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Tell me about T foil rudders.

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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 18 at 9:01am
Originally posted by Peaky

Originally posted by getafix

  ...we might see rudders ahead of keels on the new monohull AC designs. The reasoning being that this would further enable the 'bow down' hydrofoiling attitude which he said improved aerodynamics (of the 'vehicle' when 'flying' through the air) and the lifting of the crew section of the hull (potentially the weightiest bit) out of the briney and to minimise surface area when in the air.

thoughts?

Hmmm, I don't see a general aerodynamic benefit to being bow down. The cats were bow down due to a rule limiting the range of play in the rudders as I understand it. Not sure I fully understand the rest of the argument - the lift of the combined foil set up has to be longitudinally in the right place, but that won't require a forward rudder. A forward rudder would be friskier though, likely leading to more small movements which is slow, unless a very good control system was fitted to filter out unnecessary action.
Peaky is right... 

The last cup they had a limit (3 degree offset) of rake on the rudders and the main windward foil couldn't be in the water. The rule was to stop the boats generating a huge righting moment through down-force with the windward foils (because of structural and safety risks). 

To get around this, the boats ran a bow down mode to limit lift from the windward rudder once up to speed. But more than just bow down, it was twist. The platform was twisted so the windward hull was more bow down allowing the windward rudder to generate down-force and righting moment, all whilst the leeward hull was much closer to horizontal trim. 

The hulls were pretty much one design, but the fairings were open. If they wanted to generate downforce from the hull (crossbeams) they could have just set the aero fairings up with that angle of attack with the hulls in horizontal trim.  

The bow down attitude was definitely a byproduct of specific rules and I don't think we know anything that specific about the new boat rules to conclude they'll do the same again. 

Read here from the section being "The balance of transverse forces". Thee are some other quotes from the design team quoting the % of righting moment generated by twisting the hulls and the rudder. 


Edited by mozzy - 15 Feb 18 at 9:13am
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andymck View Drop Down
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Post Options Post Options   Quote andymck Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 18 at 1:37pm
We had a standard composite craft rudder.
I am sure jo Richards would talk to you about it.
He is probably still a class member. Otherwise Tom S


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ThomasShepherd View Drop Down
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Post Options Post Options   Quote ThomasShepherd Quote  Post ReplyReply Direct Link To This Post Posted: 03 Nov 20 at 7:21am
Posting here on an old thread as I'm building a tfoil rudder for my Farr3.7 . Not here to debate the pros and cons it may be a stupid thing to do from a race winning perspective but I want the experience of both building it and sailing it.

It will be pintle adjusted and plan A was to put the foil on the trailing edge, but I've been wondering since about putting it on the front edge out of any turbulence caused by the rudder blade.

Now that's got me wondering about placement relative to the stern wave.

The leading edge of the rudder will be hung off a gantry 9.5" off the transom. The rudder is pretty fat and going with the rear mounted option would put the leading edge of the foil about 14" off the transom.

Should I go fore or aft mounted?
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423zero View Drop Down
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 03 Nov 20 at 9:56am
I would go fore, as you mentioned, it will be in cleaner water, will still have some turbulence from centre board.
Robert
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Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 04 Nov 20 at 9:20pm
If you put it at the front of the foil then there is less of a moment arm pushing the bow down.

I have read that by having the T sticking out by about a third it means that the low pressure of the T is located at the high pressure area on the rudder. In theory it reduces the pressure gradient, and should be lower drag.
If it doesn't break it's too heavy; if it does it wasn't built right
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