How to widen a boat after it is built

By Mike Turner.

How to widen an existing KR boat

Existing boats can be made wider. There is some difficulty but with care it can be done. I needed shoulder room so I cut through the top longeron from just behind the front spar to behind the rear spar and down. I decided to put in an armrest for my arms/elbows so I needed to cut the sides down to just below the below the armrest. I cut out existing skin and existing truss members then just cut another 5/8 inch on just the truss member (not the existing skin) and added another intermediate longeron to the tops of the existing cut off truss members. The armrest will sit on this intermediate longeron.  To determine this location I sat in the KR until I felt comfortable. I used a magic marker and drew an outline at the approx location of the bottom of my arm/elbow. I wanted to put in side sticks anyway so the arm rest needed to go from a low point at the bottom of my elbow to a height point near the top longeron and far enough behind the instrument panel to allow control movements of the side sticks. The armrest needs to be narrow at the elbow and become wider near the top. Much like the school desk we used in school. You would be surprised how much extra room you have in the cockpit by making room for your elbows and shoulders. I did the side sticks because I had the armrest anyway and felt I could gain a little extra control with a very stable platform for my arm as opposed to resting my arm/elbow on my knee. If you choose to do this make sure you get the top of the arm rests high enough to clear your knees but wide enough for side to side control movements of the side sticks.  

The build back:

I put 2 new longeron back on out side the existing ones plus a wedge shaped piece to fill in between the existing longeron and the new ones forward of the cutout. When adding back I just added truss member at the same locations/angles except they were under the new longeron. These trusses were designed to handle the load in the configuration as set forth in the plans so I think it is important to stick with what is known to work. What I was attempting to do was just transfer the load on these existing trusses to a new location while marinating the structural integrity of the unit. Keep in mind this is going to add extra weight to the finished product. It will make you fly slower and/or reduce the useful load. I decided comfort was more important than speed at least for me. Some of the support member that were next to the existing skin forward of the front spar I used balsa wood to keep it light and tapered the supports to allow the new skin to blend with the existing at about the top of the wing. I also drilled lighting holes so I could run fuel lines/wiring ect. (Shut off valves are just in front of my knees and just below the instrument panel). I think I should point out also that rather than just epoxy the new longeron to the sides of the existing skin I made elongated cuts so epoxy would penetrate the wood cells of the new longeron instead of depending on just surface adhesion.

Once all new trusses members were in place, fuel lines ect. I epoxied new 3/32 inch mahogany skin in place. I tapered the vertical ends of the plywood on  1/12 bias just as you wood with a splice joint. I constructed the vertical ends not quite vertical. I just made them end at a truss member for extra strength and to make a nice gentle blend with the existing.

Keep in mind, anytime a change is made on an aircraft it will affect other area of the aircraft so it is important to consider all of those changes. For example this mod changes the rear deck both in width and in the shape of the rear deck. It changes the canopy size, in my case I went with gull wing doors. I wanted the gull wing doors anyway but because of the wider boat I have a wider rear deck and wider canopy which gives more room for the gull wing doors which gives me more room in the cockpit which is what I was after!! Just keep in mind changes cause more and more changes.

Proceed at your own risk!!

Mike Turner

Jackson, Missouri

Swing the prop and light the fire, dance among the stars.........N642MC

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