Wing sails, how do they trim them ?

[simonfraser]

There is a sheet at the trailing edge, can't see any tell tales or instruments that the guy on one of the rear winches uses often to control the angle.

How is it done ?

Or is it 'just' set and the boat is steered on apparent wind, which is on a mobile display ?

 

[lpdsn]

There is a sheet at the trailing edge, can't see any tell tales or instruments that the guy on one of the rear winches uses often to control the angle.

How is it done ?

Or is it 'just' set and the boat is steered on apparent wind, which is on a mobile display ?

Apart from the sheet at the trailing edge I haven't worked out how they are trimmed either. There must be two controls as there are two sections of the wings to be trimmed and you'd want to adjust the overall angle of attack plus the difference between the two sections.

They certainly don't just set them as you can deduce from the groaning of the sheet around the winch and the heavy breathing of the grinders.

There's not been a shot where I've seen tell tales, so I don't know if they have them or an equivalent or whether they measure the air flow with instruments. Aircraft have sensors to measure airflow (years ago I worked for a company that supplied them for US fighters) so I guess they could have those fitted.

I haven't noticed them adjusting twist in the wings. Maybe at 40 knots you don't need to worry about it so much.

 

[MikeBz]

On the AC72 wings they have multiple hydraulic controls to adjust twist and the angle (and probably slot gap) between the elements as well as the sheet which controls the rotation of the whole assembly. The grinders provide hydraulic power for the system.

 

[simonfraser]

Yeh they must have controls, hydraulics and rope, but how do they set it all, no tell tales ?!

I guess if you have unlimited crew and money you can 'just' try all the settings for the wing sail and keep track of all the positions for the different wind directions and strengths ?

 

[MikeBz]

My bet is that they have put enough hours in to have it fully calibrated through instrumentation. That and a very experienced trimmer on the sheet and pedals.

 

[TQA]

The top of the bottom rear section has arms at the front. Lines attached to them control the twist of the rear section. I am not sure but is seems likely that the controls are hydraulic as when NZ nearly capsized Dean can be heard shouting HYDRO HYDRO to get some hydraulic pressure from the grinders.

The left pic is from an early wing sail the right is from the current one { I think }

Re deciding what trim is appropriate I suspect that eyeballing the telltales is old hat for these guys, they will have the boat polars all computerised and they know for X windspeed at Y angle with Z boatspeed they need the following angles on the wing for best performance. Anyway I see the trimmers constantly checking a small screen as well as the wing.

It might be relevant that as well as hitting Oracle with a two race penalty they disqualified the wing trimmer, guess he is an important guy. .

BTW I am no expert on this stuff just a retired old fart who likes to know how stuff works and when I started watching the races was curious about the control mechanisms and did some online research. One interesting thing I came up with is that they are not allowed to have any stored energy which is why the grinders have to keep working.