Put the 3 piece leading and trailing edges to the side now because we are about to get into the heart of the wing and that is cutting the 1/4" wide rib strips. You can cut these out of the thickness of your choice. I use 3/32nds x 4" wide contest balsa. When I first started doing these wings I was using 1/16th contest stock and they broke if you breathed on them so I went to 3/32nds and the weight difference was negligible.
Go back to your wing plan and if you have not done so already, look at the spar on the wing plan. More than likely it is going to show 1/4" square stock for the spars but it really doesn't matter. What DOES matter is if the spar is swept back like the leading edge or if it is straight. More than likely it will be swept back like it is on the Imitation. My advice to you is to drop down a little and draw the spar in STRAIGHT as I am showing below in my drawing of the Imitation wing. Side note: I like to redraw the wing on Velum to show the straight spar but again that is a personal choice of mine, you can redraw the spar line right on the plan if you wish. When you redraw the spar, leave some room for the adjustable leadout guide to function within its normal range. The outboard end of the spar will be a little closer to leading edge but that makes no difference in building this wing. The model does not know where the spar is.
Once you have redrawn the spar as straight Or left it where it was originally, measure up from the red line you drew at the trailing edge to where the rib intersect the spar. This distance will be the part of the rib slice where the spar is going to hit that particular rib slice and it may not be the high part of the rib. I just use a ruler and mark the 6 3/4" (that is the measurement for the Imitation) or whatever the measurement is on your wing from the back of the rib slice. As you lay each rib slice on the plan to mark the spar location you will find that marks on the rib slices will move progressively toward the front of the rib as you get further outboard from the center. On my hand drawn plan you can see it but probably cannot make it out. It is 6 3/4". You are probably beginning to see why it is simpler to make the spar straight. Tom Morris once told me avoid a swept spar at all costs if you can avoid it. Since he and John came up with this, who am I to argue. All my spars are straight. On the tip rib slice on my Imitation, the spar location is 1" back from the leading edge which means the total length of the tip rib slices are 7 3/4" long.
Here is how you cut your rib slices. Make a template from the root rib on the plan. I cut the rib out of the plan and glue it to a piece of either 1/16th birch plywood or 1/8" soft ply and make a template of the rib as you see in the picture below. Measure the length of the chord in the center of the wing. If it is 9 1/2" (I am using the Imitation wing as and example and the chord of your wing will vary) cut a 4" wide piece of 3/32nd contest balsa 9 1/2" long. Using the template, drop down enough that you can use your exacto to cut along the top edge of the template to make the airfoil. Once that is done, measure down the leading edge of the piece of balsa and make little marks 1/4" apart and do the same thing at the high part of the rib. You can make a jig to do this if you are going to make more than one wing. Tom Morris gave me one he made for the Cavalier and I show a photo of it below if you want to make one. I have done this so much that I just eyeball the width of the rib slice and cut them. After a while of you doing it, you will be able to just eyeball it, slip your template down 1/4" and cut the slices.
Go to your next Outboard rib or rib # 2 or however you designate them and measure it .... on mine wing the next rib was 9 3/8 long so I adjust the piece of balsa sheet and cut it 9 3/8" long and start cutting rib strips again. You do this until you have each rib strip cut for the entire wing. Cut each length is sets of 4 because that is how many rib strips you will need for each rib position.
When get all this finished you will have about 60 ribs strips total and they will be different lengths in sets of four.
Next take a piece of paper or a cutting mat with measurements on it and do what i show below on the sheet of paper. You have to trim the back of the rib so it will sit as flat as possible on the 1/4" ledge you created when you built you 3 piece leading and trailing edges. Use a Sharpie with a fine point because the width of the mark is about 1/16th of an inch and draw a straight line as i did so you can lay your rib strips touching the line as I have shown so you can cut the correct angle at the back of the rib so it will sit flat on the ledge of the trailing edge. DO NOT DO THIS FOR THE LEADING EDGE OF THE WING. STOP.. before you cut this angle you have to know how thick the trailing edge of your wing is. If it is 1/4" thick then you want to put a mark on the back of the rib 3/32nds of an inch from the top of the rib slice. Here is why, when you install the ribs (both top and bottom, allowing for the 1/16th ledge, you will have the 1/4" trailing edge you need. Now you have to sand the trailing edge down to the height of the back of the rib but you have plenty to play with since the trailing edge at this point is 9/16" high.
If the thickness of your trailing edge is 3/8", then you want to come down 1/8" or in the center of the back of the rib and cut your angle using the same process. Honestly folks, I just come down 1/8" in both cases because I have found that it is not that critical of a measurement. I just come down to half of the thickness of the back of the rib strip and put a pencil dot and eyeball where the line on the paper touches the rib and make my cut. Looking at the picture below will help a lot.
Ok I have writers cramp so I am going to stop here and post some pictures....
Topic: Building a Millennium Wing (Read 7858 times)