One of the dimensions of the rudder spar on drawing #4 is incorrect.
Drawing #4 shows the width of the top end of the spar to be 2 1/8", which is too wide.
It should read 1 3/4".
All the other dimensions on the drawing are correct.
Hi Rick,
A quick question...
I am currently assembling my rudder (gluing the hinges, hinge supports, D-section formers, etc.) to the rudder spar and have just discovered that four of the six triangular ribs are are not the same width as the spar where they are supposed to be bonded to it.
I have double checked my spar and its physical dimensions are exactly as specified in the plans. The ribs were made using the plans as a template and my ribs match the plans with better than 1mm accuracy but I am at a loss as to why there is a growing disparity in the with of the ribs as you go up the spar:
Rib# Spar Width Rib Width Difference
6 54mm 44.5mm 9.5mm
5 63mm 58mm 5mm
4 72mm 69mm 3mm
3 82mm 79mm 3mm
2 92mm 91mm 1mm
1 102mm 103mm 1mm
Rib #6 is particularly bad - the spar is 54mm (2 1/8") wide at the top but the width of the rib where it joins the spar is 44.5mm (1 3/4") - there's no way this can be a scaling error on my printed plans! What am I missing???
Did you encounter a similar problem or did your ribs match the dimensions of the spar exactly? I've checked the scale of my drawings and it is close enough to the correct scale that this does not account for the error.
If you have a moment could you take a look at drawing #4 and measure off the width (base) of each of the triangular rudder ribs and the width of ribs #5 and #6 where they intersect with the spar?
I'd really appreciate this!
Phil.
Rick replies: "Yeah, you've discovered one of the many errors in the plans. The drawings show the overall width as 2 1/8 and the space between the rib stringers as being 1 1/4 inch. However the rib stringers are made of 1/4 spruce and 1 1/4 plus 1/4 plus 1/4 equals 1 3/4. I made notes in my plans when I found errors but missed marking this one."