The Curry Conference
Greetings to all,
I'm sure that many of you who have been following Sailrockets progress are wonderining what we are up to. Sailrocket is safely stowed away in her container down at the Walvis Bay Yacht Club awaiting our return. Helena and I have returned to the UK whilst the 'brains trust' try and understand the problems at hand.
Firstly we have to understand exactly what is initiating the dreaded 'round-ups', secondly, what contributes to their severity and thirdly, what we need to do to prevent them. Malcolm and Dan have been working on the computer modeling of Sailrockets performance in order to try and replicate the 'round-up' scenarios. They have two completely seperate models that they both built independantly of each other in order to see if they arrive at the same conclusions. The good news is that they have. Both models predict the blistering performance that this craft can deliver if it can be kept on the straight and narrow. The bad news was that, initially, neither Malcolm's nor Dan's model could replicate the crashes. There were still holes in the scenarios that didn't make logical sense and the virtual Sailrocket couldn't be made to trip up in the realistic way that the real sailrocket would. Up until last night we still hadn't come up with a full scenario that makes sense and explains the boats behaviour from start to finish.
Last night was the first time that we have had all of the Sailrocket design team in the one room for a brain-storm. Dan Bernasconi and Richy Pemberton have both been down in Valencia number crunching for the Americas Cup, Chris is based in Brighton, Andy Bellamy is working for SP Gurit in Canada, we are anywhere between Africa and Weymouth and so on. It was a great luxury to have the whole core team in the one place at the one time.
L TO R, MALC, CHRIS, ANDY, DAN, HELENA, PAUL, RICHY AT THE KUTI'S CURRY CONFERENCE HQ OXFORD STREET, S'OTON
Nothing beats a face to face meeting and we all agreed that it proved to be extremely productive. Once again Chris Hornzee-Jones highlighted an area he understood from his flying background which is applicable to Sailrockets general handling. We couldn't understand what would cause sailrocket to turn so violently... what would initiate a scenario where all the corrective force of the rudder would not be enough to prevent? Those of you who have handled 'tail-dragger' aircraft on the ground should know the dangers of being heavy with the brakes as drivers of rear engined Porsche 911 drivers are aware of the end-for-ending nature that will result if this mass imbalance is not respected. Well we think that Sailrocket may suffer from the same foibles. The centre of gravity is behind the point of traction so when a turn is initiated (even a very small one) it is this mass imbalance that overpowers the steering and sends her into a great big 'slide'. Other factors also contribute but this could be the major component. The solution is literally straight forward i.e. move the lump at the back up to the front. Moving the pilot forward is one solution but then there are others to be considered. What was exciting about this understanding was that it fit. It tied in with all the aspects of the crash scenario from the general feel in the cockpit to the loads required to overpower the rudder in the computer modelling.
Before we return to Namibia we have to understand what we have learnt. We will be modifying Sailrocket but these mods must be carefully calculated and implemented. The mods will include changes to the wing to make it have an 'off' mode where we can depower it quickly and safely. This is essential as the inability to do this has lead to a lot of carnage. Other projects on the side include a much improved instrumentation and data collection package, improving the means by which the outside world can view each individual run and the ongoing, never-ending chasing of funds to underwrite this fantastic challenge.
When we return we want to have a clearly defined path which leads to long, solid and controlled runs. If we get that then everything else that we dream about will follow. I won't put a time on our return to Namibia other than to say we are getting itchy to get back and it shouldn't be far away.
I will keep you updated as these new understandings develop.
Paul Larsen
Mobile: + 44 (0) 794 684 1929
posted by Paul at 4:04 pm
8 Comments:
If you are going to move the pilot forward it may be worthwhile considering a new cockpit with planing surface and foil in the middle of the mainhull and just behind it the beam attachment. Best weight-lift distribution I can imagine for Sailrocket and then you can sail more often with a more vertical (curved) foil.
Together with a better depowerable wing like you are planning it still seems to me like the best configuration possible. You can make the cockpit in the Uk and attach it in Namibia.
Anyway, just another dutchman's opinion. Good luck !
Hi Paul,
The best way to stop the boat turning is to remove all the turning moments!
1. put the main centreboard at the centre of mass to eliminate inertial moments (and make sure the main hull centre of lift is aft of there in case the centreboard stalls),
2. attach the outrigger to the same point via a vertical axis pivot to eliminate wing force moments,
3. let the wing fly with it's pitch controlled aerodynamically rather than by the angle of the hull to the air at the time (i.e make it a complete hangglider) - essential to stop the wing swinging about as it does now and running into your bow, or any number of other possibilities,
4. control the wing force rather than (try to control) pitch accurately and with super-human speed,
5. allow the outrigger pontoon to pivot so it tracks like a castor.
