Subject: Re: [harryproa] Re: Wings Sails
From: Dennis Cox
Date: 8/24/2010, 8:48 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Rick,
 
Two comments...
 
(1) There was the caveat from  Martin Hepperle (JavaFoil's Author) about relying on it for the symmetric, rounded tail shapes.  It seems to violate the basic assumptions he makes.  Not that I'm changing my mind... I've got the rudder blanks curing down stairs now ready for running tow tomorrow night.  BUT, I won't be traumatized if something goes awry either and its slower.  Although, with all the things I'm trying, it'll be very painful to figure out which is making it slower than you're VVP suggests....  flat bottom hulls, cambered, symmetric rudders, articulating hulls or just plain bad workmanship. 

(2) Hope you have a sense of humor... did I catch you in a brain fart?    With a cambered sail or rudder, you can't let it come about in a shunt... it always has to keep end-to-end consistent... or the camber is facing the wrong way.  Can't put a tail plane vertical stabilizer/rudder on it either... it won't like facing into the wind/water. 
 
But, I'll still follow your lead to my doom!   /
 
Dennis

From: Rick Willoughby <rickwill@bigpond.net.au>
To: harryproa@yahoogroups.com.au
Sent: Tue, August 24, 2010 7:36:48 PM
Subject: Re: [harryproa] Re: Wings Sails

 

Dennis

I doubt you could get much simpler than the arrangement Todd has on the model.  You cannot let go of control in the model but there are ways to overcome that.

From the point of view of weather cocking I expect you could set up a tail wing that would keep the wing at zero lift or adjustable AoA.  Something to think about and test - the tail wing has to shunt across or around the the wing of course during a shunt but it would be as simple as flicking a lever.  The moment on the sail is not large so the tail wing would not be very large.

The same can be done with the rudders.  They will have almost zero moment if connected with a reversing linkage so a small trailing vane off the steering linkage could be used to hold course. 

There are performance advantages in having asymmetric sections.  I don't think many have thought about the range of possibilities with proas.  

Rick

 
On 25/08/2010, at 2:42 AM, Dennis Cox wrote:

 

On a model, it seems clearly superior.  Maybe even on a small day sailer, I can imagine some advantages.  But on a cruiser... I have a big concern.  Maybe I don't understand the concept fully as it applies to the real world and its a non issue, but...
 
The concept saves you from having to reverse during a shunt.  BUT, since its balanced front to aft there is no weather vaning.  You have to actively position it versus letting the wind position it for you and just sinch down the sheet.  Doesn't this mean you actively have to be rotating it with sheets and/or winches WHILE you are shunting?  And if you're in a big wind... there seems to be a big risk of not being right and going over.  Whereas, the Easy Rig... you can just let go of the sheet, totally ignore it while shunting, and pick up the other sheet and pull it in.
 
And what happens when you are in gusty or major wind direction changes?  You'd have to be on top of it all the time.  Also, you could easily get aback while you're waiting for the winch to bring the sail into the proper location.
 
Just my 2 cents worth... or am I missing something?
 
Dennis
 

From: Peter Southwood <peter.southwood@telkomsa.net>
To: harryproa@yahoogroups.com.au
Sent: Tue, August 24, 2010 12:16:23 PM
Subject: Re: [harryproa] Re: Wings Sails

 



Thanks Rick, but not quite what I was looking for
In the case where the foil shunts, is it better to have both edges sharp or rounded?
Cheers,
Peter
 
----- Original Message -----
Sent: Tuesday, August 24, 2010 1:34 PM
Subject: Re: [harryproa] Re: Wings Sails

 

Peter

For rudders in water working below cavitation you would prefer rounded nose and feathered trailing edge.  Above cavitation speeds it goes the other way.  Similarly with wings in air only the higher speed case is concerned with mach number rather than cavitation.  This can be a consideration for relatively low mach number because the air can have quite high velocity ratio around sharp edges.

