of the bands many times before and I was just being lazy more than anything. The AC/DC might have been for a specific guest but who knows.... I was flying as high as practical in the videos also(clue)
fairly surprised no one has really figured out the real purpose of the videos(teknologika has) but there are some visual clues.

@phils that was all standard M2 kit,

@nowwhat
The foil was clean and fair
the reason you dont see any ventilation on the other tip is because the boat will naturally fly a little lower when the wand is on the leeward side, and there is no place really to mount the camera without making a fancier contraption.


a little prepeg to ooo and ah at,

Do you guys think cavitation will be a problem in Dubaiii? I am amazed when I go overseas to race, the problems that you guys face and talk about everyday, we never ever have them, does that mean im not flying high enough ??

think the bigger issues will be dodging the plastic

Attached Files

•  photo.jpg   107.94K   123 downloads

[Doug Culnane]

@FigJam: Cavitation is the water vaporizing and happens on propellers. On Moths we get Ventilation which is air from the surface getting sucked to the foil. The water is warm in Dubai so ventilation does not seam to happen as much in warm as cold water see other threads.

The tip vortex does not happen at the tip but if you look at the colorful CAD thing that was posted in this thread from Si's blog then it predicts the low pressure blue spots inboard of the tip. I do not know enought about this to really understand it but trying to put 1+1 together. Looks to me like the plan form and section is such that that the vortex is created inboard of the tip and this is predicted with the CFD model, and showen with Bora's Videos.

[pcraig]

Just tried to use fast reply and it crashed on me!

Anyway, Doug, you are right the tip vortex will move inboard but at or near the leading edge it will be pretty much be at the tip and will extend inboard as the vortex grows downstream.

It could be that the ventilation bubble is being held by the vortex system, possibly, but I think that with a carefully designed section you should be able to shake this off. Also the effect on the spanwise loading when the flap is at a non-zero position may cause a large gradient near the tip which makes the local section less able to re-attach.

As for washed out tips not working on a rudder foil due to its requirement to work in both positive and negative incidences, I disagree. Its simply a case of finding the neutral point, and from there it should work. Given that the foils are made from black stuff I'm sure you can make them strong enough to cope!

[wind_apparent]

a little prepeg to ooo and ah at,

 photo.jpg   107.94K   49 downloads

Sexy........ interesting layup. Is that 12k twill clear with alternating layers 3k plain black?

[now_what]

fairly surprised no one has really figured out the real purpose of the videos(teknologika has) but there are some visual clues.

Ok, so that made me go back and look again at the vids.

Are you getting at the systemic effects between a vortex on the main foil and the rudder foil, in the wash of the mainfoil vortex?

Given every foil has some vortex slows of some sort, minimizing interference between two foils is an easier "fix" with better return for the effort, than a lot of head scratching over how to minimize the vortex you've already got.

Clearly the main foil vortex can perpetuate a long way behind the rudder foil, and occurs further inboard than a lot of people thought.

This suggests that the rudder foil span ( tip to tip) needs to be considerably less than the span of the main foil, At the most the span of the rudder foil cannot exceed the distance between the inboard "edges" of the vortices on the main foil tips. If it does exceed that then the rudder foil is always in some pretty screwed up flow.

However this brings in the relative depths of the rudder foil and main foil; given the rudder is shallower (closer to surface) , the vortex would need to come to the surface to some degree ( the air in it ?) to interfere with the rudder foil a lot.
I guess that is your point, the vortex shows as a surface ripple / waveform, well above the mainfoil after the vortex has formed.


I wonder what the smallest rudder foil span that "will work" would be?

In terms of the albatross, the damn bird has almost no tail feathers.

[bgulari]

looking way to far into it. Maybe the youtube degrades the video enough but it was just to determine the min amount of foil in the water that i could sail with. notice the black marks. 2 inches apart and the top ones are 14 in above the horizontals

[The Black Pearl]

Liz (the photog) always commented "That thing at the front caused lots of spray". Think she is confirming your comment about the ski and chop. Although must say when we sailed in +20s, didnt see it so pronounced. May be twist offsetting or the general mayhem of foiling when windy, but man it was fast!