The helm will then be lighter than you can imagine with capacity to burn, and if/when the centreboard cavitates/ventilates/stalls the rudder will just turn you gentle towards the wing until it gets traction again. Slight understeer like in a wrx rather than 911 terminal oversteer.
This all works well on my boat; there are fewer surprises if you know where all the forces are.
Good Luck
Bill Rayner
dingbat.com.au
Hey Bill,
I agree on your first point. centreboard near the center of weight and both as much in the middle as possible and in front of the center of lift is a good principle. Makes Sailrocket safer and faster.
But a free swinging beam is for sailocket not an option I believe. The rig is in contact to the water thru the leeward pod so very oncontrolable things can happen when the resistance of this pod is not constant.
And as long as the beam has a fixed angle in relation to the hull the angle of the sail towards the beam must remain as constant as possible also to keep the load on the foil. So an aerodynamically controled wing is also no option.
And the leeward pod doesn't need to track as long as is doesn't have much lateral resistance and it is designed like that.
A really free swinging wing, pivoting near the center of resistance is best but sailrocket is designed to have as little parasitic drag as possible so the sail is put directly on the leeward pod so inherently there will be no free swinging wing even if you make the beam attachment a pivoting one. But the problems sailrocket has are not caused by this issue I believe. A better weight lift distribution and a better control of the wing is enough to get the full potential of the low parasitic drag. And below a certain windspeed a more vertical curved foil. But only if the center of lift is behind the center of weight.
Looking forward to new developments!
Cheers,
Johan
Been thinking about it, in principle it might just not be such a bad idea after all. The variability of the resitance of the leeward pod can be minimised and a good äerodynamicaly steered rigging can overcome the variations in resistance probably. And if the wing is set to make the leeward pod fly it can work very well.
But sailrocket has to be altered for it and the rigging will need to be structurally very different. The top of the wing is not on the pivoting axis. So a construction is needed that unavoidably has much more parasitic drag than sailrocket has now. Or maybe a horizontal elongation of the wing might work.
Anyway, in principle it could work, nice thought !
Cheers,
Johan
ps: funny how every "nonheeling collaege" sees it from a different (his own) perspective on this "forum". It may once melt into the ultimate nonheeling sailboat.
Hi Johan,
It DOES work! I'm not talking theory here. Both my full sized prototypes have been stable, in plan (where Sailrocket has probs) and elevation (capsize direction, where SR can’t have probs), for the same reason; all the forces go through the C of G. This was the whole basis of the design and the patent.
I forgot to mention the other big advantage; you can steer the boat with the rudder (and let the wing/outrigger look after itself) or raise the rudder and steer by turning the outrigger beam wrt the hull for minimum drag. Or if you’re lazy, lock the outrigger pivot and the wing steers you, no hands (see the second last pic on http://www.dingbat.com.au/Log.html)
You can get a wide boat like SR to be stable under some conditions, but finding the limits is dangerous. I do my own testing because at the limit, Dingbat just slows down.
Cheers, Bill
Yes, I know Dingbat and I know it works well, although I see limitations when size and general handling is involved.
But you have a self supporting wing, seperate from the sidehulls. How do you see this constructed in sailrocket ? The same way as in dingbat ? That takes a whole different construction with much more aerodynamic drag and also heavier. You need a beam AND a construction to hold the wing. Or you have to get the top of the wing on the pivoting axis so you can use the same wires as sailrocket is using now. But then you need to get the wing closer to the mainhull and more horizontal, which will make sailrocket less fast (although very interestingly Tillman told his fastest run was when he held the kite very high so maybe lift is even more important in relation to propulsion then I thought)
So I do know Dingbat works, but to make Sailrocket work the same way quite some sacrifices have to be made and I doubt whether they are necessary to reach their goal, or even getting them further away from their goal.
Good luck with Dingbat !
Cheers,
Johan
I'm not suggesting a full Dingbat conversion! All SR needs to overcome its current problems is to do a 2D version of the complete 3D solution. Tillman is right; if there’s enough air, tilt the wing until the hull comes out of the water - that’s where most of the drag is. Gliders go faster than sailing boats.
Cheers,
Bill
Hi Guys
I would like to repeat my previously given opinion on the matter. In stead of fighting to compensate for the turning momentum generated by the wing du to it placement that far away away from the sailing line of the main hull, get rid of the turning momentum !
Let the wing rotate more or less freely around the point in th ehorisontal plan, where its attached to the main hull. This wil prevent any errornous sheeting or sudden wind changes or stalls of the wing to generate any turning momentum to the main hull. Of course this will imply a major design change, but I think the benefits of losing the "spin out" problem alltogether will compensate.
Keep up the spirit guys
Regards Flemming
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