I would think that on a tapered flap the loads on the hinges decrease as you go out toward the tip because of the reduced area. Provided you put the last hinge close to the tip, say with only 1" of overhang, I dont think it is necessary to double up. The horn bearing , provided you securely mount it to the TE, is a hinge itself. I use to, but dont anymore, try and get the first hinge close as possible to the horn. Then I realized that makes the alignment all the more critical. For a given amount of mis-alignment, the closer 2 hinge points are the more binding will result as surface rotates. So now what I do is put the 1st hinge 2~3" from horn, put the last hinge 1" from the tip, and evenly space the rest of the hinges. On my last ship just recently layed out, my flaps are 22" long, I used 4 hinges and it came out exactly at 6" spacing between hinges. I felt that was right at the upper limit of acceptable hinge spacing, and if flap would have been an inch longer I would have used 5 hinges. So if your flaps are 24" I would go with 5 hinges. On the elevator I used 3 hinges and the spacing came out at 4.5".