by Gene Rosson » Thu Oct 13, 2005 3:37 pm
You can improvise a tee section by cutting an I beam down the web to suit your required dimension. I beam is more likely to be available than tees. As a matter of semantics; I beam has tapered flanges, wheras "wide flange" has flat flanges. I'd expect that the WF is more suited for the job. There are some architectural sections with the desired cross section. Also there are some rectangular tubes that have a dividing web down the center. Architectural shapes are usually extruded from a slightly different alloy such as 5052. Its a little softer than convential 6061 but the radio gear won't know the difference.
My radio board, and its' layout, is similar to the description posted. Tee section was not required. I used a flat piece of aluminum bolted directly into the ballast. The ballast slopes downward aft, so some different length spacers were used under the board to make it level. Spacers are half inch round aluminum shaft with quarter inch holes down the centerline. Ballast is drilled and tapped for quarter-20 threads in four places. Three bolts would do just as well. The RMG is mounted with the sheet metal bracket described in the RMG instructions. Jib trim servo is laying on its' side, flat against the board. Rudder servo is standing up and held in place by some aluminum spacers made from bits of 5/16 flat bar. The board is tapped, under the spacer holes, for 3-48 screws. The rudder post bellcrank resembles a C clamp with a 3/16 hole in the top to accept the rudder shaft. The bottom extends downward about an inch and a half where the arm is attached. The bottom is offset so as to clear the lower part of the rudder shaft housing. The rudder push rod is almost horizontal with that arrangement. I am including all that detail to suggest that you can have a very low set board without having to resort to hard to find extrusion shapes. My board with all the hardware including quarter inch stainless cap screws weighs 14.5 ounces. It is set well below the water line and probably below the center of bouyancy.