The faster it goes, the less the ski digs in, and the less spray. I could use a bigger one and put a step in it but it's kind of fun making all that spray! Learned lots about planing surfaces sailing with that thing; it will get small again soon.

hay there Carl glad to see the boat coming along nicely. Thanks again for that fantastic sail a while back at abyc with the mckey bros et al...just let me know any time you need a test pilot hahaha

phil

Viva Phil,

Come and join us, we're buidling a fleet and already have 4 boats inc Karl out of ABYC. PM me of your looking for a second hand boat.. Sorry karl, couldnt resist it!

Do you guys think cavitation will be a problem in Dubaiii? I am amazed when I go overseas to race, the problems that you guys face and talk about everyday, we never ever have them, does that mean im not flying high enough ??

Are there still tons of Jellies in spring time?

[kprice]

looking way to far into it. Maybe the youtube degrades the video enough but it was just to determine the min amount of foil in the water that i could sail with. notice the black marks. 2 inches apart and the top ones are 14 in above the horizontals

For drag reduction, the anhedral mail foil worked well for the hydrofoil windsurfer that R. Miller did 10 years ago.
The benefit is that you can sail with less vertical strut in the water.
The penalty is that since there is more induced drag since some of the lift is cancelling out due to the anhedral.
Also, the joint gets harder to make.
R. thought that the net was positive, i.e. the reduction in drag from less strut immersion was more that the increase in drag due to the lift cancelling out due to anhedral.

In the times I sailed it, I did not notice the adverse stability effect that Phil S. mentions, but foiling on a windsurfer is much different that foiling on a Moth in terms of balance. It was standard to sail with 15 or 20 degrees of windward heel in the board.

KP

[teknologika]

looking way to far into it. Maybe the youtube degrades the video enough but it was just to determine the min amount of foil in the water that i could sail with. notice the black marks. 2 inches apart and the top ones are 14 in above the horizontals

For drag reduction, the anhedral mail foil worked well for the hydrofoil windsurfer that R. Miller did 10 years ago.
The benefit is that you can sail with less vertical strut in the water.
The penalty is that since there is more induced drag since some of the lift is cancelling out due to the anhedral.
Also, the joint gets harder to make.
R. thought that the net was positive, i.e. the reduction in drag from less strut immersion was more that the increase in drag due to the lift cancelling out due to anhedral.

In the times I sailed it, I did not notice the adverse stability effect that Phil S. mentions, but foiling on a windsurfer is much different that foiling on a Moth in terms of balance. It was standard to sail with 15 or 20 degrees of windward heel in the board.

KP

I don't think that the join would be any harder to make than a straight one, at least not how I make my T's. One of PhilS' early foils had dihedral so he is talking from practical experience. As I understand it, a main-foil with more dihedral will have better roll stability (at least that is why they add it to aircraft, however aircraft don't use windward heal to get height upwind like we do), however it has nothing to do with drag reduction.

Please note I went to the wikipedia school of aerodynamics , so if I am wrong, please be gentle.

[gui]

looking way to far into it. Maybe the youtube degrades the video enough but it was just to determine the min amount of foil in the water that i could sail with. notice the black marks. 2 inches apart and the top ones are 14 in above the horizontals

For drag reduction, the anhedral mail foil worked well for the hydrofoil windsurfer that R. Miller did 10 years ago.
The benefit is that you can sail with less vertical strut in the water.
The penalty is that since there is more induced drag since some of the lift is cancelling out due to the anhedral.
Also, the joint gets harder to make.
R. thought that the net was positive, i.e. the reduction in drag from less strut immersion was more that the increase in drag due to the lift cancelling out due to anhedral.

In the times I sailed it, I did not notice the adverse stability effect that Phil S. mentions, but foiling on a windsurfer is much different that foiling on a Moth in terms of balance. It was standard to sail with 15 or 20 degrees of windward heel in the board.

KP

Hey Kirk, how does the Miller contraption turn? Did he try a tripod setup in his early trials? "Just" curious.