For speeds of interest for most sailors the rounded nose gives a much wider operating range than a sharp edge.  The sharp trailing edge avoids vortex shedding like you get from a blunt edge so smoother operation.  However sails have a sharp leading edge and work fine.  You just need to keep the flow attached and most use some form of tell tale for this. 

A few hours with JavaFoil can give some good insights.  As long as you avoid really odd shapes it will give valuable results.  It has a whole lot of boundary layer information and flow and pressure relationships that gives insight into what is going on.  One really useful feature is that it can handle multiple foils.

There is a more detailed manual linked that gives you some detail how it works and the background to the various empirical corrections:
This is essentially referring to air but water is similar.  It has higher density and lower kinetic viscosity than air.  With water you need to be alert to cavitation.  With speeds above 20kts cavitation should be something you check for.  You can do this by determining the pressure on the suction side from the Cp values that JavaFoil produces.

JavaFoil indicates there will be a region of flow detachment with the bi-directional rudders being discussed but it does not increase drag over a feathered trailing edge.  In practice there may be noticeable vibration at higher speed. Something to look out for.

Rick
On 24/08/2010, at 6:56 PM, Peter Southwood wrote:

 



A question for the aerodynamicists:
Which is more important, the pointy trailing edge or the rounded leading edge?
Cheers,
Peter
----- Original Message -----
Sent: Tuesday, August 24, 2010 8:03 AM
Subject: Re: [harryproa] Re: Wings Sails

Todd
The best thick wing from a performance perspective is probably around 8 to 10% thickness.  With a proa you have the slight advantage that it can be asymmetric as you have shown with your thin wing and rudders.  The first three models looked like they had symmetrical wing and the AR was low.  

Because the thick wings have higher lift coefficient they have more induced drag for the same aspect ratio.  The best way to reduce this disadvantage is to mount the wing close to the deck or plate the bottom to reduce the vortices areond the bottom.  For example Macquarie Innovation has a relatively low aspect wing but its base is so close to the water that this reduces the induced drag on that end.  Same is achieved with headsail on monohull yachts by sheeting the sail along the deck.  This will also improve the performance of your thin wing but will have more benefit on the higher lift section.  You then make the base chord longer than the middle and narrow on at the top so the CoE is a little lower.

There are not many bi-directional asymmetric wings being used on sailing boats so the experience base is quite small.  I doubt many have even thought about it let alone done any experimenting similar to what you have done.  Most would look at your full-size bi-directional rudders and your model bi-directional wing and assume you were in need of some better advice because what you have made do not have pointy trailing edges like all "good" foils should.

The attached section mirrored so you get two nicely rounded noses would be worth a try.  Aim for an aspect ratio of about 5 and say 20% less area than the thin blue wing. 

I liked the self-righting ability of the last boat.  An advantage of a buoyant wing with a decent chord length.  If the cabin top was full width you could mount the sail tight to that to reduce the induced drag.  It should then sail faster and higher to windward.   

Rick
<Picture 5.png>

On 24/08/2010, at 2:46 PM, tsstproa wrote:

 

I'll go with my instinct and testing. Somethings amiss here. Look at some of the top high end hand launch gliders. Their wings are thin and cambered in a way very similar to my single skin except for their dedicated leading and trailing edges. Granted theses are thermal gliders hand launched like a boom-rang not winch assisted heavy fast flying thermal soarers. Theramal soarers can achieve speeds over 60mph where as hand launch thermal gliders very rarely see 30mph. The l/d ratio's have to fit the speed in which the craft is meant for and the purpose of the craft and I'd assume the weight of the craft as well.

Not a number guy , I go by past experiences, on instinct, and by what I see working.

I could get the double skin to work better but to me the outcome wouldn't be worth it. Its sail seems sluggish none respnsive or slow to respond . Driving a car with a lose steering wheel. The single skin bamb... 911 porche. super responsive goes where you point it when you point it and tells you when you have gone to far quickly all ways in touch.

