Subject: Re: [harryproa] Canted Bi-directional Sail
From: Rick Willoughby
Date: 3/16/2013, 10:58 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

Nick 
Nothing fancy with the rudders.  They are 100mm deep and 40 chord snug to the flat bottom.  They are biderictional with small radius on edges.  I expect they would vortex shed annoyingly in the full scale.   Would probably use continuous rotation on full scale with less than balanced rudders so they have strong centering at least 15% thickness.

The small radius on the leading edge is not conducive to wide operating range.  They are limited to plus/minus 15 degrees and I feel they are stalling even at that angle.

We may play around with winglets on the rudders to improve span efficiency without going deeper but we are still a long way from that detail.

If the boat can be balanced with the rig through its operating range then the rudders can be quite small.  They would need to be operated independently to prevent leeway.

With the model there is slight tendency for weather helm but it is possible to avoid irons most of the time by moving the sail beyond the luffing position to  pull the leading end off the wind.  Speed drops but it slowly turns leeward.

Rick

On 16/03/2013, at 1:32 AM, nk wrote:

 

That’s really neat Rick would love to see a pic of the rudder arrangement.

 

Nick

 

From: harryproa@yahoogroups.com.au [mailto:harryproa@yahoogroups.com.au] On Behalf Of Rick Willoughby
Sent: March-15-13 2:57 AM
To: harryproa@yahoogroups.com.au
Subject: [harryproa] Canted Bi-directional Sail

 

 

A friend has been playing around with an idea I had for a canted sail and has built a quarter scale model of a 7m beach proa he is thinking about building.  There is a video clip of testing here:

 

The controls are still a bit coarse and rig too flexible but it sails quite well and responds quickly.  

 

The aim with the canted bi-directional rig is to get better alignment of drive and drag forces in 3D.  The flexibility of the rig tended to reduce the vertical component of the sail drive.  Also the sail was a bit large for some of the gusts.  A smaller sail could have increased canting angle to improve the vertical lift component.  In addition the mast could be canted to the windward side rather than being vertical to give more vertical component to counter healing.

Rick Willoughby

 

 

 



Rick Willoughby




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