Rudder placement on RC foiling cat

Discussion in 'Hydrodynamics and Aerodynamics' started by Doug Lord, Oct 25, 2014.

  1. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 348, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I'd like some input on the two choices I have:
    1) place the rudder under or behind each hull-on an rc boat ventilation is not the problem it is on full size boats but loss of pitch control is so the better position on an RC boat having two rudders seems to be behind the hull because:
    a. it's simpler to adjust rake angle for the rudder hydrofoil,
    b.it increases the "footprint"( distance between the quarter chord of the main foil and quarter chord of the rudder foil).
    ==============
    2) hang the rudder in the center of the boat behind the rear crossbeam. This reduces drag a bit but weight probably isn't less than #1 because of needing to build the structure to mount the rudder.
    Retracting the windward foil is likely to be the fastest solution but on an rc cat it is expensive requiring a top of the line, fast (RMG/Guyatt) winch to do the job and would require a rudder t-foil in each hull like the AC 72's, GC32's and Flying Phantom.
    On the other hand if the two main foils are wand controlled and left in the water, it seems that the center rudder would work fine. It would be the same configuration(but narrower overall) as my F3 foiler.
    -------
    I'd appreciate any thoughts on this to help me think it out.....

    Pictures-1) F3 foiler with two wand controlled main foils that do not retract,2) Flying Phantom foiler using UptiP foils where the windward foil is retracted:
     

    Attached Files:

  2. Doug Lord
    Joined: May 2009
    Posts: 16,679
    Likes: 348, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    single or double

    Decision: I'm going with two rudders each with a T-foil. The mainfoil will take 80% of the load and the two rudders together 20% of the load. The area of the two rudders together will equal about 33% of the total foil area. So the rudder foil loading will be less than the mainfoil loading.
    The deciding factor was my desire to experiment with retracting the windward main foil. If I had a single centered rudder and retracted the windward main foil there would be a new uncontrolled "axis of instability" formed between the central rudder and the lee main foil. With two rudders and the windward main foil retracted the pitch stability is excellent-no new "axis of instability".
     
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