I have done other double skin wings and its starting to bring back memories of why I didn't proceed.
http://www.youtube.com/watch?v=YDzG98DPvto
http://www.youtube.com/watch?v=YDzG98DPvto
http://www.youtube.com/watch?v=_PaWgwc4HwI&feature=related

But I always keep coming back to this.

http://www.youtube.com/watch?v=CCSoZOwQY6g

Cause is it just works so damn well.

Todd


--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Todd
> The thin section will perform slightly better than a fat section.
> The fat section is more forgiving. You need less sail area and the
> maximum lift will be more than the maximum drag.
>
> The fat section shape should be close to flat one side with nice
> rounding on the nose - something like attached mirrored.
>
> It should be a bit more than half the area you have now.
>
> The higher lift of the fat section is negated somewhat by the higher
> induced drag. You can reduce this negative to some degree by fencing
> the bottom. In fact any of the fixed wings should be improved by
> fencing the bottom either by having them operate close to a deck or
> fit a plate on the bottom of the sail. You could then carry the full
> chord all the way to the bottom.
>
> I could not get to the photo on the link you posted.
>
> Rick
> 
> On 23/08/2010, at 3:58 AM, tsstproa wrote:
>
> > No, you can not just let go and expect it to depower you have to
> > put the sail to the correct position to depower via controls. I
> > think of it as more of a mental block or learning curve in sailing
> > with this type of sail.
> >
> > The sail I have now is 2% thickness with a 9.6% camber. Or 1/4''
> > thick x 13 wide x 1.25 deep at center chord. The camber is pretty
> > consistent staying at about 9.6 though the bottom 3/4 of sail
> > coinciding with its chord the top 1/4 or so becomes alittle less.
> >
> > To me If I went with a 2.6'' wing thickness it kinda defeats the
> > whole purpose of going fast. Sure people will argue higher lift to
> > drag coefficient reduces drag is more efficient has a greater range
> > but look at that section of air it has to cut out. Vs 2% thickness
> > that has a camber of 10% its not a flat plate. Would it really sail
> > faster have better control have better range?
> >
> > Maybe your confusing wing thickness with camber?
> >
> > Here's a clip of a few more thorugh the water hull shots loading
> > the leeward hull while sailing into the wind to see what happens.
> >
> > http://www.youtube.com/watch?v=LrezrEfQj68
> >
> > Did a 180 sq inch 23''span ,10 '' chord, 2'' thick. Just to test
> > double skin vs
> > single skin Asymmetrical section.
> > Pics here
> > http://groups.yahoo.com/group/Wind_Powered_Shunting_Craft/photos/
> > album/2009757739/pic/list
> >
> > Here's first test 180 sq'' bi-directional asymmetric sail.
> > http://www.youtube.com/watch?v=uRYTVcfmns8
> >
> > The double skin asymmetric sail creates very little drive vs the
> > single skin cambered. Its heavier has less range and to me seems
> > piss poor in performance. Unless in higher winds . I can see where
> > a double skin could be improved upon to make work ,being a
> > combination of single skin camber and double skin thickness. But
> > were is the innovation in that all you have to do is look at the
> > oracle wing sail sail. I'll stick with my true asymmetrical single
> > skin Bi- directional for now.
> >
> > Todd
> >
> > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > wrote:
> > >
> > > Todd
> > > By feathering I am referring to a full size version where you
> > want to
> > > release sail force by releasing the sheet or whatever is controlling
> > > the sail AoA. The symmetrical sail does not feather when released or
> > > only over a very narrow range. An interesting test would be to
> > > release your control rods to the mast and see where the sail
> > rotates.
> > >
> > > The middle mounted rudders do provide a load release mechanism that
> > > allows leeway when clear of the water. I can see the benefit in