[gui]

looking way to far into it. Maybe the youtube degrades the video enough but it was just to determine the min amount of foil in the water that i could sail with. notice the black marks. 2 inches apart and the top ones are 14 in above the horizontals

For drag reduction, the anhedral mail foil worked well for the hydrofoil windsurfer that R. Miller did 10 years ago.
The benefit is that you can sail with less vertical strut in the water.
The penalty is that since there is more induced drag since some of the lift is cancelling out due to the anhedral.
Also, the joint gets harder to make.
R. thought that the net was positive, i.e. the reduction in drag from less strut immersion was more that the increase in drag due to the lift cancelling out due to anhedral.

In the times I sailed it, I did not notice the adverse stability effect that Phil S. mentions, but foiling on a windsurfer is much different that foiling on a Moth in terms of balance. It was standard to sail with 15 or 20 degrees of windward heel in the board.

KP

I don't think that the join would be any harder to make than a straight one, at least not how I make my T's. One of PhilS' early foils had dihedral so he is talking from practical experience. As I understand it, a main-foil with more dihedral will have better roll stability (at least that is why they add it to aircraft, however aircraft don't use windward heal to get height upwind like we do), however it has nothing to do with drag reduction.

Please note I went to the wikipedia school of aerodynamics , so if I am wrong, please be gentle.

It sort of has to do with drag reduction. If you believe that more rudder surface is less draggy than more strut ...

[gui]

I would be very interested in hearing about your tilting main foil. How is it constructed and how is it working in practice, seems to me that you would have a lot of movement compared to a little flap moving?

I have posted about it here before so no need to rehash. Basically it tilts, pivoting at the hull exit. When I do it again it will be different, but this seems to work well in a certain set of conditions, which frankly is more than I expected from a first attempt.

Need to dial on some height here, but you get the general idea:
 China_Girl_flyby.JPG   208.07K   37 downloads

The ski is not kind to wavelets, esp. since I slowed the foil action down:
 China_Girl_Flyby2.JPG   197.35K   47 downloads

But the boat doesn't seem to mind the added drag much, and (mostly) neither do I:
 ChinaGirl_Flyby3.JPG   327.81K   42 downloads

all photos courtesy The Black Pearl & co (many thanks Richard)

Sorry for hijack - back to ventilation now.

Looking good Karl ...

[kprice]

looking way to far into it. Maybe the youtube degrades the video enough but it was just to determine the min amount of foil in the water that i could sail with. notice the black marks. 2 inches apart and the top ones are 14 in above the horizontals

For drag reduction, the anhedral mail foil worked well for the hydrofoil windsurfer that R. Miller did 10 years ago.
The benefit is that you can sail with less vertical strut in the water.
The penalty is that since there is more induced drag since some of the lift is cancelling out due to the anhedral.
Also, the joint gets harder to make.
R. thought that the net was positive, i.e. the reduction in drag from less strut immersion was more that the increase in drag due to the lift cancelling out due to anhedral.

In the times I sailed it, I did not notice the adverse stability effect that Phil S. mentions, but foiling on a windsurfer is much different that foiling on a Moth in terms of balance. It was standard to sail with 15 or 20 degrees of windward heel in the board.

KP

Hey Kirk, how does the Miller contraption turn? Did he try a tripod setup in his early trials? "Just" curious.

Rich has a mechanism to jibe the front (planing) canard. Pull a string on the boom to get it centered, then jibe like a normal board, then pull a string to set the heel on the new side. Total angle is close to 90 degrees, which is also about the angle of the anhedral.

So yes (per your later comment) , you have to believe that wing area is less draggy than strut immersion.

Others tried a trifoil/tripod canard but there is too much yaw disturbance due to chop if the canard is not nominally flat on the water.

[Phil S]

Planes use dihedral for roll stability yes, but the also do not fly with a substantial side loading like boats do, and also do not fly at as slight yaw angle due to leeway caused by that side load.

In fact if a plane with dihedral tries to fly with some angle of yaw the wing which is yawed forward sees the apraoching air at a higher angle of attack than the wing which is yawed aft, and this creates more lift on the yawed forward wing and the plane rolls away from the forward wing. This is the exact process used to control simple radio control aircraft which have rudder and dihedral instead of ailerons.

