Go Team!!!
A plan is underway.
Chris has come up with a sound theory which seems to make sense to all. His understanding of the problem comes from looking at the problem from my viewpoint.
It seems that the boat has no directional stability at speed. It doesn't track. It is like a bike that will crash the instant you take your hands off the bars... but it is also super sensitive at speed to steering input.
It needs to be dampened down and it needs to have a better sense of direction.
It makes sense and explains many of the other scenarios that have happened in the past.
Once you identify the problem, you can devise the solution.
we are looking at fitting a fixed skeg to the back of the boat just like the tail of an aircraft. It will have a fixed section and a moving section. If you look at the videos of the runs you can see the boat 'yawing' around a bit. It doesn't always seem to track straight. It is relying totally on the rudder. This is OK on some boats but they are usually going alot slower and are a totally different base configuration to start off with.
Malcolm has put some of these potential mods into his VPP (velocity prediction program) and it makes a huge improvement to all the problem areas.
We will have to look into it fully and don't wish to blindly jump onto the first wagon offering hope but... this all makes sense. Let's at least make the boat want to go straight.
This makes me happy.
Offers of support are pouring in from near and far. We will get this fixed asap.
SP GURIT are sending us all the good stuff to carry out the repair and make the mods.
COMPOTECH is working on two new struts
A heap of MUSTO clothing has just arrived in Windhoek.
The design team are wading into the big issue...
It's great to see and motivates us immensely.
The crash is behind us. If this is what it takes to learn and make progress then hey-ho, on we go.
So click on the following video link and check out the carnage.
http://www.sailrocket.com/images/movie9.wmv
I still can't believe that the wing survived.
Check out how hard the pod gets slammed down.
Aye yi yi.
Give us two weeks to get this all back together.
Go team.
Cheers, Paul.
Chris has come up with a sound theory which seems to make sense to all. His understanding of the problem comes from looking at the problem from my viewpoint.
It seems that the boat has no directional stability at speed. It doesn't track. It is like a bike that will crash the instant you take your hands off the bars... but it is also super sensitive at speed to steering input.
It needs to be dampened down and it needs to have a better sense of direction.
It makes sense and explains many of the other scenarios that have happened in the past.
Once you identify the problem, you can devise the solution.
we are looking at fitting a fixed skeg to the back of the boat just like the tail of an aircraft. It will have a fixed section and a moving section. If you look at the videos of the runs you can see the boat 'yawing' around a bit. It doesn't always seem to track straight. It is relying totally on the rudder. This is OK on some boats but they are usually going alot slower and are a totally different base configuration to start off with.
Malcolm has put some of these potential mods into his VPP (velocity prediction program) and it makes a huge improvement to all the problem areas.
We will have to look into it fully and don't wish to blindly jump onto the first wagon offering hope but... this all makes sense. Let's at least make the boat want to go straight.
This makes me happy.
Offers of support are pouring in from near and far. We will get this fixed asap.
SP GURIT are sending us all the good stuff to carry out the repair and make the mods.
COMPOTECH is working on two new struts
A heap of MUSTO clothing has just arrived in Windhoek.
The design team are wading into the big issue...
It's great to see and motivates us immensely.
The crash is behind us. If this is what it takes to learn and make progress then hey-ho, on we go.
So click on the following video link and check out the carnage.
http://www.sailrocket.com/images/movie9.wmv
I still can't believe that the wing survived.
Check out how hard the pod gets slammed down.
Aye yi yi.
Give us two weeks to get this all back together.
Go team.
Cheers, Paul.
Paul Larsen
Mobile: + 44 (0) 794 684 1929
E-mail: paularsen1@aol.com
www.sailrocket.com
Mobile: + 44 (0) 794 684 1929
E-mail: paularsen1@aol.com
www.sailrocket.com
posted by Paul at 6:03 pm
11 Comments:
Hi Paul and team,
I've watched the most recent movie several times - it's as if when the rig powers up it flys away forwards, the hull and attached foils become an increasing source of drag off to one side, and the whole craft rounds up into wind rather like a pair of compasses. Would it be feasible to shift some (most?) of the lateral resistance carried by the hull to the float that carries the rig? This might improve the tracking of the craft under power.
Can I just say that I think Sailrocket looks fantastic. I have been following your progress with great interest and excitement, and hope you can find a solution to your control problem within the next couple of weeks.
Best wishes,
Richard
If the wing float becomes the main hull, you are back to "conventional" craft.
You are right about the main hull drag increasing and the wing hull drag in the water becomes zero as it lifts clear, making the situation worse.
The forward drive force is out on a 30' lever. If the wing is far enough ahead of the C of E of the main hull, it would balance. Moving the C of E of the main hull back would help, ie. mount the underwater foil right at the back of the hull.
