Tell me about T foil rudders.

Originally posted by Peaky

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