Both Ian Ward and myself tried dihedral main foils years ago and we both found that the yaw effect from leeway gave a noticable roll to windward, enough to require sitting in from fully hiked. Sounds good but it was very inconsitant and difficult to predict and manage to benefit. So we do not use it now.

Some of this affect is neutralised when we sail efficiently healed to windward and use the canted lift from the main foil to balance the side loadings and hence eliminate leeway. No leeway= no yaw effect, so maybe now that we understand and execute the science better a dihedral foil might be worth another go.

Anhedral would be expected to impose a leeward roll with leeway so lgically would make sailing more difficult.

[gui]

Planes use dihedral for roll stability yes, but the also do not fly with a substantial side loading like boats do, and also do not fly at as slight yaw angle due to leeway caused by that side load.

In fact if a plane with dihedral tries to fly with some angle of yaw the wing which is yawed forward sees the apraoching air at a higher angle of attack than the wing which is yawed aft, and this creates more lift on the yawed forward wing and the plane rolls away from the forward wing. This is the exact process used to control simple radio control aircraft which have rudder and dihedral instead of ailerons.

Both Ian Ward and myself tried dihedral main foils years ago and we both found that the yaw effect from leeway gave a noticable roll to windward, enough to require sitting in from fully hiked. Sounds good but it was very inconsitant and difficult to predict and manage to benefit. So we do not use it now.

Some of this affect is neutralised when we sail efficiently healed to windward and use the canted lift from the main foil to balance the side loadings and hence eliminate leeway. No leeway= no yaw effect, so maybe now that we understand and execute the science better a dihedral foil might be worth another go.

Anhedral would be expected to impose a leeward roll with leeway so lgically would make sailing more difficult.

Sorry. I'm getting the terminology mixed up ... That's anhedral that I'm talking about.

[atg]

Sorry. I'm getting the terminology mixed up ... That's anhedral that I'm talking about.

Upwind I can't see much of a stability issue, provided the whole thing is heeled properly. Sure the more deeply immersed wing half picks up yaw load and it is not on centerline so might decrease the righting moment a bit, but then the vertical lift is cranking onto the leeward half with increasing heel, so perhaps these would cancel each other out to a large degree, and perhaps one can simply heel further with this setup to compensate for the decreased leverarm.

Getting the tips down buys Bora a couple more marks on his daggerboard before ventilation, which seems relevant given the vids being shot at all. This effect increases with the span of the foil; one could go considerably higher span with anhedral, though this may not really be necessary. Might make a light air weapon though.

Gybing seems like where you would pick up the leeward roll Phil mentions, but we counter a lot of leeward roll moment the way it is, so it is only a question of whether a different technique (go to the new side earlier? hike harder there earlier?) might compensate and whether the effect develops too suddenly or overwhelmingly for the helm to react. Maybe slip some other design tricks in to compensate.

It is trickier to join three foils than two and of course doubling the number of flaps.

Kirk the yaw effect of the sensor (and the stability I guess) would seem to depend hugely upon the angle of the dangle, as Steve Clark calls it. I mean, there's anhedral, and there's ANHEDRAL. I can't see running 45deg per side on a Moth. Pick a number, any number...

[gui]

[...]

Kirk the yaw effect of the sensor (and the stability I guess) would seem to depend hugely upon the angle of the dangle, as Steve Clark calls it. I mean, there's anhedral, and there's ANHEDRAL. I can't see running 45deg per side on a Moth. Pick a number, any number...

mine's from a 2x4 that was lying on my shop floor. Maybe next time I'll use somebody's brain before i glue stuff together.

[atg]

[...]

Kirk the yaw effect of the sensor (and the stability I guess) would seem to depend hugely upon the angle of the dangle, as Steve Clark calls it. I mean, there's anhedral, and there's ANHEDRAL. I can't see running 45deg per side on a Moth. Pick a number, any number...

mine's from a 2x4 that was lying on my shop floor. Maybe next time I'll use somebody's brain before i glue stuff together.