Sailrocket could have an emergency brake by launching a small drogue on a rope from the wing float. It would slow or stop the round up allowing the rudder to operate.
We do have a braking device fitted on the float. I missed the window for deployment this time as I was still trying the normal tricks and generally trying to work out what was happening. The boat does have more of a tendency to round-up and in a reply to another forum response, no I haven't yet felt lee-helm. that isn't expected to come until higher speeds when the apparent is forward and the resultant drive of the sail is also rotated forward of the foil. We were previously searching for this promised land and this perhaps distracted us from the far bigger issues of instability and sensitivity. If we get lee helm at 25 knots it will only get steadily worse as we go faster. still it is a safer direction to lose control in. We have plenty of scope to swing the beam further forward but right now this is not our prime concern.
Cheers, Paul.
Hi Paul,
I think, I know, which mistake you made:
You didnt sheet on ENOUGH !
You should have OVERsheeted the wingsail. Its again an experience from kiting: If you pull the backlines very much, the kite flies backwards. In the same way you can use your wingsail as a brake, which stops the boat turning into the wind.
If you think about it, it may be possible to steer your boat only with your wingsail. Then you dont need any rudder anymore...
cheers
tilmann (who really likes the spirit in your team :)
Hi Tilman, I agree and that is what I did in Run 4. She was sheeted past the centreline at the end of that one. The round up started this time when I sheeted on... but I'm not saying that was the cause. In truth I'm not sure. But because that is when it happened it wasn't my next reaction to go for more. I think it will be next time. It can't do anything but stall and slow the boat and round-up. I only have a 6:1 advantage so it will take a few armfulls. We need the purchase to work the sheet at full steam. reducing this load was a reason for having the mast, and thus the pivot axis of rotation so far aft. this has resulted in alot of crashes. it is a difficult thing to change without a big change... not that we aren't looking at it.
Cheers, Paul.
Why not put the pivot axis exactly in the middle of the sailwing and then have a front and a backline (like a kite) for a quick and easy control ?
my idea is not really new :)
http://images.google.de/imgres?imgurl=http://www.luebeck.de/filmtage/fotodb/pics/692/s_692.jpg&imgrefurl=http://www.luebeck.de/filmtage/de/presse/pressefotos/view.html%3Fmode%3Dslideshow%26size%3Ds%26cat_id%3D361%26pic%3D692&h=1034&w=1417&sz=213&hl=de&start=4
The wing needs to react faster to windchanges by itsself. The centre of the sailforce is to close to the axis for that. If the wind comes in more forward/leeward a negative force on the frontleeward side of the wing is created before the wing rotates. Putting the axis in the middle will only make things worse. If rotaing the wing needs to be done by hand you are too late.
To rebuild the wing is a lot of trouble but you could give the wing a fixed tale. This is not a lot of work. 2 tubes and a piece of plywood would even suffice. But you can even give the tale a wingprofile so it is no extra drag but even an extra driving force
Drawback is the heavier sheeting.
But no heavier than the softsail
I hope the fin will make sailrocket more course stable, although I see it as taking on the symptom and not dealing with the real problem. But maybe the great distance between wing and foil will always give these problems.
On the other hand, my models are always easy on the helm and have a great sail-foil distance too.
And changes in the apparent wind do not change the direction of the sailforce much as long as the wing is not rotated and the angle of the attack of the wind in the wing is not too low. And if too low there would be a leeward tendency of sailrocket. And stalling of the wing also doesn't give a windward rotation.
In short, I still do not understand the round up but I do understand the wing coming down.
If I were you I would want op be very sure of the fin before I would let te wing unchanged.
Anyway, good luck, hope it works !
Johan
Hi Johan,
Perhaps Paul should have some trainings sessions with a kite, before he uses the expensive sailwing again. Then he gets a feeling for the reactions and how to handle front and back lines automatically. I think after some training and practice with a kite its not very difficult to handle the wingsail with a pivot axis in the middle...
cheers
tilmann
Hi Tillman,
With a kite letting go of the bar-backlines too much has no consequenses. And a kite is a free swinging rig and so regulates it's own angle of attack with the lines (bar) fixed. Sailrocket is different. You have to adjust the angle of attack yourself and if too low the wing comes down.
Another idea of bringing the axis more foward of the center of sailforce without a lot of work on the wing is to attach a profile to the bottom end of the wing that extends forward so you can shift the bottom rotation point forward in relation to the wing. The wing will be under an angle then but you can compensate that with the lines attachted to the top of the wing.
If this is structurally possible I can not say but you can.
Can you move SR's CE while sailing?
Looks like the front of the windward pod was dragging too (lots of increased spray), almost in some sort of slow harmonicity. Might explain the pirouette. Wave frequency?
Paul
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