Foil Cams Options

[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.blogspot.com/2009/11/moth-hy...astic-flap.html

(IMG:http://4.bp.blogspot.com/_q5Gns3dbe0A/SwXEyuqe4YI/AAAAAAAAD2o/Mizb4JsXvrA/s640/Moth_elastic_flap-2.jpg)
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 ) Number of downloads: 13

[Doug Culnane]

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

http://sipayne.blogspot.com/2008/09/hidden-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.blogspot.com/2008/09/hidden-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.