At least it hasn't fallen apart; first things first!

[dr.lojz]

The tip vortex does not happen at the tip but if you look at the colorful CAD thing that was posted in this thread from Si's blog then it predicts the low pressure blue spots inboard of the tip. I do not know enough about this to really understand it but trying to put 1+1 together. Looks to me like the plan form and section is such that that the vortex is created inboard of the tip and this is predicted with the CFD model, and showen with Bora's Videos.

@Doug can I ask for the link, Iam too stupid to found it the Si's blog, you write about.

Well I was put together the idea based on Giga flaps on next level.........
More to read here:
http://drlojz.blogsp...astic-flap.html


On request the CAD model and the specifications can be made........

touch and go
dr.lojz

[atg]

touch and go
dr.lojz

Dr.L,

Almost all Moths have full width flaps, so there is no place to put the elastomer fairing. But it is a cool idea.

[teknologika]

touch and go
dr.lojz

Dr.L,

Almost all Moths have full width flaps, so there is no place to put the elastomer fairing. But it is a cool idea.

Here is an example ... from one of my designs "in progress"

 Snapz_Pro_XScreenSnapz039.jpg   13.53K   32 downloads

[Doug Culnane]

@Doug can I ask for the link, Iam too stupid to found it the Si's blog, you write about.

http://sipayne.blogs...den-dragon.html

[dr.lojz]

@Doug can I ask for the link, Iam too stupid to found it the Si's blog, you write about.

http://sipayne.blogs...den-dragon.html

Thanks Doug, I must to apologies my self to mr.S.Payne, sure I was not recognize the Si's blog as him!
Good to have people like him to take care to push the sport and products so far forward!

And not at least, you are only 400km away from my place you know, with the beast regards
from our lake
http://www.bled.si

touch and go
dr.Lojz

[Doug Culnane]

Thanks Doug, I must to apologies my self to mr.S.Payne, sure I was not recognize the Si's blog as him!
Good to have people like him to take care to push the sport and products so far forward!

And not at least, you are only 400km away from my place you know, with the beast regards
from our lake
http://www.bled.si

touch and go
dr.Lojz

You are welcome neighbor. BTW there is a Moth in Croatia that is up for sale.

Si Payne published a few of Amac's CAD drawings, but I do not think he had much design input. I do not really understand the CAD drawing on the linked page but the blue bits are where the air bits on the video are so there must be a link.

I am confused now. Is the consensus that the tip vortex always happens at the very tip or does happen where the air is? I thought the later was the case.

[gui]

[...]

Kirk the yaw effect of the sensor (and the stability I guess) would seem to depend hugely upon the angle of the dangle, as Steve Clark calls it. I mean, there's anhedral, and there's ANHEDRAL. I can't see running 45deg per side on a Moth. Pick a number, any number...

mine's from a 2x4 that was lying on my shop floor. Maybe next time I'll use somebody's brain before i glue stuff together.

At least it hasn't fallen apart; first things first!

It exploded at least 3 times. The matress core was a poor idea, but the bleeder core seems to be doing ok.

[atg]

[...]

Kirk the yaw effect of the sensor (and the stability I guess) would seem to depend hugely upon the angle of the dangle, as Steve Clark calls it. I mean, there's anhedral, and there's ANHEDRAL. I can't see running 45deg per side on a Moth. Pick a number, any number...

mine's from a 2x4 that was lying on my shop floor. Maybe next time I'll use somebody's brain before i glue stuff together.

At least it hasn't fallen apart; first things first!

It exploded at least 3 times. The matress core was a poor idea, but the bleeder core seems to be doing ok.

Nat is perfecting bog core foils out here; seem to be doing OK on the water. My bleeder plan went well but eventually I had these nice windsurfer fins sitting around so I just stuck them on instead.

[teknologika]

Si Payne published a few of Amac's CAD drawings, but I do not think he had much design input. I do not really understand the CAD drawing on the linked page but the blue bits are where the air bits on the video are so there must be a link.