> > that.
> > >
> > > At speeds above a few knots on a full size craft ventilation will be
> > > performance limiting. Hence I see merit in under the hull rudders.
> > > They could be under the windward hull if you want some force release
> > > mechanism. The instant that they ventilate will cause the boat to
> > > round up a little so some inbuilt protection. If the front one goes
> > > first then there will be an instant of lee helm before the aft one
> > > lets go.
> > >
> > > Your cambered thin wing will have a working range of a few degrees
> > > when on the wind. The lift drops to under half about 5 degrees
> > > either side of maximum lift. The 10% series 07 foil will work over
> > > twice that range and if you went up to a 20% thick section it would
> > > have twice the lift and work over 25 degree range - so more
> > > progressive. Having double the lift coefficient allows you to halve
> > > the sail area. This means the maximum drag when the sail is
> > > perpendicular to the wind is halved so risk of capsize is reduced.
> > > You can provide this same protection by putting more curve into your
> > > thin sail and reducing the area but it will still only have a narrow
> > > range of operation.
> > >
> > > Rick
> > > On 19/08/2010, at 2:58 PM, tsstproa wrote:
> > >
> > > > Thanks Rick
> > > >
> > > > What do you mean by feathering?
> > > >
> > > > More range in what way pointing ability or same sail size for
> > > > higher wind strengths or both ?
> > > >
> > > > I'm sailing right in front of a shallow shelf so tring to keep
> > boat
> > > > close for through water hull shots. At 5:00 in Last part of video
> > > > thinking of a way to show leeway if any. I'm not moving the
> > > > steering boards just manipulating the sail only. Boat pretty much
> > > > stays in same position as it see-saws back and forth actually
> > gains
> > > > ground in the puffs.
> > > >
> > > > Also starting at 2:35 on the clip look as it heels and slides
> > > > sideways don't no if thats a good thing or not, but better than
> > > > digging and catching an edge. An argument for center hung
> > boards vs
> > > > leeward hung boards might correct of hinder the situation. I know
> > > > the canted of hull helped the slide.
> > > >
> > > > No, I'm using symmetrical.
> > > >
> > > > When I put the camera down the performance goes up two hands vs
> > > > one. Towards the end of the day I was tring everything to get
> > it to
> > > > ride on leeward hull alone in the 4.5 mph wind it wouldn't thats a
> > > > good thing to me. I'm hoping in about 6 to 8 range it will still
> > > > stay somewhat planted. In more wind canting the rig to windward or
> > > > reducing sail size.
> > > >
> > > > Todd
> > > >
> > > > --- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@>
> > > > wrote:
> > > > >
> > > > > Todd
> > > > > Very nice work.
> > > > >
> > > > > It is so simple with the rigid bi-directional wing. The only
> > problem
> > > > > is lack of feathering but that could be overcome.
> > > > >
> > > > > A thick sail section like I did for the rudder would have wider
> > > > range
> > > > > of control. It might be a bit more progressive on the controls
> > > > >
> > > > > Are you using asymmetrical rudders?
> > > > >
> > > > > Rick
> > > > > On 19/08/2010, at 11:05 AM, tsstproa wrote:
> > > > >
> > > > > > CatPrao ProaCat AURORA 36'' x 1/2'' x 3'' with 12'' rocker.
> > hulls
> > > > > > are canted 20degrees outward.
> > > > > >
> > > > > > http://www.youtube.com/watch?v=FCEvPdnhShk
> > > > > >
> > > > > > Todd
> > > > > >
> > > > > >
> > > > >
> > > > > Rick Willoughby
> > > > > rickwill@
> > > > > 03 9796 2415
> > > > > 0419 104 821
> > > > >
> > > >
> > > >
> > >
> > > Rick Willoughby
> > > rickwill@
> > > 03 9796 2415
> > > 0419 104 821
> > >
> >
> >
>
> Rick Willoughby
> rickwill@...
> 03 9796 2415
> 0419 104 821
>


Rick Willoughby
03 9796 2415
0419 104 821





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