I am confused now. Is the consensus that the tip vortex always happens at the very tip or does happen where the air is? I thought the later was the case.

The image is not from a CAD program, it is from a Computational Fluid Dynamics (CFD) program, in this case ANSYS. The image essentially shows the differences in pressure around the M2 main foil.

The simulation of the M2 main foil flow appears to accurately simulate the tip vortices that are created which can be seen on the surface in Bora's video.

The "air" is completely different. It is occurring because ventilation is allowing air into the flow of water around the foil and it is following a similar flow pattern, because of the water around it.

[DSmith]

best regards
from our lake
http://www.bled.si

touch and go
dr.Lojz

That is one special place! We stumbled upon Lake Bled when driving from Hungary to Italy. At the time, I was wishing that I could charter a 49er to explore the lake. A moth would have been good but I'm not sure about getting the missus on board.

[flutter]

hey, great thread!

flicked through it a couple of times, firstly Bora is that a steel mould for the autoclave? so impressed. im guessing its a rudder. and the shiny black im guessing is uni, so that means theres lots more +-45 carbon that ive seen before, but that makes heaps of sense when i think about it. Im interested to know how you join the top laminate with the bottom. Glue around the edges? bladder mould? spine of some sort? cnc foam core? Anyway thats probably your secret, you might as well keep it!

second, there was a post before about the tail thing with the albatross. youll find that you can actually build gliders with no tails at all (I think that came up earlier as well) except with a moth you get huge pitching forces from the rig, and the tailplane has to keep everything stable. I think the importance of the rudder and the balance between the foils is sometimes underrated. When the force in the rig induced pitching by more than say 0.5 degrees, you have real problems sailing through gusts. eg. boat powers up, pitches down, goes down, foil powers up, bounces back up. (repeat). scary.

[now_what]

second, there was a post before about the tail thing with the albatross. youll find that you can actually build gliders with no tails at all (I think that came up earlier as well) except with a moth you get huge pitching forces from the rig, and the tailplane has to keep everything stable. I think the importance of the rudder and the balance between the foils is sometimes underrated. When the force in the rig induced pitching by more than say 0.5 degrees, you have real problems sailing through gusts. eg. boat powers up, pitches down, goes down, foil powers up, bounces back up. (repeat). scary.

From SA front page article:

The Australian Moth Nationals in Perth were a well run series - well done to John Illet and all at the South Perth Yacht Club. The racing was glamour with a mix of winds - none over 20 knots though - which I think no one missed.

I think the best thing about the regatta was the feeling that we were the entertainers. The number of regatta volunteers who came up to me and said how much fun it was to watch us warmed my heart.

I was on standard Mach2 gear - although up to the the last day I used a cut down rudder hydrofoil that was possibly slipperier, but I could amost never foil tack. With the standard rudder on the last day I seemed just as quick and got lots of foil tacks. The sail was an out of the box MSL13 - no tweaks, not even to the battens.


Interesting comment by AMAC above ("plus ca change" Aussi nats rticle) where he acknowledges chopping his rudder horizontal foil, and that it came at a cost of being able to get foiling tacks in marginal foiling air. However, by all accounts he was virtually unbeatable offwind in these conditions.

Any one know how much of a chop job did those foils get? (photos?)

...nw

[aus_stevo]

Any one know how much of a chop job did those foils get? (photos?)

...nw

no photos, but it looked to be about 30/40mm chopped out each side, just outboard of the bulb. it wasnt much (if any) smaller than what luka and i were running, just a bit smaller than the m2 std. his mainfoil was a bit tweaked also

[dr.lojz]

Axeman again fly over
Mahalo,
a couple nano seconds later,
here we are or I am again.
Maybe someone says dr. is not serious writing on the topic
after 3y, but the new foil is finished ;-)



I am happy about to have the "old Axeman" in action again!
As I wrote in previews posts
http://drlojz.blogsp...ofoil-2011.html
and this year
http://drlojz.blogsp...012-update.html
The new hydrofoil set up was finished and ready to test.

See the result
http://drlojz.blogsp...n-fly-over.html

touch and go
Primoz